Breakthrough photothermal ammonia decomposition via low-barrier Ni-CeO_2-x interfaces on carbon nanotubes

Domain: chemistry
Published: 2025-12-17
Editorial outcome: major_revision

Abstract
Efficient ammonia decomposition is crucial for hydrogen economy, but inexpensive Ni catalysts require excessively high temperatures due to limited N-N coupling. Here, we overcome this challenge by constructing a photothermal catalyst with closely interfaced, defect-rich CeO2-x nanodomains and electron-rich Ni nanoparticles on carbon nanotubes. The Ni-CeO2-x/CNTs catalyst achieves a hydrogen production rate of 298.4 mmol gcat-1 min-1 under full-spectrum light irradiation, which exceeds that of most reported Ru catalysts, and maintained stable activity for over 50 h in continuous-flow operation. The high performance arises from the synergistic effect of thermally promoted photocatalytic N-H bond cleavage and a largely reduced N-N coupling barrier, enabled by efficient photothermal conversion of carbon nanotubes and the up-shifted d-band center of the Ce-Ov-Ni interface (Ov = oxygen vacancy).

Introduction
The hydrogen economy is hindered by challenges in storage and transport, primarily due to hydrogen’s low volumetric energy density and safety concerns associated with its explosiveness1. Ammonia (NH3) has emerged as a promising hydrogen carrier, offering a high hydrogen content (17.8 wt.%), facile liquefaction under mild conditions (8–10 bar at 20°C), and a carbon-free decomposition route (2NH3 → N2 + 3H2)2. Nickel-based catalysts, as cost-effective non-noble metal alternatives, are attractive for catalytic ammonia decomposition. However, their performance is limited by the high energy barrier associated with N-adatom recombination and desorption, necessitating elevated reaction temperatures and strong resistance to sintering3.

Light-driven catalysis offers a sustainable strategy for overcoming activation barriers by harnessing photon energy, enabling high reactivity under mild conditions4–6. In photocatalytic ammonia decomposition, light primarily excites the photocatalyst to generate electron–hole pairs, where photogenerated holes serve as strong oxidants that effectively promote N–H bond cleavage7,8. However, another key step—N-adatom recombination and desorption—requires substantial thermal energy to overcome its high activation barrier9–12. Purely photocatalytic systems lack sufficient heat to drive this step efficiently, resulting in sluggish reaction kinetics and extremely low hydrogen evolution rates (<0.01 mmol gcat–1 min–1)7,13–17. In contrast, photothermal catalysis, through the synergistic interplay of light and heat, effectively addresses this limitation18–20. In such systems, light energy facilitates N–H bond activation, while thermal energy promotes N–N coupling, collectively enabling efficient and low-temperature ammonia decomposition with significantly enhanced reaction rates.

An ideal photothermal catalyst for ammonia decomposition should integrate several key attributes to fully exploit the synergistic effect of light and heat21. First, it must exhibit superior light-harvesting capability and efficient charge separation to convert ultraviolet and visible light into chemical energy with high efficacy. Second, the catalyst should feature rationally designed active sites that facilitate ammonia adsorption, promote N–H bond cleavage, and optimize the N–N coupling to lower activation barriers and enhance the efficiency of the overall reaction pathway. Additionally, it should efficiently convert low-energy light—particularly near-infrared (NIR), which cannot drive charge separation—into heat and deliver it to active sites, transforming otherwise wasted photons into a driving force for N–N coupling and enhanced charge carrier dynamics. Long-term resistance to ammonia and light-induced corrosion is also essential to ensure structural and functional stability. Moreover, the use of earth-abundant transition metals such as Ni or Fe is vital for scalable and sustainable applications. Realizing all these features in a single catalyst, however, remains a significant challenge.

Herein, we develop one of the most efficient photothermal catalysts to date, achieved by integrating CeO2-x nanodomains and Ni nanoparticles onto CNTs with close interfacial contact. The exceptional performance originates from the synergistic combination of UV-visible photocatalysis driven by CeO2-x and rationally engineered interface sites. CNT’s remarkable light-to-heat conversion and electron transport capabilities significantly enhance the photoexcited carrier separation in CeO2-x, thereby accelerating the photocatalytic N–H bond cleavage. The formed Ce–Ov–Ni interface upshifts the Ni d-band center, promoting the adsorption of N intermediates and significantly reducing the N–N coupling barrier from 1.34 eV (in conventional Ni catalysts) to 0.53 eV, completely breaking the intrinsic limitation of Ni-based catalysts.

Results
Structures and properties of catalysts
A series of CeO2-x modified carbon nanotube (CNTs) composites were synthesized via a liquid-phase alkaline precipitation method (Fig. 1a). The target composite, denoted as CeO2-x/CNTs, was obtained by adjusting the mass ratio of CeO2 to CNTs to 0.5 (mCeO2/mCNTs = 0.5), while pure CeO2 and CNTs were served as control samples. Subsequently, 10 wt.% Ni was deposited onto the composites via a NaBH4-assisted chemical reduction method, yielding the Ni-CeO2-x/CNTs, Ni/CeO2, and Ni/CNTs catalysts, respectively. Inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis confirmed that the actual Ni loading of all catalysts was in close agreement with the nominal values (Supplementary Table 1).

Powder X-ray diffraction (XRD) patterns (Supplementary Fig. 1) reveal the coexistence of characteristic peaks corresponding to the cubic fluorite structure of CeO2 and the graphitic features of CNTs in CeO2-x/CNTs22. Compared to pure CeO2, the diffraction peaks of CeO2-x in CeO2-x/CNTs are significantly broadened, indicating a reduced crystallite size. Transmission electron microscopy (TEM) images (Supplementary Fig. 2) further confirm that CeO2-x is uniformly dispersed on the CNTs surface with an average particle size of 6.6 nm—substantially smaller than that of pure CeO2 (17.4 nm). This size reduction can be attributed to the high surface area of CNTs (Supplementary Fig. 3), which provides abundant anchoring sites and suppresses CeO2 crystal growth23–25. Raman spectroscopy (Supplementary Fig. 4) reveals a pronounced defect band (D-band) at 620 cm−1 in CeO2-x/CNTs, with an intensity ratio (ID/IF2g) of 0.14 relative to the intrinsic F2g mode of CeO2 at 467 cm−1—14 times higher than that of pure CeO2. Quantitative analysis of oxygen vacancies was performed by X-ray photoelectron spectroscopy (XPS) of the O 1s and Ce 3d regions (Supplementary Fig. 5). The O 1s spectrum indicates that oxygen vacancies account for 42% of the total oxygen species, while the Ce3+/(Ce3++Ce4+) ratio derived from the Ce 3d spectrum reaches 43%. These results, summarized in Fig. 1b and Supplementary Table 2, demonstrate the formation of highly dispersed, defect-rich CeO2-x nanodomains on the CNTs surface.

The nature of Ni nanoparticles was elucidated by combining XRD patterns, TEM images, and XPS spectra. As shown in the XRD patterns (Fig. 1c), distinct metallic Ni diffraction peaks are observed only for Ni/CeO2, indicating that Ni species in Ni/CNTs and Ni-CeO2-x/CNTs exhibit smaller particle sizes and higher dispersion. TEM images (Supplementary Fig. 6) confirm that the average Ni particle sizes on CeO2, CNTs, and CeO2-x/CNTs are 10.2 nm, 5.8 nm, and 5.5 nm, respectively. Notably, high-resolution TEM (HRTEM, Fig. 1d) and elemental line-scanning images (Fig. 1e) clearly reveal that in Ni-CeO2-x/CNTs, Ni nanoparticles (highlighted in blue) preferentially anchor around CeO2-x nanodomains (highlighted in yellow) on the CNT surface, forming intimate Ni-CeO2-x interfaces. This phenomenon can be attributed to strong metal-support interaction (SMSI) between Ni and CeO2, which stabilizes Ni nanoparticles through interfacial Ce–O–Ni bonding26–28. XPS analysis of the Ni 2p3/2 region (Fig. 1f) indicates a higher proportion of Ni2+ and Niδ+ species in Ni-CeO2-x/CNTs compared to Ni/CNTs, further supporting the formation of the Ni-CeO2-x interface29.

Ultraviolet photoelectron spectroscopy (UPS, Supplementary Fig. 7) shows a decreasing trend in work function (WF) across the support materials: CeO2 (5.79 eV), CNTs (4.91 eV), and CeO2-x/CNTs (4.71 eV). Correspondingly, Ni-CeO2-x/CNTs exhibits a downward shift in Ni 2p binding energy (Fig. 1F), showing 0.25 eV and 0.07 eV lower values compared to Ni/CeO2 and Ni/CNTs, respectively. Density functional theory (DFT) calculations of work function (WFcal., Supplementary Fig. 8) further support this trend, indicating that oxygen vacancy-rich CeO2-x_Ov (4.63 eV) and CNTs (4.72 eV) within the CeO2-x/CNTs composites synergistically act as electron donors, promoting electron transfer to metallic Ni (5.17 eV). In contrast, pure CeO2 exhibits a higher work function (5.94 eV) and behaves as an electron acceptor. Bader charge analysis and differential charge density maps (Fig. 1g and Supplementary Figs. 9 and 10) further corroborate these findings, showing that CeO2-x_Ov donates 0.101 |e| to Ni8, while pure CeO2 withdraws 0.218 |e| from Ni8. These experimental and theoretical results collectively confirm the enhanced electron-donating capability of CeO2-x/CNTs-supported Ni nanoparticles.

Finally, we constructed a well-defined Ni-CeO2-x/CNTs catalyst with closely interfaced, defect-rich CeO2-x nanodomains and highly dispersed Ni nanoparticles on carbon nanotubes (CNTs). This architecture combines spatial confinement from CNTs, strong Ce–O–Ni interfacial interactions for sintering resistance, and directional electron transfer that enriches Ni active sites.

