Light-driven restructuring generates nanoisland NiIr alloy for efficient methane dry reforming

Domain: chemistry
Published: 2026-01-15
Editorial outcome: major_revision

Abstract
The simultaneous utilization of methane and carbon dioxide via dry reforming holds promise for sustainable syngas production, yet conventional thermocatalytic processes suffer from energy-intensive operation and catalyst deactivation. Here, we report a light-driven methane dry reforming strategy utilizing sinter-resistant nano-island alloys catalyst, which are dynamically evolved from partially oxidized NiIr nanoclusters anchored on TiO2 under photoexcitation. In situ characterization reveals interfacial charge oscillations on the catalyst induce a support-Ni-Ir electron transfer pathway, stabilizing oxidized Ni linkages while electronically modulating surface Ir sites. This dual functionality promotes CHxO* intermediate formation, suppressing coking during 100-h operation under intermittent illumination. By decoupling photoelectric and photothermal contributions, we demonstrate that localized photogenerated electrons dominate balanced syngas production, whereas photothermal effects enhance molecular vibrations. The optimized catalyst achieves a syngas rate of 10841 mmol g-1 h-1 with 25.0% light-to-fuel efficiency, establishing a design paradigm for solar-driven alloy catalysts in greenhouse gas valorization.

Introduction
Mitigating greenhouse gas emissions while securing sustainable routes for chemical energy conversion remains a central challenge in the transition toward a low-carbon future. Dry reforming of methane (DRM), which simultaneously converts methane (CH4) and carbon dioxide (CO2) into syngas (CO and H2) as valuable chemical feedstocks, offers a promising pathway for greenhouse gas utilization1,2. Yet, the highly endothermic nature of DRM (CH4(g) + CO2(g) → 2CO(g) + 2H2(g), ΔHo298K = +247.3 kJ mol-1) necessitates harsh operating conditions (typically 700–1000 °C) in conventional thermocatalysis. Such high temperatures consume substantial fossil fuels, undermining environmental benefits of CO2 utilization3–5. In addition, the reverse water-gas shift (RWGS) reaction (CO2(g) + H2(g) → CO(g) + H2O(g), ΔHo298K = +41.2 kJ mol-1), being thermodynamically favored under the high-temperature conditions, compromises syngas selectivity by lowering the H2/CO ratio6. Solar light-driven catalysis has emerged as an energy-efficient alternative by synergistically combining photoelectric effects and photothermal heating to promote the dissociation of CH4 and CO2 without external heating7–9.

In materials terms, noble metals as active sites display high intrinsic activity toward CH4 and CO2 activation but suffer from low atom efficiency and over-strong intermediate binding, often leading to side reactions10. Nickel-based catalysts are more economically viable and exhibit notable CH4 activation capacity, which are prone to deactivation via carbon deposition11. Alloying noble metals with Ni modulates the electronic structure to optimize the balance between reactant activation and intermediate adsorption, thereby suppressing side reactions and improving noble metal utilization efficiency. Moreover, ultrafine nanoclusters (<2 nm) could further enhance catalytic efficiency through maximized surface exposure and metal utilization12,13. However, stabilizing such clusters against aggregation under reaction conditions remains challenging. Recent studies14–16 have demonstrated that integrating oxide nano-islands at metal-support interfaces can effectively suppress sintering through strong charge-mediated interactions. For instance, anchoring Pt14 or Pd16 on CeO2 nano-islands has been shown to spatially confine metal mobility. However, extending this nano-island strategy to ultrafine alloy architectures requiring both interfacial stabilization and electronic tuning has yet to be reported.

In addition, catalyst structural stability at the atomic scale under intense light irradiation and elevated temperatures, which are conditions inherent to photothermal catalysis, remains challenging for elucidating catalytic mechanisms. Whether such conditions preserve the active phase or drive transformations from metastable intermediates to thermodynamically favored structures is still poorly understood. Beyond thermal vibrations that commonly induce surface reconstruction at high temperatures, photoexcitation can trigger substantial charge redistribution between the support and active site17–20. This photoinduced charge transfer may alter the electronic structure of surface chemical bonds, reducing bond energies and promoting dynamic surface reconstruction21,22. Despite growing interest, elucidating the nature and formation of the active phase under photothermal conditions as well as disentangling the respective roles of photoelectric and photothermal effects in light-driven DRM, remains a critical yet unresolved challenge, limiting progress toward rational catalyst design.

In this work, we demonstrate that photoinduced interfacial charge oscillations in NiIr/TiO2 trigger dynamic structural reconstruction into TiO2-supported NiIr nano-island alloys stabilized by oxidized Ni linkages (NiIr/TiO2-LNi). This structural evolution arises from accelerated electron transfer across the support-Ni-Ir interface under light excitation. The spatially and electronically synergistic configuration promotes CHxO* intermediate formation, effectively mitigates carbon deposition, and maintains stable performance for 100 h under intermittent illumination. Mechanistic investigations reveal that photoelectric effects dominate the reaction, contributing 57.5% of the syngas production rate and 91.7% of the H2/CO ratio by facilitating C-H/C=O scission and H-H coupling, while photothermal effects enhance molecular vibrations and reactant diffusion. Under full feed gas flow, NiIr/TiO2-LNi achieves a syngas production rate of 10841 mmol g-1 h-1, with a light-to-fuel efficiency (LTFE) of 25.0% and a turnover frequency (TOF) of 23 s-1.

Results
Synthesis and atomic-scale structural analysis of partially oxidized NiIr nanoclusters on TiO2
To construct bimetallic NiIr nanoclusters on TiO2 with precise atomic pairing, we adopted a directional adsorption strategy23 (Fig. 1a; see Methods for synthesis details). This approach leverages sequential electrostatic adsorption of cationic Ni complexes and anionic Ir precursors onto alkalized TiO2 nanosheets, ensuring preferential Ir anchoring onto pre-adsorbed Ni sites. For the Ir precursor, we used a species complexed with quaternary ammonium cations to enable its phase transfer into an aprotic solvent. This controlled process prevents Ir ripening and leaching. Consequently, by conducting adsorption in this manner, we minimized competitive adsorption of Ni and Ir, effectively overcoming a key limitation of conventional co-impregnation methods. Subsequent H2 calcination eliminated organic ligands while strengthening Ni-Ir metallic interactions, yielding ultrafine bimetallic clusters with uniform dispersion on the TiO2 support (Fig. 1b). Inductively coupled plasma-atomic emission spectrometry (ICP-AES) confirms controlled metal loadings across NiIrx/TiO2 samples (Supplementary Fig. 1 and Table S1), where x denotes the Ir/Ni theoretical atomic ratio. The sublinear increase in Ir/Ni ratios with x suggests saturation of Ir adsorption onto pre-adsorbed Ni sites, excluding independent Ir deposition. For comparison, monometallic Ni/TiO2 and Ir/TiO2 were prepared with a theoretical loading of 1 wt% for each metal. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) analysis revealed that Ni species or Ir species on TiO2 exhibited sub-1.2 nm clusters (Supplementary Figs. 2–3), whereas the NiIrx nanoclusters on TiO2 showed an increase in size, progressively reaching up to 1.61 nm with higher Ir content (Supplementary Figs. 4). This trend supports the co-stabilization of Ni and Ir atoms within the bimetallic clusters. This size evolution directly supports the formation of bimetallic NiIr nanoclusters, as the incorporation of Ir stabilizes the clusters and promotes their growth.

Atomic-scale characterization of NiIr0.5/TiO2 provided further insights into the spatial distribution of Ni and Ir atoms. Filtered and color-coded HAADF-STEM images and the corresponding intensity profiles (Fig. 1c, d, Supplementary Fig. 5b, c) revealed intertwined Ni-Ir distributions within individual clusters. The 3D surface plot of a selected region (Fig. 1f) highlighted Ir atoms (whitish-yellow peaks within blue dashed marks) surrounding Ni atoms (darker yellow bumps), demonstrating cohesive bimetallic nanocluster formation. Conversely, monometallic samples exhibited only metal-TiO2 contrast (Supplementary Figs. 2g-h, 3e-f). Moreover, EDS line scans (Fig. 1g) and elemental mapping (Fig. 1h and Supplementary Fig. 5d-i) confirmed the intimate contact between Ni and Ir atoms. Owing to the higher atomic ratio of Ni to Ir, trace amounts of isolated Ni species inevitably persist. Crucially, all Ir atoms preferentially occupy Ni-associated sites, with no detectable isolated Ir single atoms observed on the TiO2 support (Fig. 1b).

Next, we elucidate the chemical structure and coordination environment of the NiIr nanoclusters. X-ray diffraction (XRD) patterns confirm exclusive anatase-phase TiO2 (Supplementary Fig. 6), with no detectable reflections from metallic Ni or Ir phases, consistent with HAADF-STEM evidence of dispersed sub-2 nm clusters. Normalized Ir L3-edge and Ni K-edge X-ray absorption near-edge spectroscopy (XANES) analysis reveal partially oxidized states of Ni and Ir (Supplementary Fig. 7a, b). Linear combination fitting (Supplementary Fig. 7c-d) shows higher Ir oxidation in Ir/TiO2 (+3.6) than NiIr0.5/TiO2 (+2.7), and more reduced Ni in Ni/TiO2 (+1.6) versus NiIr0.5/TiO2 (+1.8), indicating electron transfer from Ni to Ir, later corroborated by in situ analyses. Extended X-ray absorption fine structure (EXAFS) at the Ir L3-edge provides atomic-scale coordination details (Fig. 1i). All samples exhibit a prominent peak at ~1.60 Å and a relatively weaker peak at ~2.56 Å, corresponding to Ir-O scattering and Ir-Ir scattering, respectively. Notably, NiIrx/TiO2 samples exhibit an additional peak at 2.18 Å, which can be attributed to Ni-Ir scattering. These results demonstrate that NiIr nanoclusters exhibit a partially oxidized state, with electronic modulation between Ni and Ir atoms. The partial oxidation probably arises from the interface reconstruction between nanocluster and the surface lattice O atoms of TiO2 during the calcination process and the exposure to air during storage. This electronic structure, coupled with their ultrafine size, positions these partially oxidized NiIr nanoclusters (Ox-NiIr) as promising candidates for the adsorption of CH4 and CO2 due to their inherent thermal instability19.

In situ CO probe molecule diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) analyses were conducted to unravel the surface structure and adsorption behavior of NiIr nanoclusters (Supplementary Fig. 8 and Fig. 1j). Ni/TiO2 exhibited negligible *CO chemisorption signals (<2100 cm-1), which vanished entirely upon heating to 100 °C. This confirms the inadequacy of individual Ni sites for CO adsorption. In contrast, Ir-containing samples (NiIrx/TiO2, Ir/TiO2) display intense *CO chemisorption bands (2100–1990 cm-1), with adsorption strength scaling with Ir content. Heating-up desorption revealed a volcanic trend: *CO intensity peaked at 200 °C and declined continuously to 400 °C. It demonstrates reversible CO binding, which is a critical feature for sustaining DRM activity. Detailed comparison of the desorption spectra at 25 °C (Fig. 1j) highlights distinct Ir coordination environments. For Ir/TiO2, three CO species were resolved: (i) multi-carbonyl Ir-(CO)n (2068 cm-1, low-coordination sites)24, (ii) linear CO on metallic Ir (Ir-CO, 2033 cm-1)25, and (iii) bridged CO at Ir-TiO2 interfaces (Ir-if-CO, 1994 cm-1)26. For Ni/TiO2, only weak peaks of Ni-CO and Ni-if-CO can be observed. In NiIrx/TiO2, the dominant Ir-(CO)n peak progressively shifts downward (2063→2044 cm-1) with increasing Ir content, signaling enhanced π-backdonation from Ir to CO. The observed redshift arises from Ni-to-Ir electron transfer, which elevates Ir’s d-orbital occupancy, strengthens Ir-C bonds, and weakens C-O bonds. These results confirm that in partially oxidized NiIr nanoclusters, Ir serves as the main center for CO adsorption, while Ni modulates Ir’s electronic properties to optimize the balance between adsorption strength and desorption kinetics.

Photoelectric-photothermal synergy in light-driven dry reforming of methane over NiIr/TiO2
Light-driven DRM over TiO2-supported NiIr nanoclusters was investigated under full-spectrum irradiation (Supplementary Fig. 9). Ni and Ir modification significantly enhanced DRM activity compared to pure TiO2 (Fig. 2a, Supplementary Fig. 10). NiIr0.5/TiO2 achieved optimal performance (Fig. 2a, Supplementary Fig. 11 and Note 1) with syngas generation rates of 2512 mmol g-1cat h-1 and feed gas conversions near 60% at the condition of CH4:CO2:Ar = 1:1:8. Increasing the Ir/Ni ratio (x) from 0.05 to 1.0 elevated H2/CO from 0.68 to 1.03, demonstrating Ir-Ni synergy in balancing CH4-CO2 activation (Fig. 2a). NiIr0.15/TiO2 (equivalent Ir loading to 0.5% Ir/TiO2) exhibited 2.13-fold higher activity (CH4 conversion: 17%→42%), underscoring the critical role of bimetallic interactions. Highly diluted conditions (CH4:CO2:Ar = 1:1:98) achieved 90% conversion (Fig. 2b). Strikingly, at undiluted feed gas, the system achieved syngas generation rates of 10841 mmol g-1cat h-1, with a LTFE of 25.0% and a TOF of 23 s-1. However, for gas conservation and safety considerations, subsequent tests were conducted using a feed gas mixture of CH4:CO2:Ar = 1:1:8. Light irradiation dramatically reduced the apparent activation energies for CO and H2 production to 35.33 and 44.65 kJ mol-1, respectively, which is less than half those of thermal catalysis (68.76 and 99.19 kJ mol-1), effectively breaking the limitation of thermal catalysis (Fig. 2c, Supplementary Fig. 12).

Activity surged above a threshold light intensity of 2 W cm-2, marking the onset of photoelectric-photothermal synergy (Fig. 2d and Supplementary Fig. 13). Specifically, at lower intensities (<1.95 W cm-2, TCenter < 336 °C), the observed activity originated predominantly from photoelectric effects. This assignment is confirmed by the sustained syngas production under illumination, which stands in clear contrast to the negligible activity observed in dark thermal catalysis experiments conducted below the 350 °C threshold (as shown in Fig. 2c and Supplementary Fig. 12a). The interplay between photothermal and photoelectric contributions peaked at 3.89 W cm-2 (TCenter = 506 °C; TAVG = 403 °C). Beyond 4.27 W cm-2, the system approached a state of photon absorption saturation. At this point, the catalyst could no longer utilize the additional photons for charge carrier generation, and consequently, the excess energy was redirected into thermal pathways. This mechanistic shift is evidenced by a distinct decline in the per-unit-light efficiency (syngas generation rates/light intensity), which occurred despite the continued rise in the catalyst temperature (TCenter exceeding 600 °C). This nonlinear response highlights the delicate balance between photocarriers generation and thermal dissipation in light-driven systems.

Controlled condensation experiments (Fig. 2e) decoupled photothermal and photoelectric effects by selectively suppressing thermal contributions. The blue trend line maintained constant light intensity (3.89 W cm-2) to preserve the photoelectric effect and used condensation cooling to suppress photothermal contributions, while the yellow trend line varied light intensity (from 3.89 to 1.30 cm-2) without condensation and diminished both effects simultaneously. By comparing the syngas production rates and H2/CO ratios from these two paths at matched catalyst surface temperatures, it was determined that the photoelectric-dominated system (with condensation) contributed 57.5% to syngas rates and 91.7% to H2/CO balance, compared to the photothermal-assisted system (without condensation). This contrast confirms that photogenerated carriers preferentially drive H-H coupling and carbon intermediate oxidation, while thermal energy primarily enhances vibration and mobility of reactants. Comparative tests on NiIr0.5/TiO2 and NiIr0.5/SiO2 (Supplementary Fig. 14 and Note 2) further confirmed that TiO2-supported NiIr nanoclusters uniquely harness coupled photothermal-photoelectric effects to achieve efficient and stable DRM catalysis.

The UV-Vis-NIR spectra (Supplementary Fig. 15) revealed that the introduction of Ni and Ir significantly enhanced broadband light absorption across the entire spectral range compared to TiO2. Crucially, the absorption profile across the full spectral range of NiIr0.5/TiO2 exhibited a strong correlation with the wavelength-dependent DRM activity (Fig. 2f), confirming that the reaction is primarily driven by photoexcitation rather than thermal effects and evidencing its light-driven nature. Long-term stability tests (Supplementary Fig. 16 and Note 3) demonstrated considerable durability as NiIr0.5/TiO2 retained >97% activity over 720 min under light, with near-unity carbon balance. In contrast, thermal catalysis at 500 °C suffered a 20% activity drop and significant carbon deposition, emphasizing light’s role in suppressing deactivation. Moreover, NiIr/TiO2 sustained 100-hour stability under 20% reactant flow during five light/dark cycles (Fig. 2g), retaining >80% syngas generation rates with H2/CO > 0.9 throughout the test. Monometallic controls (Supplementary Fig. 17) further validated Ni-Ir synergy that Ni/TiO2 rapidly deactivated due to CH4 accumulation, while Ir/TiO2 maintained 70% stability over 720 min but exhibited suppressed H2/CO ratios, probably due to RWGS side reaction.

These results reveal that UV-Vis- induced hot electrons at the NiIr-TiO2 interface, consistent with ultrafast (<10 fs) UV photo-induced electrons in TiO2 27, collaboratively cleave C-H/C=O bonds and mediate H-H coupling. Meanwhile, infrared absorption enhances local temperatures. This photoelectric-photothermal synergy suppresses carbon deposition and stabilizes active sites, achieving DRM efficiency in photothermal and even certain thermal systems (Supplementary Table 3) 7–9, 28–40.

Light-induced dynamic restructuring to form NiIr nano-island alloy on TiO2
Alloy structural evolution under operando light conditions is critical to unraveling true catalytic mechanisms, which was therefore systematically investigated. In situ X-ray absorption spectroscopy (XAS) and near-ambient pressure XPS (NAP-XPS) analyses revealed the light-induced structural reorganization of NiIr nanoclusters. Under light irradiation, Ir L3-edge EXAFS spectra of NiIr0.5/TiO2 (Fig. 3a) show a dominant Ir-Ni scattering peak at 2.18 Å, replacing the initial Ir-O coordination observed in the dark. Concurrently, Ni K-edge EXAFS of NiIr0.5/TiO2 (Fig. 3b) retains Ni-O (1.60 Å) and Ni-Ni (2.09 Å) scattering alongside emerging Ni-Ir (2.18 Å) coordination, indicating alloy formation without complete Ni reduction. In contrast, monometallic Ni/TiO2 under identical conditions transitions fully to metallic Ni-Ni bonds, while Ir/TiO2 retains residual Ir-O coordination (Supplementary Fig. 18). This indicates that during the dynamic alloy formation under light, electrons are transferred from Ni to Ir. Quantitative EXAFS fitting analysis (Fig. 3c, Supplementary Fig. 19–20, Supplementary Tables 4–5) quantifies this structural evolution. Under light irradiation, NiIr0.5/TiO2 exhibits nearly 100% Ir-Ni coordination at the Ir L3-edge and 32% Ir-Ni coordination at the Ni K-edge, alongside 37% Ni-O interfacial bonds. This contrasts sharply with monometallic Ni/TiO2. The nearly 100% Ni-Ni coordination in Ni/TiO2 likely drives its rapid deactivation (Supplementary Fig. 18), as non-oxidized Ni sites exhibit diminished ability to activate CH4 and oxidize carbonaceous intermediates, leading to CHx accumulation and irreversible poisoning. The absence of Ir-O coordination in NiIr0.5/TiO2 under light confirm that Ir in the alloy phase does not directly interact with TiO2, while Ni maintains interfacial Ni-O bonds, forming a nano-island architecture that isolates the NiIr alloy from the support (Supplementary Fig. 21). This structure formation is critical for efficient and stable DRM catalysis.

In situ NAP-XPS analyses corroborate the XAS findings. To decouple photochemical and photothermal contributions, we first monitored structural evolution under unfocused light. The Ir 4f spectra (Fig. 3d) reveal a pronounced shift toward lower binding energy, with the Ir0 fraction increasing from 36.96% (dark) to 60.65%. Upon switching to focused light, the Ir0 fraction further rises to 62.31%. Figure 3e quantifies this trend: the Ir0/Irδ+ ratio increases by 0.95 under unfocused light, with only an additional 0.11 gain under focused irradiation, demonstrating that low-intensity light suffices to initiate alloying. Monometallic Ir/TiO2 exhibits a smaller Ir0/Irδ+ increase of 0.61 under unfocused light (Supplementary Fig. 22), aligning with its higher oxidation state observed in in situ XAS. Moreover, air exposure restores the initial oxidized state (Fig. 3e, Supplementary Figs. 22–23), confirming the reversibility of the NiIr-LNi phase. Parallel in situ Ni 2p NAP-XPS (Supplementary Fig. 24a-c) shows analogous trends, with Ni0/Ni2+ ratios tracking Ir’s redox dynamics. While Ti 2p and O 1s exhibit the positive shift in the binding energy of Ti and O Lattice under light irradiation (Supplementary Fig. 24d-e), this demonstrates that electrons migrate from the TiO2 support to Ni-Ir under illumination. Post-reaction characterizations (Supplementary Figs. 25–26) reveal that prolonged light-driven DRM preserves Ni-Ir intimacy. Re-oxidation in post-EXAFS (Supplementary Fig. 27 and Note 4) and reversible NAP-XPS trends confirm that NiIr/TiO2-LNi exists transiently only under light irradiation. Thermal catalysis induces limited Ni or Ir reduction (Ir0/Irδ+ = 0.61 at 500 °C vs. 1.54 under unfocused light) and fails to form obvious Ni-Ir bonds (Supplementary Figs. 28–29), resulting in poor DRM performance. Conversely, light irradiation in pure Ar still forms dominant Ni-Ir scattering (Supplementary Figs. 30–31 and Note 5), proving that reactant gases are non-essential for NiIr alloying. Moreover, light cessation triggers rapid re-oxidation, with full structural recovery after air exposure.

