Multiscale electric fields direct charges to single-atom cobalt sites for photocatalytic H_2 production

Domain: biology
Published: 2026-04-04
Editorial outcome: major_revision

Abstract
The photocatalytic efficiency of covalent organic frameworks is often limited by poor charge separation and inaccessible catalytic sites. Here, we overcome these challenges by constructing a biomimetic “alveoli-on-lamina” heterostructure through coordination-directed assembly. This strategy concurrently exfoliates a bulk covalent organic framework into ordered lamellae and creates atomic-scale Co-N/O bridges, anchoring high-density, atomically dispersed cobalt sites. Crucially, this architecture spontaneously generates a multi-scale electric field, integrating a strong interfacial field for charge separation with an intra-structure potential gradient for directional electron transport. This field-driven vectorial charge flow delivers electrons to the catalytic sites, enabling a competitive photocatalytic performance: a hydrogen evolution rate of 534.6 mmol g-1 h-1 under standard irradiation without noble metals, an apparent quantum yield of 90.2% at 500 nm, and retained stability. This work demonstrates that engineering built-in electric fields across multiple scales is a valuable paradigm for advanced solar-to-fuel conversion.

Introduction
The conversion of solar energy into chemical fuels through artificial photosynthesis represents a pivotal pathway toward a sustainable energy future. Among emerging photocatalytic materials, covalent organic frameworks (COFs) have garnered significant attention due to their crystalline porosity, tunable optoelectronic properties, and molecularly precise architectures1-4. The extended π-conjugated networks in COFs facilitate directional charge transport, while their high surface areas and engineered pore environments promote reactant diffusion and active-site accessibility5-7. These attributes position COFs as ideal scaffolds for constructing advanced photocatalytic systems8-10.

Despite these inherent advantages, the photocatalytic efficiency of most COFs remains constrained by two interrelated fundamental limitations: inefficient charge separation due to strong exciton binding, and inadequate utilization of catalytic sites buried within bulk structures11-14. The former leads to rapid non-radiative recombination, while the latter restricts mass transport and surface reaction kinetics.

To mitigate these issues, significant efforts have focused on exfoliating bulk COFs into ultrathin two-dimensional (2D) lamellae15,16. This structural refinement reduces charge migration distances and exposes more internal active sites17,18. However, conventional exfoliation techniques (e.g., sonication, mechanical peeling) often suffer from irreproducible yields, structural damage, and poor scalability19,20. More critically, these methods typically create physical mixtures rather than chemically integrated heterostructures, failing to establish atomic-level interfacial connections essential for efficient charge transfer21. Concurrently, the incorporation of atomically dispersed metal centers has proven highly effective for maximizing atom-utilization efficiency and providing well-defined catalytic environments22,23. The key challenge lies in seamlessly integrating these two concepts — achieving atomic dispersion within a precisely exfoliated, intimately coupled architecture — to create synergistic charge-transfer highways from the photoabsorber to the catalytic site.

In this work, we address a biomimetic design strategy that addresses these challenges through atomic-scale interfacial synergy and multi-scale structural ordering. We report a biomimetic “alveoli-on-lamina” heterostructure, constructed by the precise integration of hollow “CS alveoli” (derived from sulfidized ZIF-67) into an in-situ exfoliated COF matrix via interfacial coordination chemistry. This one-pot process concurrently achieves three critical functions: (i) controlled exfoliation of the bulk COF into ordered, ultrathin lamellae, (ii) formation of dense, atomic-scale Co-N/O coordination bridges that serve as directed electron-transfer pathways, and (iii) anchoring of high-density, atomically dispersed cobalt sites (1.81 × 1021 atoms g-1) within the conductive network. The resulting architecture (denoted as CT-x, x = mass of CS in mg) mimics pulmonary alveoli, maximizing interfacial area (akin to alveolar sacs), minimizing mass-transfer barriers (resembling alveolar membranes), and enabling confined nanoreactor effects. Crucially, we demonstrate that this design establishes a multi-scale electric field — comprising a strong interfacial field and an ordered intra-structure potential gradient — which ensures vectorial charge separation and rapid transport. This multi-scale integration yields exceptional photocatalytic performance, with the optimized CT-35 catalyst achieving a hydrogen evolution rate of 534.6 mmol g-1 h-1 under AM 1.5G irradiation, an apparent quantum yield of 90.2% at 500 nm, and outstanding stability. This work demonstrates a rational design paradigm that integrates atomic-level site engineering with biomimetic hierarchical structuring and multi-scale charge management, offering a generalized platform for high-efficiency solar-to-chemical energy conversion.