Photothermal catalytic ammonia decomposition
Photothermal ammonia decomposition was initially conducted in a batch reactor under visible-IR irradiation (300 W xenon lamp equipped with a 400 nm cut-off filter, 1.4 W cm−2) without external heating (Supplementary Fig. 11). As shown in Supplementary Fig. 12, Ni-CeO2-x/CNTs exhibited the highest decomposition efficiency among a broad range of photothermal catalysts with varied supports, oxides, and metal centers. Comparative studies revealed that its hydrogen production rate significantly surpassed those of single-component catalysts (Ni-CeO2 and Ni/CNTs) and their physical mixture (Ni-CeO2 + Ni/CNTs), underscoring the importance of the synergistically integrated nanocomposite architecture in boosting photothermal activity (Fig. 2a). No hydrogen was detected over metal-free CeO2-x/CNTs, confirming that metal active sites are essential for the reaction. Upon light irradiation at 1.4 W cm−2, the surface temperature of Ni-CeO2-x/CNTs rapidly rose to 155 °C within 30 s and remained steady (Supplementary Fig. 13). In contrast, no ammonia decomposition was observed at the same temperature in the dark, ruling out any contribution from thermal catalysis alone.

To further distinguish the contributions of photocatalysis and thermo-catalysis, light power dependence experiments and thermal catalytic ammonia decomposition were separately conducted on Ni-CeO2-x/CNTs. As shown in Supplementary Fig. 14 and Fig. 2b, when the light intensity increased from 1.4 W cm−2 to 2.4 W cm−2, the catalyst surface temperature rose from 155 °C to 208 °C, resulting in a nearly six-fold increase in the hydrogen production rate, from 22.3 mmol gcat−1 min−1 to 128.8 mmol gcat−1 min−1. However, under the corresponding temperature conditions in the dark thermal catalytic system, the hydrogen production rate remained below 0.1 mmol gcat−1 min−1. This clearly demonstrates that the reaction is primarily driven by photocatalysis rather than by the light-to-heat effect.

Wavelength dependence experiment of the hydrogen formation rate reveals that, although carbon nanotubes exhibit broad absorption characteristics across the entire UV-visible-near-infrared spectrum (Supplementary Fig. 15), ammonia decomposition over Ni-CeO2-x/CNTs occurs significantly only at wavelengths shorter than 600 nm (Fig. 2c). The hydrogen formation rate at different wavelengths closely aligns with the absorption spectrum of CeO2-x. This result unambiguously demonstrates that the photoexcited electron–hole pairs generated in CeO2-x under UV-visible light irradiation (≤600 nm) are the key driving force for ammonia decomposition in Ni-CeO2-x/CNTs.

The cooperative photothermal strategy enables efficient utilization of the full solar spectrum, leveraging visible light for photo-excitation and infrared light for thermal effects. To validate this concept under realistic conditions, we conducted an outdoor test using a low-cost Fresnel lens to concentrate natural sunlight to an average intensity of 1.08 W cm−2 (Fig. 2d). The system achieved a solar-to-hydrogen (STH) efficiency of 3.6%, strongly corroborating the practical potential of our approach for low-cost solar hydrogen production.

To further assess the catalyst’s performance under steady-state conditions, we investigated its stability in a continuous-flow reactor. As shown in Fig. 2e, Ni-CeO2-x/CNTs exhibited excellent stability during ammonia decomposition under 1.4 W cm−2 visible-IR irradiation with a 20% NH3/80% Ar flow (24 mL min−1). The hydrogen production rate over Ni-CeO2-x/CNTs remained approximately 25 mmol gcat−1 min−1 over the 55-h continuous-flow conditions. XRD and HRTEM analysis (Supplementary Figs. 16 and 17) confirm that, after long-term testing, the structure of Ni-CeO2-x/CNTs and the dispersion of Ni nanoparticles remained intact, with no obvious structural damage or sintering.

We further evaluated the activity of Ni-CeO2-x/CNTs at higher light intensity. As shown in Fig. 2f and Supplementary Tables 3 and 4, under full-spectrum light irradiation at 3.5 W cm−2 without external heating, the hydrogen production rate of Ni-CeO2-x/CNTs reached an impressive 403.8 mmol gcat−1 min−1 and 298.4 mmol gcat−1 min−1 under the batch and continuous-flow reaction conditions, respectively. Under 3.5 W cm−2 irradiation, a photothermal temperature of 306 °C and a maximum conversion of 92.9% were achieved, which corresponds to a thermodynamic equilibrium temperature of 231 °C. This performance, achieved in a continuous-flow setup, is 10 times higher than that of the state-of-the-art Ru-based photothermal catalyst30 and 9 times higher than that of the best-performing Ni-based thermal catalyst at 450 °C31.

The effect of CNTs in boosting photocatalytic performance
Although thermal energy alone cannot drive ammonia decomposition over Ni-CeO2-x/CNTs, it significantly accelerates the photocatalytic process. As shown in Fig. 3a, under monochromatic 400 nm light irradiation (1.4 W cm−2, cold LED), the catalyst surface temperature reached 74 °C, yielding a hydrogen production rate of 6.7 mmol gcat−1 min−1. With external heating to 155 °C, the rate sharply increased to 17.5 mmol gcat−1 min−1, achieving an apparent quantum efficiency (AQE) of 12.7%, the highest value reported to date for photocatalytic ammonia decomposition. Temperature-dependent photoluminescence (TD-PL) spectroscopy further revealed that elevated temperatures suppress charge recombination, with PL intensity decreasing by over 70% from −150 °C to 150 °C (Fig. 3b)32. This enhancement stems from improved charge mobility, supported by electrochemical impedance spectroscopy, which shows a clear reduction in charge transfer resistance with rising temperature (Supplementary Fig. 18)33.

The introduction of CNTs significantly contributes to the increase in the temperature of the photocatalyst and thus facilitates charge separation34–36. As shown in Supplementary Fig. 19, under 920 nm monochromatic light irradiation (1.4 W cm−2), the surface temperature of CNTs reached 114 °C, while pure CeO2 only reached 65 °C. This demonstrates the superior light-to-heat conversion capability of CNTs, particularly for the typically wasted near-infrared (NIR) light, which cannot drive photoexcited charge separation in CeO2-x.

Photocurrent measurements further show that the photocurrent density of Ni-CeO2-x/CNTs is significantly higher than that of Ni/CeO2 and Ni/CNTs (Supplementary Fig. 20) even at the same temperature. This enhancement can be attributed to the nanocomposite structure formed by CeO2-x and CNTs, where CeO2-x generates photoexcited electron–hole pairs, and the highly conductive CNTs serve as an “electron transport channel”, facilitating rapid interfacial electron migration and effectively suppressing carrier recombination (Supplementary Fig. 21)37. The accelerated interfacial charge transfer is further confirmed by time-resolved photoluminescence (TR-PL) spectroscopy. As shown in Fig. 3c and Supplementary Table 5, the introduction of CNTs reduces the average carrier lifetime (τave) from 36.66 ns in Ni/CeO2 to 11.65 ns in Ni-CeO2-x/CNTs, which is consistent with the enhanced carrier separation observed in carbon-based materials as reported in the literature38.

Therefore, CNTs contribute to a synergistic effect that significantly enhances the photoexcited carrier separation of Ni-CeO2-x/CNTs: their efficient photothermal conversion ability raises the catalyst temperature, reducing carrier transport resistance, while their high electrical conductivity accelerates interfacial electron transfer. As shown in Fig. 3d, light intensity-dependent photocurrent measurements reveal that the photocurrent density of Ni-CeO2-x/CNTs is not only significantly higher than that of Ni/CeO2, but the rate of increase in photocurrent with light intensity (slope) is also much greater, fully demonstrating the dual-promoting mechanism of CNTs.

Reaction mechanism
In situ XPS analysis elucidated the charge transfer pathway during the photocatalytic process. As shown in Fig. 4a, light irradiation induces a 0.14 eV negative shift in the Ni 2p3/2 binding energy of Ni-CeO2-x/CNTs, indicating that photogenerated electrons from CeO2-x migrate and accumulate on the Ni nanoparticles. Simultaneously, an increase in Ce4+ concentration suggests that photogenerated holes remain in CeO2-x. Photocurrent measurements reveal a sharp rise in photocurrent density from 42 μA cm−2 (under Ar) to 134 μA cm−2 upon NH3 introduction (Fig. 4b), confirming that the holes are predominantly consumed by NH3 via oxidative dehydrogenation (NH3 + h+ → NHx + H+). EPR spectroscopy (Supplementary Fig. 22) further indicates that oxygen vacancies in CeO2-x serve as hole-trapping centers (Ov + h+ → Ov+), playing a crucial role in NH3 activation.

DFT calculations further demonstrate that oxygen vacancies in CeO2-x significantly enhance the adsorption of NHx (x=3, 2, 1, 0) at the intimately contacted Ni-CeO2-x interface. As shown in Fig. 4c, the d-band center of interfacial Ni in the oxygen-deficient Ni8/CeO2_Ov model shifts upward to –1.03 eV, compared to –2.00 eV in the vacancy-free Ni8/CeO2 and –1.17 eV in the Ni(111) surface. Consequently, as illustrated in Supplementary Fig. 23, vacancy-induced Ce–Ov–Ni interface in Ni8/CeO2_Ov provides enhanced N adsorption sites with an adsorption energy of –1.26 eV, surpassing those of Ni8/CeO2 (–0.49 eV) and Ni(111) (–0.95 eV). This upward shift improves the electronic coupling between the Ni d-states and the LUMO of N*, thereby promoting the coupling of N–N on the catalyst surface39,40.