Figure 3f illustrates the light-induced structural dynamics in NiIr/TiO2. Initial Ox-NiIr/TiO2 adsorbs CH4/CO2 but remains inefficient and prone to coking. Under light irradiation, interfacial oscillations drive electrons from Ni to Ir, and Ir atoms migrate away from the interface, forming NiIr island alloy anchored via oxidized Ni linkages on TiO2. The Ir-Ni binary phase diagram (Supplementary Fig. 32) and positive segregation energy (0.23 eV)41 confirm alloy feasibility under photoexcitation. We further constructed DFT structures (Supplementary Fig. 33) for a series of samples based on the above analysis and actual Ni/Ir atomic ratios. Figure 3g confirms NiIr/TiO2-LNi’s stability with a lower formation energy than the hypothetical Ir-linked model (NiIr/TiO2-LIr), where Ir-O bonds elongate (black arrow indication, >3.0 Å), destabilizing the interface. These results demonstrate that light excitation dynamically restructures Ox-NiIr/TiO2 into NiIr/TiO2-LNi. The reversibility of NiIr/TiO2-LNi under ambient conditions highlights its transient, light-governed property, serving as a suitable model for further investigation of photoelectric-dominated reaction mechanisms.

It is worth elucidating that the light-induced surface restructuring observed in this study is supported by prior findings regarding bimetallic systems. It is established that electron transfer in bimetallic clusters can drive surface segregation of one of the metals42,43. A pertinent mechanism involves atomic size, in which the introduction of a larger-radius atom (e.g., Sn in PtCu) can promote surface extraction and alloy reorganization21,44. In our system, Ir has a larger inherent atomic radius than Ni. Critically, the light-induced electron transfer from Ni to Ir reduces Ir’s oxidation state, further exacerbating this radius disparity (Ir0 > Irδ+ > Niδ+) and thereby strongly promoting the surface exposure of Ir. This process is further enabled by the photo-weakening of metal-support bonds, a phenomenon known to induce structural dynamics under illumination22,44,45. To confirm that the improved catalytic activity is induced by light-driven structural reorganization, DRM reaction experiment with external heating (Supplementary Fig. 34 and Note 6) were conducted. Under light irradiation with additional heating, a gradual decline in activity is observed over 30 min after the light is turned off. This is attributed to the immediate loss of the photoelectric–photothermal synergy, while the structural reversion of the alloy occurs more slowly, underscoring that light-induced structural reorganization together with the photoelectric-photothermal effect jointly contribute to the high DRM performance of the NiIr0.5/TiO2 catalyst.

Intermediate tracking and photoexcited charge transfer investigation
In situ synchrotron radiation-diffuse reflectance infrared Fourier transform spectroscopy (SR-DRIFTS) analysis during CO2-CH4 co-adsorption revealed distinct molecular activation patterns on NiIr0.5/TiO2 under dark conditions (Fig. 4a and Supplementary Fig. 35a). Characteristic vibrational modes emerged at 3014/1304 cm-1 (CH4 deformation), 2346 cm-1 (C=O stretching), 1354 cm-1 (OCO stretching vibration, ν(OCO)), and 1536 cm-1 (monodentate carbonate, m-CO32-), confirming robust adsorption of both reactants on partially oxidized NiIr nanoclusters. Temperature-programmed desorption (TPD) (Fig. 4b, Supplementary Fig. 35b) further demonstrated that NiIr0.5/TiO2 exhibited high CH4 chemisorption with a prominent desorption peak at 417 °C attributed to Ni-Ir dual sites, while maintaining stable CO adsorption through ensemble-dependent Ni or Ir adsorption at 546 °C.

Light irradiation or external heating induced surface intermediates over NiIr/TiO2-LNi during DRM reaction as monitored by time-resolved SR-DRIFTS (Fig. 4c-f). Under focused light, the complete conversion of m-CO32- to intensified ν(OCO) indicates light-triggered formation of NiIr/TiO2-LNi, optimizing CO2 adsorption configuration on NiIr alloy sites. Continuously detected gaseous CO (2024 cm-1), characteristic vibrations of HCO* (1786 cm-1) and *CH2 (1490 cm-1)8,46, confirmed efficient light-driven DRM activity (Fig. 4c). In contrast, dark thermal activation at 500 °C resulted in gradual emergence of attenuated CO signals after 12 min (Fig. 4d), aligning with its poor catalytic performance. Notably, transient intermediate signatures between 1120-920 cm-1 (Fig. 4e, Supplementary Fig. 36a) demonstrated ultrafast generation and decomposition of CHO* species37,47 under illumination. Conversely, thermal catalysis produced prominent C-C stretching vibrations (974 cm-1)48 (Fig. 4f, Supplementary Fig. 36b), consistent with coke accumulation observed in Supplementary Fig. 16. Isotopic mass spectrometry (Supplementary Fig. 37) revealed that photo-activated *O species primarily originated from CO2 dissociation; these *O species combined with *CHx fragments to form metastable CHxO* intermediates, establishing a dehydrogenation-dominated pathway that suppressed carbon deposition. Comparative studies of monometallic systems (Supplementary Fig. 38) highlighted the necessity of Ni-Ir synergy. Ni/TiO2 exhibited negligible CO production with C-C coupling signals (873/893 cm-1), while Ir/TiO2 promoted *COOH formation (1678 cm-1) via RWGS pathways. These findings underscore the necessity of Ni-Ir interaction in maintaining both C-H activation kinetics and intermediate stabilization.

To dissect photogenerated charge dynamics, femtosecond transient absorption (fs-TA) spectroscopy was employed (Fig. 4g, Supplementary Fig. 39a-c). Upon 325 nm excitation, all samples exhibited a ground-state bleach (GSB) at ca. 415 nm, reflecting the excited state relaxation49. Accompanied by excited state absorption (SA) between 460–570 nm, arising from electronic transitions from the singlet state (S1) to higher energy excited states (Sn)50. Notably, NiIr0.5/TiO2 displayed the pronounced TA intensity, confirming NiIr alloy-enhanced charge separation. Time-decay fitting of the SA signal at 560 nm (Fig. 4h and Supplementary Fig. 39d-f) revealed a 520.3 fs lifetime for NiIr0.5/TiO2, which was markedly longer than TiO2 (110.9 fs) or Ni/TiO2 (233.1 fs), directly evidencing retarded charge recombination via Ni-Ir interaction. In addition, compared to pure TiO2, NiIr nanoclusters show enhanced photocurrent density, lower electrochemical impedance, and quenched PL intensity; these respectively indicate stronger charge separation, faster charge transfer, and a greater number of effective photocarriers collected for reactions (Supplementary Fig. 39g-i and Note 7).

Ground-state and excited-state calculations resolved the interfacial charge transfer mechanism. Electron-density distributions (Supplementary Fig. 40a-d and Note 8) indicate Ni-mediated charge polarization enriches electrons at Ir sites. Simultaneously, density-of-states profiles (Supplementary Fig. 40e-h) reveal that NiIr alloy-induced d-band center modulation optimizes the trade-off between adsorption strength and intermediate desorption kinetics, suppressing both carbon deposition and parasitic reactions. Time-dependent DFT (TD-DFT) simulations (Fig. 4i) further identified excitation-dependent charge redistribution on NiIr/TiO2-LNi. Electrons in photoexcited states preferentially accumulate at Ir sites distal to the TiO2 interface, designating these Ir atoms as primary active centers for CO2 reduction or H-H coupling during DRM. Electron/hole (e-/h+) ratio statistics reveal preferential electron capture at both Ir and Ni sites under the S0 → S1/S2 excited state, evidencing electron migration from the TiO2 support to NiIr nanoclusters. The S0 → S2 excited state exhibits a smaller Sr index (the geometric mean overlap function of hole and electron distributions), representing less overlap between the electron and hole, and further indicating superior charge separation. Mechanistically, S0 → S2 promotes hole accumulation at Ni sites alongside electron enrichment at Ir sites, which creates a spatial charge segregation that drives photoexcited electrons toward Ir centers in higher-energy states. Computational analysis of chemical bond strength changes between the ground and excited states (Supplementary Table 6) provides further mechanistic insight. The photoinduced charge transfer weakens the chemical bonds, which synergizes with thermal effects, facilitates atomic rearrangement into a more stable configuration. A detailed comparison reveals a more pronounced bond energy difference between the excited state and the ground state in Ir-O bond (-28.06 kJ mol-1) compared to that of the Ni-O bond (-9.36 kJ mol-1). This indicates a preferential destabilization and breaking of the Ir-O bonds, thereby facilitating the migration of Ir atoms. Furthermore, under the excited state, the Ni-Ir bond (92.35 kJ mol-1) is stronger than the Ir-O bond (69.64 kJ mol-1). These bond energy differences provides support for the formation of the Ni-Ir alloy under light irradiation.

Synergy between Ni-mediated charge transfer and Ir-tailored adsorption establishes a self-optimizing catalytic cycle under illumination. Transient intermediate tracking demonstrates light-driven suppression of coking pathways through metastable CHxO* formation, while fs-TA reveals hierarchical charge transfer from TiO2 → Ni → Ir. This dual functionality, achieved through NiIr nano-island architecture, enables simultaneous enhancement of photogenerated carrier utilization and surface reaction kinetics.

Theoretical calculation of reaction mechanism and natural sunlight validation
DFT calculations (Supplementary data 1) coupled with in situ spectroscopic evidence unraveled the light-induced dynamic restructuring mechanism governing reaction pathway selectivity. Site-resolved adsorption analysis on the NiIr/TiO2-LNi model (Supplementary Fig. 41) revealed that the Ir1-Ni3 asymmetric sites exhibited optimal CO2 adsorption (Eads = -1.22 eV) via ν(OCO) configuration. In contrast, the Ni1-Ni2-O domain exhibited negligible CO2 adsorption in the form of m-CO32- (Eads = −0.03 eV). Charge complementarity between Niδ+ and Irδ- drives complete CO2 adsorption mode transition from m-CO32- under dark to ν(OCO) upon illumination, as evidenced by time-resolved SR-DRIFTS. CH4 preferentially anchors at Ir2 sites through H···Ir interaction, where accumulated electrons from Ni-mediated interfacial transfer stabilize the C-H scission transition state. Comparative studies confirmed NiIr/TiO2-LNi’s superior adsorption (Supplementary Fig. 42), with Ni/TiO2 performing poorest, which is consistent with TPD trends.

For the initial bond cleavage of CO2 and CH4 molecules as shown in Fig. 5a-b and Supplementary Figs. 43–44, NiIr/TiO2-LNi demonstrates both thermodynamic and kinetic advantages. Compared to monometallic Ni/TiO2 and Ir/TiO2, NiIr/TiO2-LNi exhibits a significantly greater energy reduction after direct C=O scission of CO2 and the first C-H scission of CH4, indicating its superior thermodynamic favorability. Meanwhile, NiIr/TiO2-LNi exhibits activation energies (Ea) of the transition states at +0.26 eV for C=O scission and +0.30 eV for C-H scission. These values are lower than the transition state barriers for the first C-H scission of CH4 and direct CO2 scission on Ni/TiO2 and Ir/TiO2, indicating the kinetic advantage of the nanoisland NiIr alloy. Supplementary Fig. 45 further compares the pathway of direct C=O scission of CO2 with the indirect activation route via *COOH pathways. The results reveal Ir/TiO2’s propensity for *COOH formation, aligning with in situ SR-DRIFTS detected RWGS activity and a suboptimal H2/CO ratio. In contrast, NiIr/TiO2-LNi enables concerted C=O scission, where Ni sites stabilizes dissociative oxygen and Ir site coordinates carbon, directly yielding CO and *O species.

Regarding the subsequent activation process after the initial bond cleavage of CH4, *CH3 may undergo further direct C-H scission until a C atom remains. Alternatively, *CH3 can be assisted by activation through combination with O species from CO2 activation (O_CO2) or lattice oxygen (O_L). Figure 5c compares the thermodynamic energy changes before and after the reaction for these three possible activation pathways. The results show that the sequential direct C-H scission pathway (*CH3 → *CH2 → *CH → *C) on NiIr/TiO2-LNi requires prohibitively high energy, particularly 1.18 eV for cleaving the second C-H bond. For the *O-assisted C-H scission routes, O_CO2-assisted pathways proved unfavorable due to the high *CH3 migration energy of 1.30 eV. Conversely, *O species from CO2 dissociation adsorbed on Ni sites in NiIr/TiO2-LNi enabled thermodynamically favorable *CH3O formation with ΔE = -0.61 eV, and subsequent dehydrogenation required only 0.29 eV, consistent with isotopic labeling results. Comparative studies between NiIr/TiO2-LNi and monometallic Ni/TiO2 and Ir/TiO2 in Supplementary Fig. 46 further highlight the optimal performance of NiIr/TiO2-LNi. Specifically, in *O_CO2-assisted pathways, while Ni/TiO2 struggled with CH4 activation exhibiting a second C-H barrier of 0.75 eV and Ir/TiO2 suffered from poor *O stabilization, the NiIr alloy achieved balanced kinetics through asymmetric Ni-Ir sites. Figure 5d quantitatively contrasts key steps that Ir/TiO2 excels in initial C-H scission but falters in *CH3O stabilization, whereas NiIr/TiO2-LNi synergizes Ir’s C-H activation prowess with Ni’s oxygen affinity, enabling stepwise dehydrogenation without carbon buildup. Product desorption studies (Supplementary Fig. 47) revealed moderate H2/CO adsorption on NiIr/TiO2-LNi, ensuring sustained catalytic turnover. In addition, Ox-NiIr/TiO2 exhibited excessive CO adsorption but poor C=O scission capacity (Supplementary Fig. 48), while thermal conditions promoted direct CH4 cracking into carbon deposits (Supplementary Fig. 49). This starkly contrasts with photoinduced NiIr nano-island alloy, underscoring light’s critical role in structural optimization. We note that our DFT calculations are based on idealized slab models and static configurations and therefore provide qualitative insight into trends rather than a completed description of the real catalyst under operando conditions.

We also conducted an outdoor DRM experiment under actual sunlight using a Fresnel lens for light concentration (Fig. 5e-f). During 2-hour sunlight irradiation, light intensity varied from 3.22 to 4.08 W cm-2, catalyst temperature ranged 438–505 °C. NiIr0.5/TiO2 exhibits a maximum syngas generation rate of 2782 mmol g-1cat h-1 (65.7% CO2 conversion) with 20% feed gas flow, indicating the feasibility of this system in the utilization of sunlight. Figure 5f and the Supplementary Movie 1 show the real-time colorimetric response of the PdCl2 indicator during the DRM reaction under focused natural sunlight. After illumination, the originally yellow PdCl2 solution gradually turns black, indicating that a large amount of CO generated in the system adsorbs on the Pd2+ sites and reduces them to Pd0, verifying the high efficiency of the NiIr/TiO2 system under natural sunlight.

Figure 5g illustrates the overall reaction mechanism. Under light excitation, Ox-NiIr/TiO2 undergoes interfacial charge oscillations, with electrons sequentially transferring from the TiO2 to Ni sites and subsequently to Ir atoms. This triggers the upward migration of Ir atoms, leading to the formation of NiIr nano-island alloys. A portion of Ni atoms act as linkages, spatially isolating the NiIr alloy from the support to form the NiIr/TiO2-LNi configuration. During light-driven DRM reaction, photoelectric effects dominate the activation of C-H and C=O bonds at NiIr alloy sites, coupled with efficient H-H coupling via localized photogenerated electrons. Concurrently, the oxygen affinity of the Ni linkages steers the reaction pathway toward the formation of key CHxO* intermediates, thereby achieving robust coking resistance. Meanwhile, photothermal effects facilitate molecular vibrations, intermediate migration, and product desorption. The synergistic interplay of photoelectric and photothermal effects on the NiIr nano-island alloy enables highly efficient and stable DRM performance.

In summary, this work reveals that light-induced NiIr nano-island alloy formation enables efficient DRM by synergizing photoelectric and photothermal effects. The interfacial charge oscillation mechanism not only stabilizes ultrafine alloy architectures against sintering but also creates dual-active sites. Specifically, Ni linkages with oxygen affinity favor coke suppression, while Ir sites modulated by Ni optimize reactant activation. Our experimental method for decoupling photoelectric/photothermal contributions reveals that photoelectric effects primarily govern syngas selectivity, achieved 25.0% LTFE and 100-h stability under practical feed conditions underscore the viability of solar-driven DRM. Importantly, the methodology combining in situ structural analysis with charge dynamics kinetics provides a universal approach to probe light–matter interactions in heterogeneous catalysis.

Methods
Catalyst preparation
Ox-NiIr/TiO2 catalysts were synthesized via an optimized directional adsorption strategy23. Typically, 200 mg of ground TiO2 nanosheets was dispersed in 0.01 M NaOH aqueous solution. After 3 h, the TiO2 was centrifuged and redispersed in deionized (DI) water through multiple cycles until the supernatant reached pH=9, ensuring a negatively charged TiO2 surface for cation adsorption. NiCl2 (Sigma-Aldrich) aqueous solution (containing Ni equivalent to 1 wt% of TiO2) was added to the TiO2 suspension and stirred for 12 h prior to centrifugation. Complete metal cation adsorption was confirmed by testing the first supernatant with NaBH4 (Thermo Fisher), which showed no color change. The cation-loaded TiO2 was washed with DI water and dried at 60 °C for 12 h. Co2+ (Co(NO3)2·6H2O, Macklin), Fe3+ (FeCl3·6H2O, Aladdin), and Pt(NH3)4 2+ ([Pt(NH3)4]Cl2, Sigma-Aldrich) cations were similarly adsorbed using their respective chloride salts.

The dried cation-loaded TiO2 was subsequently used for complex metal anion adsorption IrCl6 3- (Na3IrCl6, Sigma-Aldrich), PtCl4 2- (K2PtCl4, Sigma-Aldrich), PdCl4 2- (Na2PdCl4, Sigma-Aldrich), AuCl4 - (HAuCl4·3H2O, Sigma-Aldrich), and RuCl6 2- ((NH4)2RuCl6, Sigma-Aldrich) with controlled theoretical anion/cation atomic ratios. Anion solutions were prepared via a phase-transfer method using tetrabutylammonium cations (TBA+) in dichloromethane (TBA+/anion molar ratio = 3) under vortex mixing. After centrifugation, the dichloromethane phase was retained, and mixed with cation-loaded TiO2 in dichloromethane. After 12 h of stirring, TiO2-supported double complex salts were centrifuged, dried at room temperature, and reduced under 5% H2 flow at 400 °C for 30 min. Monometallic TiO2-supported catalysts (Ni2+ and Ir3+) were prepared analogously without anion adsorption steps.

Catalytic reactivity measurements
Light-driven DRM experiments were performed in a custom quartz reactor (Supplementary Fig. 9) at 0.1 MPa without extra heating. The reactor features an outer layer for condensate circulation and an inner chamber containing a quartz sand bed for supporting catalyst and optimize gas distribution. A type-K thermocouple (0–1150 °C range, 0.5 mm diameter, ±0.1 °C accuracy) was embedded in the quartz sand bed, with a 90°-bent tip protruding 1.0 mm above the surface. The thermocouple was pre-calibrated against standard reference sources, and its performance was verified at multiple temperature setpoints to ensure consistency across the experimental range. TCenter (the center temperature of catalyst surface) was detected by the thermocouple probe placed in direct contact with the upper surface of the catalyst at its center, enabling capture of the highest local temperature under irradiation (as shown by the red indicator line representing the thermocouple in Supplementary Fig. 9). This arrangement minimizes the thermal resistance effect by avoiding indirect measurement through the gas phase or reactor materials. Infrared (IR) thermography was used to validate the accuracy of TCenter measurements from the thermocouple probe. TAVG (average surface temperature) was obtained by moving the thermocouple probe, measuring temperatures at five different points on the catalyst surface (center and edges) and using the formula below:

TAVG = (TCenter + 2×TEdge) / 3 (1)

Catalyst (5 mg) was dispersed in DI water (1.0 mL), spread on a quartz fiber membrane, and vacuum-dried. The membrane was positioned on the quartz sand bed, and depressed by a tweezer align the thermocouple tip flush with the catalyst surface. Real-time temperature monitoring at catalyst center and edge positions was achieved by adjusting the thermocouple position via its stretchable connector. Note that unlike conventional temperature probes positioned below the catalyst, our small-diameter temperature probes are placed directly on the catalyst surface, enabling more accurate and sensitive temperature measurement. Prior to irradiation using a 300 W Xe lamp (PLS-SXE 300+, Beijing PERFECTLIGHT; spectral range: 300–1000 nm), the reactor was introduced with CH4: CO2 (1:1) gas mixture at 20 mL min-1. A biconvex lens (diameter: 70 mm) was employed for light focusing. Light intensity was controlled by adjusting lamp current and measured using an optical power meter (range: 0–20 W, resolution: 1 mW).

Thermal catalytic tests were conducted in a dedicated reactor (PLR-PTSR II, Beijing PERFECTLIGHT) under dark conditions, using identical catalyst supporting and thermocouple configurations to those in the custom quartz reactor. Natural sunlight experiments utilized the custom quartz reactor with Fresnel lens focusing. All other experimental parameters (gas flow, catalyst weight, etc.) remained consistent across light-driven, thermal, and natural sunlight conditions.

The monochromatic light activity tests were carried out in a dedicated reactor (PLR-PTSR II, Beijing PERFECTLIGHT) with external heating at 500 °C. A 300 W Xenon lamp was used as the light source, coupled with optical filters to obtain monochromatic light of specific wavelengths. In each test, an optical power meter was used to accurately measure and calibrate the incident light intensity in front of the reactor window. Dividing the measured syngas generation rates by the light intensity under the corresponding monochromatic light yields the contributions of monochromatic light at different wavelength bands to the activity per unit light intensity. All other test conditions were consistent with those of the light-driven conditions.

The CO products were analyzed by GC with a flame-ionization detector (FID). H2 was analyzed by GC with a high-sensitivity thermal conductivity detector (TCD). The H2 and CO generation rates were defined as follows:

RH2 = CoutH2 × Fout × 60 = (Vm × M) (2)

RCO = CoutCO × Fout × 60 = (Vm × M) (3)

Where RH2 (mmol g-1 h-1) and RCO (mmol g-1 h-1) are the H2 and CO generation rates, respectively. CoutH2 (dimensionless) and CoutCO (dimensionless) are the concentrations of H2 and CO detected by gas chromatography. Fout (ml/min) is the space velocity of the gas exiting the reactor, Vm (L/mol) is the gas molar volume under standard conditions, and M (g) is the mass of catalyst. 60 refers to the exponent needed to convert ml/min into the standard unit ml/h.

The CH4 and CO2 conversion were defined as follows:

CH4 conversion: XCH4 (%) = (CinCH4 - CoutCH4) / CinCH4 × 100 (4)

CO2 conversion: XCO2 (%) = (CinCO2 - CoutCO2) / CinCO2 × 100 (5)

Where Cin (dimensionless) and Cout (dimensionless) indicate the inlet and outlet concentration of products detected by gas chromatography, respectively.