Results
The fabrication of the heterostructure follows a two-step, coordination-directed assembly process. Fig. 1 illustrates the construction of the dibenzothiophene-S,S-dioxide-based COF and the subsequent formation of the integrated CT-x architecture. First, hollow “CS alveoli” were synthesized through the solvothermal sulfidation of ZIF-67 precursors, yielding a porous sulfide framework with abundant under-coordinated cobalt sites. The key synthetic innovation lies in the functionalization of these “CS alveoli” with amine groups via in-situ Co-N coordination using the TDS (3, 7 diaminodibenzo [b,d] thiophene-5, 5-dioxide) linkers. These tethered amine groups then undergo interfacial Schiff-base condensation with the aldehyde functionalities of the TP (2, 4, 6- triformylphloroglucinol) monomers in a subsequent integrated step. This dual interfacial chemistry accomplishes two critical outcomes in one pot: (i) Co-N coordination anchors the “CS alveoli” at the atomic scale; (ii) concurrent Schiff-base reactions between tethered amines and aldehyde functionalities drive the dynamic exfoliation of the COF into ultrathin lamellae. Critically, this one-pot process simultaneously establishes dense, covalent Co-N/O coordination bridges at the interface.

The resulting CT-x architecture is a purpose-built biomimetic system that translates the structural-functional principles of pulmonary alveoli into an efficient photocatalytic platform. This design is achieved through four integrated mechanisms: (i) Maximized interfacial area. Analogous to alveolar sacs, the “CS alveoli” form a high-density array of atomically dispersed Co sites (1.81 × 1021 atoms per gram; page 6 in the SI), ensuring maximum accessibility to catalytic centers. (ii) Ultrathin mass-transfer barriers. The structure combines ultrathin COF lamellae with thin-walled alveoli (Supplementary Fig. 1 and Fig.2), mimicking the alveolar-capillary membrane to minimize diffusion resistance for H O and H . (iii) Efficient electron-transfer network. Continuous Co-N/O bonds create atomic-scale “highways,” similar to capillary networks, enabling rapid electron delivery to catalytic Co sites. (iv) Confined photothermal nanoreactor. Each hollow alveolus acts as a confined cavity where localized photothermal heating reduces the activation barrier for water dissociation, analogous to optimized concentration gradients in alveolar spaces. This synergistic design ensures that structural order, efficient charge transport, and localized reaction environments are seamlessly integrated from the atomic to the microscopic scale.

The morphological evolution from precursors to the final biomimetic architecture was characterized by electron microscopy. The ZIF-67 precursor exhibits a uniform rhombic dodecahedral morphology (Fig. 2a). After sulfidation, the resulting “CS alveoli” largely retain this framework but with a roughened surface and partially collapsed structure, forming hollow cavities that function as efficient light-trapping nanoreactors (Fig. 2b). In contrast, the pure TP-TDS COF self-assembles into an interconnected, three-dimensional coral-like network (Fig. 2c). Strikingly, the integration of “CS alveoli” during COF synthesis induces a dramatic morphological transformation. The CT-35 hybrid displays a well-defined marigold-like superstructure composed of radially arranged petal-like lamellae (Fig. 2d, e). This indicates that the presence of cobalt centers drives the exfoliation and oriented reassembly of the COF into a two-dimensional lamellar architecture. We reason that such a highly ordered and anisotropic superstructure could potentially establish a directional internal electric field, which would be pivotal for long-range vectorial charge transport. The validity of this reasoning is directly confirmed by subsequent spatially resolved potential measurements (discussed later). To confirm that this morphological evolution is governed by Co-N/O coordination rather than a template effect, we performed control experiments. When CoCl was used instead of “CS alveoli” under identical conditions, the resulting CoCl @TP-TDS exhibited an essentially identical marigold-like morphology (Fig. 2f), demonstrating that cobalt coordination is the decisive factor. Conversely, physically milled mixtures of pre-formed components (milled CoCl /TP-TDS or milled CT-35) yielded only featureless aggregates without any defined superstructure (Supplementary Fig. 3), confirming that in-situ coordination bonding is essential. The structural consequence of this coordination-directed assembly was quantified by atomic force microscopy (AFM). To directly evaluate the exfoliation effect, we first measured the pristine TP-TDS COF, which exhibits a typical thickness of ~71.5 nm (Fig. 2g). Upon coordination-directed integration, the resulting CT-35 forms highly ordered, ultrathin lamellae with a uniform thickness of ~6.4 nm (Fig. 2h) — representing an order-of-magnitude thinning (~11-fold reduction). In contrast, the milled CT-35 control, which lacks defined interfacial bonds, consists of irregular aggregates with a typical height of ~132.7 nm (Supplementary Fig. 6). Together, this order-of-magnitude thinning and the formation of ordered lamellae provide direct, quantitative evidence that the Co-N/O coordination bonds mediate the precise exfoliation and ordered stacking of the COF layers. The dispersion of catalytic sites within this architecture was examined at multiple scales. TEM imaging confirms the uniform distribution of “CS alveoli” throughout the COF laminae (Fig. 2i). To directly visualize the atomic dispersion of Co species, HAADF-STEM images reveal high-density, isolated bright dots corresponding to single cobalt atoms in both the “CS alveoli” and the CT-35 composite (Fig. 2j-l). This visual evidence is further corroborated by large-area STEM-EDS elemental mapping, which demonstrate the homogeneous spatial distribution of all constituent elements (Co, C, N, O, S) throughout the hybrid without aggregation (Fig. 2m, S6, S7). These microscopic and elemental analyses provide compelling visual evidence for the high-density atomic dispersion of Co species (1.81 × 1021 atoms Co/g), which is a key structural feature underlying its enhanced photocatalytic performance.