In traditional nickel-based catalysts, N–H bond cleavage occurs relatively easily, while the N–N coupling barrier is very high (rate-determining step), leading to the accumulation of N* species on the catalyst surface. This accumulation inhibits the catalytic cycle and becomes the main bottleneck limiting decomposition efficiency. The distribution of nitrogen species on the surface of Ni-CeO2 and Ni-CeO2-x/CNTs catalysts after reaction was analyzed using XPS N 1s spectra. As shown in Fig. 4d and Supplementary Fig. 24 and Supplementary Table 6, 48% of the surface nitrogen on Ni-CeO2 remained as atomic N* after reaction, indicating that N atoms tend to accumulate and poison the surface. In contrast, Ni-CeO2-x/CNTs showed a markedly reduced N* fraction of only 15%, suggesting that N–N coupling proceeded smoothly.

The change in the rate-determining step of ammonia decomposition over Ni-CeO2-x/CNTs is further confirmed through kinetic isotope effect (KIE, kH/kD) experiments. As shown in Fig. 4d, when ND3 replaced NH3 in the ammonia decomposition reaction, the KIE value measured on Ni/CeO2 was 1.0±0.1, confirming that the rate-determining step in traditional nickel-based catalysts is N–N coupling, not N–H bond activation. In contrast, the KIE value for Ni-CeO2-x/CNTs reached 1.8±0.2, suggesting that N–N coupling is no longer the rate-determining step and has shifted to N–H bond activation41,42. Ni-CeO2-x/CNTs exhibits kinetic characteristics markedly different from those of conventional Ni-based catalysts. As shown in Supplementary Fig. 25, the corresponding reaction orders were determined to be 0.72 for Ni-CeO2-x/CNTs, 0.54 for Ni/CNTs, and 0.44 for Ni/CeO2. The higher reaction order observed for Ni-CeO2-x/CNTs, indicates a stronger dependence of the rate on NH3 concentration. This result aligns well with the pronounced KIE values previously observed, together providing robust evidence that N–H bond dissociation constitutes the critical kinetic step in ammonia decomposition. Therefore, the highly efficient photo-driven N–H bond cleavage and rapid N–N coupling enable unprecedented ammonia decomposition efficiency, effectively overcoming the intrinsic limitations of traditional nickel-based catalysts.

Reaction pathway calculations provide a comprehensive overview of the ammonia decomposition process (Fig. 4e and Supplementary Fig. 26). The ammonia decomposition reaction (2NH3 → N2 + 3H2) on the catalyst surface proceeds through several steps: NH3 adsorption, N–H bond cleavage (NH3* → NH2* → NH* → N*), and N–N coupling (2N* → N2* → N2(g)). As shown in Supplementary Fig. 27, during the NH3 adsorption step, ammonia preferentially adsorbs on the Ni cluster surface in the Ni8/CeO2 model. However, in the Ni8/CeO2_Ov model, the Ce–Ov–Ni interface exhibits stronger NH3 adsorption, making it the active site for ammonia decomposition. NH3 adsorbed at the Ce–Ov–Ni interface undergoes a deprotonation process to form NHx (x=2, 1, 0) intermediates. Notably, for the Ni8/CeO2_Ov interface, the *NH→*N+*H step shows a relatively high barrier (0.74 eV), though still lower than the highest deprotonation barriers on Ni(111) (1.09 eV) and Ni8/CeO2 (0.79 eV). Simultaneously, N* remains at the Ce–Ov–Ni site and recombines with another N* to form N2. For conventional nickel-based catalysts, the relatively weak Ni–N bonds lead to high N–N coupling energy barriers (1.34 eV and 0.98 eV for Ni(111) and Ni8/CeO2, respectively). However, the enhanced Ni–N bond strength at the Ce–Ov–Ni interface significantly lowers the N–N coupling energy barrier to 0.53 eV in Ni8/CeO2_Ov. Finally, the electron-rich Ni can efficiently donate electrons to the N2 π* orbitals, facilitating nitrogen desorption.

Methods
Preparation of CeO2-x/CNTs support
The CeO2-x/CNTs support was synthesized using the precipitation method. In a typical procedure, 190 mg of Ce(NO3)3·6H2O and 150 mg of multi-walled carbon nanotubes (MWCNTs, with an outer diameter of 10–20 nm and length of 10-30 μm, surface area >120 m2 g−1, provided by Shenzhen Co., Ltd.) were dispersed in 100 mL deionized water. The resulting mixture was stirred for 12 h, followed by the addition of ammonia solution until pH = 9.0, with vigorous stirring for 30 min. The precipitate was washed three times each with deionized water and ethanol, then dried overnight in a vacuum oven at room temperature. Subsequently, the obtained powder was calcined at 873 K for two hours in a tubular furnace under a nitrogen atmosphere (heating rate: 5 K min−1; nitrogen flow rate: 60 mL min−1). The synthesized sample with a mass ratio of CeO2 to MWCNTs of 0.5 will be referred to simply as CeO2-x/CNTs throughout the manuscript. In this study, we prepared a series of samples with varying mass ratios of CeO2 to MWCNTs, including 10 wt% CeO2-x/CNTs, 30 wt% CeO2-x/CNTs, 100 wt% CeO2-x/CNTs, 200 wt% CeO2-x/CNTs, 1000 wt% CeO2-x/CNTs, and 2000 wt% CeO2-x/CNTs, along with the CeO2-x/CNTs sample described above. CeO2-x was also synthesized following the same procedure but without incorporating CNTs.

Preparation of Ni-supported catalysts
The nickel-loaded catalysts were prepared using the chemical reduction method. In a typical procedure, 100 mg of CeO2-x/CNTs, commercial CeO2 and CNTs support were individually dispersed in a solution containing 50 mg Ni(NO3)2·6H2O dissolved in 100 mL deionized water. The mixture was stirred overnight in the dark to ensure complete dispersion and adsorption. Thereafter, 50 mg NaBH4 was rapidly added to the solution under vigorous stirring for 30 min. The resulting suspension was filtered, and the collected precipitate was washed three times each with deionized water and ethanol. Finally, the product was dried in a vacuum oven at room temperature. The synthesized samples were named Ni-CeO2-x/CNTs, Ni/CeO2 and Ni/CNTs.

Characterization
Elemental composition was determined through inductively coupled plasma optical emission spectroscopy (ICP-OES) measurements executed on a Thermo Scientific iCAP 7600 system. Powder X-ray diffraction (XRD) analysis was conducted on a Rigaku D/Max 2550 diffractometer employing monochromated Cu Kα radiation (λ=1.5406 Å), with data acquisition parameters set to 10° min−1 scan rate across a 2θ angular range of 20–60°. Microstructural characterization was performed using a Thermo Scientific Talos F200S G2 transmission electron microscope operating at 200 kV, which provided both Transmission electron microscopy (TEM) and high-angle annular dark-field scanning TEM (HAADF-STEM). Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis were obtained using a Helios NanoLab 600l from FEI Company. Surface area quantification was implemented through nitrogen adsorption isotherms at 77 K (Micromeritics ASAP 2020M), with specific surface areas calculated via the Brunauer-Emmett-Teller (BET) method and pore size distributions derived from Barrett-Joyner-Halenda (BJH) analysis. In situ X-ray photoelectron spectroscopy (XPS) was analyzed by Thermo Scientific ESCALAB 250Xi with Al Kα excitation (1486.6 eV), where binding energy calibration referenced the adventitious carbon 1s peak at 284.8 eV using Avantage processing software. Raman spectra were carried out using the Raman Microscope DXR3 with incident radiation at 532 nm (diode lasers of energies 2.33 eV). Ultraviolet photoelectron spectroscopy (UPS) was carried out by a Prevac spectrometer with a VG Scienta R3000 hemispherical electron energy analyzer. UV-vis diffuse reflectance spectroscopy (UV-vis DRS) was tested in the range of 200–2000 nm using PerkinElmer Lambda 950. Electrochemical characterization involved photocurrent measurements using a CHI 660E workstation in a three-electrode configuration (FTO working electrode, Pt counter electrode, Ag/AgCl reference). Photoluminescence (PL), Temperature-dependent PL (TD-PL), and Time-resolution PL (TR-PL) spectroscopies were conducted on an Edinburgh Instruments FLS1000 spectrometer. In situ electron paramagnetic resonance (EPR) spectroscopy (JEOL JES-FA 200) operated at 9.43 GHz with 337 mT center field and 0.998 mW microwave power.

Performance evaluation
Under batch reaction conditions, photocatalysis was conducted in the customized quartz reactor chamber designed to enable uniform illumination and precise temperature control (Supplementary Fig. 11). 5 mg of catalyst was uniformly dispersed as a thin film onto the quartz reactor base. Then the reactor chamber underwent vacuum degassing (<0.1 mbar) at 473 K for 2 h to rigorously eliminate surface-adsorbed contaminants. After cooling to ambient temperature (298 K), 0.5 mmol of ammonia gas (NH3, 99.99% purity) was introduced into the reactor. The catalyst was irradiated using a 300 W xenon lamp (CEL-HXF300) equipped with a 400 nm cut-off filter. The intensity of the incident light at the catalyst surface was detected using an optical power meter (CEL-NP2000-10). Reaction temperature was regulated using a closed-loop refrigerated/heated circulating bath connected to the reactor jacket. Catalyst surface temperature was monitored by an infrared camera and validated by an embedded thermocouple positioned near the catalyst layer. The products were sampled at defined intervals and quantified using a gas chromatograph (GC-2014, Shimadzu) equipped with a Thermal Conductivity Detector (TCD).

Photocatalytic performance under natural sunlight was evaluated using a setup similar to that employed in batch experiments. Sunlight was concentrated using a Fresnel lens (30 cm in diameter) to an 8 cm diameter spot on the reactor, yielding an average light intensity of 1.08 W cm−2. 0.5 mmol of NH3 (99.99% purity) was introduced, and the system was irradiated under concentrated sunlight for 1 min.