Total carbon balance is considered using the following equation:

Total carbon balance = (CoutCO + CoutCO2 + CoutCH4) / (CinCO2 + CinCH4) × 100 (6)

TOF under kinetics-controlled regime per second can be calculated with the following equation:

TOF (s-1) = (Number of produced H2 per second + Number of produced CO per second) / (0.5 × Nactive metal × Dispersion) (7)

The LTFE (η) was determined with the following equation:

η = (RH2 × ΔHoCH2 + RCO × ΔHoCCO + RCH4 × ΔHoCCH4) × M / P_irradiation (8)

Where RH2 (mmol g-1 h-1), RCO (mmol g-1 h-1) and RCH4 (mmol g-1 h-1) are the H2, CO generation rates, and CH4 conversion rates. ΔHoCH2, ΔHoCCO, and ΔHoCCH4 are the standard combustion heats (298.15 K) of H2, CO, and CH4 as fuels, respectively. Note that the ΔHoCCO2 is 0. M (g) is the mass of catalyst. P_irradiation (W) is the irradiation power.

Characterization
HAADF-STEM imaging was performed on an aberration-corrected FEI Themis Z instrument, with a convergence semi-angle set to 11 mrad and annular detection ranges of 59 mrad (inner) and 200 mrad (outer). Elemental mapping and EDS analysis were carried out utilizing the integrated four-quadrant Super-X detector system. Powder XRD measurements were obtained using a Rigaku D/MAX 2550 diffractometer equipped with Cu Kα radiation (λ = 1.5406 Å), operating at 40 kV and 40 mA, with 2θ scanned from 10° to 80°. Raman spectroscopy was performed on a Renishaw inVia system using a 532 nm laser excitation source. UV–Vis-NIR diffuse reflectance spectra were recorded using a Varian Cary 500 spectrophotometer equipped with an integrating sphere, using BaSO4 as a reference. For sample preparation, the powder sample was pressed into a flat, uniform pellet in a culture dish to ensure data reliability and reproducibility. The absorbance was represented by the Kubelka-Munk function:

F(R) (where F(R) = (1-R)2 / 2R) (9)

which is derived from the measured reflectance data. Inductively coupled plasma atomic emission spectrometry (ICP-AES, Varian 730-ES, Agilent) quantified the metal loadings of catalysts. Thermogravimetric analysis (TGA) of spent catalysts was conducted on a Netzsch STA449F5 analyzer under air flow (50 mL min-1), heating from 100 °C to 800 °C at 10 °C∙min-1. Temperature-programmed desorption (TPD) experiments were performed on an AutoChem II 2920 (Micromeritics, USA) in pure He, ramping to 770 °C at 10 °C∙min-1. H2-O2 titration was performed on a temperature programmed chemisorption analyzer (VDSorb-91i) to measure metal dispersion. Photoluminescence (PL) spectra were acquired at room temperature using a Cary Eclipse fluorescence spectrometer (Agilent). Femtosecond transient absorption (fs-TA) spectroscopy was performed on a Helios pump-probe system (Ultrafast Systems, USA) with an 800 nm Ti:sapphire laser (Coherent Legend, 85 fs pulse width, 1 kHz repetition rate). The pump beam (325 nm, 80 μW) was generated via frequency doubling in a β-barium borate (BBO) crystal, while the probe beam (near-infrared continuum) monitored photoexcited states. Isotope labeling experiments employed a high-precision gas isotope mass spectrometer (Nu Instruments Horizon, UK): a 1:1 mixture of CH4 and C18O2 was introduced into a batch reactor in the dark, followed by 15-min irradiation (300 W Xe lamp, 3.89 W cm-2). Reaction products were cryogenically separated and analyzed for C16O and C18O isotopes.

In situ XAS measurements conditions
In situ XAS measurements at Ir L3-edge and Ni K-edge were performed with Si(111) crystal monochromators at the BL14W Beamline at the Shanghai Synchrotron Radiation Facility (SSRF) (Shanghai, China). Typically, the powdered sample was pressed into a self-supporting wafer and placed into a reaction microdevice equipped with an extra window for light irradiation. Before the test, the sample surface was purged with Ar gas flow (50 ml min-1). Afterwards, the gas mixture (CH4: CO2: Ar = 1:1:8) or pure Ar was continuously introduced into the reactor with a flow rate of 20 mL min-1. The microdevice was irradiated by the 300 W Xe lamp at the light intensity of 3.89 W cm-2. The XAFS spectra were recorded in situ in the dark or after 10-min light irradiation. The data reduction and analysis of the XAFS spectra were conducted using the Demeter software package (ATHENA and ARTEMIS, respectively)51. All fits were performed in the R space with a k-weight of 2.

In situ NAP-XPS conditions
In situ NAP-XPS experiments were conducted on a SPECS Proven-X NAP instrument (Germany) equipped with a monochromatic X-ray source μ-FOCUS 600 NAP. Prior to the test, the sample surface was cleaned using an Ar gas flow (50 ml min-1). Subsequently, a gas mixture (CH4: CO2: Ar = 1:1:8) or pure Ar was continuously introduced into the reactor with a flow rate of 20 mL min-1. The NAP-XPS spectra were recorded in situ in the dark or after 10-min light irradiation. The irradiation started with unfocused light at an intensity of 1.58 W cm-2 and then switched to focused light at 3.89 W cm-2. Noted that under light conditions, no additional heating was applied, while under thermal conditions, the heating temperature was set at 500 °C. The NAP-XPS spectra were obtained with charge correction, using the C 1s binding energy of 284.60 eV as the energy reference.

In situ SR-DRIFTS conditions
In situ synchrotron radiation DRIFTS were performed at the BL01B Beam line at the Shanghai Synchrotron Radiation Facility (SSRF) (Shanghai, China). The spectra were recorded by a Bruker infrared spectrometer (70 V) equipped with a liquid nitrogen-cooled mercury-cadmium-telluride (MCT) detector. Integrated with a high-brightness synchrotron radiation source, the setup achieved a spatial resolution near the theoretical diffraction limit, producing infrared spectra with high intensity and signal-to-noise ratio. The catalysts were first sealed in the chamber and purged with an Ar gas flow (50 ml min-1). Subsequently, a flowed mixture gas (CH4: CO2: Ar = 1:1:8) or pure Ar was introduced into the chamber with a flow rate of 20 mL min-1. The chamber was then irradiated with the 300 W Xe lamp at a light intensity of 3.89 W cm-2.

In situ CO-probe DRIFTS conditions
In situ CO-probe DRIFTS was recorded by a Fourier-transform infrared spectrometer (Bruker VERTEX 80v, Germany) equipped with a designed reaction cell. Catalysts were initially degassed at 100 °C for 1 h and then cooled to 25 °C under a flow of Ar (50 ml min-1). Subsequently, catalysts were exposed to a mixture of 20% CO in Ar (30 ml min-1) for 30 min at 25 °C, which proved sufficient to saturate the catalyst surface. After saturation, the CO flow was replaced with an Ar flow (30 ml min-1), and CO DRIFTS spectra were collected at 25 °C for 25 min. Then, the temperature was sequentially increased to 100 °C, 200 °C, 300 °C, and 400 °C, with spectra recorded at each temperature for 10 min.

Electrochemical measurements
Electrochemical measurements were conducted at room temperature using a Zahner Zennium potentiostat (Zahner-elektrik GmbH, Germany) with a three-electrode configuration: a fluorine-doped tin oxide (FTO) working electrode, a graphite counter electrode and a saturated calomel reference electrode (SCE). For working electrode preparation, 5 mg of catalyst was dispersed in 0.5 mL ethanol, and 20 μL of the slurry was drop-cast onto FTO (1 cm2 active area) and dried under ambient conditions. Transient photocurrent responses were measured in N2-saturated 0.5 M Na2SO4 under 300 W Xe lamp irradiation. The pH of the 0.5 M Na2SO4 electrolyte was measured to be 6.8 ± 0.1 (n=3). Electrochemical impedance spectroscopy (EIS) was performed in the frequency range from 100 kHz to 0.1 Hz using an N2-saturated potassium ferricyanide mixed electrolyte (25 mM K3Fe(CN)6, 25 mM K4Fe(CN)6, and 0.1 M KCl), whose pH was 7.0 ± 0.1 (n=3). All electrochemical measurements were performed without iR correction. All potentials were converted to the reversible hydrogen electrode (RHE) scale according to the formula below:

ERHE = ESCE + 0.241 V + 0.059 × pH (10)

where 0.241 V is the standard potential of the saturated calomel electrode versus RHE at 25 °C.

Theoretical calculations
All density functional theory (DFT) calculations were performed using the Materials Studio software and the Vienna ab initio simulation package (VASP)52–54. The exchange-correlation interactions were treated within the generalized gradient approximation (GGA), employing the Perdew–Burke–Ernzerhof (PBE) functional55,56. The projector augmented-wave (PAW) method was used to describe core-valence electron interactions, with a plane-wave basis set and a kinetic energy cutoff set to 400 eV. The Gaussian smearing scheme with a width of 0.05 eV was applied for partial orbital occupancy. Convergence criteria were set to 10-5 eV for electronic self-consistent iterations and 0.05 eV/Å for ionic relaxation during geometry optimization. A vacuum layer of 15 Å was added perpendicular to the surface model to avoid periodic interactions. For surface calculations, the Brillouin zone was sampled using a 2 × 2 × 1 Monkhorst–Pack k-point mesh. The adsorption energy was calculated according to the following formula:

Ead = EA-S - (ES + EA) (11)

where EA-S is the energy of the slab together with the adsorbate, EA is the total energy of the free adsorbate and ES is the total energy of the bare slab.

The d-band center (εd) was calculated as follow formula:

εd = ∫+1-1 n_d(ε)εdε / ∫+1-1 n_d(ε)dε (12)

The transition states corresponding to elementary reaction steps were located using a sequential approach combining the nudged elastic band (NEB) and dimer methods57. First, the reaction pathway connecting the reactant and product states was sampled using the NEB method, which represents the path as a discrete set of structural images. From this set, the image possessing the highest energy, indicative of the most probable transition state configuration, was selected. This structure subsequently served as the initial guess for precise transition-state optimization using the dimer method.

Excitation-dependent charge redistribution calculations are performed with ORCA software58. The functional employed was PBE0, and the basis set used was def2-SVP. (This basis set is an all-electron basis set for the first four periods and a pseudopotential basis set starting from the fifth period, so no mixed basis set is required.) The electron-hole structures were calculated using Multiwfn59, and the visualization data were obtained using the visual molecular dynamics VMD software60. The geometric mean overlap function of hole and electron distributions (S) was calculated as follows:

Sr(r) = √[ρhole(r)ρele(r)] (13)