The crystal structures and phase purity of the materials were analyzed by X-ray diffraction (XRD). The ZIF-67 precursor shows sharp peaks matching the simulated pattern, confirming high crystallinity (Supplementary Fig. 9a)24. After sulfidation, the resulting “CS alveoli” exhibit characteristic peaks at 31.36° and 50.22°, corresponding to the (311) and (511) planes of Co S (Supplementary Fig. 9b)25, with its stoichiometry further verified by ICP-OES ( Supplementary Table. 3). The structural integrity of the COF component upon hybridization is clearly retained. Both pristine TP-TDS and CT-35 show the characteristic (100) peak at ~3.47° and a broad peak at ~26° attributed to π-π stacking (Supplementary Fig. 9c), confirming the preservation of the TP-TDS COF framework26. Notably, in CT-35 the (100) peak intensity is reduced, indicating a preferential orientation of the exfoliated lamellae parallel to the substrate27. Concurrently, the enhanced intensity of the ~26° peak suggests improved layer-to-layer stacking order, which we attribute to the aligning effect of the interfacial Co-N/O coordination bonds. This structural ordering is conducive to extended π-conjugation and efficient inter-layer charge transport28. The absence of distinct diffraction signals from “CS alveoli” in CT-35 strongly indicates their atomic-scale dispersion within the COF matrix, consistent with the electron microscopy observations. Fourier-transform infrared (FT-IR) spectroscopy provides complementary evidence at the molecular level (Supplementary Fig. 10). Both TP-TDS and CT-35 show signature bands for the C=N stretch (~1350 cm-1), O=S=O symmetric stretch (~1301 cm-1), and C=O stretch (~1627-1658 cm-1), confirming the integrity of the ketenimine-linked framework29,30. Crucially, a new vibrational band emerges at ~460 cm-1 in CT-35, which is characteristic of Co-N stretching modes31. This spectroscopic evidence directly confirms the formation of interfacial coordination bonds. These bonds constitute the key chemical interaction responsible for directing the exfoliation and structural ordering observed by XRD.