Under continuous-flow conditions, 5 mg of catalyst was well mixed with 100 mg of quartz sand and evenly spread on a sintered quartz plate in a custom-designed quartz reactor. The reaction was performed under irradiation from a 300 W Xe lamp (CEL-HXF300) with a 400 nm cut-off filter, using a gas feed of NH3 at a flow rate of 24 mL min−1. The gas products were continuously analyzed by gas chromatography (FL9790).

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Tan et al. reported a Ni–CeO2-x/CNTs photothermal catalyst that delivers exceptionally high H2 production rates under light\nwithout external heating and claims >91% NH3 conversion at 155 °C with strong cycling stability. The mechanistic picture\nattributes the performance to (i) efficient light harvesting/photothermal conversion by CNTs, (ii) photo-assisted N–H\nactivation on CeO2-x, and (iii) a Ce–OV–Ni interfacial site that upshifts the Ni d-band center and lowers the N–N coupling\nbarrier (DFT), supported by UPS/XPS/EPR, photocurrent, and (TR)PL. The topic is timely for low-temperature NH3 cracking\nand will be of interest to readers in the fields of catalysis, photothermal chemistry, and hydrogen carriers. My comments are\nprimarily related to the DFT calculations since my research background is associated with computational catalysis. Attached\nbelow are the major comments to be addressed before this manuscript can be recommended for publication.\n1. The title of this manuscript includes “barrierless interfaces,” yet the DFT results indicate a reduced but finite N–N coupling\nbarrier (i.e., 0.65 eV) at Ni8/CeO2_Ov sites (vs ≥1.10 eV on Ni). The authors should avoid overstatement in the\ntitle/abstract/results: e.g., “near-barrierless with respect to conventional Ni” or “drastically reduced barrier.”\n2. The authors should also include the benchmarking test on some key results, considering a relatively low cut-off energy\nwas selected for all the calculations: “cut-off energy of the plane wave basis was set to 400 eV”. Benchmarking testing on\nconvergence is necessary.\n3. How were the holes modelled in these reactions, considering VASP cannot sufficiently model the localized\npositive/negative charges in the systems; however, the authors stated that the computed energetics are for the reactions\nsuch as “NH3 + h+ → NH2 + H+”?\n4. The authors should compute the transition state energies for the multiple NHx deprotonation reaction steps. From Fig. 4e,\nthe deprotonation of *NHx to *N is the step with the largest energy change, which might indicate the most significant kinetic\nbarriers. Therefore, it is not sufficient to conclude based solely on the TS energies of *N-*N coupling to *N2.", "reviewer_2": "This manuscript reports a Ni-CeO2-x/CNTs composite photothermal catalyst for ammonia decomposition, achieving a\nrecord-breaking hydrogen production rate of 403.8 mmol gcat-1 min-1 under full-spectrum light irradiation—2.1 times higher\nthan that of the state-of-the-art Ru-based photo-thermal catalyst. The catalytic performance is impressive, particularly in\novercoming the high-temperature limitations typically associated with conventional Ni-based catalysts. Supported by both\nexperimental data and DFT calculations, the authors convincingly elucidate the synergistic photothermal mechanism in\npromoting both N–H bond activation and N–N coupling.\nThe manuscript is clearly written, well-organized, and the results are presented with high scientific rigor. I recommend this\nmanuscript for publication in Nature Communications after the authors address the following comments:\n1. The authors have demonstrated the effectiveness of the alkaline precipitation method for constructing highly dispersed,\ndefect-rich CeO2-x nanodomains on CNTs. The question is whether this synthetic strategy possesses general applicability\nto other commonly supports, such as activated carbon (AC) or MgO. Could the author comment on the application potential\nfor forming small and oxygen-vacancy-rich CeO2-x domains on the support?\n2. The excellent catalytic performance under simulated sunlight (Xe lamp) is promising. For broader relevance and potential\nreal-world applicability, the authors are encouraged to conduct validation experiments under natural sunlight, including the\nrecording of key parameters such as light intensity, temperature, and solar-to-hydrogen (STH) efficiency. These data would\nstrengthen the practical impact of the study.\n3. The manuscript emphasizes the critical role of CNTs in enhancing electron transport and facilitating photogenerated\ncharge separation. To further support this, additional electronic band structure analysis—particularly focusing on the nature\nof the CeO2-x/CNT interface (e.g., Schottky junction or S-scheme heterojunction)—would help elucidate the interfacial\ncharge transfer mechanism.\n4. Complementary investigation into the reaction order with respect to NH3 partial pressure would establish a more robust\nkinetic foundation, thereby reinforcing the KIE interpretation.\n5. The significant reduction in the N–N coupling barrier (from 1.34 eV to 0.65 eV) as revealed by DFT is an important\nmechanistic insight. It would be beneficial to complement this with experimental determination of the apparent activation\nenergy (Ea) for ammonia decomposition over both Ni/CeO and Ni–CeO2-x/CNTs. This would provide a more complete\npicture of the intrinsic activity enhancement brought about by the interfacial engineering.", "reviewer_3": "In this work, Tan and collaborators report a novel photothermal ammonia decomposition catalyst based on Ni–CeO₂₋ₓ\nsupported on carbon nanotubes. By integrating defect-rich CeO₂₋ₓ nanodomains and electron-rich Ni nanoparticles on\ncarbon nanotubes, the system achieves highly efficient light-assisted hydrogen production, reaching a remarkable hydrogen\ngeneration rate of 403.8 mmol gcat⁻¹·min⁻¹. The enhanced activity arises from synergistic N–H bond activation by\nphotocatalysis and barrierless N–N coupling enabled by Ce–OV–Ni interfaces. The work could be of interest in the field of\nphoto-thermal catalysis, particularly for NH3 cracking. However, from my point of view, authors did not provide a fair and\naccurate comparison of their results from the current state-of-the-art, thus overestimating the real impact of their own work.\nFurthermore, the experimental methodology should be improved, in particular those related with the stability.\nFor all these reasons, I cannot recommend the publication of this work in Nature Communications. Detailed comments to\nsupport this decision can be found below:\na) Authors wrote: “Herein we develop the most efficient photo-thermal catalyst to date”. I think this statement should be\nsomehow rephrased as this manuscript lacks relevant references in the field to ensure a meaningful comparison. Authors\nshould make a distinction between batch and continuous-flow reactors, otherwise the comparison is not appropriate.\nb) In line with my previous comment, it is quite surprising that authors did not refer to any of the works of prof. Gascon and\ncolleagues, who were one of the pioneer groups in developing photo-thermal systems for the decomposition of NH3 under\ncontinuous flow configuration (check doi.org/10.1002/cssc.202500068, doi.org/10.1002/cssc.202401896,\ndoi.org/10.1002/smll.202411468)\nc) Authors should clarify if they use visible or visible-IR radiation. As per λ≥400 nm is not clear.\nd) Authors perform a series of 100 reaction cycles to assess the stability of the system. At first this number of cycles could\nseem significant, but taking into account that the reaction time is one minute, this stability test represents a total reaction time\nbelow 2 hours. A longer stability test (at least 50 hours) is needed in order to properly evaluate the integrity of this system\nwith others already available in the literature, especially taking into account that the performance shows a subtle but steady\ndeactivation upon reuses. Authors should also include the complete characterization of the long-term spent sample.\ne) In line with my previous comment, why using a total reaction time of 1 minute? This is an extremely short time which\nmakes very difficult to assess stability or the kinetics of the system. Authors have to increase the initial amount of NH3, as\nnow is limited to only 12 mL. This will also demonstrate the applicability of the system.\nf) Most of the works on photo-thermal ammonia decomposition have been performed under continuous-flow configuration,\nwhich is closer to real application. Authors should perform their activity tests under these conditions to contextualize their\nresults.\ng) In line 173, authors claim that the conversion surpasses the thermodynamic equilibrium. As we cannot trick\nthermodynamics, this means that the actual temperature of the active sites is higher than that registered by the thermocouple\n(155 degrees Celsius). Authors claim that the temperature was also monitored by IR but there aren’t any IR thermal images\nneither in the main manuscript nor in the SI. I suggest authors to back-calculate the actual temperature of the active sites in\ntheir system, for instance using their actual conversion at the equilibrium. See the work from prof. Zhang\n(doi.org/10.1002/anie.202304452)"}, "author_response": "Responses (R) to Referees’ Comments (C)\nWe thank all the Reviewers for their comments on the manuscript.\nReferee 1\n1. The title of this manuscript includes “barrierless interfaces,” yet the DFT results indicate a reduced but finite N–N coupling\nbarrier (i.e., 0.65 eV) at Ni /CeO _Ov sites (vs ≥1.10 eV on Ni). The authors should avoid overstatement in the\n8 2\ntitle/abstract/results: e.g., “near-barrierless with respect to conventional Ni” or “drastically reduced barrier.”