ρhole and ρele represent the electron density of the hole and the excited electron at the spatial position r, respectively.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "In this work, Zhang et al. reported light-driven restructuring generated nano-island alloy catalyst NiIr/TiO2-LNi, which demonstrated excellent catalytic activity during photothermal methane dry reforming reaction. The authors carefully studied the catalytic reaction process, the role of each component, and the reaction mechanism by combining in situ characterization, theoretical calculations and controlled experiments under different conditions. However, some of the key conclusions lacks of solid evidence, and the necessary experiment must be supplemented before accepted. Here are several issues that should be concerned:\n1. The authors provides the completely opposite conclusion in the Supplementary information and main text. In the manuscript, the conclusion was that “the reactant gases are non-essential for NiIr alloying”, while the Supplementary information in Note 6 demonstrated that “reactant gases are dispensable for alloy formation”. From the author's argument, it seems that the conclusion of SI might have been written wrongly. If the increase in activity is caused by light-induced structural reorganization, then will the material excited by light be able to enhance its activity when used in a thermal catalytic reaction?\n2. In the conclusion that \"Under light excitation, Ox-NiIr/TiO undergoes interfacial charge oscillations…This triggers the upward migration of Ir atoms, leading to the formation of NiIr nano-island alloys\", the key evidence is lost. The author merely discovered through XPS and XAS that there was an electron transfer process of Ni-ir under light conditions, but this does not necessarily imply the formation of a nano-island structure. Furthermore, before the illumination, what is the state of the Ir atoms? And how does the illumination cause the migration of the Ir atoms?\n3. The results of PL and EIS tests show that Ir/TiO exhibits the best ligh-induced charge separation ability, while NiIr0.5/TiO shows the strongest current intensity in i-t curves. This seems to be contradictory, and the more detailed explanation should be included.\n4. When the Ni/Ir ratio of NiIr/TiO is larger than 0.5, why does the H2/CO ratio increase while the total yield of the product decreases?\n5. The evidence of the direction of electron transfer is insufficient, the XPS results of Ti and O orbits should be included to prove the electron transfer pathway of O-Ni-Ir. Moreover, it is generally considered that the appearance of completely overlapping peaks in XPS spectra is incorrect. In this manuscript, many such cases occur in the NAP-XPS spectra.\n6. The fonts in all charts are too small, compromising readability. We recommend increasing the font size. Additionally, some figures present excessive content, making them challenging to interpret; for instance, Figure 1d could be simplified. Finally, Figure 4g appears to lack necessary annotations, which should be added for clarity.\n7. Why does the photoelectric effect disappear when the light intensity larger than 3.89 W/cm2, and how to distinguish the contribution of photoelectric effect and photothermal effect? And how is the TAVG (average surface temperature of the catalyst) in Figure 1d calculated?\n8. There are some conclusions without evidence or reference in the manuscript, such as “Activity surged above a threshold light intensity of 2 W cm-2, marking the onset of photoelectric-photothermal synergy (Fig. 1d)”, and “Beyond 4.27 W cm-2, photon absorption saturation redirected excess energy into thermal pathways, diminishing the per-unit-light efficiency despite continued temperature increases (TCenter > 600 °C).” There is no reference or experimental evidence to support these conclusions.\n9. The light intensity and temperature in the monometallic control experiment should be included. Under the same conditions, why is the catalytic activity of NiIr0.5/TiO with condensation equipment better than that without it?\n10. The explanation for Figure 1 f is too simplistic. Under the full-spectrum condition, both the Ir and Ni surfaces can be excited by light to generate hot electrons. Moreover, Fig 1f shows Ir has a stronger light absorption ability to than Ni. Will the LSPR effect on Ir trigger the transfer of hot electrons to Ni?\n11. There is a mistake in Figure 2c, where there are two “Ir foil” in the figure. Moreover, in the sentence of \"The S0→S2 excited state exhibits a smaller Sr index, directly indicating superior charge separation\", it seems that \"Sr\" here might be written wrongly.", "reviewer_2": "This paper investigates the structural dynamic evolution of NiIr/TiO2 under light irradiation, which represents a critical challenge in light-driven catalysis. Furthermore, the NiIr/TiO2 system demonstrates comprehensively favorable efficiency in the dry reforming of methane reaction, with its anti-coking mechanism thoroughly explained. The authors’ elegant experimental design using condensation equipment and light intensity thresholds to deconvolute photoelectric and thermal effects is methodologically sound and mechanistically informative. Overall, this work is innovative, and the experimental results sufficiently support the conclusions. Therefore, I recommend this paper for acceptance in Nature Communications after the following revisions.\n1. In the catalyst preparation section, the authors state: \"By conducting the adsorption process in an aprotic solvent and introducing an anionic Ir precursor complexed with quaternary ammonium, we minimized competitive adsorption of Ni and Ir and effectively reduced metal leaching.\" Please clarify the specific role of the quaternary ammonium in this process. Explain why IrCl3 could not be used directly for targeted adsorption instead of the complexed precursor. If this strategy effectively overcomes the drawbacks of conventional co-impregnation methods, its clear explanation will provide valuable guidance for future synthesis.\n2. The authors provide a detailed discussion of the morphology and structure of TiO2-supported partially oxidized NiIr nanoclusters (Ox-NiIr/TiO2) in the Supplementary Information, demonstrating Ni-Ir interactions while maintaining their oxidized states via the cationic-anionic pair adsorption strategy. This information is fundamental for understanding the subsequent structural dynamic transformations. Please consider moving this discussion to the main text if space permits.\n3. The accuracy of temperature measurement is critical for understanding photothermal effects. The authors used a thermocouple to monitor the catalyst temperature, but significant thermal resistance between the gas phase and the thermocouple may lead to inaccurate readings, as noted. It is necessary to clarify the detailed setup of temperature measurement (e.g., thermocouple position, calibration methods) or explain how potential thermal resistance effects were mitigated. Additionally, whether complementary methods such as infrared thermography were used to verify the measured temperatures should be addressed.\n4. In Fig. 1f, the UV-VIS-NIR spectrum shows an absorption intensity of ~1.35 in the ultraviolet region, which theoretically should be below 1 for diffuse reflectance spectra. The authors need to explain this discrepancy, including details of the measurement parameters (e.g., baseline correction, sample preparation) that might lead to this result. Furthermore, the experimental setup and operational details of the monochromatic light activity tests (marked by red dots) should be elaborated.\n5. The oxidation state of the catalyst under light-off conditions is a concern. The authors mention that the catalyst contacts air when the light is turned off, and Ni and Ir are prone to oxidation. However, the in situ XAS results (Fig. 2a and b) indicate non-negligible Ni-O and Ir-O signals even under illumination, suggesting that oxidized states coexist with metallic states. It is necessary to discuss whether the reaction mechanism changes when the catalyst is in an oxidized state, especially during light-off periods.\n6. The caption for Supplementary Fig. 9 requires verification to ensure it accurately corresponds to the labels within the figure itself, facilitating reader comprehension. Fig. 4g is missing its caption. The authors need to perform a thorough check of all figure caption information.", "reviewer_3": "Authors performed experiments and DFT calculations to explore a light-driven methane dry reforming strategy utilizing sinter-resistant nano-island alloys catalyst (NiIr/TiO -LNi). This manuscript addresses an important topic in photocatalytic materials design. However, significant flaws in methodology, analysis, and mechanistic interpretation necessitate major revision before further consideration.\n1.In the theoretical calculation section, the Monkhorst-Pack k-point sampling was generated with a 1×1×1 grid. For two-dimensional structure (NiIr/TiO -LNi), a minimum of 2×2×1 grid should be used.\n2.Regarding dynamic reconstruction, the following questions arise:\na.“This photoinduced charge transfer may alter the electronic structure of surface chemical bonds, reducing bond energies and promoting dynamic surface reconstruction.” This statement lacks evidence.\nb.Regarding structural rationality, how light exposure selectively breaks Ir-O bonds while enabling their reformation in darkness — a claim implying dynamic reversibility without supporting DFT evidences?\n3.The manuscript insufficiently clarifies the origin of photogenerated electrons in NiIr/TiO -LNi under illumination. Crucially, the text fails to explicitly state:\na.What physical mechanism drives their generation?\nb.What mechanism drives their generation?\n4.The positive and negative values of the Mulliken charges analysis should be explained.\n5.For the proposed reaction pathways, critical bond-breaking steps (e.g., *CO → *CO*O, *CH → *H*CH ) require transition state analysis with corresponding energy barriers. Without these kinetic validations, the mechanistic pathway lacks practical significance and fails to establish a credible catalytic cycle.\n6.For Fig.4c, regardless of the catalyst structure employed, since reactants and products remain identical, the energy of initial and final states should be identical relative to those reactants and products.\n7.CO has a linear configuration in its free state, While all adsorbed CO species in this study exhibit a bent (V-shaped) geometry."}, "author_response": "Reply to the Comments of Reviewers\nResponse to Reviewer 1\nGeneral comments: In this work, Zhang et al. reported light-driven restructuring generated nano-island alloy catalyst NiIr/TiO -LNi, which demonstrated excellent catalytic activity during photothermal methane dry reforming reaction. The authors carefully studied the catalytic reaction process, the role of each component, and the reaction mechanism by combining in situ characterization, theoretical calculations and controlled experiments under different conditions. However, some of the key conclusions lacks of solid evidence, and the necessary experiment must be supplemented before accepted. Here are several issues that should be concerned:\nReply: We appreciate the reviewer for the careful reading of our manuscript and providing valuable comments, which has helped us further clarify and improve the manuscript. Since our manuscript was directly transferred from Nature Catalysis to Nature Communications, and Nature Catalysis has strict word limits, we included many detailed Notes in the Supplementary Information. We apologize if this has caused any inconvenience during your previous reading. The suggestions and comments have been carefully considered, and we made the corresponding revision to address the points the reviewer has raised, as shown below. We hope our revision can make the paper much more acceptable for publication in the Nature Communications.\nComment 1: The authors provide the completely opposite conclusion in the Supplementary information and main text. In the manuscript, the conclusion was that “the reactant gases are non-essential for NiIr alloying”, while the Supplementary information in Note 6 demonstrated that “reactant gases are dispensable for alloy formation”. From the author's argument, it seems that the conclusion of SI might have been written wrongly. If the increase in activity is caused by light-induced structural reorganization, then will the material excited by light be able to enhance its activity when used in a thermal catalytic reaction?\nReply: We sincerely thank the reviewer for this valuable comment, which has helped us further clarify and improve the manuscript.\n(1) We would like to clarify that the conclusion in the main text “the reactant gases are non-essential for NiIr alloying” is consistent with the characterization and statement in the Supplementary Information. The word “dispensable” in Note 5 (the original Note 6) has the same meaning as “non-essential”. Moreover, as evidenced by Fig. 3, Supplementary Figs. 30-31, and Supplementary Note 5 in the revised version, under light irradiation, the characteristic of NiIr alloy formation is observed both in the Ar atmosphere and in the CO -CH atmosphere. This confirms that the presence of CH and CO is not required for the formation of nanoisland NiIr alloy, more importantly, light irradiation is the key driving factor for NiIr alloying. The reviewer’s misunderstanding may have arisen from our inconsistent wording (non-essential vs dispensable) in the original Supplementary Information and main text. We now use the same word “non-essential” in Supplementary Note 5.\n(2) Regarding the question of whether the increase in activity is caused by light-induced structural reorganization:\nLight not only induces the formation of NiIr alloy structure (as is evidenced in Fig. 3 and Supplementary Figs. 28-31 in the revised version) but also introduces photoelectric-photothermal synergistic effects (as is evident Fig. 2e in the revised version).\nTo further assess the effect of light-induced alloying on the DRM activity, we conducted experiment as suggested by the reviewer. In this experiment, an automatically temperature-controlled photothermal reactor was used. When external light irradiation is applied, an unavoidable temperature increase of the system occurs, and the instrument automatically reduces the power of external heating in order to maintain the preset overall temperature. First, we carried out a conventional thermocatalytic run (see below Supplementary Fig. 34). Under pure heating, the reaction activity is low (CO production rate is lower than 200 mmol g -1 h-1) and the H /CO product cat 2 ratio is far less than 1. After the system was held at 500 °C for a period of time, introducing light resulted in an instantaneous increase in activity (CO production rate is close to 1200 mmol g -1 h-1). This is because the emergence of the photoelectric-photothermal synergistic effect strongly promotes the reaction, and the light-induced structural transformation can proceed rapidly, so that, under the combined contribution of the newly formed alloyed active structure and the photothermal-photoelectric synergy, an activity far exceeding that of the purely thermal process is achieved, with the H /CO ratio approaching 1. Importantly, when the light was switched off while the temperature was kept constant at 500 °C, the activity decreased gradually over the following ~30 min rather than dropping immediately. This is because, after the light is turned off, the photoelectric-photothermal synergy vanishes instantaneously, whereas the reversion of the alloy structure is much slower (see Fig. 3e and Supplementary Fig. 31 in the revised version). As a result, for a certain period after the light is off, the activity remains higher than that before illumination, which confirms that light has induced a structural transformation of the catalyst, and that the NiIr alloy, even under purely thermal conditions, still exhibits higher activity than the non-alloyed structure. Eventually, in the absence of light, the NiIr alloy structure gradually returns to its pre-illumination state, and both the activity and the product distribution approach their initial values.\nTherefore, it can be concluded that light-induced structural reorganization together with the photoelectric-photothermal effect jointly contribute to the high DRM performance of the NiIr /TiO catalyst.\nRevision made:\n(1) The original sentence in Supplementary Information has been revised to the following contents: Notably, light irradiation in Ar still induces a distinct Ni-Ir scattering peak at 2.18 Å in the Ir L -edge EXAFS spectra (Supplementary Fig. 30), confirming that reactant gases are non-essential for the formation of NiIr alloy, while the light irradiation is the critical factor driving NiIr alloying. (Please refer to the marked contents on page 32 in the supplementary information.)\n(2) The following contents have been added into Manuscript and Supplementary Information:\nTo confirm that the improved catalytic activity is induced by light-driven structural reorganization, DRM reaction experiment with external heating (Supplementary Fig. 34 and Note 6) were conducted. Under light irradiation with additional heating, a gradual decline in activity is observed over 30 minutes after the light is turned off. This is attributed to the immediate loss of the photoelectric–photothermal synergy, while the structural reversion of the alloy occurs more slowly, underscoring that light-induced structural reorganization together with the photoelectric-photothermal effect jointly contribute to the high DRM performance of the NiIr /TiO catalyst.\n(Please refer to the marked contents on lines 323-330 in the manuscript.)\nSupplementary Fig. 34. DRM performance of NiIr /TiO under light on/off conditions under 0.5 2 external heating at 500 ℃.\n(500 ℃ external heating, CH :CO :Ar =1:1:8, the light intensity is 3.89 W cm-2).\n4 2\nSupplementary Note 6.\nTo further assess the effect of light-induced alloying on the DRM activity, we conducted a DRM reaction experiment with external heating. In this experiment, an automatically temperature-controlled photothermal reactor was used. When external light irradiation is applied, an unavoidable temperature increase of the system occurs, and the instrument automatically reduces the power of external heating to maintain the preset overall temperature. First, we carried out a conventional thermocatalytic run (Supplementary Fig. 34). Under pure heating, the reaction activity is low (CO production rate is lower than 200 mmol g -1 h-1) and the H /CO product ratio is far less than 1.\ncat 2\nAfter the system was held at 500 ℃ for a period of time, introducing light resulted in an instantaneous increase in activity (CO production rate is close to 1200 mmol g -1 h-1). This is because the emergence of the photoelectric-photothermal synergistic effect strongly promotes the reaction, and the light-induced structural transformation can proceed rapidly, so that, under the combined contribution of the newly formed alloyed active structure and the photothermal-photoelectric synergy, an activity far exceeding that of the purely thermal process is achieved, with the H /CO ratio approaching 1. Importantly, when the light was switched off while the temperature was kept constant at 500 ℃, the activity decreased gradually over the following ~30 min rather than dropping immediately. This is because, after the light is turned off, the photoelectric-photothermal synergy vanishes instantaneously, whereas the reversion of the alloy structure is much slower (as shown in Fig. 3e and Supplementary Fig. 31). As a result, for a certain period after the light is off, the activity remains higher than that before illumination, which confirms that light has induced a structural transformation of the catalyst, and that the NiIr alloy, even under purely thermal conditions, still exhibits higher activity than the non-alloyed structure. Eventually, in the absence of light, the NiIr alloy structure gradually returns to its pre-illumination state, and both the activity and the product distribution approach their initial values. Therefore, it can be concluded that light-induced structural reorganization together with the photoelectric-photothermal effect jointly contribute to the high DRM performance of the NiIr /TiO catalyst.\n(Please refer to the marked contents on page 36 in the supplementary information.)\nComment 2: In the conclusion that “Under light excitation, Ox-NiIr/TiO undergoes interfacial charge oscillations. This triggers the upward migration of Ir atoms, leading to the formation of NiIr nano-island alloys”, the key evidence is lost. The author merely discovered through XPS and XAS that there was an electron transfer process of Ni-ir under light conditions, but this does not necessarily imply the formation of a nano-island structure. Furthermore, before the illumination, what is the state of the Ir atoms? And how does the illumination cause the migration of the Ir atoms?\nReply: We sincerely thank the reviewer for this valuable comment, which has helped us further clarify and improve the manuscript.\n(1) Regarding the state of Ir and Ni atoms on the TiO surface before illumination:\nDuring sample preparation, our directional adsorption strategy ensured preferential Ir anchoring onto pre-adsorbed Ni sites, guaranteeing a certain degree of mutual contact between Ni and Ir atoms in the initial state. This has been confirmed by filtered and color-coded HAADF-STEM images (Fig. 1c-d, Supplementary Fig. 5b-c in the revised version), 3D surface plots (Fig. 1f in the revised version), EDS line scans (Fig. 1g in the revised version), and elemental mapping (Fig. 1h and Supplementary Fig. 5d-i in the revised version). However, despite this contact, a complete alloy structure between Ni and Ir was not fully formed initially. Instead, the NiIr nanoclusters exhibited a partially oxidized state, with electronic modulation occurring between Ni and Ir atoms (as evidenced by EXAFS and CO-probe DRIFTS spectra in Fig. 1i-j and Supplementary Fig. 7 in the revised version). This indicates that both Ni and Ir atoms had strong interactions with the oxygen atoms on the TiO support surface. Therefore, before illumination, the state of both Ir and Ni atoms was predominantly oxidized. While there was some interaction between Ni and Ir, this mutual interaction was weaker than their respective interactions with the TiO support.\n(2) Concerning the evidence for nano-island alloy formation under light conditions:\nIn situ X-ray Absorption Spectroscopy (XAS) is a powerful technique that directly probes the local atomic structure and coordination environment around specific elements. By analyzing the EXAFS region, we can directly identify the types and numbers of neighboring atoms and their bond distances, providing direct evidence for structural changes, including alloy formation. In situ Near-Ambient Pressure XPS (NAP-XPS) analysis is a surface-sensitive technique that monitors changes in the chemical states and elemental composition of surfaces under realistic reaction conditions. It serves as a complementary technique to in situ XAS by providing evidence of electronic transfer and chemical state evolution.\nThe section of \"Light-induced dynamic restructuring to form NiIr nano-island alloy on TiO \" in the manuscript provides a detailed comparative analysis of the structural evolution of NiIr/TiO under both light irradiation and heating. Under light irradiation, Ir L -edge EXAFS spectra of NiIr /TiO (Fig. 3a in the revised version) show a dominant Ir-Ni scattering peak at 2.18 Å, replacing the initial Ir-O coordination observed in the dark. Concurrently, Ni K-edge EXAFS of NiIr /TiO (Fig. 3b in the revised version) retains Ni-O (1.60 Å) and Ni-Ni (2.09 Å) scattering alongside emerging Ni-Ir (2.18 Å) coordination, indicating alloy formation without complete Ni reduction. Quantitative EXAFS fitting analysis (Fig. 3c, Supplementary Fig. 19-20, Supplementary Tables 4-5 in the revised version) quantifies this structural evolution. Under light irradiation, NiIr /TiO exhibits nearly 100% Ir-Ni coordination at the Ir L -edge and 32% Ir-Ni coordination at the Ni K-edge, alongside 37% Ni-O interfacial bonds. This confirms that Ir in the alloy (red ball in above figure) phase does not directly interact with TiO , while Ni maintains interfacial Ni-O bonds (green ball in above figure), forming a nano-island architecture. The TiO substrate serves as the “sea” with Ni atoms bonded to TiO forming the “island” base (green ball), while the Ni-Ir alloy located on top of the island does not come into direct contact with the “sea”. In other words, the absence of Ir-O bonds confirms that Ir does not come into contact with the “sea” (TiO ) and therefore remains confined to the “island.” Only such a nano-island alloy configuration ensures nearly 100% Ir-Ni coordination together with partial Ni-O coordination corresponding to oxidized Ni species. This specific coordination environment is direct evidence for the formation of NiIr nano-island architecture under light irradiation. In contrast, under dark thermal conditions (Supplementary Fig. 28 in the revised version), thermal catalysis induces limited Ni or Ir reduction (Ir0/Irδ⁺=0.61 at 500 ℃ vs. 1.54 under unfocused light) and fails to form obvious Ni-Ir bonds. This intuitively demonstrates that light irradiation is essential for promoting the formation of the NiIr nano-island alloy. Furthermore, re-oxidation in post-EXAFS (Supplementary Fig. 27 and Note 4) and reversible NAP-XPS trends confirm that NiIr/TiO -L Ni exists transiently only under light irradiation. These analyses provide factual evidence that Ox-NiIr/TiO undergoes a structural transformation under light irradiation, leading to the formation of a NiIr nano-island alloy.\n(3) Regarding the mechanism of how illumination causes Ir atom migration and the feasibility of NiIr nano-island alloy formation:\nFirstly, we have performed DFT calculations to rationalize the formation of the NiIr nano-island alloy. As discussed in the manuscript: “We further constructed DFT structures (Supplementary Fig. 33) for a series of samples based on the above analysis and actual Ni/Ir atomic ratios. Fig. 3g confirms NiIr/TiO -L ’s stability with a lower formation energy than the hypothetical Ir-linked model (NiIr/TiO -L ), where Ir-O bonds elongate (black arrow indication, >3.0 Å), destabilizing the interface.” Electron-density distributions (Supplementary Fig. 40a-d and Note 8) indicate Ni-mediated charge polarization enriches electrons at Ir sites. Simultaneously, density-of-states profiles (Supplementary Fig. 40e-h) reveal that NiIr alloy-induced d-band center modulation optimizes the trade-off between adsorption strength and intermediate desorption kinetics, suppressing both carbon deposition and parasitic reactions. Time-dependent DFT simulations (Fig. 4i) further identified excitation-dependent charge redistribution on NiIr/TiO -L .\nSecondly, we added relevant literature in the revised version to strengthen the theoretical foundation. Numerous works have studied the structural features of bimetallic nanoclusters via theoretical and/or experimental approaches. For instance, according to DFT, Au atoms in bimetallic Au Ag clusters (2≤m+n≤8) tend to occupy the surface sites because of the charge transfer from Ag to Au, which is consistent with the experimental observation with bimetallic Au Ag (m+n = 34) nanoclusters. (J. Chem. Phys. 125, 014303 (2006); Nat. Commun. 11, 2229 (2020); Chem. Rev. 123, 4855-4933 (2023)) These references demonstrate that when electronic transfer interactions exist in bimetallic nanoclusters, one metal would preferentially occupy more surface sites.