The formation and nature of these interfacial Co-N/O bonds were investigated at complementary levels: X-ray photoelectron spectroscopy (XPS) probed the surface chemical states and charge redistribution, while synchrotron-based X-ray absorption fine structure (XAFS) provided quantitative insights into the local coordination geometry and atomic dispersion. In the pristine “CS alveoli”, the Co 2p spectrum displays characteristic peaks indicative of mixed oxidation states32 (Fig. 3a). In striking contrast, the Co 2p spectrum of CT-35 exhibits two distinct features at 782.1 eV and 784.5 eV, which are assigned to Co-O and Co-N coordination environments, respectively33,34. Correspondingly, the N 1s spectrum of CT-35 shows a new component consistent with Co-coordinated nitrogen, which is absent in both pristine components (Fig. 3b). These shifts provide direct evidence for charge redistribution and the formation of Co-N/O bonds at the interface. The critical dependence of these bonds on the synthetic pathway was confirmed by control experiments. XPS analysis of milled CT-35 shows no characteristic Co-N/O signatures (Supplementary Fig. 13), confirming that simple physical proximity cannot induce the coordination chemistry observed in CT-35. To further decouple the interface formation process, we examined an intermediate: amine-functionalized “CS alveoli” (CS-NH ), prepared by stirring “CS alveoli” with TDS followed by rigorous washing. The Co 2p spectrum of CS-NH exhibits a distinct satellite peak at 784.5 eV (Supplementary Fig. 14), characteristic of Co-N coordination and identical to the feature observed in CT-35. This control experiment confirms that TDS acts as a nitrogen donor, directly coordinating with Co sites via covalent Co-N bonds during the initial functionalization step, prior to COF formation35,36. Together, the XPS analyses establish a clear sequence for the interfacial bond formation: (i) Co-N bonds form between “CS alveoli” and TDS linkers, creating the CS-NH intermediate; (ii) these pre-anchored amines then participate in the in-situ formation of the COF framework via Schiff-base condensation with TP; (iii) the final coordination environment in CT-35, encompassing both Co-N and Co-O characteristics, is achieved through this one-pot, coordination-directed synthesis.

To quantify the precise local structure resulting from this synthesis — specifically, the bond lengths and coordination numbers of the proposed Co-N/O bridges — we performed synchrotron-based XAFS spectroscopy. The XANES spectrum shows the Co K-edge of CT-35 positioned between CoO (Co2+) and Co foil, indicating an intermediate valence state resulting from interfacial charge redistribution (Fig. 3c). It shows no detectable Co-Co coordination path (Fig. 3d, Supplementary Table. 4). This absence provides definitive evidence that Co species exist in an atomically dispersed state throughout the entire sample, with no Co-based clusters or nanoparticles present within the detection limit of the technique. This bulk-sensitive finding is fully consistent with the local STEM observations and confirms the global atomic dispersion of Co. With the atomic dispersion established, we then performed quantitative fitting to resolve the local coordination environment. The fitting reveals that the Co center in CT-35 maintains a primary coordination shell of S atoms (Co-S coordination number, CN = 3.9 ± 0.4; bond distance, R = 2.25 ± 0.02 Å), analogous to pristine “CS alveoli”. Concurrently, a distinct secondary coordination shell is identified, corresponding to the interfacial Co-N/O bonds (CN = 0.7 ± 0.4; R = 1.95 ± 0.06 Å). This non-integer CN reflects the heterogeneous yet definitive presence of these interfacial linkages. Wavelet-transform analysis further validates the atomic dispersion of Co and the specific coordination geometry37 (Fig. 3e-f). Thus, the XAFS analysis both verifies atomic dispersion through bulk-sensitive spectroscopy and quantitatively establishes the newly formed Co-N/O bonds (R ≈ 1.95 Å) as the atomic-scale bridges connecting the exfoliated COF lamellae to the catalytic “CS alveoli”38-42.

To evaluate the functional impact of the atomic-scale connectivity, we performed photoelectrochemical measurements. We first optimized the loading of “CS alveoli” and found that CT-35 delivers the highest photocurrent density — 8-fold and 10-fold higher than that of the pristine TP-TDS COF and pure “CS alveoli,” respectively (Fig. 4a). To unequivocally attribute this enhancement to the Co-N/O coordination network, we conducted a controlled experiment by comparing CT-35 with a structurally disrupted counterpart (milled CT-35), in which the defined interfacial bonds are absent. This comparison reveals a decisive contrast: CT-35 exhibits a substantially lower charge-transfer resistance (EIS) and a significantly higher, stable photocurrent, whereas the milled sample shows a severely suppressed response (Supplementary Fig. 19, 20). This stark difference directly confirms that the atomic-scale coordination bonds are indispensable for establishing efficient charge-transfer pathways. In summary, the integration of atomic-scale spectroscopy (XAFS/XPS) with macroscopic functional testing (photocurrent, EIS) establishes a coherent evidence chain: the in-situ formed Co-N/O bonds are the fundamental origin of superior charge separation and transport.