\nR: We sincerely thank the reviewer for this valuable comment. We agree that the use of “barrierless” is an overstatement, as\nthe DFT results show that the N–N coupling barrier, while drastically reduced, still remains non-negligible. We have revised\nthe title to: “Breakthrough Photothermal Ammonia Decomposition via Low-Barrier Ni-CeO Interfaces on Carbon\n2-x\nNanotubes.” Throughout the manuscript, “barrierless” has been replaced with more accurate terms such as “significantly\nreduced barrier” or “rapid reaction kinetics.”\n2. The authors should also include the benchmarking test on some key results, considering a relatively low cut-off energy was\nselected for all the calculations: “cut-off energy of the plane wave basis was set to 400 eV”. Benchmarking testing on\nconvergence is necessary.\nR: We sincerely thank the reviewer for this important methodological comment regarding the plane-wave cutoff energy. In\nour initial calculations, we selected a cutoff energy of 400 eV, balancing efficiency and accuracy, following several prior\nstudies on CeO -based systems for ammonia decomposition (10.1002/aenm.202202459; 10.1002/anie.202501898;\n2\n10.1016/j.cej.2023.145371). However, we fully acknowledge that not performing convergence tests for the specific systems\nin this study was inadequate, and we apologize for this oversight.\nAccordingly, we have now conducted a systematic convergence test. For both the Ni /CeO and Ni /CeO _Ov models,\n8 2 8 2\nthe results (Table R1–2) indicate that a cutoff energy of 550 eV is required to converge the total energy within 1 meV per\natom. This value is consistent with the recommended 1.3× ENMAX (400 eV) guideline. Therefore, we have recalculated all\nresults related to Ni /CeO and Ni /CeO _Ov using a cutoff energy of 550 eV, and updated Fig. 1G, Fig. 4C and E, as well as\n8 2 8 2\nSupplementary Figs. 9, 10, 23, 26, and 27 in the revised manuscript.\nTable R1. Convergence test of Ni /CeO _O model\n8 2 V\nCut-off energy Energy ∆Energy\n(eV) (eV) (meV/atom)\n300 -1298.71258\n350 -1291.36366 -48.67\n400 -1287.97054 -22.47\n450 -1286.39880 -10.41\n500 -1285.82940 -3.77\n550 -1285.69113 -0.92\nTable R2. Convergence test of Ni /CeO model\n8 2\nCut-off energy Energy ∆Energy\n(eV) (eV) (meV/atom)\n300 -1304.49842\n350 -1299.56142 -32.48\n400 -1296.74989 -18.50\n450 -1295.32655 -9.36\n500 -1294.78561 -3.56\n550 -1294.66622 -0.79\nFor the Ni(111) surface model, the pseudopotential ENMAX value is 269.532 eV. Combined with the convergence test\nresults (Table R3), this indicates that a cutoff energy of 400 eV is sufficient to achieve energy convergence well below 1 meV\nper atom. Therefore, we have retained the original parameters for this model, and the corresponding results remain unchanged.\nTable R3. Convergence test of Ni(111) model\nCut-off energy Energy ∆Energy\n(eV) (eV) (meV/atom)\n350 -249.89151\n400 -249.84658 -0.94\n450 -249.83974 -0.14\nIt is worth emphasizing that all key conclusions and energy trends remain fully consistent after recalculation. The\nobserved reduction in the N–N coupling barrier and the enhancement of interfacial catalytic activity are unchanged. We have\nupdated the cutoff energy settings in the Computational Methods section of the manuscript and sincerely apologize once again\nfor the earlier oversight in parameter selection. We are deeply grateful to the reviewer, whose comments have significantly\nimproved the rigor and accuracy of our computational analysis.\n3. How were the holes modelled in these reactions, considering VASP cannot sufficiently model the localized\npositive/negative charges in the systems; however, the authors stated that the computed energetics are for the reactions such\nas “NH + h+ → NH + H+”?\n3 2\nR: We sincerely thank the reviewer for pointing out this issue in the computational description. The original manuscript\nincorporated reactions such as \"NH + h+ → NH + H+\" with the intention of illustrating the respective roles of photogenerated\n3 2\nholes and electrons in the photocatalytic ammonia decomposition reaction. However, we fully acknowledge that placing such\ndescriptions in the computational methodology section may lead to misunderstanding, as VASP does not explicitly model\nlocalized positive/negative charges.\nTo avoid ambiguity, we have removed the descriptions related to photogenerated charge-involved steps (e.g., NH + h+ →\n2\nimportant clarification, which has significantly improved the accuracy of our computational narrative.\n4. The authors should compute the transition state energies for the multiple NHx deprotonation reaction steps. From Fig. 4e,\nthe deprotonation of *NHx to *N is the step with the largest energy change, which might indicate the most significant kinetic\nbarriers. Therefore, it is not sufficient to conclude based solely on the TS energies of *N-*N coupling to *N2.\nR: We thank the reviewer for this valuable suggestion. In our initial work, we followed prior studies\n(10.1002/aenm.202202459; 10.1016/j.cej.2023.145371), where N–N coupling on Ni-based catalysts is generally regarded as\nthe rate-determining step, and transition-state calculations for N–H activation are often omitted. To reduce computational cost,\nwe therefore did not calculate all deprotonation transition states. However, we fully agree with the reviewer’s point that in\nFig. 4e, the deprotonation process from *NH to *N exhibits a considerable energy change, and its kinetic contribution cannot\nx\nbe neglected.\nFollowing your suggestion, we systematically recalculated the transition states for all deprotonation steps from NH to\n3 2 2 8 2 8 2\nR1). Notably, for the Ni /CeO _Ov interface, the *NH → *N + *H step shows a relatively high barrier (0.74 eV), though still\n8 2\nlower than the highest deprotonation barriers on Ni(111) (1.09 eV) and Ni /CeO (0.79 eV). Moreover, as shown in the revised\n8 2\nFig. 4E, the deprotonation barriers on Ni(111) and Ni /CeO surfaces remain lower than their respective N–N coupling barriers,\n8 2\nwhile at the Ni /CeO _Ov interface the deprotonation barrier, although significantly reduced, still exceeds the corresponding\n8 2\nN–N coupling barrier.\nThis new finding further confirms that for highly active Ni-based catalysts, the rate-determining step shifts from N–N\ncoupling to N–H bond cleavage, in agreement with our in situ XPS and KIE experimental results. We have revised the relevant\ndiscussion in the manuscript to incorporate these computational results, ensuring greater comprehensiveness and accuracy.\nWe are once again grateful to the reviewer for helping us strengthen the scientific rigor of this study.\nN-H cleavage N-N coupling\nE =1.09 eV\n1 a\nE =0.43 eV E =0.52 eV\nE =0.71 eV a a E =1.34 eV\na E =0.79 eV E =0.74 eV a\nE =0.33 eV a a E =0.98 eV\na E =0.55 eV a\nE =0.26 eV a E =0.53 eV\n)0 a a\nV\ne\n(\ny\ng\ne r-1\nn\nE Ce\nO\n-2\nNi Ni (111)\nN Ni /CeO\n8 2\nH Ni /CeO _O\n-3 8 2 v\nNH 3 (g) NH 3 * TS1 NH 2 *+H* NH 2 * TS2 NH*+H* NH* TS3 N*+H* N*+N* TS4 N 2 *\nFigure R1. Energy profiles for NH3 decomposed on Ni(111), Ni /CeO and Ni /CeO _O surfaces (Revised Fig. 4E).\n8 2 8 2 V\nReferee 2\n1. The authors have demonstrated the effectiveness of the alkaline precipitation method for constructing highly dispersed,\ndefect-rich CeO nanodomains on CNTs. The question is whether this synthetic strategy possesses general applicability to\n2-x\nother commonly supports, such as activated carbon (AC) or MgO. Could the author comment on the application potential\nfor forming small and oxygen-vacancy-rich CeO domains on the support?\n2-x\nR: We sincerely thank the reviewer for this important question. Following your suggestion, we applied the same alkaline\nprecipitation method on activated carbon (AC) and MgO supports. TEM images (Figure R2) show severe particle\nagglomeration on both AC and MgO, unlike the highly dispersed, nanoscale CeO domains obtained on CNTs. This indicates\n2-x\nthat the method strongly depends on the surface chemistry of the support. CNTs, with their sp2-hybridized surface, large\nsurface area, and tunable functional groups, provide effective nucleation sites and suppress overgrowth, enabling the\nformation of small, oxygen-vacancy-rich CeO domains. In contrast, the disordered porous surface of AC and the highly\n2-x\npolar surface of MgO hinder uniform anchoring and dispersion, leading to aggregation.\nFigure R2. TEM images of CeO /AC (a) and CeO /MgO (b)\n2 2\nWe fully agree with the reviewer that constructing highly dispersed, defect-rich CeO domains on diverse supports is\n2-x\nof great importance. In fact, incorporating rare-earth oxide nanostructures onto conventional supports has been shown to\neffectively suppress metal sintering, tune electronic structures, and enhance catalytic stability and activity (e.g., Zhou et al.,\nNat. Mater. 2025; Gao et al., Nature 2024; Li et al., Chem Catal. 2024). Our results suggest that while the alkaline precipitation\nmethod works most effectively on CNTs, broadening its applicability through tailored support–oxide interface engineering\nremains a promising pathway for designing high-performance catalysts.\n2. The excellent catalytic performance under simulated sunlight (Xe lamp) is promising. For broader relevance and potential\nreal-world applicability, the authors are encouraged to conduct validation experiments under natural sunlight, including the\nrecording of key parameters such as light intensity, temperature, and solar-to-hydrogen (STH) efficiency. These data would\nstrengthen the practical impact of the study.\nR：We sincerely thank the reviewer for this insightful suggestion. Conducting validation experiments under natural sunlight\nis indeed essential to assess the real-world application potential of the catalyst. To this end, we performed outdoor tests in\nChangchun under clear-sky conditions to explore the catalyst’s practical performance. In the experiment, a Fresnel lens (30\ncm in diameter) was used to concentrate sunlight into an 8 cm diameter spot, yielding an average light intensity of 1.08 W/cm2.