\nMore importantly, under light irradiation, prior studies have demonstrated that photoexcited electrons can weaken the intrinsic metal–oxygen (M–O) bonds at metal/oxide interfaces, thereby altering surface structural sites (Nat. Catal. 6, 519–530 (2023)). For example, Wang et al. reported that the introduction of Mn induces charge transfer from La to Mn; the Mn centers capture a fraction of the photoexcited electrons, lowering the Mn valence state and reorganizing the perovskite electronic structure, which in turn weakens the La–O–Mn linkages (J. Am. Chem. Soc. 147(17), 14705–14714 (2025)). More recently, Prof. Xiong described a light-induced dissolution–reprecipitation process using high-entropy oxides (HEOs) as supports (Adv. Mater. 37(21), 2500928 (2025)), wherein illumination weakens metal–O bonds in the HEO, leading to Co and Ni leaching and subsequent alloy formation. Taken together, these results strongly corroborate our finding that light-induced charge transfer weakens metal-O bonding. In our work, before illumination both Ir and Ni interact strongly with the TiO support, exhibiting partial Ir–O and Ni–O coordination. Upon irradiation, electron transfer from the support to the metals similarly weakens these metal–O bonds, as confirmed by our original characterizations and the additional computations below, thereby facilitating the formation of the IrNi alloy.\nMoreover, Gong et al. utilizing XAFS, XPS, and DFT analysis, explained that introducing Sn into a PtCu alloy can extract Pt atoms to the alloy surface. Addition of Sn to the alloy led to the formation of surface Pt Sn dimers. The larger atomic radius of Sn compared to Cu drove it to the surface, and its stronger interactions with Pt abstracted it from the bulk, ultimately achieving efficient surface exposure of Pt atoms to reduce the total energy of system (Science, eadw3053 (2025). DOI:10.1126/science.adw3053). In our system, the atomic radius of Ir is also larger than that of Ni. Under light-induced electron transfer from Ni to Ir, the radius disparity between Ir and Ni is exacerbated (atomic radius: Ir0 > Irδ⁺ > Niδ⁺), thereby promoting the surface exposure of Ir and consequently reducing the overall energy of the system. This thermodynamic stability induced by the atomic radius difference facilitates the extraction of the larger Ir atoms to the surface during alloy formation following metal–O bond cleavage. Consequently, Ir atoms are preferentially distributed on the surface of the nanoislands rather than at their bottom. This observation is consistent with our experimental results, where the absence of Ir–O bonds under illumination confirms that Ir does not reside at the bottom of the Ir–Ni alloy nanoislands.\nFinally, to further elucidate the structural rearrangements induced by photoexcitation, we performed comparative calculations of chemical bond strength variations between the excited and ground states using our original DFT model. It is worth noting that the recently published article (Science, eadw3053 (2025). DOI:10.1126/science.adw3053), the authors used the differences in chemical bond energies as key evidence to demonstrate bond reconstruction, thereby validating the atomic extraction process and the accompanying structural transformation. As shown in Supplementary Table 6 of the revised manuscript, the bond energies of Ir-Ni, Ir-O, and Ni-O in the excited state are all lower than those in the ground state. This arises from bond weakening caused by photoinduced charge transfer, consistent with the aforementioned literatures. In concert with thermal effects, the photoexcited state thus facilitates atomic rearrangement toward a more stable structural configuration. A detailed comparison reveals that in the O -NiIr/TiO structure, the difference in Ir-O bond energy between the excited state and the ground state is larger (-28.06 kJ mol-1), while the difference for the Ni-O (-9.36 kJ mol-1) bond is smaller. This indicates that under photoexcitation, the Ir-O bond becomes more unstable and is weakened more significantly, thus it preferentially breaks, facilitating Ir migration. In addition, simulations under photoexcitation show that the Ni-Ir bond strength (92.35 kJ mol-1) in the NiIr/TiO -L alloy structure in the excited state is more stable than the Ir-O bond strength (69.64 kJ mol-1) in the excited state of the O -NiIr/TiO structure. This provides supporting evidence for the formation of the Ni-Ir alloy under light irradiation.\nRevision made: The following contents have been revised in Manuscript and Supplementary Information:\nSupplementary Fig. 21. Schematic illustration of TiO -supported NiIr nano-island alloys stabilized by oxidized Ni linkages (NiIr/TiO -L ).\nNote that the Ir in the alloy (red ball) phase does not directly interact with TiO , while Ni maintains interfacial Ni-O bonds (green ball), forming a nano-island architecture. The TiO substrate serves as the “sea” with Ni atoms bonded to TiO forming the “island” base (green ball), while the Ni-Ir alloy located on top of the island does not come into direct contact with the “sea”. That is to say, the absence of Ir-O bonds confirms that Ir does not come into contact with the “sea” (TiO ) and therefore remains confined to the “island.”\n(Please refer to the marked contents on page 23 in the supplementary information.)\nThe absence of Ir-O coordination in NiIr /TiO under light confirms that Ir in the alloy phase does not directly interact with TiO , while Ni maintains interfacial Ni-O bonds, forming a nano-island architecture that isolates the NiIr alloy from the support (Supplementary Fig. 21).\n(Please refer to the marked contents on lines 275-278 in the manuscript.)\nIt is worth elucidating that the light-induced surface restructuring observed in this study is supported by prior findings regarding bimetallic systems. It is established that electron transfer in bimetallic clusters can drive surface segregation of one of the metals42,43. A pertinent mechanism involves atomic size, in which the introduction of a larger-radius atom (e.g., Sn in PtCu) can promote surface extraction and alloy reorganization21,44. In our system, Ir has a larger inherent atomic radius than Ni. Critically, the light-induced electron transfer from Ni to Ir reduces Ir's oxidation state, further exacerbating this radius disparity (Ir0 > Irδ⁺ > Niδ⁺) and thereby strongly promoting the surface exposure of Ir. This process is further enabled by the photo-weakening of metal-support bonds, a phenomenon known to induce structural dynamics under illumination22, 44, 45. (Please refer to the marked contents on lines 314-322 in the manuscript.)\n21. Jiang, H., Wang, L., Kaneko, H. et al. Light-driven CO methanation over Au-grafted Ce Ru O solid-solution catalysts with activities approaching the thermodynamic limit. Nat. Catal. 6, 519-530 (2023).\n22. Li J., Zhao J., Wang S. et al. Activating lattice oxygen in perovskite ferrite for efficient and stable photothermal dry reforming of methane. J. Am. Chem. Soc. 147, 17, 14705-14714 (2025).\n42. Zhao, G. F. & Zeng Z. Geometrical and electronic structures of Au Ag (2 ≤ M + N ≤ 8). J. Chem. Phys. 125, 014303 (2006).\n43. Liu, L. & Corma A. Bimetallic sites for catalysis: from binuclear metal sites to bimetallic nanoclusters and nanoparticles. Chem. Rev. 123, 4855-4933 (2023).\n44. Sun, G., Luo, R., Fu D. et al. Full utilization of noble metals by atom abstraction for propane dehydrogenation. Science, eadw3053 (2025). DOI:10.1126/science.adw3053.\n45. Guo, C., Cui, Y., Zhang, W. et al. Light-driven metal exsolution-redissolution of high-entropy oxide enabling high-performance dry reforming of methane. Adv. Mater. 37, 2500928 (2025).\n(Please refer to the marked contents on lines 692-696 and lines 736-743 in the manuscript.)\nComputational analysis of chemical bond strength changes between the ground and excited states (Supplementary Table 6) provides further mechanistic insight. The photoinduced charge transfer weakens the chemical bonds, which synergizes with thermal effects, facilitates atomic rearrangement into a more stable configuration. A detailed comparison reveals a more pronounced bond energy difference between the excited state and the ground state in Ir-O bond (-28.06 kJ mol-1) compared to that of the Ni-O bond (-9.36 kJ mol-1). This indicates a preferential destabilization and breaking of the Ir-O bonds, thereby facilitating the migration of Ir atoms. Furthermore, under the excited state, the Ni-Ir bond (92.35 kJ mol-1) is stronger than the Ir-O bond (69.64 kJ mol-1). These bond energy differences provide support for the formation of the Ni-Ir alloy under light irradiation. (Please refer to the marked contents on lines 415-424 in the manuscript.)\nSupplementary Table 6. Bond energy of NiIr/TiO -L and Ox-NiIr/TiO structures at ground state and excited states.\nBond energy\nModel Ground state Excited state\ndifference\nNiIr/TiO -L Ni-Ir 101.69 kJ mol-1 92.35 kJ mol-1 -9.34 kJ mol-1\nIr-O 97.70 kJ mol-1 69.64 kJ mol-1 -28.06 kJ mol-1\nOx-NiIr/TiO\nBond energy difference = The bond energy at excited state - The bond energy at ground state.\n(Please refer to the marked contents on page 58 in the supplementary information.)\nComment 3: The results of PL and EIS tests show that Ir/TiO exhibits the best light-induced charge separation ability, while NiIr /TiO shows the strongest current intensity in i-t curves. This seems to be contradictory, and the more detailed explanation should be included.\nReply: We thank the reviewer for the insightful observation, which highlights the importance of clarifying the distinct physical meanings of PL, EIS, and photocurrent i-t curves in describing photogenerated charge behavior. PL spectroscopy reflects the recombination degree of photogenerated electron-hole pairs. A quenched PL intensity indicates fewer recombination events. EIS characterizes the resistance of charge transfer, and lower impedance suggests more efficient charge migration after separation. Photocurrent i-t curves directly exhibit the number of effective photogenerated carriers that are ultimately collected. This is not solely determined by separation efficiency but also depends on the total number of photogenerated carriers initially excited.\nThe PL intensities of Ir/TiO and NiIr /TiO are comparable, indicating a similar recombination degree. The higher EIS resistance of NiIr /TiO can be attributed to the incorporation of Ni as an electron-conducting bridge, which inevitably increases the charge transfer resistance compared to the pure noble metal Ir. Nevertheless, NiIr /TiO exhibits enhanced light absorption (as supported by UV-Vis spectroscopy result in Supplementary Fig. 15). This stronger light absorption leads to a greater total number of photogenerated electron-hole pairs. Even with a marginally higher EIS resistance, the larger initial pool of excited carriers results in a greater number of effective carriers that escape recombination and contribute to the photocurrent. To address the reviewer’s concern, we have revised the relevant sentence, aimed at explicitly linking each characterization to its corresponding physical meaning in the Manuscript, and have added detailed explanations in the Supplementary Information.\nRevision made: The original sentence in Manuscript have been revised to the following contents: In addition, compared to pure TiO , NiIr nanoclusters show enhanced photocurrent density, lower electrochemical impedance, and quenched PL intensity; these respectively indicate stronger charge separation, faster charge transfer, and a greater number of effective photocarriers collected for reactions (Supplementary Fig. 39g-i and Note 7).(Please refer to the marked contents on lines 394-398 in the manuscript.)\nThe following contents have been added into Supplementary Information:\nSupplementary Note 7.\nThe photoluminescence spectroscopy reflects the recombination degree of photogenerated electron-hole pairs. A quenched PL intensity indicates fewer recombination events. EIS characterizes the resistance of charge transfer, and lower impedance suggests more efficient charge migration after separation. Photocurrent i-t curves directly exhibit the number of effective photogenerated carriers that are ultimately collected. This is not solely determined by separation efficiency but also depends on the total number of photogenerated carriers initially excited. The higher EIS resistance of NiIr /TiO can be attributed to the incorporation of Ni as an electron-conducting bridge, which inevitably increases the charge transfer resistance compared to the pure noble metal Ir. Nevertheless, NiIr /TiO exhibits enhanced light absorption (as supported by UV-Vis spectroscopy result in supplementary Fig. 15). This stronger light absorption leads to a greater total number of photogenerated electron-hole pairs. Even with a marginally higher EIS resistance, the larger initial pool of excited carriers results in a greater number of effective carriers that escape recombination and contribute to the photocurrent.\n(Please refer to the marked contents on page 41 in the supplementary information.)\nComment 4: When the Ni/Ir ratio of NiIr/TiO is larger than 0.5, why does the H /CO ratio increase while the total yield of the product decreases?\nReply: We sincerely thank the reviewer for this valuable comment, which has helped us further clarify and improve the manuscript. We would like to clarify that activity and product selectivity are often not directly correlated and are even difficult to achieve simultaneously in many reactions. The change in the H /CO ratio is mainly due to the unmatched conversion rates of CH and CO and side reaction such as reverse water-gas shift reaction. Increasing the Ir/Ni ratio from 0.05 to 1.0 elevated the H /CO ratio, demonstrating the Ir-Ni synergy in balancing CH -CO activation, which indicates that the introduction of Ir atoms, in cooperation with Ni, is conducive to improving the efficiency of CH conversion for generating H with efficient H-H coupling. This point is also explained accordingly in the mechanism section of the article (Fig. 5 in the revised version).\nThe overall total production rate exhibits a volcano-shaped trend with the increase of the Ni/Ir ratio, which is a phenomenon widely observed in heterogeneous catalysis. The interfacial interaction between the relatively larger NiIr cluster size (as supported in Supplementary Fig. 4d in the revised version) and TiO would be weakened to a certain extent, which impairs the transfer efficiency of photogenerated electrons from TiO to the NiIr active sites, reducing the number of available charge carriers for CH /CO activation. The proportion of the most active Ni-Ir alloy components may also decrease in larger NiIr cluster size, further reducing the density of the most effective catalytic sites. These factors result in the decline of total product generation rates at higher Ni/Ir ratios. Among them, NiIr /TiO achieved the optimal performance, as it not only maintains an H /CO ratio close to 1 but also exhibits the highest production rates of H and CO.\nComment 5: The evidence of the direction of electron transfer is insufficient, the XPS results of Ti and O orbits should be included to prove the electron transfer pathway of O-Ni-Ir. Moreover, it is generally considered that the appearance of completely overlapping peaks in XPS spectra is incorrect. In this manuscript, many such cases occur in the NAP-XPS spectra.\nReply: We sincerely thank the reviewer for this valuable comment, which has helped us further clarify and improve the manuscript.\n(1) According to the reviewer's suggestion, we have added the in situ NAP-XPS results of Ti and O orbitals in the revised manuscript. Although the shifts in Ti and O are less pronounced than those of Ni and Ir (given that the actual loading of Ni-Ir is below 2 wt.% relative to the TiO support), they still provide supporting evidence for the electron transfer pathway. In situ NAP-XPS of Ti 2p and O 1s (Supplementary Fig. 24d-e) reveal the positive shift in the binding energy of Ti and O under light irradiation, indicating electron migration from the TiO support to the Ni-Ir sites under illumination. Moreover, in the activity test section, we compared TiO with a non-photocatalytic semiconductor support, SiO . Comparative tests on NiIr /TiO and NiIr /SiO (Supplementary Fig. 14 and Note 2) further confirmed that TiO -supported NiIr nanoclusters uniquely harness coupled photothermal-photoelectric effects to achieve efficient and stable DRM catalysis. This comparison underscores the essential role of the TiO support under illumination.\n(2) In addition, while we appreciate the reviewer's attention to this point, we would like to note that the evidence for the direction of electron transfer is not exclusively based on the in situ NAP-XPS spectra. In situ XAS analysis (Fig. 3a-c and Supplementary Figs. 18-20 in the revised version) also corroborates this electron migration pathway. In the mechanism discussion, we also analyzed the time-decay fitting of the transient absorption signal at 560 nm (Fig. 4h and Supplementary Fig. 39d-f in the revised version), which revealed a 520.3 fs lifetime for NiIr /TiO , markedly longer than TiO (110.9 fs) or Ni/TiO (233.1 fs), directly evidencing retarded charge recombination via Ni-Ir interaction. DFT calculations (Fig. 4i in the revised version) further show that electrons in photoexcited states preferentially accumulate at Ir sites distal to the TiO interface. S →S promotes hole accumulation at Ni sites alongside electron enrichment at Ir sites, a spatial charge segregation that drives photoexcited electrons toward Ir centers in higher-energy states. Related explanations were also provided in our response to your Comment 2.\n(3) We also sincerely thank the reviewer for the valuable comments regarding the seemingly overlapping peaks in the Ir 4f XPS spectra. We fully understand the concern and would like to clarify that the partially overlapping features of Ir are intrinsic to the nature of its 4f core levels and to the coexistence of multiple oxidation states in our catalyst, rather than a result of inappropriate fitting.\nFirst, the Ir 4f region is inherently complex. The Ir 4f core level consists of two spin-orbit components, Ir 4f and Ir 4f , with a relatively consistent spin-orbit splitting. In our NiIr /TiO system, three oxidation states of Ir coexist. The metallic Ir0 component is located at around 60.4-60.6 eV (4f ) and 62.9-63.2 eV (4f ), while Ir4+ appears at 61.5-61.7 and 63.9-64.2, and Ir3+ at approximately 62.2-62.4 eV and 65.1-65.3 eV. The chemical shifts among these species are relatively small, typically less than 1 eV, which is comparable to or even smaller than the experimental energy resolution of Al Kα radiation. As a result, the six sub-peaks corresponding to these three oxidation states (each consisting of two spin-orbit doublets) exhibit a certain degree of overlap, but no individual peak completely envelopes another individual peak. This spectral convolution is well recognized in many reports on Ir-based oxides and supported Ir catalysts (e.g., Science 387,791-796(2025); Nat. Commun. 16, 181 (2025); Cited from J. Am. Chem. Soc. 146. 19327-19336 (2024)), all showing similarly Ir 4f peaks.\nIt is also important to note that Ir3+ sometimes exhibits slightly higher binding energy than Ir4+, which may appear counterintuitive. This behavior has been widely discussed and is attributed to final-state screening effects and the covalent character of Ir-O bonds. In Ir3+ environments, stronger Ir-O hybridization weakens the screening of the core hole, leading to a higher apparent binding energy compared with the more ionic Ir4+ species. Therefore, the small energetic overlap between Ir3+ and Ir4+ components and their reversed binding energy order are both physically reasonable and consistent with the literature (Science 387,791-796(2025); Nat. Commun. 16, 181 (2025); Cited from J. Am. Chem. Soc. 146. 19327-19336 (2024)).\nRegarding the fitting procedure, our peak deconvolution was performed using the Xpeak software, and it strictly followed standard and reproducible XPS fitting principles. The spin-orbit splitting for each Ir component was fixed, and the area ratio of Ir 4f to Ir 4f was constrained to 4:3 according to their theoretical degeneracy. The full width at half maximum (FWHM) was kept consistent across different oxidation states within the same sample, and a Shirley background was applied. The peak profiles were modeled using a Gaussian-Lorentzian (GL(30)) line shape, which is widely used for transition-metal XPS analysis. To further demonstrate the robustness of the fitting, we have provided representative fitting-parameter screenshots and numerical fitting tables from XPEAK in below figure, confirming that all components were treated under uniform and physically meaningful constraints.\nFurthermore, even without detailed deconvolution, the evolution of the raw Ir 4f spectra itself clearly supports our interpretation. As indicated by the green arrows in Fig. 3d below, the intensity near 60.6 eV, corresponding to the Ir 4f component of metallic Ir0, gradually increases from the dark condition to the unfocused light and then to the focused light conditions. This visible enhancement in the low-binding-energy shoulder directly evidences the photo-induced reduction of Ir species and the generation of additional metallic Ir0 domains under illumination, which is in excellent agreement with the quantitative increase of the Ir0 fraction obtained from the fitted peak areas.\nFig. 3d. In situ NAP-XPS spectra of Ir 4f for NiIr /TiO under different irradiation conditions in a gas flow of CH :CO :Ar =1:1:8 (Unfocused light: 1.58 W cm-2; focused light: 3.89 W cm-2).\nIn summary, the apparent overlap of Ir 4f peaks is an intrinsic characteristic of Ir due to the small energy separation among its oxidation states and spin–orbit components. Our XPS fitting performed with XPEAK strictly followed accepted conventions and yielded physically meaningful and self-consistent results. The trend observed in the raw spectra independently confirms the light-induced enrichment of metallic Ir0, further validating the correctness and reliability of our XPS interpretation.\nRevision made: The following contents have been added into Manuscript and Supplementary Information:\nParallel in situ Ni 2p NAP-XPS (Supplementary Fig. 24a-c) shows analogous trends, with Ni0/Ni2+ ratios tracking Ir's redox dynamics. While Ti 2p and O 1s exhibit the positive shift in the binding energy of Ti and O under light irradiation (Supplementary Fig. 24d-e), this demonstrates that electrons migrate from the TiO support to Ni-Ir under illumination.\n(Please refer to the marked contents on lines 288-292 in the manuscript.)\nSupplementary Fig. 24. NAP-XPS analysis of Ni 2p for NiIr /TiO . (a) In situ NAP-XPS spectra of Ni 2p under different irradiation conditions in a gas flow of CH :CO :Ar =1:1:8 (Unfocused light: 1.58 W cm-2; focused light: 3.89 W cm-2). (b) XPS spectra of Ni 2p for spent NiIr /TiO exposed in air for 5 days. (c) Ni0/Ni2+ ratio evolution of NiIr /TiO during in situ NAP-XPS conditions and post-air exposure, derived from deconvolution of the XPS spectra. In situ NAP-XPS spectra of (d) Ti 2p and O 1s under different irradiation conditions in a gas flow of CH :CO :Ar =1:1:8 (Unfocused light: 1.58 W cm-2; focused light: 3.89 W cm-2).\n(Please refer to the marked contents on page 26 in the supplementary information.)\nComment 6: The fonts in all charts are too small, compromising readability. We recommend increasing the font size. Additionally, some figures present excessive content, making them challenging to interpret; for instance, Figure 1d could be simplified. Finally, Figure 4g appears to lack necessary annotations, which should be added for clarity.\nReply: We thank the reviewer for pointing this out, enabling us to improve our manuscript. The unclear fonts in some charts are also related to the low resolution of the images. We have adjusted the fonts in these charts and provided higher-resolution images. We apologize for the poor reading experience this may have caused. In accordance with the reviewer's suggestion, we have appropriately simplified the text in Fig. 2d (the original Fig. 1d). Additionally, thank you for the reviewer's reminder, we have added the necessary caption of Fig. 5g (the original Fig. 4g).\nRevision made:\nFig. 1 | Synthesis and structural characterization of TiO₂-supported partially oxidized NiIr nanoclusters. (a) Schematic of the directional adsorption strategy for synthesizing NiIr nanoclusters supported on TiO . (b) Aberration-corrected HAADF-STEM image of NiIr /TiO and cluster size distribution (inset). (c) Color-coded atomic map of region 1 (marked by the white dashed box in b) after image filtering. (d) Intensity profiles along the white line in c. (e) Aberration-corrected HAADF-STEM image of NiIr nanoclusters on TiO . (f) 3D surface plot with atomic overlapping region 3 in e. Blue dashed circles indicate the Ir atoms in NiIr nanocluster. Inset: Filtered image of region 3. (g) EDS line-scan profiles of Ni and Ir across a cluster along the yellow arrow in e. (h) HAADF-STEM image and corresponding EDS elemental mapping of NiIr /TiO . (i) k2-weighted Fourier transform of Ir L -edge EXAFS spectra (without phase correction) for Ir foil, IrO , NiIr /TiO , and Ir/TiO . (j) In situ CO-probe DRIFTS spectra of NiIr /TiO , Ni/TiO ,and Ir/TiO at the 15th minute of Ar-flow during desorption (25 ℃); schematic models of surface structures are included in j.\nFig. 2 | Light-driven dry reforming of methane performance of NiIr/TiO . a, Syngas generation rates and H /CO ratios of TiO , Ni/TiO , Ir/TiO , and NiIr /TiO under 3.89 W cm-2 light irradiation (feed gas: CH :CO :Ar =1:1:8). Note: the same * or # marks indicate that the actual Ir loading amounts of the two samples are similar. b, Feed-gas composition dependence of syngas generation rates, H /CO ratios, and conversion rates for NiIr /TiO (light intensity: 3.89 W cm-2). c, Syngas generation rates of NiIr /TiO under light irradiation or external heating. (CH :CO :Ar =1:1:8, the heating temperature is near to the detected light irradiation temperature at catalyst center.) d, DRM activity per-unit light intensity, detected temperatures, and conversion rates of NiIr /TiO under varied light intensities (CH :CO :Ar =1:1:8). Note that the T and T indicate the average and the center temperature of catalyst surface measured by a thermocouple, which agree with the results from the IR camera (Supplementary Fig. 13). e, Syngas generation rates and H /CO ratio of NiIr /TiO with (blue lines) or without (yellow lines) condensation equipment. (CH :CO :Ar =1:1:8, condensate temperatures noted in blue font) Note that the PT and PE represent photothermal contribution and photoelectric contribution, respectively. f, UV-Vis-NIR spectrum and wavelength-dependent DRM activity (per W cm-2) of NiIr /TiO under monochromatic light (with 500 ℃ external heating, CH :CO :Ar =1:1:8). g, 100-hour stability of NiIr /TiO under light on/off cycles (Light on: 3.89 W cm-2, CH :CO :Ar =1:1:8; Light off: exposed to air). Reaction conditions for a-g: 5 mg catalyst, flow rate = 20 ml min-1; The error bars indicate that there were at least three independent tests. h, Performance comparison of NiIr/TiO (at the condition of CH :CO :Ar =1:1:0) against literature DRM systems: reaction temperature, syngas generation rates, H /CO ratio, TOF, and LTFE.