Building upon this established charge-transfer superiority, the CT-35 catalyst delivers exceptional photocatalytic hydrogen evolution performance without precious-metal co-catalysts (Fig. 4b). Under AM 1.5G irradiation, pristine “CS alveoli” and TP-TDS show negligible activity (0.12 and 0.26 mmol g-1 h-1, respectively). In stark contrast, the optimized CT-35 achieves a competitive rate of 534.6 mmol g-1 h-1, representing enhancements of ~4555-fold and ~2056-fold over the individual components, as visually demonstrated in Supplementary Movies 1 and 2. This performance is accompanied by a record apparent quantum yield of 90.2% at 500 nm (Fig. 4c). Under visible-light irradiation (λ ≥ 420 nm), CT-35 retains over 51% of its full-spectrum rate (Supplementary Fig. 22), highlighting efficient visible-light utilization. The activity exhibits a clear optimum with “CS alveoli” loading (CT-35 > CT-45, Fig. 4b). The performance decline at higher loadings is attributed to two factors: (i) light-shielding by excessive “CS alveoli”, which attenuates photon absorption by the COF, and (ii) the potential formation of Co-based clusters that act as charge-recombination centers43,44. CT-35 exhibits competitive operational stability, maintaining high activity over 10 consecutive cycles (Fig. 4d). Post-reaction characterization confirms its robust integrity: ICP-OES detects negligible leaching of Co or S (Supplementary Table. 6); SEM and XRD show preserved morphology and crystallinity (Supplementary Fig. 23, 24); and XPS/EXAFS analyses confirm that the atomic-scale coordination environment (both Co-S and Co-N/O bonds) remains intact after prolonged operation (Supplementary Fig. 25, Supplementary Table. 7). Moreover, CT-35 achieves the a high reported photocatalytic hydrogen evolution (HER) rate among state-of-the-art COF-based photocatalysts (Supplementary Table. 8). The competitive photocatalytic performance of CT-35 originates from its well-defined “alveoli-on-lamina” architecture. This architecture is built upon a foundation of high-density, atomically dispersed Co sites within the “CS alveoli,” which provide the essential catalytic centers. The full potential of these sites is unlocked through two integrated design strategies: (i) connecting them to exfoliated COF lamellae via covalent Co-N/O coordination bridges for directed charge transfer, and (ii) employing the electron-withdrawing TDS linker to optimize interfacial charge separation. To rigorously validate that both strategies are essential — and not merely correlative — for achieving the observed performance, we conducted control experiments that systematically decouple their contributions (Fig. 4f). First, the necessity of covalent Co–N/O bridges over physical mixing was tested using a mechanically mixed sample (milled CT-35). Its drastically lower HER rate (2.26 mmol g-1 h-1) and photocurrent confirm that intimate electronic coupling via chemical bonds is indispensable. Second, the critical role of the specific coordination pathway was examined using a sample synthesized without the amine-functionalization step (traditional CT-35). Its significantly reduced activity (~29-fold lower HER rate) demonstrates that the in-situ formation of Co-N bonds during the initial functionalization is a prerequisite for creating an efficient interface. Finally, the indispensable electronic function of the TDS linker was isolated by synthesizing a control COF where TDS was replaced by 2,7-diaminofluorene (TD, Supplementary Fig. 27), yielding CS@TP-TD. Despite structural similarity, CS@TP-TD exhibits a HER rate over 10 times lower than CT-35 and a higher charge-transfer resistance (Supplementary Fig. 28). This result provides direct experimental proof that the electron-withdrawing sulfone group in TDS is crucial for facilitating hole extraction and optimizing the interfacial energy alignment, thereby enabling efficient electron injection into the catalytic sites. In conclusion, this triad of control experiments establishes a clear causal chain. The record-breaking performance of CT-35 is not accidental but is directly and exclusively enabled by the synergistic integration of (i) covalent Co-N/O interfacial bridges, (ii) their specific in-situ formation pathway, and (iii) the tailored electronic function of the TDS linker within the biomimetic “alveoli-on-lamina” architecture.