\nThe reactor was a custom-designed flat circular chamber, with its base uniformly coated with a thin catalyst film (Figure R3).\nAfter vacuum drying, 0.5 mmol of high-purity NH was introduced into the system, which was then irradiated by natural\n3\nsunlight for 1 min. The hydrogen produced was quantified using the same online gas chromatography method described in\nthe main text, yielding a total H production of 494.76 μmol.\n(Revised Fig. 2D).\nWe further evaluated its solar-to-hydrogen (STH) conversion performance according to the standard formula:\nChemical energy output\nSTH \nSolar energy input\nHydrogen production rateG\n 2 2 2 2\nLight intensityIrradiated area\nr (mol s-1)G\nH 1\n 2 2 2 2\nP(W cm-2)S(cm2)\nwhere r is the hydrogen evolution rate, ΔG is the Gibbs free energy change for the reaction H O → H + 1/2O (237 kJ\nH2 2 2 2\nmol−1), P is the incident light intensity, and S is the irradiated area.The specific calculation process is as follows:\n494.76106\nmol s-1237000 J mol1\n1.08 W cm-250 cm2\nUnder natural sunlight, the Ni-CeO /CNTs catalyst achieved a solar-to-hydrogen (STH) efficiency of 3.6%, which\n2-x\nsurpasses that of most previously reported photocatalytic systems (10.1021/acsenergylett.1c02591). This result demonstrates\nthe catalyst’s exceptional capability for efficient hydrogen generation under real sunlight conditions. These findings clearly\nindicate that the catalyst can drive ammonia decomposition without any external energy input, thereby highlighting its strong\npotential for practical solar-driven applications.\nThis result and related methods has been incorporated into the revised manuscript and the corresponding figure (Revised\nFig. 2D) has been added.\n3. The manuscript emphasizes the critical role of CNTs in enhancing electron transport and facilitating photogenerated charge\nseparation. To further support this, additional electronic band structure analysis—particularly focusing on the nature of the\nCeO /CNT interface (e.g., Schottky junction or S-scheme heterojunction)—would help elucidate the interfacial charge\n2-x\ntransfer mechanism.\nR： We sincerely thank the reviewer for this insightful and critical suggestion. A detailed analysis of the electronic band\nstructure, particularly at the CeO /CNT interface, is indeed crucial for elucidating the interfacial charge transfer mechanism.\n2-x\nWe fully agree that incorporating this analysis substantially strengthens the central argument of our manuscript regarding the\nrole of CNTs in facilitating electron transport and charge separation. We employed a combination of ultraviolet photoelectron\nspectroscopy (UPS, to determine the work function) measurements to investigate the band structure, XPS valence band (XPS-\nVB, to determine the position of the Fermi energy level), and UV-vis DRS (to determine the band gap) of CeO /CNTs, CeO\n2-x 2-,\n, and CNTs. The detailed results are presented in the figure below (Figure R4-5).\nx\na UPS b XPS-VB c\nCeO /CNTs F  4.71 eV\n2-x\nCNTs\nCeO /CNTs\nI\nnt e n\nsit y ( a.\nu.)\nC\nC\n1.\nN\ne\n2\ns\ne\n3\n-\nV\nx\n. 4 7 e V\nF\nF\n\n\n4 .\n4\n9\n. 1\n6 7\ne V\neV\n17.70\n2 0\ne\n.\nV\n02 eV\nI\nnt e n\nsit y ( a.\nu.)\n2.21 eV\nCeO 2-x /\nC\nC\nN\nN\nT\nT\ns\ns\nA b\ns or\npti o n ( a.\nu.)\n2.53 eV\nCeO 2\n2\n-\n-\nx\nx\n1.95 eV\nCeO\n1.29 eV 17.60 eV 2-x\n0 6 12 18 0 2 4 6 8 10 400 800 1200 1600 2000\nBinding Energy (eV) Binding Energy (eV) Wavenumber (cm-1)\nFigure R4. (a) Ultraviolet photoelectron spectroscopy (UPS). (b) XPS valence band (XPS-VB) spectra. (c) UV-vis diffuse\nreflectance spectra (UV-vis DRS).\nFigure R5. The band structure of CeO , CNTs and CeO /CNTs.\n2-x 2-x\nAs shown in Figure R5, the work function of CNTs (4.91 eV) is higher than that of CeO (4.67 eV). Upon forming a\n2-x\nclose interface, electrons spontaneously transfer from CNTs to CeO until their Fermi levels equilibrate, with the composite\n2-x\nexhibiting a work function of 4.71 eV. This redistribution of charge bends the bands of CeO upward at the interface,\n2-x\ngenerating an internal electric field directed from CNTs to CeO . Such a built-in field effectively drives photogenerated\n2-x\nelectrons from CeO toward CNTs while pushing holes in the opposite direction. The Schottky barrier formed between the\n2-x\nmetallic CNTs and semiconducting CeO , together with the resulting space-charge separation gradient, enables efficient\n2-x\ncarrier separation and markedly suppresses recombination.\nIn summary, our analysis confirms the formation of a Schottky junction at the CeO /CNT interface. This mechanism\n2-x\nclearly explains the role of CNTs as efficient electron acceptors: the built-in field of the Schottky junction greatly promotes\nelectron separation and extraction. This conclusion is strongly supported by our experimental observations, including\nshortened carrier lifetimes (TR-PL) and significantly enhanced photocurrent responses, thereby providing compelling\nevidence for the pivotal role of CNTs in enhancing photocatalytic performance.\n4. Complementary investigation into the reaction order with respect to NH partial pressure would establish a more robust\n3\nkinetic foundation, thereby reinforcing the KIE interpretation.\nR: We sincerely thank the reviewer for this valuable suggestion. Investigating the reaction order with respect to NH partial\n3\npressure indeed provides a more rigorous kinetic basis for interpreting the kinetic isotope effect (KIE). Following this\nrecommendation, we systematically measured the initial reaction rates of Ni-CeO /CNTs, Ni/CNTs, and Ni/CeO catalysts\n2-x 2\nunder varying NH partial pressures.\n3 3\nAs shown in Figure R6, the corresponding reaction orders were determined to be 0.72 for Ni-CeO /CNTs, 0.54 for\n2-x\nNi/CNTs, and 0.44 for Ni/CeO . The higher reaction order observed for Ni-CeO /CNTs, approaching unity, indicates a\n2 2-x\nstronger dependence of the rate on NH concentration. This finding suggests that N–H bond cleavage is more likely to be\n3\ninvolved in the rate-determining step for this catalyst. Importantly, this conclusion aligns well with the pronounced KIE values\npreviously observed, together providing robust evidence that N–H bond dissociation constitutes the critical kinetic step in\nammonia decomposition. This analysis has been incorporated into the revised manuscript, and the corresponding figure has\nbeen added (RevisedSupplementary Fig. 25), thereby strengthening the kinetic foundation of our study.\n5. The significant reduction in the N–N coupling barrier (from 1.34 eV to 0.65 eV) as revealed by DFT is an important\nmechanistic insight. It would be beneficial to complement this with experimental determination of the apparent activation\nenergy (Ea) for ammonia decomposition over both Ni/CeO and Ni–CeO /CNTs. This would provide a more complete picture\n2 2-x\nof the intrinsic activity enhancement brought about by the interfacial engineering.\nR: We sincerely thank the reviewer for this valuable suggestion. Measuring and comparing the apparent activation energies\n(Ea) of Ni/CeO and Ni-CeO /CNTs catalysts provides direct experimental evidence for the reduced energy barrier in\n2 2-x\nammonia decomposition. To address this, we conducted complementary kinetic experiments. Under different light intensities,\nwe measured the corresponding photothermal temperatures and ammonia decomposition rates of the catalysts. By fitting the\ndata with the Arrhenius equation, we successfully determined the apparent activation energies (Figure R7).\nThe results show that the apparent activation energy of Ni/CeO is 70.3 kJ mol-1, whereas that of Ni-CeO /CNTs is\n2 2-x\nmarkedly reduced to 47.7 kJ mol-1. From an experimental kinetics perspective, this strongly confirms that the interfacial\nstructure formed by oxygen-vacancy-rich CeO and CNTs effectively optimizes the reaction pathway and significantly\n2-x\nlowers the overall energy barrier of ammonia decomposition.\nFigure R7. Arrhenius plots of Ni/CeO and Ni-CeO /CNTs catalyst\n2 2-x\nReferee 3\na) Authors wrote: “Herein we develop the most efficient photo-thermal catalyst to date”. I think this statement should be\nsomehow rephrased as this manuscript lacks relevant references in the field to ensure a meaningful comparison. Authors\nshould make a distinction between batch and continuous-flow reactors, otherwise the comparison is not appropriate.\nb) In line with my previous comment, it is quite surprising that authors did not refer to any of the works of prof. Gascon\nand colleagues, who were one of the pioneer groups in developing photo-thermal systems for the decomposition of NH under\n3\ncontinuous flow configuration (check doi.org/10.1002/cssc.202500068, doi.org/10.1002/cssc.202401896,\ndoi.org/10.1002/smll.202411468)\nR: We sincerely thank the reviewer for this critical suggestion, which has greatly improved the rigor of our work. We fully\nagree that our original statement of having developed “the most efficient photo-thermal catalyst to date” was overstated,\nparticularly given the lack of sufficient comparison with different reactor systems, especially continuous-flow configurations.\nWe also sincerely apologize for not citing the pioneering contributions of Prof. Gascon’s group in the field of continuous-\nflow photothermal ammonia decomposition. Their work has been instrumental in advancing the understanding of\nphotothermal catalysis under flow conditions. We have now cited these studies in the revised introduction (Ref. 18–20).\nTo address the reviewer’s comment and enable a more rigorous comparison, we performed additional validation\nexperiments under continuous-flow conditions (Figure R8). Specifically, 5 mg of catalyst was mixed with 100 mg of quartz\nsand and evenly spread on a sintered quartz plate in a custom-designed quartz reactor. Under irradiation with a 300 W Xe\nlamp (CEL-HXF300, 3.5 W cm-2), high-purity NH (99.99%) was fed at 24 mL min-1 (WHSV = 288,000 mL g-1 h-1). The gas\n3\nproducts were continuously analyzed by gas chromatography (FL9790). Under these conditions, the Ni-CeO /CNTs catalyst\n2-x\nachieved 92.9% NH conversion with a hydrogen production rate of 298.4 mmol g-1 min-1.