\nFig. 3 | In situ XAS and NAP-XPS analysis of light-induced structural dynamics in NiIr/TiO . a, b, In situ k2-weighted Fourier transform of Ir L -edge (a) and Ni K-edge (b) EXAFS spectra for NiIr /TiO during light-driven DRM conditions (CH :CO :Ar =1:1:8, 3.89 W cm-2; data are not phase-corrected). c, Normalized coordination numbers (CN) of different samples from EXAFS fitting. d, In situ NAP-XPS spectra of Ir 4f for NiIr /TiO under different irradiation conditions in a gas flow of CH :CO :Ar =1:1:8 (Unfocused light: 1.58 W cm-2; focused light: 3.89 W cm-2). e, Ir0/Irδ+ ratio evolution of NiIr /TiO during in situ NAP-XPS conditions and post-air exposure, derived from deconvolution of the XPS spectra. f, Schematics of light induced oscillatory of NiIr/TiO -L formation. g, DFT-optimized structures of NiIr/TiO -L and NiIr/TiO -L . The key distances between Ni/Ir linkages and TiO are annotated in black font. Ir, Ni, Ti, and O atoms are shown in pink, yellow, grey, and blue colors.\nFig. 4 | Time-resolved in situ tracking of reaction intermediates and photoexcited charge dynamics in NiIr/TiO . a, In-situ SR-DRIFTS of NiIr /TiO during CO -CH co-adsorption in the dark (25 ℃, CH :CO :Ar =1:1:8). b, CH -TPD profiles of TiO , Ni/TiO , NiIr /TiO , and Ir/TiO . c, d, In-situ SR-DRIFTS (4000-1200 cm-1) of NiIr /TiO under 3.89 W cm-2 focused light (c) vs. 500 ℃ dark heating (d) in a gas flow of CH :CO :Ar =1:1:8. e, f, Time-resolved evolution of dominant sub-1200 cm-1 SR-DRIFTS peaks under focused light (e) and dark heating (f). g, 2D fs-TA spectroscopy mapping of NiIr /TiO . h, Normalized fs-TA decay kinetics of NiIr /TiO at 560 nm. i, TD-DFT calculated electron-hole pairs distribution on NiIr/TiO -L under S →S /S excitations, and the corresponding electron/hole (e-/h+) ratio statistics of total Ir and Ni sites. The green and purple group represent the distribution of electrons and holes, respectively. The isosurface level is 0.005 e Å-3. Ir, Ni, Ti, and O atoms are shown in pink, yellow, grey, and blue colors, respectively.\nFig. 5 | DFT calculations of reaction pathway and natural sunlight experiments. a, Reaction energy profiles (including transition states) for C=O bond scission of CO on NiIr/TiO -L , Ni/TiO , and Ir/TiO models. b, Reaction energy profiles (including transition states) for C-H bond scission of CH on NiIr/TiO -L , Ni/TiO , and Ir/TiO models. c, Reaction energy profiles for different CH activation pathways on NiIr/TiO -L model. d, Energy evolution of key steps (pink-shaded indicator in Supplementary Fig. 46a) during the first C-H scission of CH and the formation of *CH O intermediate. Ir, Ni, Ti, and O atoms are shown in pink, yellow, grey, and blue colors, respectively. e, DRM performance over NiIr /TiO under concentrated natural sunlight, with measured reaction temperature and incident light intensity (CH :CO :Ar =1:1:8, 20 ml min-1). Inset: experimental setup. f, DRM reaction demonstration under concentrated sunlight, with gas outlet directly interfaced to a PdCl indicator solution for CO detection. g, Schematic illustration of light-driven DRM mechanism.\nComment 7: Why does the photoelectric effect disappear when the light intensity larger than 3.89 W/cm2, and how to distinguish the contribution of photoelectric effect and photothermal effect? And how is the TAVG (average surface temperature of the catalyst) in Figure 1d calculated?\nReply: We sincerely thank the reviewer for this valuable comment, which has helped us further clarify and improve the manuscript.\n(1) We would like to clarify that the photoelectric effect does not disappear when the light intensity exceeds 3.89 W cm-2. As the light intensity increases further, the catalyst's photon absorption reaches saturation. Consequently, the excess light energy is increasingly converted into thermal energy, making the thermal effect more pronounced. This explains why in Fig. 2d (the original Fig. 1d), we observe that while the actual surface temperature of the catalyst continues to rise as the light intensity increases from 3.89 W cm-2 to 4.27 W cm-2 and beyond, the activity contribution per unit light intensity (left Y-axis) begins to decrease. We consider 3.89 W cm-2 to be the light intensity that offers the optimal utilization of the photoelectric effect. At higher intensities, while the photoelectric effect still exists, we emphasize that the thermal contribution becomes increasingly dominant in the overall reaction. Regarding this point, we have provided the explanation in the manuscript, \"Beyond 4.27 W cm-2, photon absorption saturation redirected excess energy into thermal pathways, diminishing the per-unit-light efficiency despite continued temperature increases (T > 600 °C). This nonlinear response highlights the delicate balance between photocarriers generation and thermal dissipation in light-driven systems.\" Regarding Fig. 2d (the original Fig. 1d), we have also addressed this in our response of your Comment 8.\n(2) Distinguishing the contributions of the photoelectric effect and the photothermal effect has always been a challenge in light-driven catalytic reactions, especially in systems like ours without external heating, where light induces both effects. Nevertheless, this study includes corresponding experimental designs to differentiate them appropriately.\nFirstly, in Fig. 2d (the original Fig. 1d), by calculating the activity contribution per unit light intensity, we indicated that the light intensity range where the photoelectric effect plays a significant role is < 1.95 W cm-2. As the light intensity increases further, the photoelectric and photothermal effects act synergistically, leading to the rapid rise in activity observed (1.95-3.89 W cm-2). When the light intensity exceeds 3.89 W cm-2, photon absorption becomes saturated. Although the photothermal effect continues to increase, the rate of increase in CH and CO conversion rates beyond 3.89 W cm-2 becomes more gradual compared to the range of 1.95-3.89 W cm-2. This indirectly suggests that the increase in the photothermal effect contributes less to the activity boost than the increase in the photoelectric effect does within that optimal range.\nTo further distinguish which effect contributes more during the rapid activity increase phase, we conducted the condensation equipment experiment shown in Fig. 2e (the original Fig. 1e). The blue trend line in Fig. 2e represents the results under a constant light intensity of 3.89 W cm-2, while condensate (the temperature of the condensate is marked in blue font) were circulated around the reactor to achieve cooling. The X-axis records the real-time monitored temperature at the catalyst's center point. This setup allows us to observe the DRM activity and H /CO ratio while maintaining the photoelectric effect (constant light intensity) and reducing the photothermal effect (via condensation). For comparison, the yellow trend line in Fig. 2e represents the results obtained by directly varying the light intensity without extra condensation. This simultaneously reduces both the photoelectric and photothermal effects (different light intensity values are marked in yellow font), with the X-axis showing the actual temperature monitored at the catalyst's center resulting from the reduced light intensity. By comparing the yellow and blue trend lines at matched catalyst surface center temperatures, we can estimate the contributions that the variation along the blue trend line allows calculation of the activity contribution from the photoelectric effect, while the yellow trend line reflects the combined contribution of photoelectric and photothermal effects. As stated in the manuscript, \"At matched surface temperatures, the photoelectric-dominated system contributed 57.5% to syngas rates and 91.7% to H /CO balance, compared to the photothermal-assisted system.\" That is to say, the photothermal effect contributed only about 42.5% to the syngas production rate and 8.3% to the H /CO balance under these conditions. These results demonstrate the dominant role of the photoelectric effect in this system.\nAdditionally, in the Supplementary Information, we compared a non-photocatalytic semiconductor, SiO as the support. \" Comparative tests on NiIr /TiO and NiIr /SiO (Supplementary Fig. 14 and Note 2) further confirmed that TiO -supported NiIr nanoclusters uniquely harness coupled photothermal-photoelectric effects to achieve efficient and stable DRM catalysis.\" This result again emphasizes the significance of the photoelectric effect.\nThe reviewer's question may arise because our original description of Fig. 2e was perhaps not sufficiently detailed. Therefore, we have revised the manuscript to provide a more detailed explanation of the related content.\n(3) Regarding the calculation of T (average surface temperature of the catalyst) in Fig. 1d (now Fig. 2d): The built-in thermocouple position is movable. The average surface temperature was calculated by measuring temperatures at five different points on the catalyst surface (as shown below).\nIn Fig. 2d, we labeled both T (the average temperature of catalyst surface)and T (the center temperature of catalyst surface)to comprehensively represent the catalyst surface temperature distribution. Since the temperature at the catalyst center is the highest, T is used for investigation and analysis elsewhere in the paper.\nWe have also supplemented infrared IR thermal imaging data (Supplementary Fig. 13) which verified the accuracy of our temperature measurement method. We hope this clarification satisfactorily addresses the reviewer's concern. Furthermore, we have provided a more detailed description of the temperature measurement methodology in the Methods section.\nRevision made: The following contents have been revised in Manuscript:\nControlled condensation experiments (Fig. 2e) decoupled photothermal and photoelectric effects by selectively suppressing thermal contributions. The blue trend line maintained constant light intensity (3.89 W cm-2) to preserve the photoelectric effect and used condensation cooling to suppress photothermal contributions, while the yellow trend line varied light intensity (from 3.89 to 1.30 cm-2) without condensation and diminished both effects simultaneously. By comparing the syngas production rates and H /CO ratios from these two paths at matched catalyst surface temperatures, it was determined that the photoelectric-dominated system (with condensation) contributed 57.5% to syngas rates and 91.7% to H /CO balance, compared to the photothermal-assisted system (without condensation). This contrast confirms that photogenerated carriers preferentially drive H-H coupling and carbon intermediate oxidation, while thermal energy primarily enhances vibration and mobility of reactants. (Please refer to the marked contents on lines 200-210 in the manuscript.)\nA type-K thermocouple (0-1150 °C range, 0.5 mm diameter, ±0.1 °C accuracy) was embedded in the quartz sand bed, with a 90°-bent tip protruding 1.0 mm above the surface. The thermocouple was pre-calibrated against standard reference sources, and its performance was verified at multiple temperature setpoints to ensure consistency across the experimental range. T (the center temperature of catalyst surface)was detected by the thermocouple probe placed in direct contact with the upper surface of the catalyst at its center, enabling capture of the highest local temperature under irradiation (as shown by the red indicator line representing the thermocouple in Supplementary Fig. 9). This arrangement minimizes the thermal resistance effect by avoiding indirect measurement through the gas phase or reactor materials. Infrared (IR) thermography was used to validate the accuracy of T measurements from the thermocouple probe. T (average surface temperature) was obtained by moving the thermocouple probe, measuring temperatures at five different points on the catalyst surface (center and edges) and using the formula below:\nT = (T_Center + 2*T_Edge) / 3\n(Please refer to the marked content on lines 533-546 in the manuscript.)\nNote that the T and T indicate the average and the center temperature of catalyst surface measured by a thermocouple, which agree with the results from the IR camera (Supplementary Fig. 13).\n(Please refer to the marked content on lines 225-227 in the manuscript.)\nThe following contents have been added in Supplementary Information:\nSupplementary Fig. 13. The center temperature of NiIr /TiO detected by IR camera. (a) Photographs taken with an IR camera under different light intensities. (b) The center temperature of catalyst surface detected by thermocouple and IR camera.\n(Please refer to the marked content on page 15 in the supplementary information.)\nComment 8: There are some conclusions without evidence or reference in the manuscript, such as “Activity surged above a threshold light intensity of 2 W cm-2, marking the onset of photoelectric-photothermal synergy (Fig. 1d)”, and “Beyond 4.27 W cm-2, photon absorption saturation redirected excess energy into thermal pathways, diminishing the per-unit-light efficiency despite continued temperature increases (T > 600 °C).” There is no reference or experimental evidence to support these conclusions.\nReply: We thank the reviewer for pointing this out, enabling us to improve our manuscript.\n(1) The conclusion that \"Activity surged above a threshold light intensity of 2 W cm-2, marking the onset of photoelectric-photothermal synergy\" is in fact supported by experimental evidence. As shown in Fig. 2d (originally Fig. 1d), when the light intensity is below 2 W cm-2, the catalyst surface center temperature (T ) and average temperature (T ) remain below 350 °C. Referring to Fig. 2c and Supplementary Fig. 12a, thermal catalytic experiments under dark conditions show almost no H or CO production when the temperature is below 350 °C, indicating negligible thermal catalytic activity in this range. Therefore, under illumination without external heating, when the photothermal heating remains below 350 °C, the contribution can be primarily attributed to the photoelectric effect. As the light intensity increases beyond 2 W cm-2, the thermal effect from illumination becomes non‐negligible, which is why we describe the regime beyond this point as photoelectric-photothermal synergy.\n(2) The statement \"Beyond 4.27 W cm-2, photon absorption saturation redirected excess energy into thermal pathways, diminishing the per-unit-light efficiency despite continued temperature increases (T > 600 °C)\" is also experimentally substantiated. From Fig. 2d (the original Fig. 1d), we observe that although the actual surface temperature of the catalyst continues to rise as light intensity increases beyond 3.89 W cm-2 to 4.27 W cm-2 and further, the activity per unit light intensity (left Y-axis) begins to decline. This occurs because the catalyst has a finite capacity for photon absorption. Once the light intensity exceeds a certain level, the catalyst reaches photon absorption saturation. At this stage, the photoelectric contribution no longer increases significantly with light intensity, whereas the photothermal effect continues to increase. Therefore, beyond 4.27 W cm-2, the increase in overall activity is mainly attributed to the thermal effect, and the per-unit-light efficiency (syngas generation rates/light intensity) decreases. This clearly indicates that photon absorption saturation redirects excess energy into thermal pathways, thereby reducing per-unit-light efficiency despite the continued rise in temperature. Therefore, 3.89 W cm-2 can be regarded as the light intensity that achieves optimal utilization of the photoelectric effect. At higher intensities, we do not deny the presence of the photoelectric effect, but emphasize that the thermal effect becomes increasingly dominant in the reaction.\nWe recognize that the original expression was perhaps too concise, potentially causing confusion for the reviewer. To address this, we have provided more detailed elaboration on these aspects in the revised manuscript.\nRevision made: The following contents have been revised in Manuscript:\nActivity surged above a threshold light intensity of 2 W cm-2, marking the onset of photoelectric-photothermal synergy (Fig. 2d and Supplementary Fig. 13). Specifically, at lower intensities (< 1.95 W cm-2, T < 336 °C), the observed activity originated predominantly from photoelectric effects. This assignment is confirmed by the sustained syngas production under illumination, which stands in clear contrast to the negligible activity observed in dark thermal catalysis experiments conducted below the 350 °C threshold (as shown in Fig. 2c and Supplementary Fig. 12a). The interplay between photothermal and photoelectric contributions peaked at 3.89 W cm-2 (T = 506 ℃; T = 403 ℃). Beyond 4.27 W cm-2, the system approached a state of photon absorption saturation. At this point, the catalyst could no longer utilize the additional photons for charge carrier generation, and consequently, the excess energy was redirected into thermal pathways. This mechanistic shift is evidenced by a distinct decline in the per-unit-light efficiency (syngas generation rates/light intensity), which occurred despite the continued rise in the catalyst temperature (T exceeding 600 °C). This nonlinear response highlights the delicate balance between photocarriers generation and thermal dissipation in light-driven systems.\n(Please refer to the marked contents on lines 185-197 in the manuscript.)\nComment 9: The light intensity and temperature in the monometallic control experiment should be included. Under the same conditions, why is the catalytic activity of NiIr /TiO with condensation equipment better than that without it?\nReply: We sincerely thank the reviewer for this valuable comment, which has helped us further clarify and improve the manuscript.\n(1) Regarding the first point, the light intensity used (3.89 W cm-2) in the monometallic control experiment has been added in the caption of Supplementary Fig. 17. The corresponding catalyst surface temperature under that light intensity has already been provided in Supplementary Fig. 15b.\n(2) As for the second question, it is important to clarify that the systems “with condensation” and “without condensation” were operated under fundamentally different light conditions. In the “with condensation” configuration, the light intensity was maintained constant at 3.89 W cm-2, while the temperature was controlled by circulating condensate. In contrast, in the “without condensation” configuration, the temperature was varied by directly adjusting the light intensity itself. Therefore, when comparing the two trend lines at similar catalyst surface temperatures, the higher activity observed in the “with condensation” case can be attributed to the preserved photoelectric effect under constant light intensity. This comparison allows us to distinguish and estimate the individual contributions of the photoelectric and photothermal effects, as we also addressed in our response to your Comment 7. We have included explanations of the blue and yellow trend lines in the revised manuscript for clarity.\nRevision made: The following contents have been revised in Manuscript and Supplementary Information:\nSupplementary Fig. 17. Stability test of Ni/TiO andIr/TiO and carbon deposition analysis.\n(a) Long-term catalyst stability of Ni/TiO andIr/TiO under continuous light irradiation (Light intensity: 3.89 W cm-2, feed gas: CH :CO :Ar =1:1:8, 5 mg catalyst, flow rate = 20 ml min-1). (b) Raman spectra and (c) Thermogravimetric analysis of Ni/TiO andIr/TiO after long-time light irradiation.\n(Please refer to the marked content on page 19 in the supplementary information.)\nControlled condensation experiments (Fig. 2e) decoupled photothermal and photoelectric effects by selectively suppressing thermal contributions. The blue trend line maintained constant light intensity (3.89 W cm-2) to preserve the photoelectric effect and used condensation cooling to suppress photothermal contributions, while the yellow trend line varied light intensity (from 3.89 to 1.30 cm-2) without condensation and diminished both effects simultaneously. By comparing the syngas production rates and H /CO ratios from these two paths at matched catalyst surface temperatures, it was determined that the photoelectric-dominated system (with condensation) contributed 57.5% to syngas rates and 91.7% to H /CO balance, compared to the photothermal-assisted system (without condensation). This contrast confirms that photogenerated carriers preferentially drive H-H coupling and carbon intermediate oxidation, while thermal energy primarily enhances vibration and mobility of reactants.\n(Please refer to the marked contents on lines 200-210 in the manuscript.)\nComment 10: The explanation for Figure 1 f is too simplistic. Under the full-spectrum condition, both the Ir and Ni surfaces can be excited by light to generate hot electrons. Moreover, Fig 1f shows Ir has a stronger light absorption ability to than Ni. Will the LSPR effect on Ir trigger the transfer of hot electrons to Ni?\nReply: We sincerely thank the reviewer for this valuable comment, which has helped us further clarify and improve the manuscript. Regarding the light absorption ability, Supplementary Fig. 15a shows that the monometallic Ir/TiO exhibits slightly stronger absorption than Ni/TiO , though the difference is not substantial. This moderate enhancement may be attributed to the intrinsic properties of noble metals. Furthermore, light absorption is also influenced by metal loading. In the NiIr/TiO series, while the Ni loading remains essentially constant, the total metal loading increases with higher Ir/Ni ratios (as shown in Supplementary Fig. 1). Consequently, the overall light absorption capacity of the NiIr/TiO catalysts is further enhanced.\nRegarding Fig. 2f (the original Fig. 1f), it demonstrates that the wavelength-dependent DRM activity (per W·cm-2) of NiIr /TiO aligns with its UV-Vis-NIR absorption profile. This strong correlation confirms that the reaction is primarily driven by photoexcitation rather than thermal effects, as the activity directly follows the photons absorbed by the catalyst. We have enhanced the corresponding description in the revised manuscript.\nAs for the electron transfer pathway, our mechanistic investigations have demonstrated that under illumination, electrons are transferred from Ni to Ir sites. In situ NAP-XPS analyses provide direct evidence of this light-induced electron transfer. The Ir 4f spectra (Fig. 3d-e) reveal a pronounced shift toward lower binding energy, with the Ir0 fraction increasing from 36.96% (dark) to 60.65%. Upon switching to focused light, the Ir0 fraction further rises to 62.31%. This indicates that Ir gains electrons under irradiation. Parallel in situ Ni 2p NAP-XPS (Supplementary Fig. 24a-c) shows analogous trends, with Ni0/Ni2+ ratios tracking Ir's redox dynamics. While Ti 2p and O 1s exhibit the positive shift in the binding energy of Ti and O under light irradiation (Supplementary Fig. 24d-e), this demonstrates that electrons migrate from the TiO support to Ni-Ir under illumination. Subsequently, electrons are further transferred from Ni to Ir. In situ XAS analysis (Fig. 3a-c, Supplementary Fig. 19-20, and Supplementary Tables 4-5) also supports this mechanism. It reveals that Ir in the alloy phase does not directly interact with TiO , while Ni maintains interfacial Ni-O bonds, forming a nano-island structure that isolates the NiIr alloy from the support. This configuration formation indicates the electron transfer from Ni to Ir under light irradiation. Additionally, time-dependent DFT (TD-DFT) simulations (Fig. 4i) show that electrons in photoexcited states preferentially accumulate at Ir sites distal to the TiO interface. S →S promotes hole accumulation at Ni sites alongside electron enrichment at Ir sites, a spatial charge segregation that drives photoexcited electrons toward Ir centers in higher-energy states.\nRevision made: The following contents have been revised in Manuscript:\nThe UV-Vis-NIR spectra (Supplementary Fig. 15) revealed that the introduction of Ni and Ir significantly enhanced broadband light absorption across the entire spectral range compared to TiO . Crucially, the absorption profile across the full spectral range of NiIr /TiO exhibited a strong correlation with the wavelength-dependent DRM activity (Fig. 2f), confirming that the reaction is primarily driven by photoexcitation rather than thermal effects and evidencing its light-driven nature.\n(Please refer to the marked contents on lines 237-242 in the manuscript.)\nComment 11: There is a mistake in Figure 2c, where there are two “Ir foil” in the figure. Moreover, in the sentence of \"The S0→S2 excited state exhibits a smaller Sr index, directly indicating superior charge separation\", it seems that \"Sr\" here might be written wrongly.\nReply: We thank the reviewer for pointing this out. Regarding the issue with Fig. 2c (which is now Fig. 3c in the revised manuscript), we sincerely apologize for the oversight where \"Ir foil\" was mistakenly labeled twice. We have now corrected this error in the revised figure.\n\"Sr\" here is not a typo but refers to a specific quantum chemical parameter (as shown in the formula below), which represents the geometric mean overlap function of hole and electron distributions. A smaller Sr value indicates less overlap between the electron and hole, which directly corresponds to more efficient charge separation, which consistent with our description in the manuscript. To avoid confusion, we have added an explicit definition of \"Sr\" in the revised manuscript to clarify its physical meaning, and supplemented the formula of Sr in the Supplementary Methods.\nS(r) = √[𝜌ℎ𝑜𝑙𝑒(r) 𝜌𝑒𝑙𝑒(r)];\nr\nρhole and ρele represent the electron density of the hole and the excited electron at the spatial position r, respectively.\nRevision made: The following contents have been revised in Manuscript and Supplementary Information:\nFig. 3 | In situ XAS and NAP-XPS analysis of light-induced structural dynamics in NiIr/TiO . a, b, In situ k2-weighted Fourier transform of Ir L -edge (a) and Ni K-edge (b) EXAFS spectra for NiIr /TiO during light-driven DRM conditions (CH :CO :Ar =1:1:8, 3.89 W cm-2; data are not phase-corrected). c, Normalized coordination numbers (CN) of different samples from EXAFS fitting. d, In situ NAP-XPS spectra of Ir 4f for NiIr /TiO under different irradiation conditions in a gas flow of CH :CO :Ar =1:1:8 (Unfocused light: 1.58 W cm-2; focused light: 3.89 W cm-2). e, Ir0/Irδ+ ratio evolution of NiIr /TiO during in situ NAP-XPS conditions and post-air exposure, derived from deconvolution of the XPS spectra. f, Schematics of light induced oscillatory of NiIr/TiO -L formation. g, DFT-optimized structures of NiIr/TiO -L and NiIr/TiO -L . The key distances between Ni/Ir linkages and TiO are annotated in black font. Ir, Ni, Ti, and O atoms are shown in pink, yellow, grey, and blue colors.\n(Please refer to the marked contents on lines 332-342 in the manuscript.)\nThe S →S excited state exhibits a smaller Sr index (the geometric mean overlap function of hole and electron distributions), representing less overlap between the electron and hole, and further indicating superior charge separation.\n(Please refer to the marked contents on lines 410-412 in the manuscript.)\nThe geometric mean overlap function of hole and electron distributions (S) was calculated as follows:\nS (r) = √[𝜌ℎ𝑜𝑙𝑒(r) 𝜌𝑒𝑙𝑒(r)];\nr\nρhole and ρele represent the electron density of the hole and the excited electron at the spatial position r, respectively.\n(Please refer to the marked content on page 2 in the supplementary information.)\nResponse to Reviewer 2\nGeneral comments: This paper investigates the structural dynamic evolution of NiIr/TiO under light irradiation, which represents a critical challenge in light-driven catalysis. Furthermore, the NiIr/TiO system demonstrates comprehensively favorable efficiency in the dry reforming of methane reaction, with its anti-coking mechanism thoroughly explained. The authors' elegant experimental design using condensation equipment and light intensity thresholds to deconvolute photoelectric and thermal effects is methodologically sound and mechanistically informative. Overall, this work is innovative, and the experimental results sufficiently support the conclusions. Therefore, I recommend this paper for acceptance in Nature Communications after the following revisions.