\n3\n(c) Image of the\ncustomized quartz reactor.\nWe have added these results to the revised Supplementary Table 4, together with data from Prof. Gascon’s studies, and\nclearly indicated the reactor types for each system to ensure a fair comparison. Remarkably, even under flow conditions, Ni–\nCeO /CNTs maintains a high hydrogen production rate, which is approximately ten times higher than that of the previously\n2-x\nreported benchmark photothermal catalyst (Ru/γ-Al O ). This reinforces the robustness and outstanding performance of our\n2 3\ncatalyst in both batch and flow systems.\nRevised Supplementary Table 4. Summary of various reported catalysts in photo- and photo-thermal catalysis for ammonia\ndecomposition.\nr\nH2\nAmmonia Light T\nEntry Catalysts Reactor type (mmol · Ref.\nH2\nsource source (℃)\ng -1∙min-1)\ncat\nAmmonia UV 8 W\n2\nsolution Hg pen-ray lamp\nAmmonia UV 8 W\n2 rGO/TiO NWs Batch reactor r.t. 3.5×10-3 27\n2\nsolution Hg pen-ray lamp\nAmmonia 2000 W\n0.9 0.1 2\nsolution Xe lamp\nNH with 300 W\n3\n2\nwater vapour Xe lamp\nContinuous-\n2 3\nflow reactor\nKCC-1-NH - Continuous-\n2\nK-promoted 300 W Continuous-\nRu-S-1 NH gas 400 W Continuous-\n3\n9 400 7.2 34\n(GaOH) (99.999%) Xe lamp flow reactor\nNH gas White-light Continuous-\n3\n(99.99%) laser flow reactor\nNH gas 300 W Continuous-\n3\n2 3\n(99.999%) Xe lamp flow reactor\nRu NPs/GaN Ammonia 300 W\nNWs/Si solution Xe lamp\nNi-CeO NH gas 300 W This\n2-x 3\n14a Batch reactor 155 22.3\n/CNTs (99.99%) Xe lamp work\nNi-CeO NH gas 300 W This\n2-x 3\n15b Batch reactor 310 403.8\n/CNTs (99.99%) Xe lamp work\nNi-CeO 300 W Continuous- This\n2-x\n16c 20% NH gas 152 25.4\n3\n/CNTs Xe lamp flow reactor work\nNi-CeO NH gas 300 W Continuous- This\n2-x 3\n17d 306 298.4\n/CNTs (99.99%) Xe lamp flow reactor work\na Batch reaction conditions: Under standard testing conditions, catalytic ammonia conversion (0.5 mmol) was conducted\nusing 5 mg catalyst under light irradiation (300 W Xe lamp, equipped with a 400 nm cut-off filter) with light density\nmaintained at 1.4 W/cm2, duration = 1 min.\nb Batch reaction conditions: Catalytic ammonia conversion (0.5 mmol) was conducted using 1 mg catalyst under light\nirradiation (300 W Xe lamp) with light density maintained at 3.5 W/cm2, duration = 1 min.\nc Continuous-flow reaction conditions: A mixture of 5 mg catalyst and 100 mg quartz sand was tested with a 20% NH /80%\nmaintained at 1.4 W/cm2.\nd Continuous-flow reaction conditions: A mixture of 5 mg catalyst and 100 mg quartz sand was tested with a pure NH flow\n3\nrate of 24 mL/min, under light irradiation (300 W Xe lamp) with light density maintained at 3.5 W/cm2.\nIn summary, we have made three major revisions to the manuscript in response to the reviewer’s comments. First, we\nhave incorporated and highlighted the key contributions of Prof. Gascon’s group in this field (Revised References 18–20,\nRevised Supplementary References 32–33, 35, and Revised Fig. 2F). Second, we have added experimental data on the\nperformance of our catalyst under continuous-flow conditions and summarized these results in Revised Supplementary Table\n4, where the reactor configurations of each study are clearly indicated. Finally, we have revised the absolute claim “the most\nefficient” to “one of the most efficient,” providing a more accurate representation of our findings.\nWe sincerely thank the reviewer once again for these highly constructive comments, which have significantly improved\nthe rigor and comprehensiveness of our work.\nc) Authors should clarify if they use visible or visible-IR radiation. As per λ≥400 nm is not clear.\nR：We sincerely thank the reviewer for raising this important point regarding the precise description of our light source.\nIn our standard tests, we utilized a 300 W xenon lamp equipped with a 400 nm cut-off filter, providing irradiation spanning\nthe visible to near-infrared spectrum (visible-IR irradiation). To address this concern unequivocally and prevent any potential\nmisunderstanding, we have revised the manuscript accordingly.\nSpecifically, in Section 2.2 of the revised manuscript, we now clearly state: \"Photothermal ammonia decomposition was\nconducted in a fixed-bed reactor under visible-IR irradiation (300 W xenon lamp equipped with a 400 nm cut-off filter, 1.4\nW/cm2) without external heating.\" Furthermore, all instances of the vague term \"visible radiation\" have been replaced with\nthe accurate \"visible-IR irradiation\" throughout the manuscript. The Methods section has also been updated to explicitly state\nthat, unless otherwise specified, all photocatalytic reactions were carried out under illumination from the 300 W xenon lamp\nwith the 400 nm cut-off filter.\nWe are grateful to the reviewer for this valuable comment, which has significantly enhanced the precision and scientific\nrigor of our work.\nd) Authors perform a series of 100 reaction cycles to assess the stability of the system. At first this number of cycles could\nseem significant, but taking into account that the reaction time is one minute, this stability test represents a total reaction time\nbelow 2 hours. A longer stability test (at least 50 hours) is needed in order to properly evaluate the integrity of this system\nwith others already available in the literature, especially taking into account that the performance shows a subtle but steady\ndeactivation upon reuses. Authors should also include the complete characterization of the long-term spent sample.\nR: We sincerely thank the reviewer for this crucial suggestion. In response, and to comprehensively evaluate the catalyst’s\nstability, we conducted a continuous-flow stability test for over 50 hours using the flow reactor system (Figure R8). The\nexperimental conditions were as follows: 5 mg of catalyst was mixed with 100 mg of quartz sand and placed in the reactor.\nThe system was irradiated with a 300 W xenon lamp (equipped with a 400 nm cutoff filter, light intensity 1.4 W/cm2), and a\n20% NH /Ar mixture was passed through at a flow rate of 24 mL/min (WHSV = 57,600 mL g-1 h-1).\n2-x\napproximately 25 mmol g -1 min-1 over the 55-hour continuous reaction, demonstrating excellent catalytic stability.\ncat.\nFurthermore, we conducted comprehensive microscopic structural characterization of the spent catalyst (long-term used\nsample). X-ray diffraction (XRD) and aberration-corrected HAADF-STEM-EDS analysis (Figures R10-R11) confirmed that,\nafter long-term testing, the dispersion of Ni nanoparticles on CNTs remained perfectly intact, with no observable sintering or\nparticle growth. In contrast, the Ni nanoparticles on Ni/CNTs aggregated, which contributed to the observed decrease in\nhydrogen production rate. These characterization results provide direct structural evidence supporting the outstanding stability\nof our catalyst.\nFigure R9. Durability test over Ni-CeO /CNTs, Ni/CeO and Ni/CNTs (Revised Fig. 2E)\n2-x 2\nFigure R10. Powder XRD patterns for Ni-CeO /CNTs before and after the 55-h stability test (post-test sample mixed with\n2-x\nquartz sand) (Revised Supplementary Fig. 16)\nFigure R11. HRTEM images and size distribution of Ni nanoparticles taken from Ni-CeO /CNTs before (a-c) and after (d-\n2-x\nf, Revised Supplementary Fig. 17) the 55-hour stability test.\nThis valuable suggestion from the reviewer has prompted us to elevate the stability tests to a more convincing and\ncomparable standard. These new data greatly strengthen our conclusions regarding the catalyst’s durability, and we have fully\nintegrated them into the Results and Discussion sections of the revised manuscript (Revised Fig. 2E and Revised\nSupplementary Fig. 16-17). Once again, we sincerely thank you for helping us significantly improve the quality and rigor of\nthis study.\ne) In line with my previous comment, why using a total reaction time of 1 minute? This is an extremely short time which\nmakes very difficult to assess stability or the kinetics of the system. Authors have to increase the initial amount of NH3, as\nnow is limited to only 12 mL. This will also demonstrate the applicability of the system.\nR: We sincerely thank the reviewer for raising this important issue. The choice of a 1-minute total reaction time was a carefully\nconsidered decision, primarily aimed at ensuring that we could accurately and reliably measure the intrinsic reaction rate of\nthe system, while minimizing the effects of product concentration changes and revealing its true kinetics.\nThis short duration is critical because it ensures that the reaction occurs in the low-conversion region (<20%). Under\nthese conditions, the effects of reactant (NH ) consumption and product (H , N ) accumulation on the reaction rate are\n3 2 2\nminimized, allowing the rate to remain constant and unaffected by mass transfer limitations or shifts in thermodynamic\nequilibrium. As confirmed by our supplementary data (Figure R12), when the reaction time exceeds 1 minute, the apparent\nreaction rate begins to decline due to the increasing consumption of reactants and product inhibition effects. At this point, it\nbecomes difficult to distinguish whether the observed decline is due to the intrinsic activity of the catalyst or concentration-\ninduced kinetic decay. Therefore, the selection of 1 minute as the experimental time was a thoughtful choice to capture the\nmost accurate and representative kinetic data, free from significant concentration changes that could introduce confusion.\nAdditionally, we fully understand and agree with the reviewer’s point that a 1-minute short-term test is insufficient to\nassess the long-term stability of the catalyst, which is crucial for evaluating its practical application potential. To address this\nconcern and more comprehensively demonstrate the catalyst's performance, we have followed the reviewer’s suggestion and\nadded a flow reactor cycling experiment lasting over 50 hours in response to question (d).