\nReply: We appreciate the reviewer for the careful reading and the generous recommendation of our manuscript. The suggestions and comments have been carefully considered, and we made the corresponding revision to address the points the reviewer has raised, as shown below. We hope our revision can make the paper much more acceptable for publication in the Nature Communications.\nComment 1: In the catalyst preparation section, the authors state: \"By conducting the adsorption process in an aprotic solvent and introducing an anionic Ir precursor complexed with quaternary ammonium, we minimized competitive adsorption of Ni and Ir and effectively reduced metal leaching.\" Please clarify the specific role of the quaternary ammonium in this process. Explain why IrCl could not be used directly for targeted adsorption instead of the complexed precursor. If this strategy effectively overcomes the drawbacks of conventional co-impregnation methods, its clear explanation will provide valuable guidance for future synthesis.\nReply: We thank the reviewer for this insightful comment. Regarding the adsorption of Ir and Ni precursors on the TiO surface, our approach was inspired by a previously reported strategy (Science 362, 560-564 (2018)), which employs sequential adsorption of cationic and anionic species. As described in the Methods section, the surface of the alkalized TiO was first treated with an aqueous NiCl solution. To promote interaction between the Ir precursor and the pre-adsorbed Ni sites, we subsequently used an anionic Ir complex, Na IrCl . This enables electrostatic anchoring of the Ir species around the Ni sites via cation-anionic interaction. In contrast, IrCl exists predominantly in cationic form in aqueous solution and would not be suitable for this targeted adsorption strategy.\nThe role of the quaternary ammonium cations (tetrabutylammonium, TBA⁺) is to facilitate phase transfer of the IrCl 3- anions from the aqueous phase into an aprotic organic solvent (CH Cl ). This process enhances the stability of the Ir precursor and allows for controlled, slow adsorption, thereby minimizing unwanted ripening or leaching of Ir that could occur in an aqueous environment.\nWe have provided a detailed description of this preparation procedure in the Methods section. In addition, as suggested, we have now included a clearer explanation of the role of the quaternary ammonium cations in the revised manuscript to better highlight the advantages of this synthetic strategy.\nRevision made: The following contents have been revised in Manuscript:\nTo construct bimetallic NiIr nanoclusters on TiO with precise atomic pairing, we adopted a directional adsorption strategy23 (Fig. 1a; see Methods for synthesis details). This approach leverages sequential electrostatic adsorption of cationic Ni complexes and anionic Ir precursors onto alkalized TiO nanosheets, ensuring preferential Ir anchoring onto pre-adsorbed Ni sites. For the Ir precursor, we used a species complexed with quaternary ammonium cations to enable its phase transfer into an aprotic solvent. This controlled process prevents Ir ripening and leaching. Consequently, by conducting adsorption in this manner, we minimized competitive adsorption of Ni and Ir, effectively overcoming a key limitation of conventional co-impregnation methods.\n(Please refer to the marked contents on lines 83-90 in the manuscript.)\nComment 2: The authors provide a detailed discussion of the morphology and structure of TiO -supported partially oxidized NiIr nanoclusters (Ox-NiIr/TiO ) in the Supplementary Information, demonstrating Ni-Ir interactions while maintaining their oxidized states via the cationic-anionic pair adsorption strategy. This information is fundamental for understanding the subsequent structural dynamic transformations. Please consider moving this discussion to the main text if space permits.\nReply: Thank you for the reviewer's valuable suggestion. As recommended, we have moved the key characterization and corresponding discussion regarding the morphology and structure of Ox-NiIr/TiO to the main text.\nRevision made: The relevant content from the original Supplementary Fig. 1 and original Supplementary Note 1 has been moved to the main manuscript:\nSynthesis and atomic-scale structural analysis of partially oxidized NiIr nanoclusters on TiO .\nTo construct bimetallic NiIr nanoclusters on TiO with precise atomic pairing, we adopted a directional adsorption strategy23 (Fig. 1a; see Methods for synthesis details). This approach leverages sequential electrostatic adsorption of cationic Ni complexes and anionic Ir precursors onto alkalized TiO nanosheets, ensuring preferential Ir anchoring onto pre-adsorbed Ni sites. For the Ir precursor, we used a species complexed with quaternary ammonium cations to enable its phase transfer into an aprotic solvent. This controlled process prevents Ir ripening and leaching. Consequently, by conducting adsorption in this manner, we minimized competitive adsorption of Ni and Ir, effectively overcoming a key limitation of conventional co-impregnation methods.\nSubsequent H calcination eliminated organic ligands while strengthening Ni-Ir metallic interactions, yielding ultrafine bimetallic clusters with uniform dispersion on the TiO support (Fig. 1b). Inductively coupled plasma-atomic emission spectrometry (ICP-AES) confirms controlled metal loadings across NiIrₓ/TiO samples (Supplementary Fig. 1 and Table S1), where x denotes the Ir/Ni theoretical atomic ratio. The sublinear increase in Ir/Ni ratios with x suggests saturation of Ir adsorption onto pre-adsorbed Ni sites, excluding independent Ir deposition. For comparison, monometallic Ni/TiO and Ir/TiO were prepared with a theoretical loading of 1 wt.% for each metal.\nAberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) analysis revealed that Ni species or Ir species on TiO exhibited sub-1.2 nm clusters (Supplementary Figs. 2-3), whereas the NiIr nanoclusters on TiO showed an increase in size, progressively reaching up to 1.61 nm with higher Ir content (Supplementary Figs. 4). This trend supports the co-stabilization of Ni and Ir atoms within the bimetallic clusters. This size evolution directly supports the formation of bimetallic NiIr nanoclusters, as the incorporation of Ir stabilizes the clusters and promotes their growth. Atomic-scale characterization of NiIr /TiO provided further insights into the spatial distribution of Ni and Ir atoms. Filtered and color-coded HAADF-STEM images and the corresponding intensity profiles (Fig. 1c-d, Supplementary Fig. 5b-c) revealed intertwined Ni-Ir distributions within individual clusters. The 3D surface plot of a selected region (Fig. 1f) highlighted Ir atoms (whitish-yellow peaks within blue dashed marks) surrounding Ni atoms (darker yellow bumps), demonstrating cohesive bimetallic nanocluster formation. Conversely, monometallic samples exhibited only metal-TiO contrast (Supplementary Figs. 2g-h, 3e-f). Moreover, EDS line scans (Fig.1g) and elemental mapping (Fig. 1h and Supplementary Fig. 5d-i) confirmed the intimate contact between Ni and Ir atoms. Owing to the higher atomic ratio of Ni to Ir, trace amounts of isolated Ni species inevitably persist. Crucially, all Ir atoms preferentially occupy Ni-associated sites, with no detectable isolated Ir single atoms observed on the TiO support (Fig. 1b).\nNext, we elucidate the chemical structure and coordination environment of the NiIr nanoclusters.\nX-ray Diffraction (XRD) patterns confirm exclusive anatase-phase TiO (Supplementary Fig. 6), with no detectable reflections from metallic Ni or Ir phases, consistent with HAADF-STEM evidence of dispersed sub-2 nm clusters. Normalized Ir L₃-edge and Ni K-edge X-ray absorption near-edge spectroscopy (XANES) analysis reveal partially oxidized states of Ni and Ir (Supplementary Fig.7a-b). Linear combination fitting (Supplementary Fig. 7c-d) shows higher Ir oxidation in Ir/TiO (+3.6) than NiIr /TiO (+2.7), and more reduced Ni in Ni/TiO (+1.6) versus NiIr /TiO (+1.8), indicating electron transfer from Ni to Ir, later corroborated by in situ analyses.\nExtended X-ray absorption fine structure (EXAFS) at the Ir L₃-edge provides atomic-scale coordination details (Fig. 1i). All samples exhibit a prominent peak at ~1.60 Å and a relatively weaker peak at ~2.56 Å, corresponding to Ir-O scattering and Ir-Ir scattering, respectively. Notably, NiIr /TiO samples exhibit an additional peak at 2.18 Å, which can be attributed to Ni-Ir scattering.\nThese results demonstrate that NiIr nanoclusters exhibit a partially oxidized state, with electronic modulation between Ni and Ir atoms. The partial oxidation probably arises from the interface reconstruction between nanocluster and the surface lattice O atoms of TiO during the calcination process and the exposure to air during storage. This unique electronic structure, coupled with their ultrafine size, positions these partially oxidized NiIr nanoclusters (Ox-NiIr) as promising candidates for the adsorption of CH and CO due to their inherent thermal instability19.\nIn situ CO probe molecule diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analyses were conducted to unravel the surface structure and adsorption behavior of NiIr nanoclusters (Supplementary Fig. 8 and Fig. 1j). Ni/TiO₂ exhibited negligible *CO chemisorption signals (<2100 cm⁻¹), which vanished entirely upon heating to 100 ℃. This confirms the inadequacy of individual Ni sites for CO adsorption. In contrast, Ir-containing samples (NiIrₓ/TiO , Ir/TiO ) display intense *CO chemisorption bands (2100-1990 cm⁻¹), with adsorption strength scaling with Ir content. Heating-up desorption revealed a volcanic trend: *CO intensity peaked at 200 ℃ and declined continuously to 400 ℃. It demonstrates reversible CO binding, which is a critical feature for sustaining DRM activity. Detailed comparison of the desorption spectra at 25 ℃ (Fig. 1j) highlights distinct Ir coordination environments. For Ir/TiO₂, three CO species were resolved: (i) multi-carbonyl Ir-(CO) (2068 cm-¹, low-coordination sites)24, (ii) linear CO on metallic Ir (Ir-CO, 2033 cm-¹)25, and (iii) bridged CO at Ir-TiO interfaces (Ir -CO, 1994 cm-¹)26. For Ni/TiO₂, only weak peaks of Ni-CO and Ni -CO can be observed. In NiIr /TiO , the dominant Ir-(CO) peak progressively shifts downward (2063→2044 cm-¹) with increasing Ir content, signaling enhanced π-backdonation from Ir to CO. The observed redshift arises from Ni-to-Ir electron transfer, which elevates Ir's d-orbital occupancy, strengthens Ir-C bonds, and weakens C-O bonds. These results confirm that in partially oxidized NiIr nanoclusters, Ir serves as the main center for CO adsorption, while Ni modulates Ir's electronic properties to optimize the balance between adsorption strength and desorption kinetics.\nFig. 1 | Synthesis and structural characterization of TiO₂-supported partially oxidized NiIr nanoclusters. (a) Schematic of the directional adsorption strategy for synthesizing NiIr nanoclusters supported on TiO . (b) Aberration-corrected HAADF-STEM image of NiIr /TiO and cluster size distribution (inset). (c) Color-coded atomic map of region 1 (marked by the white dashed box in b) after image filtering. (d) Intensity profiles along the white line in c. (e) Aberration-corrected HAADF-STEM image of NiIr nanoclusters on TiO . (f) 3D surface plot with atomic overlapping region 3 in e. Blue dashed circles indicate the Ir atoms in NiIr nanocluster. Inset: Filtered image of region 3. (g) EDS line-scan profiles of Ni and Ir across a cluster along the yellow arrow in e. (h) HAADF-STEM image and corresponding EDS elemental mapping of NiIr /TiO . (i) k2-weighted Fourier transform of Ir L -edge EXAFS spectra (without phase correction) for Ir foil, IrO , NiIr /TiO , and Ir/TiO . (j) In situ CO-probe DRIFTS spectra of NiIr /TiO , Ni/TiO ,and Ir/TiO at the 15th minute of Ar-flow during desorption (25 ℃); schematic models of surface structures are included in j.\n(Please refer to the marked content on lines 82-167 in the manuscript.)\nComment 3: The accuracy of temperature measurement is critical for understanding photothermal effects. The authors used a thermocouple to monitor the catalyst temperature, but significant thermal resistance between the gas phase and the thermocouple may lead to inaccurate readings, as noted. It is necessary to clarify the detailed setup of temperature measurement (e.g., thermocouple position, calibration methods) or explain how potential thermal resistance effects were mitigated. Additionally, whether complementary methods such as infrared thermography were used to verify the measured temperatures should be addressed.\nReply: We thank the reviewer for the insightful comment. In response to the concern about potential thermal resistance between the gas phase and the thermocouple, we would like to clarify our experimental setup and validation approach.\nIn contrast to many reported studies where the thermocouple is placed at the bottom of the catalyst bed or even further away, which may not fully capture the direct photothermal heating effect on the upper catalyst surface. In our configuration, the thermocouple probe was placed in direct contact with the upper surface of the catalyst at its center (T ), allowing us to capture the highest local temperature under irradiation (as shown by the red indicator line representing the thermocouple in Supplementary Fig. 9). This arrangement minimizes the thermal resistance effect by avoiding indirect measurement through the gas phase or reactor materials. It is also worth noting that, since gas molecules typically adsorb and react on the catalyst surface, measuring the temperature at the upper surface is a reasonable approach for evaluating the actual reaction conditions. A type-K thermocouple (0-1150 °C range, 0.5 mm diameter, ±0.1 °C accuracy) was embedded in the quartz sand bed, with a 90°-bent tip protruding 1.0 mm above the surface. This high-precision thermocouple was selected to reduce measurement deviation. Regarding calibration, the thermocouple was pre-calibrated against standard reference sources, and its performance was verified at multiple temperature setpoints to ensure consistency across the experimental range. In Methods section, we provided a more detailed description of this device in the revised version. To further address any concerns about thermal resistance and measurement reliability, we performed complementary temperature validation using infrared (IR) thermography. The results obtained from the IR camera showed agreement with the thermocouple results, confirming that our temperature measurement approach is both accurate and reliable.\nRevision made: The following contents have been revised in Manuscript:\nA type-K thermocouple (0-1150 °C range, 0.5 mm diameter, ±0.1 °C accuracy) was embedded in the quartz sand bed, with a 90°-bent tip protruding 1.0 mm above the surface. The thermocouple was pre-calibrated against standard reference sources, and its performance was verified at multiple temperature setpoints to ensure consistency across the experimental range. T (the center temperature of catalyst surface)was detected by the thermocouple probe placed in direct contact with the upper surface of the catalyst at its center, enabling capture of the highest local temperature under irradiation (as shown by the red indicator line representing the thermocouple in Supplementary Fig. 9). This arrangement minimizes the thermal resistance effect by avoiding indirect measurement through the gas phase or reactor materials. Infrared (IR) thermography was used to validate the accuracy of T measurements from the thermocouple probe. T (average surface temperature) was obtained by moving the thermocouple probe, measuring temperatures at five different points on the catalyst surface (center and edges) and using the formula below:\nT = (T_Center + 2*T_Edge) / 3\n(Please refer to the marked content on lines 544-557 in the manuscript.)\nNote that the T and T indicate the average and the center temperature of catalyst surface measured by a thermocouple, which agree with the results from the IR camera (Supplementary Fig. 13).\n(Please refer to the marked content on lines 225-227 in the manuscript.)\nThe following contents have been added in Supplementary Information:\nSupplementary Fig. 13. The center temperature of NiIr /TiO detected by IR camera. (a) Photographs taken with an IR camera under different light intensities. (b) The center temperature of catalyst surface detected by thermocouple and IR camera.\n(Please refer to the marked content on page 15 in the supplementary information.)\nComment 4: In Fig. 1f, the UV-VIS-NIR spectrum shows an absorption intensity of ~1.35 in the ultraviolet region, which theoretically should be below 1 for diffuse reflectance spectra. The authors need to explain this discrepancy, including details of the measurement parameters (e.g., baseline correction, sample preparation) that might lead to this result. Furthermore, the experimental setup and operational details of the monochromatic light activity tests (marked by red dots) should be elaborated.\nReply: We thank the reviewer for their careful observation. Your comment regarding the Y-axis value exceeding 1 in Fig. 2f (the original Fig. 1f) is pertinent, as this is indeed a common point of discussion when interpreting diffuse reflectance spectra. We would like to clarify that the Y-axis values in Fig. 2f (the original Fig. 1f) in fact represent the Kubelka-Munk function, F(R) (where F(R) = (1-R)2/2R), which is derived from the measured reflectance data and is directly proportional to the absorption coefficient of the material. It is important to note that the Kubelka-Munk function has no theoretical upper limit. Therefore, a value of ∼1.35 in the UV region is entirely expected and confirms the strong intrinsic absorption of our material in this range. As shown in the original manuscript, the Y-axis was labeled as \"Absorbance (a.u.)\", not reflectance.\nRegarding the measurement parameters and sample preparation, the instrument used was a UV-Vis-NIR spectrophotometer (Varian Cary 500) equipped with an integrating sphere. Before measurement, baseline correction was performed using a standard barium sulfate (BaSO ) white reference. For sample preparation, the powder sample was pressed into a flat, uniform pellet in a culture dish to ensure data reliability and reproducibility. This strong absorption signal remained significant after baseline correction, further confirming its origin from the sample itself. We have added a description of these experimental details in the Supplementary Methods section.\nIn addition, following the reviewer's suggestion, we have provided detailed experimental methods for the monochromatic light activity tests in the revised manuscript. The monochromatic light activity tests were carried out in a dedicated reactor (PLR-PTSR II, Beijing PERFECTLIGHT) with external heating at 500 ℃. A 300 W Xenon lamp was used as the light source, coupled with optical filters to obtain monochromatic light of specific wavelengths. In each test, an optical power meter was used to accurately measure and calibrate the incident light intensity in front of the reactor window. Dividing the measured syngas generation rates by the light intensity under the corresponding monochromatic light yields the contributions of monochromatic light at different wavelength bands to the activity per unit light intensity. All other test conditions were consistent with those of the light-driven conditions.\nRevision made: The following contents have been added in Supplementary Information:\nUV-Vis-NIR diffuse reflectance spectra were recorded using a Varian Cary 500 spectrophotometer equipped with an integrating sphere, using BaSO as a reference. For sample preparation, the powder sample was pressed into a flat, uniform pellet in a culture dish to ensure data reliability and reproducibility. The absorbance was represented by the Kubelka-Munk function, F(R) (where F(R) = (1-R)2/2R), which is derived from the measured reflectance data.\n(Please refer to the marked content on page 1 in the supplementary information.)\nThe monochromatic light activity tests were carried out in a dedicated reactor (PLR-PTSR II, Beijing PERFECTLIGHT) with external heating at 500 ℃. A 300 W Xenon lamp was used as the light source, coupled with optical filters to obtain monochromatic light of specific wavelengths. In each test, an optical power meter was used to accurately measure and calibrate the incident light intensity in front of the reactor window. Dividing the measured syngas generation rates by the light intensity under the corresponding monochromatic light yields the contributions of monochromatic light at different wavelength bands to the activity per unit light intensity. All other test conditions were consistent with those of the light-driven conditions.\n(Please refer to the marked content on lines 575-582 in the manuscript.)\nComment 5: The oxidation state of the catalyst under light-off conditions is a concern. The authors mention that the catalyst contacts air when the light is turned off, and Ni and Ir are prone to oxidation. However, the in situ XAS results (Fig. 2a and b) indicate non-negligible Ni-O and Ir-O signals even under illumination, suggesting that oxidized states coexist with metallic states. It is necessary to discuss whether the reaction mechanism changes when the catalyst is in an oxidized state, especially during light-off periods.\nReply: We thank the reviewer for their insightful comment. In our system, the NiIr nanoclusters have an average particle size of less than 1.2 nm, which leads to strong interactions with the TiO support. The in situ XAS results reflect average structural information, and at this sub-nanometer scale, it is expected that some metal atoms coordinate with oxygen from the support. Even under illumination, where Ni-Ir alloy formation occurs, a fraction of atoms particularly at the interface may still bond with surface oxygen atoms of TiO . Specifically, under light irradiation, the in situ XANES and EXAFS analyses (Fig. 3a and b, originally Fig. 2a and b) show that NiIr /TiO exhibits negligible Ir-O coordination compared to the adjacent baseline signal, with a coordination number of zero as shown in Supplementary Fig. 19-20 and Supplementary Tables 4-5, while the dominant contribution comes from Ir-Ni bonds. On the other hand, the presence of Ni-O coordination is reasonable and structurally essential, as it reflects the interfacial bonding between Ni and the TiO support. This is further corroborated by the fitting results summarized in Fig. 3c (originally Fig. 2c) and the supplementary data. As stated in the manuscript, \"Under light irradiation, NiIr /TiO exhibits nearly 100% Ir-Ni coordination at the Ir L -edge and 32% Ir-Ni coordination at the Ni K-edge, alongside 37% Ni-O interfacial bonds.\"\nMoreover, comparison with monometallic references (Supplementary Fig. 18) reveals that under identical conditions, Ni/TiO transforms almost entirely into metallic Ni-Ni bonds, whereas Ir/TiO still shows residual Ir-O coordination. The absence of Ir-O coordination in NiIr /TiO under light confirms that Ir in the alloy phase does not directly interact with TiO , while Ni maintains interfacial Ni-O bonds, forming a nano-island architecture that isolates the NiIr alloy from the support.\nRegarding the reaction mechanism when the catalyst is in an oxidized state, we have included relevant discussion in the mechanism section. As noted in the manuscript, \"Ox-NiIr/TiO exhibited excessive CO adsorption but poor C=O scission capacity (Supplementary Fig. 48), while thermal conditions promoted direct CH cracking into carbon deposits (Supplementary Fig. 49). This starkly contrasts with photoinduced NiIr nano-island alloy, underscoring light's critical role in structural optimization.\" In the absence of light, the catalyst remains in an oxidized state and follows a different reaction pathway. However, the central focus of this study is the light-driven formation of the NiIr alloy and the superior performance and reaction mechanism of this alloy compared to monometallic or oxidized counterparts. Therefore, further investigation into the reaction mechanism over the oxidized catalyst is beyond the scope of the present work.\nComment 6: The caption for Supplementary Fig. 9 requires verification to ensure it accurately corresponds to the labels within the figure itself, facilitating reader comprehension. Fig. 4g is missing its caption. The authors need to perform a thorough check of all figure caption information.\nReply: We thank the reviewer for their careful reminder. In the revised version, we have revised the captions for Supplementary Fig. 8 (the original Supplementary Fig. 9) and Fig. 5g (the original Fig. 4g). In addition, we have conducted a thorough check on all other figure captions in the manuscript.\nRevision made: The following contents have been revised in Manuscript and Supplementary Information:\nSupplementary Fig. 8. In situ CO-probe DRIFTS spectroscopy analysis. (a-b) Ni/TiO . (c-d) NiIr /TiO . (e-f) NiIr /TiO . (g-h) NiIr /TiO . (i-j) Ir/TiO . All samples underwent CO adsorption at 25 ℃ for 30 min, followed by Ar-flow desorption at 25 ℃ (30 min) and heating-up desorption up to 400 ℃. Gas-phase CO peaks (2171, 2117 cm⁻¹) were observed during adsorption stage for all samples.\n(Please refer to the marked content on page 10 in the supplementary information.)\nFig. 5 | DFT calculations of reaction pathway and natural sunlight experiments. a, Reaction energy profiles (including transition states) for C=O bond scission of CO on NiIr/TiO -L , Ni/TiO , and Ir/TiO models. b, Reaction energy profiles (including transition states) for C-H bond scission of CH on NiIr/TiO -L , Ni/TiO , and Ir/TiO models. c, Reaction energy profiles for different CH activation pathways on NiIr/TiO -L model. d, Energy evolution of key steps (pink-shaded indicator in Supplementary Fig. 46a) during the first C-H scission of CH and the formation of *CH O intermediate. Ir, Ni, Ti, and O atoms are shown in pink, yellow, grey, and blue colors, respectively. e, DRM performance over NiIr /TiO under concentrated natural sunlight, with measured reaction temperature and incident light intensity (CH :CO :Ar =1:1:8, 20 ml min-1). Inset: experimental setup. f, DRM reaction demonstration under concentrated sunlight, with gas outlet directly interfaced to a PdCl indicator solution for CO detection. g, Schematic illustration of light-driven DRM mechanism.\n(Please refer to the marked content on lines 501-511 in the manuscript.)\nResponse to Reviewer 3\nGeneral comments: Authors performed experiments and DFT calculations to explore a light-driven methane dry reforming strategy utilizing sinter-resistant nano-island alloys catalyst (NiIr/TiO -LNi). This manuscript addresses an important topic in photocatalytic materials design. However, significant flaws in methodology, analysis, and mechanistic interpretation necessitate major revision before further consideration.\nReply: We sincerely thank the reviewer for their thorough assessment of our work and for acknowledging the significance of our study on light-driven DRM using sinter-resistant nano-island alloy catalysts. In response to the comments, we have conducted additional experiments, performed further DFT calculations, and revised the manuscript to address these concerns. We believe the revised version has been greatly improved and hope it now meets the high standards of Nature Communications.\nComment 1: In the theoretical calculation section, the Monkhorst-Pack k-point sampling was generated with a 1×1×1 grid. For two-dimensional structure (NiIr/TiO -LNi), a minimum of 2×2×1 grid should be used.