\nFigure R12. Ammonia conversion over time on Ni-CeO /CNTs.\n2-x\nf) Most of the works on photo-thermal ammonia decomposition have been performed under continuous-flow configuration,\nwhich is closer to real application. Authors should perform their activity tests under these conditions to contextualize their\nresults.\nR：We sincerely thank the reviewer for this valuable suggestion. As outlined in our previous response, we have fully\nincorporated the experiments conducted in the continuous-flow reactor in the revised manuscript. Additionally, we have\ncompared the ammonia decomposition activity and long-term cycling stability of the catalysts developed in this study with\nthose of classic catalysts reported in the literature under identical continuous-flow conditions. Once again, we greatly\nappreciate the reviewer’s constructive feedback, which has significantly enhanced the completeness and rigor of our research.\ng) In line 173, authors claim that the conversion surpasses the thermodynamic equilibrium. As we cannot trick\nthermodynamics, this means that the actual temperature of the active sites is higher than that registered by the thermocouple\n(155 degrees Celsius). Authors claim that the temperature was also monitored by IR but there aren’t any IR thermal images\nneither in the main manuscript nor in the SI. I suggest authors to back-calculate the actual temperature of the active sites in\ntheir system, for instance using their actual conversion at the equilibrium. See the work from prof. Zhang\n(doi.org/10.1002/anie.202304452)\nR：We sincerely thank the reviewer for this important suggestion. In photothermal catalysis, both light and thermal effects\ncan operate separately or synergistically. As a result, photothermal catalysis can be classified into different types based on\ntheir specific reaction pathways, namely thermochemical or photochemical pathways. Our work falls under thermal-assisted\nphotocatalysis, where the primary reaction pathway is photochemical. In this reaction, light excites the catalyst into an\nelectron-excited state, and thermal energy plays a supporting role by facilitating the migration of photogenerated charge\ncarriers and enhancing the mass transfer rate, thereby accelerating the reaction process.\nUnlike photo-assisted thermal catalytic reactions, where light is primarily used to generate heat (similar to traditional\nthermal catalysis) with minimal contribution from the photochemical pathway, the main driving force in our system is the\nenergy of photons (photocatalysis-dominated). Photocatalytic reactions harness photon energy to drive \"uphill\" reactions (ΔG >\n0), enabling reactions that would typically require high temperatures to occur at low temperatures or even at room temperature.\nMany studies have demonstrated that photocatalysis can break the limitations of traditional thermal catalysis, achieving\nconversion rates that surpass the thermodynamic equilibrium limits at the same temperature\n(doi.org/10.1016/j.nanoen.2024.109401, doi.org/10.1038/s41929-019-0419-z, doi.org/10.1002/anie.202108870,\ndoi.org/10.1038/s41929-019-0419-z).\nIn photocatalysis, the input of light energy drives the system into a non-thermal equilibrium state, allowing significant\nconversion rates at apparent temperatures much lower than those required for thermal catalysis. This phenomenon—where\nthe apparent conversion rate exceeds the thermodynamic equilibrium limit at the same temperature—is one of the key features\nthat distinguishes photocatalytic reactions from traditional thermal catalysis.\nWe fully understand the reviewer’s concern that an apparent conversion rate surpassing the thermodynamic equilibrium\nlimit at the given temperature could indicate that the local temperature of the active sites is higher than the average bulk\ntemperature. To ensure the absolute rigor of our conclusions and account for potential temperature measurement errors, we\nhave removed statements and related figure (Fig. 2B) regarding \"conversion surpassing thermodynamic equilibrium\" from\nthe revised manuscript.\nOnce again, we deeply appreciate your invaluable suggestion, which has greatly helped us improve the rigor and\nscientific accuracy of our manuscript.\nResponses to the Reviewers’ Comments and the Corresponding Revisions\nReferee 1\nA minor comment: while most figures are high-resolution vector graphics, the atomic\nconfiguration panels, particularly Fig. 4E, make it difficult to distinguish among intermediates. I\nsuggest that the authors enhance the resolution of these images.\nAside from this, the authors have adequately addressed all of my comments, and I am pleased\nto recommend the manuscript for publication in Nature Communications.\nR：We thank the reviewer for their positive recommendation and for this helpful suggestion. In\nresponse, we have revised Fig. 4E (and all similar atomic configuration panels) at a higher resolution.\nThe local views of the optimized structures in Fig. 4E have enlarged to help readers clearly\ndistinguish the intermediates. The complete structural diagrams are provided in Supplementary Fig.\n26.\n△E=-0.14 eV Light\nu.) 120\na.\nsit y\n(\n850 855 860 865\nnt e n Ce 3d 60% 60\nI Light\n67%\nCe4+/(Ce4+ + Ce3+)\n0\n882 896 910 924 0 60 120 180 240\nBingding Energy (eV)\nV)0\ne y ( er g -1.03 eV -1.17 eV\nn-2\nE -2.00 eV\n-4\nNi/CeO-O Ni/CeO Ni(111) 8 2 v 8 2\nN-H cleavage N-N coupling\nE=1.09 eV\nV)0 1 E E E a a a = = = 0 0 0 . . . 7 3 2 1 3 6 e e e V V V E E E a a a = = = 0 0 0 . . . 4 7 5 3 9 5 e e e V V V E E a a a = = 0 0 . . 5 7 2 4 e e V V E E E a a a = = = 1 0 0 . . . 3 9 5 4 8 3 e e e V V V\ne\ny\n(\ng\ner-1\nn\nE\n-2 Ni (111)\nNi/CeO\n8 2\nNi/CeO_O\n-3 8 2 v\nNH3 (g) NH3 * TS1 NH2 *+H* NH2 * TS2 NH*+H* NH* TS3 N*+H* N*+N* TS4 N2 *\nRevised Fig. 4E\n)2mc/Am(\nytisned\ntnerrucotohP\na b\nNH Ni-CeO /CNTs 3 2-x\nAr\nTime (s)\nc d\n18%*NH3 2.0 Ni-CeO 2-x /CNTs\n37%\n24%*NH2\n15% 1.6 10%*NH k /k H D\n34% 1.2 Ni/CeO 2\n48%*N\n15%\n0.8\nNi-CeO2-x/CNTs Ni/CeO2 Photoc atalyst\ne\nCe\nO\nNi\nN\nH\nReferee 3\nI appreciate the time and effort of the authors to address my comments. Overall, I think the\nmanuscript improved its clarity after this revision.\nRegarding my question about reaction time, now it is clear that authors used 1 min reaction\ntime to measure initial reaction rates. And the actual conversion of those experiments is 91 % after\n20 minutes of reaction (as per new figure R12). Still it is quite surprising that the catalyst is able to\nachieve a 92 % conversion under continuous-flow (24 mL/min flow rate of pure NH ) only at 300\n3\ndegrees Celsius. Specially taking into account that under batch conditions a total reaction time of\n20 min was necessary to convert 91 % of 12 mL of NH .\nconversions, but probably these data could be useful to estimate the real temperature, which most\nlikely will be higher than 300 degrees Celsius.\nR：We sincerely thank the reviewer for their thoughtful comments and the opportunity to\nfurther clarify the apparent discrepancy in conversion between the batch and flow systems. The high\nconversion achieved in the continuous-flow reactor at 300 °C is reliable and can be well explained\nby several key experimental differences.\nFirst, the batch reaction yielding 91% conversion in 20 minutes was conducted under a light\nintensity of 1.4 W/cm2, while the continuous-flow experiment was performed under a significantly\nhigher intensity of 3.5 W/cm2, which raised the catalyst temperature from 155 °C to 306 °C. This\nincrease in photon flux greatly enhances the photocatalytic driving force. Moreover, the batch\nsystem is inherently limited by dead volume and inefficient contact between the catalyst and reactant,\nwhich slows reaction kinetics. In contrast, the continuous-flow configuration ensures thorough and\ncontinuous contact between NH and the catalyst, fully leveraging its high intrinsic activity and\n3\nenabling more efficient conversion. Therefore, the 92% conversion obtained under flow—supported\nby both higher photon flux and superior mass transfer—is well justified.\nIn addition, we fully understand the reviewer’s concern regarding the actual reaction\ntemperature. To address this directly, we performed infrared thermal image under 3.5 W/cm2\nirradiation, which confirmed that the catalyst bed temperature remained consistently at 306 °C\n(Figure R1).\nFigure R1 Infrared thermal image of Ni-CeO /CNT surface under 3.5 W/cm2 illumination.\n2-x\nFurthermore, following the reviewer’s suggestion, we performed a back-calculation based on\nthe equilibrium conversion. As shown in Figure R2, the thermodynamic limiting temperature\ncorresponding to 92.9% conversion is approximately 231 °C (blue point). However, the measured\ntemperature in our continuous-flow system was 306 °C (orange point), and the conversion obtained\nunder this condition is slightly below the theoretical maximum conversion at this temperature. This\nresult confirms that the reported macroscopic temperature is consistent and credible.\nFigure R2 The limitation of the thermal system for ammonia decomposition (blue line).\nIn conclusion, the high performance in the continuous-flow reactor arises from the combined\neffect of enhanced photon flux (3.5 W/cm²) and optimized reactant-catalyst contact in the\ncontinuous-flow configuration. We have also added relevant explanations in the revised manuscript\nregarding the photo-thermal temperature and its relation to the thermodynamic limit: “Under 3.5 W\ncm-2 irradiation, a photothermal temperature of 306 °C and a maximum conversion of 92.9% were\nachieved, which corresponds to a thermodynamic equilibrium temperature of 231 °C”."}]

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