\nReply: We sincerely thank the reviewer for the careful reminder. After re-checking our original input files, we found that the description in the Methods section was inaccurate. As shown in the screenshot below, the Monkhorst-Pack k-point sampling used in all our calculations was actually 2 ×2×1, rather than 1×1×1 as previously written. In the revised manuscript, all new calculations also applied the 2×1×1 grid. We have corrected this typographical error in the revised manuscript. We truly appreciate the reviewer’s attention to detail, which helped us improve the clarity and accuracy of our computational description.\nRevision made: The following contents have been revised in Supplementary Information:\nDensity functional theory (DFT) calculations were implemented by materials studio and Vienna ab initio simulation package (VASP)1,2. Perdew-Burke-Ernzerhof (PBE) of the generalized gradient approximation (GGA) was employed to describe the exchange-correlation functional3,4.The projected augmented wave (PAW) potentials were applied to describe the ionic cores and take valence electrons into account using a plane wave basis set with a kinetic energy cutoff of 400 eV. Partial occupancies of the Kohn-Sham orbitals were allowed using the Gaussian smearing method and a width of 0.05 eV. The electronic energy was considered self-consistent when the energy change was smaller than 10-5 eV. A geometry optimization was considered convergent when the force change was smaller than 0.05 eV/Å. The vacuum spacing perpendicular to the plane of the structure is 15 Å. The Brillouin zone integral utilized the surfaces structures of 2×2×1 monkhorst pack K-point sampling. The adsorption energy (eV) was defined as follows: E = E – (E + E ), where E is the energy of the slab together with the adsorbate, E is the total energy of the free adsorbate and E is the total energy of the bare slab. The d band center (ε ) was calculated as follows:\nε =∫ n (ε)ε𝑑ε/∫ n (ε)𝑑ε.\nTransition states for elementary reaction steps were determined by a combination of the nudged elastic band (NEB) method and the dimer method. In the NEB method, the path between the reactant and product is discretized into a series of structural images. The image that is closest to a likely transition state structure was then employed as an initial guess structure for the dimer method.\nExcitation-dependent charge redistribution calculations are performed with ORCA software5. The functional employed was PBE0, and the basis set used was def2-SVP. (This basis set is an all-electron basis set for the first four periods and a pseudopotential basis set starting from the fifth period, so no mixed basis set is required.) The electron-hole structures were calculated using Multiwfn6, and the visualization data were obtained using the visual molecular dynamics VMD software7. The geometric mean overlap function of hole and electron distributions (S) was calculated as follows:\nS (r) = √[𝜌ℎ𝑜𝑙𝑒(r) 𝜌𝑒𝑙𝑒(r)];\nr\nρhole and ρele represent the electron density of the hole and the excited electron at the spatial position r, respectively.\n(Please refer to the marked content on page 2 in the supplementary information.)\nComment 2: Regarding dynamic reconstruction, the following questions arise:\na. “This photoinduced charge transfer may alter the electronic structure of surface chemical bonds, reducing bond energies and promoting dynamic surface reconstruction.” This statement lacks evidence.\nb. Regarding structural rationality, how light exposure selectively breaks Ir-O bonds while enabling their reformation in darkness — a claim implying dynamic reversibility without supporting DFT evidences?\nReply: We sincerely thank the reviewer for this valuable comment, which has helped us further clarify and improve the manuscript.\n(1) Regarding your Comment 2 (a), the statement in question was included in the introduction to provide a general background on photoinduced effects in catalytic systems, and it is supported by multiple references (Refs. 17-20). For instance, Marimuthu et al. (Ref 17, Science 339, 1590-1593 (2013)) demonstrated that plasmon-induced hot carriers and local fields lead to dynamic interconversion between metallic (Cu0) and oxidized (Cu+/Cu2+) states on Cu nanoparticles, thereby modulating reaction pathways. Lee et al. (Ref 18, Nat. Mater. 18, 620-626 (2019)) showed that localization of photogenerated electrons dynamically tunes the valence state of isolated Cu atoms, activating TiO and improving photocatalytic performance. Ye et al. (Ref 19, J. Am. Chem. Soc. 145, 20530-20538 (2023)) revealed that photoexcited charge carriers induce structural restoration of Cu/TiO from inactive Cu O to metallic Cu during methanol steam reforming. Ren et al. (Ref 20, J. Am. Chem. Soc. 145, 28276-28283 (2023)) reported that double oxygen vacancies form and recover during CO photoreduction, altering product selectivity. These studies collectively illustrate that light-driven charge redistribution can modify surface properties and induce structural dynamics.\nIn addition, we have now added further supporting literature to strengthen this argument:\nJiang et al. (Nat. Catal. 6, 519-530 (2023)) confirms that photoexcited electrons can weaken original metal-oxygen (M-O) bonds, leading to changes in surface structure. Wang et al. (J. Am. Chem. Soc. 147, 17, 14705-14714 (2025)) reported that Mn-induced charge transfer and photoexcited electron capture reduce the Mn valence state and weaken the La-O-Mn bond in perovskites, further illustrating how light-induced electron transfer between bimetallic sites can weaken metal-support bonds and induce structural reorganization. Prof. Xiong described a light-induced dissolution–reprecipitation process using high-entropy oxides (HEOs) as supports (Adv. Mater. 37(21), 2500928 (2025)), wherein illumination weakens metal–O bonds in the HEO, leading to Co and Ni leaching and subsequent alloy formation. Thus, the statement is well-grounded in previous and recent experimental studies.\n(2) Regarding Comment 2 (b), we agree that a clear mechanistic rationale is essential and have also addressed this point in our response to Reviewer 1's Comment 2. Our experimental and computational results provide strong support for the proposed reversible bond breaking and reformation.\nFirstly, we have conducted direct experimental evidence from in situ XAS. Under light, Ir L -edge EXAFS of NiIr /TiO shows a dominant Ir-Ni peak at 2.18 Å replacing the initial Ir-O coordination, while Ni K-edge EXAFS retains Ni-O and Ni-Ni paths alongside a new Ni-Ir coordination, indicating alloy formation without full Ni reduction (Fig. 3a-b). Quantitative EXAFS fitting (Fig. 3c, Supplementary Fig. 19-20, Supplementary Tables 4-5 in the revised version) shows nearly 100% Ir-Ni coordination at the Ir L -edge and 32% Ir-Ni at the Ni K-edge under light. This confirms that Ir in the alloy phase does not directly interact with TiO , while Ni maintains interfacial Ni-O bonds, forming a nano-island architecture that isolates the NiIr alloy from the support. In dark thermal conditions, limited reduction occurs and no significant Ni-Ir bonds form, proving light is essential. Furthermore, re-oxidation in post-EXAFS (Supplementary Fig. 27 and Note 4) and reversible NAP-XPS trends confirm that NiIr/TiO -L exists transiently only under light irradiation.\nSecondly, we have performed DFT calculations to provide evidences. The formation energy of NiIr/TiO -L is lower than that of a hypothetical Ir-linked model (NiIr/TiO -L ), in which Ir-O bonds elongate (>3.0 Å), destabilizing the interface (Fig. 3g, Supplementary Fig. 33). Electron density distributions (Supplementary Fig. 40a-d and Note 8) show that Ni-mediated charge polarization enriches electrons at Ir sites. Density of states profiles (Supplementary Fig. 40e-h) reveal that NiIr alloy formation modulates the d-band center, optimizing the trade-off between adsorption strength and desorption kinetics. Time-dependent DFT simulations (Fig. 4i) further illustrate excitation-dependent charge redistribution in NiIr/TiO -L .\nIn addition, we supplemented our DFT analysis with comparative calculations of bond strengths in the excited state versus the ground state (Supplementary Table 6). The bond energy in the excited state is lower compared to the ground state. This is because photoinduced charge transfer leads to the weakening of chemical bonds, which combined with thermal effects, facilitates atomic movement towards a more stable structure. A detailed comparison reveals that in the O -NiIr/TiO structure, the difference in Ir-O bond energy between the excited state and the ground state is larger, while the difference for the Ni-O bond is smaller. This indicates that under photoexcitation, the Ir-O bond becomes more unstable and is weakened more significantly, thus it preferentially breaks, facilitating Ir migration. In addition, simulations under photoexcitation show that the Ni-Ir bond strength (92.35 kJ mol-1) in the NiIr/TiO -L alloy structure in the excited state is more stable than the Ir-O bond strength (69.64 kJ mol-1) in the excited state of the O -NiIr/TiO structure. This provides supporting evidence for the formation of the Ni-Ir alloy under light irradiation.\nRevision made: The following contents have been revised in Manuscript:\nBeyond thermal vibrations that commonly induce surface reconstruction at high temperatures, photoexcitation can trigger substantial charge redistribution between the support and active site17-20. This photoinduced charge transfer may alter the electronic structure of surface chemical bonds, reducing bond energies and promoting dynamic surface reconstruction21-22. (Please refer to the marked contents on lines 62-66 in the manuscript.)\n21. Jiang, H., Wang, L., Kaneko, H. et al. Light-driven CO methanation over Au-grafted Ce Ru O solid-solution catalysts with activities approaching the thermodynamic limit. Nat. Catal. 6, 519-530 (2023).\n22. Li J., Zhao J., Wang S. et al. Activating lattice oxygen in perovskite ferrite for efficient and stable photothermal dry reforming of methane. J. Am. Chem. Soc. 147, 17, 14705-14714 (2025).\n(Please refer to the marked contents on lines 692-696 in the manuscript.)\nComputational analysis of chemical bond strength changes between the ground and excited states (Supplementary Table 6) provides further mechanistic insight. The photoinduced charge transfer weakens the chemical bonds, which synergizes with thermal effects, facilitates atomic rearrangement into a more stable configuration. A detailed comparison reveals a more pronounced bond energy difference between the excited state and the ground state in Ir-O bond (-28.06 kJ mol-1) compared to that of the Ni-O bond (-9.36 kJ mol-1). This indicates a preferential destabilization and breaking of the Ir-O bonds, thereby facilitating the migration of Ir atoms. Furthermore, under the excited state, the Ni-Ir bond (92.35 kJ mol-1) is stronger than the Ir-O bond (69.64 kJ mol-1). These bond energy differences provide support for the formation of the Ni-Ir alloy under light irradiation. (Please refer to the marked contents on lines 415-424 in the manuscript.)\nSupplementary Table 6. Bond energy of NiIr/TiO -L and Ox-NiIr/TiO structures at ground state and excited states.\nBond energy\nModel Ground state Excited state\ndifference\nNiIr/TiO -L Ni-Ir 101.69 kJ mol-1 92.35 kJ mol-1 -9.34 kJ mol-1\nIr-O 97.70 kJ mol-1 69.64 kJ mol-1 -28.06 kJ mol-1\nOx-NiIr/TiO\nBond energy difference = The bond energy at excited state - The bond energy at ground state.\n(Please refer to the marked contents on page 53 in the supplementary information.)\nComment 3: The manuscript insufficiently clarifies the origin of photogenerated electrons in NiIr/TiO -LNi under illumination. Crucially, the text fails to explicitly state:\na.What physical mechanism drives their generation?\nb.What mechanism drives their generation?\nReply: We sincerely thank the reviewer for this valuable comment, which has helped us further clarify and improve the manuscript. Regarding the physical mechanism of photogenerated electron generation, it originates from the fundamental principles of photocatalysis. TiO , as a semiconductor with UV-visible light response, possesses a band structure consisting of a valence band (VB) and a conduction band (CB), separated by a bandgap. Upon irradiation with photons of energy matching or exceeding the bandgap, electrons in the VB are excited and jump to the CB, generating electron-hole pairs. These photogenerated charge carriers then migrate to the catalyst surface, where they drive the catalytic reactions. Under concentrated light intensity, the NiIr alloy can be further excited, generate hot electrons, and contribute to a local temperature rise. While both photoelectric and photothermal effects are present and synergistic, the controlled condensation experiments (Fig. 2e) confirm that the photoelectric effect plays a more dominant role.\nConcerning the electron transfer pathway, our comprehensive mechanistic investigations have clearly demonstrated a support-Ni-Ir electron transfer pathway under illumination. In situ NAP-XPS analyses provide direct evidence of this light-induced electron transfer. The Ir 4f spectra (Fig. 3d-e) reveal a pronounced shift toward lower binding energy, with the Ir0 fraction increasing from 36.96% (dark) to 60.65%. Upon switching to focused light, the Ir0 fraction further rises to 62.31%. This indicates that Ir gains electrons under irradiation. Parallel in situ Ni 2p NAP-XPS (Supplementary Fig. 24a-c) shows analogous trends, with Ni0/Ni2+ ratios tracking Ir's redox dynamics. While Ti 2p and O 1s exhibit the positive shift in the binding energy of Ti and O under light irradiation (Supplementary Fig. 24d-e), this demonstrates that electrons migrate from the TiO support to Ni-Ir under illumination. Subsequently, electrons are further transferred from Ni to Ir. In situ XAS analysis (Fig. 3a-c, Supplementary Fig. 19-20, and Supplementary Tables 4-5) also supports this mechanism. It reveals that Ir in the alloy phase does not directly interact with TiO , while Ni maintains interfacial Ni-O bonds, forming a nano-island structure that isolates the NiIr alloy from the support. This configuration formation indicates the electron transfer from Ni to Ir under light irradiation. Additionally, time-dependent DFT (TD-DFT) simulations (Fig. 4i) show that electrons in photoexcited states preferentially accumulate at Ir sites distal to the TiO interface. S →S promotes hole accumulation at Ni sites alongside electron enrichment at Ir sites, a spatial charge segregation that drives photoexcited electrons toward Ir centers in higher-energy states.\nComment 4: The positive and negative values of the Mulliken charges analysis should be explained.\nReply: We sincerely thank the reviewer for this valuable comment, which has helped us further clarify and improve the manuscript. In Mulliken population analysis, the calculated atomic charge reflects the balance between the number of valence electrons associated with an atom in the isolated state and the electron density assigned to it within the molecule or solid. Positive Mulliken charge indicates that the atom has lost electron density relative to its neutral atomic state. This is commonly interpreted as electron donation toward neighboring atoms or into the bonding network, consistent with an electron-deficient or partially oxidized character. Negative Mulliken charge signifies that the atom has gained electron density, i.e., it has accepted charge from its surroundings. Such atoms are considered electron-rich or partially reduced relative to their neutral state. It should be noted that Mulliken charges are semi-quantitative and mainly used to capture relative charge-transfer trends rather than absolute electron counts. We have added the corresponding explanation in the supplementary information to further enhance the clarity of this analysis.\nRevision made: The following contents have been revised in Supplementary Information:\nMulliken charge analysis quantifies distinct patterns of interfacial charge redistribution: Positive charges indicate electron density loss relative to the neutral atom, reflecting electron donation to the neighbors or bonding network. Negative charges signify electron density gain from the surroundings, indicating an electron-rich/partially reduced character.\n(Please refer to the marked content on page 42 in the supplementary information.)\nComment 5: For the proposed reaction pathways, critical bond-breaking steps (e.g., *CO → *CO*O, *CH → *H*CH ) require transition state analysis with corresponding energy barriers. Without these kinetic validations, the mechanistic pathway lacks practical significance and fails to establish a credible catalytic cycle.\nReply: We sincerely thank the reviewer for this valuable comment, which has helped us further clarify and improve the manuscript. As rightly noted, the initial bond cleavage of CO and CH is indeed a critical step in DRM. In response, we have supplemented the transition state analysis in our revised manuscript as suggested. For the initial bond cleavage of CO and CH molecules, as shown in the updated Fig. 5a-b and Supplementary Figs. 43-44, NiIr/TiO -L demonstrates both thermodynamic and kinetic advantages. Compared to monometallic Ni/TiO and Ir/TiO , NiIr/TiO -L exhibits a significantly greater energy reduction after direct C=O scission of CO and the first C-H scission of CH , indicating superior thermodynamic favorability. Furthermore, NiIr/TiO -L exhibits transition state activation energies (Ea) of +0.26 eV for C=O scission and +0.30 eV for C-H scission. These values are lower than the corresponding transition state barriers on both Ni/TiO and Ir/TiO , clearly indicating the kinetic advantage of the nanoisland NiIr alloy. To clearly present these new kinetic validations, we have also accordingly reorganized the panel structure of Fig. 5 (the original Fig. 4).\nRevision made: The following contents have been revised in Manuscript and Supplementary Information:\nFor the initial bond cleavage of CO and CH molecules as shown in Fig. 5a-b and Supplementary Figs. 43-44, NiIr/TiO -L demonstrates both thermodynamic and kinetic advantages. Compared to monometallic Ni/TiO and Ir/TiO , NiIr/TiO -L exhibits a significantly greater energy reduction after direct C=O scission of CO and the first C-H scission of CH , indicating its superior thermodynamic favorability. Meanwhile, NiIr/TiO -L exhibits activation energies (Ea) of the transition states at +0.26 eV for C=O scission and +0.30 eV for C-H scission. These values are lower than the transition state barriers for the first C-H scission of CH and direct CO scission on Ni/TiO and Ir/TiO , indicating the kinetic advantage of the nanoisland NiIr alloy. Supplementary Fig. 45 further compares the pathway of direct C=O scission of CO with the indirect activation route via COOH pathways. The results reveal Ir/TiO 's propensity for *COOH formation, aligning with in situ SR-DRIFTS detected RWGS activity and a suboptimal H /CO ratio. In contrast, NiIr/TiO -L enables concerted C=O scission, where Ni site stabilizes dissociative oxygen and Ir site coordinates carbon, directly yielding CO and *O species.\nRegarding the subsequent activation process after the initial bond cleavage of CH , *CH may undergo further direct C-H scission until a C atom remains. Alternatively, *CH can be assisted by activation through combination with O species from CO activation (O ) or lattice oxygen (O ). Fig. 5c compares the thermodynamic energy changes before and after the reaction for these three possible activation pathways. The results show that the sequential direct C-H scission pathway (*CH3→*CH2→*CH→*C) on NiIr/TiO -L requires prohibitively high energy, particularly 1.18 eV for cleaving the second C-H bond. For the *O-assisted C-H scission routes, O -assisted pathways proved unfavorable due to the high *CH migration energy of 1.30 eV. Conversely, *O species from CO dissociation adsorbed on Ni sites in NiIr/TiO -L enabled thermodynamically favorable *CH O formation with ΔE = -0.61 eV, and subsequent dehydrogenation required only 0.29 eV, consistent with isotopic labeling results. Comparative studies between NiIr/TiO -L and monometallic Ni/TiO and Ir/TiO in Supplementary Fig. 46 further highlight the optimal performance of NiIr/TiO -L . Specifically, in *O -assisted pathways, while Ni/TiO struggled with CH activation exhibiting a second C-H barrier of 0.75 eV and Ir/TiO suffered from poor *O stabilization, the NiIr alloy achieved balanced kinetics through asymmetric Ni-Ir sites.\n(Please refer to the marked contents on lines 443-470 in the manuscript.)\nSupplementary Fig. 43. DFT-optimized configurations of C=O scission of CO on (a) NiIr/TiO -L , (b) Ir/TiO , and (c) Ni/TiO models.\n(Ir, Ni, Ti, and O atoms are shown in pink, yellow, grey, and blue colors, respectively.)\n(Please refer to the marked contents on page 46 in the supplementary information.)\nSupplementary Fig. 44. DFT-optimized configurations of 1st C-H scission of CH on (a) NiIr/TiO -L , (b) Ir/TiO , and (c) Ni/TiO models.\n(Ir, Ni, Ti, and O atoms are shown in pink, yellow, grey, and blue colors, respectively.)\n(Please refer to the marked contents on page 47 in the supplementary information.)\nSupplementary Fig. 46 (a) Reaction energy profiles for O assisted C-H scission of CH on NiIr/TiO -L , Ni/TiO , and Ir/TiO models. DFT-optimized reaction configurations on (b) Ni/TiO and (c) Ir/TiO model.\n(Ir, Ni, Ti, and O atoms are shown in pink, yellow, grey, and blue colors, respectively.)\n(Please refer to the marked contents on page 49 in the supplementary information.)\nFig. 5 | DFT calculations of reaction pathway and natural sunlight experiments. a, Reaction energy profiles (including transition states) for C=O bond scission of CO on NiIr/TiO -L , Ni/TiO , and Ir/TiO models. b, Reaction energy profiles (including transition states) for C-H bond scission of CH on NiIr/TiO -L , Ni/TiO , and Ir/TiO models. c, Reaction energy profiles for different CH activation pathways on NiIr/TiO -L model. d, Energy evolution of key steps (pink-shaded indicator in Supplementary Fig. 46a) during the first C-H scission of CH and the formation of *CH O intermediate. Ir, Ni, Ti, and O atoms are shown in pink, yellow, grey, and blue colors, respectively. e, DRM performance over NiIr /TiO under concentrated natural sunlight, with measured reaction temperature and incident light intensity (CH :CO :Ar =1:1:8, 20 ml min-1). Inset: experimental setup. f, DRM reaction demonstration under concentrated sunlight, with gas outlet directly interfaced to a PdCl indicator solution for CO detection. g, Schematic illustration of light-driven DRM mechanism.\n(Please refer to the marked contents on lines 501-511 in the manuscript.)\nComment 6: For Fig.4c, regardless of the catalyst structure employed, since reactants and products remain identical, the energy of initial and final states should be identical relative to those reactants and products.\nReply: We appreciate the reviewer's thoughtful comment regarding the energy reference used in Fig. 5 (the original Fig.4). We fully agree with the thermodynamic statement that, for the reaction CH + CO → 2CO + 2H , the overall reaction energy must be identical across catalysts when the initial and final states are defined as gas-phase reactants and gas-phase products with a fully restored (clean) surface. Under this unified reference, the catalyst energy cancels out and the net reaction energy depends only on the molecular species.\nThe goal of Fig. 5c (the original Fig.4b) is to establish that the O-assisted C-H scission pathway, in which an oxygen atom generated by prior CO dissociation participates in breaking the C-H bond, is energetically much more favorable than the direct removal of the second hydrogen from CH . Motivated by this result, Supplementary Fig. 46 (the original Fig.4c) and Fig. 5d focuses exclusively on comparing the elementary-step energetics along the O-assisted pathway on three catalysts. Accordingly, in Fig. 5c, the initial state corresponds to a clean surface; however, in the third (iii) step, an oxygen atom generated from CO dissociation (O ) is introduced to demonstrate the oxygen-assisted C–H bond activation mechanism. Therefore, the adsorption energy difference of the oxygen species derived from CO dissociation is also incorporated into the overall energy variation of this system.\nThe reaction sequence reads: (i) CH adsorption → (ii) the first C-H scission to *CH + *H → (iii) coupling of *CH with *O to *CH O → (iv–vi) stepwise dehydrogenation to *adsorbed CO. The *desorption of CO and surface restoration are not included in Supplementary Fig. 46 (the original Fig.4c), because the panel is designed to highlight stepwise energetics rather than the full thermodynamic cycle. The energy change of an elementary step is thus the difference between two successive states (ΔE = E - E ). For example, on Ni/TiO the CH adsorption is endothermic by +0.12 eV, and the subsequent C-H scission reduces the energy from +0.12 to -0.26 eV, i.e., -0.38 eV for that step. These vertical drops between adjacent plateaus are precisely what we compare across catalysts to quantify the driving force differences for the O-assisted C-H activation.\nBecause the third step in Supplementary Fig. 46 (the original Fig.4c) explicitly introduces the adsorption energy of oxygen (O) and the terminal state (adsorbed CO) is also an adsorbed state, variations in the adsorption strength and interfacial bonding of O and CO among different catalysts naturally lead to differences in their absolute energies. Therefore, the start-to-end offsets in Supplementary Fig. 46 (the original Fig.4c) are not expected to be identical. This is fully consistent with the purpose of the figure, which is to compare the energetics of elementary steps under an O-covered surface condition rather than to depict a complete thermodynamic reaction profile.\nComment 7: CO has a linear configuration in its free state, While all adsorbed CO species in this study exhibit a bent (V-shaped) geometry.\nReply: We thank the reviewer for this insightful comment. The reviewer is correct that the free CO molecule in the gas phase exhibits a linear geometry. However, all configurations shown in our study represent CO molecules in the adsorbed state. Upon adsorption onto the catalyst surface, CO undergoes significant electronic and structural changes due to interaction with the active sites. Specifically, charge transfer and orbital rehybridization between CO and the catalyst lead to a bending of the O-C-O angle, which is a well-established indicator of CO activation in heterogeneous catalysis. This bent configuration corresponds to a chemisorbed and activated state of CO , which is a crucial precursor step facilitating its subsequent conversion. Therefore, the observed V-shaped geometry in our models is consistent with the expected behavior of activated CO in catalytic systems and validates the effectiveness of the considered catalysts in promoting CO activation. This behavior is consistent with many previous theoretical findings in CO activation studies (Angew. Chem. Int. Ed. 58, 6916 (2019), doi.org/10.1002/anie.201900565; J. Am. Chem. Soc. 142, 3214-3221 (2020), doi.org/10.1021/jacs.9b13280; J. Phys. Chem. C 123, 6516-6525(2019), doi.org/10.1021/acs.jpcc.8b11816; ACS Catal. 15, 2916-2926 (2025), doi.org/10.1021/acscatal.4c07178)."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors performed detailed revisions and addressed all concerns. I suggest to accept the revised version for publication.", "reviewer_2": "The authors have addressed my concerns. I recommend the manuscript for publication.", "reviewer_3": "I am pleased to recommend this manuscript for publication."}, "author_response": ""}]

Decision letter