The charge carrier dynamics were investigated using time-resolved photoluminescence (TR-PL). CT-35 exhibits an average carrier lifetime (τ) of 4.43 ns, which is 22.2-fold and 9.0-fold longer than those of the isolated “CS alveoli” (0.20 ns) and the pristine TP-TDS COF (0.49 ns), respectively (Fig. 5a). This pronounced extension indicates significantly suppressed charge recombination, primarily due to the efficient interfacial charge extraction enabled by the Co-N/O coordination bridges. The role of the exfoliated lamellar architecture in promoting the initial separation of photogenerated charges was quantified by temperature-dependent PL spectroscopy. The extracted exciton binding energy (Eb) decreases substantially from 72.26 meV for pristine TP-TDS to 34.9 meV for CT-35 (Fig. 5b, c). This reduction confirms that exfoliation and the extended π-conjugation within the hybrid framework effectively weaken Coulombic interactions, facilitating the dissociation of excitons into free carriers45. Direct evidence for the consequent accumulation of these separated charges at reactive sites comes from electron paramagnetic resonance (EPR) spectroscopy. Under illumination, CT-35 generates the most intense signal for superoxide radicals (•O ⁻), which are produced by the reaction of surface-accumulated electrons with adsorbed oxygen (Fig. 5d). This result demonstrates a higher yield of long-lived, mobile electrons that can migrate to the surface and participate in reduction reactions, consistent with the prolonged carrier lifetime and reduced Eb. In summary, this triad of spectroscopic techniques —TR-PL, temperature-dependent PL, and EPR — provides a coherent, multistep picture of optimized charge management. The interfacial Co-N/O bridges and the ordered lamellar superstructure work in concert to first facilitate charge separation (reduced Eb), then suppress their recombination (extended τ), and ultimately promote the accumulation of free electrons at catalytic surfaces for reaction (enhanced EPR signal).

Complementary to the optimized charge dynamics, the hierarchical structure of CT-35 enhances mass transport and utilizes the full solar spectrum, contributing synergistically to its overall efficiency. Nitrogen physisorption analysis reveals how the integration of “CS alveoli” modifies the pore architecture (Fig. 5e, f). While the BET surface area of CT-35 (321.70 m2 g-1) is reduced compared to pristine TP-TDS (986.51 m2 g-1) — due to partial pore occupation — the pore size distribution shifts significantly to a larger average diameter (4.9 nm for CT-35 vs. 3.5 nm for TP-TDS). This expansion is attributed to a pillaring effect, wherein the coordinated “CS alveoli” spacers increase the interlamellar distance of the COF. Direct HRTEM measurement confirms an interlayer spacing of 4.94 ± 0.2 nm (Supplementary Fig. 29), quantitatively aligning with the BET data and visually confirming the structural expansion, which is beneficial for reactant and product mass transport. The heterojunction exhibits broad-spectrum light absorption across 200-800 nm (Supplementary Fig. 30), comparable to that of pristine TP-TDS, ensuring efficient harvesting of the full solar spectrum.

In addition to efficient photon capture, CT-35 exhibits a pronounced photothermal conversion capability. Under illumination in air, its surface temperature rapidly rises to 144.1 °C, substantially higher than that of TP-TDS (107.7 °C) under identical conditions (Fig. 5g, h). More critically, during actual photocatalytic HER operation in aqueous solution, the bulk reaction temperature reaches a steady-state 74.7 °C (Fig. 5i), confirming a substantial thermal effect within the operating environment. To rigorously deconvolute the role of this heating from the photochemical process, we performed decisive control experiments. Operating the system in darkness while maintaining the bulk solution at ~75 °C or 144 °C yielded no detectable hydrogen evolution (Fig S31). This unequivocally establishes that the reaction remains strictly photo-driven; thermal energy alone cannot initiate the HER. Therefore, we refine the mechanistic interpretation: the photothermal effect does not serve as an independent driving force but functions as a kinetic enhancer within the photo-driven process. The elevated local thermal environment accelerates subsequent surface-reaction steps (e.g., H* adsorption/desorption) via Arrhenius-type kinetics, thereby synergistically boosting the overall HER rate without altering the fundamental photochemical initiation step.

The electronic structure at the heterojunction interface dictates the thermodynamic driving force and direction for charge transfer. Ultraviolet photoelectron spectroscopy (UPS) determines the work functions (Φ ) of “CS alveoli” and TP-TDS to be 2.95 eV and 3.08 eV, respectively (Fig. 6a, b). Accordingly, the Fermi level of “CS alveoli” is higher than that of TP-TDS. Upon intimate contact via Co-N/O coordination, electrons spontaneously transfer from “CS alveoli” to TP-TDS to equilibrate the Fermi levels, establishing a robust built-in electric field at the interface. The direction of this field points from TP-TDS (electron accumulation side) toward “CS alveoli” (electron depletion side)46,47. This ground-state charge redistribution is directly visualized by the calculated charge density difference (Fig. 6c), which shows clear electron accumulation on TP-TDS and depletion on “CS alveoli”, corroborating the UPS-deduced electron transfer direction. The strength of this interfacial field was quantified by Kelvin probe force microscopy (KPFM). A line-scan across the CT-35 interface reveals a sharp contact potential difference (CPD) of ~215.2 mV over a width of ~475 nm (Fig. 6d, Supplementary Fig. 33). This corresponds to a substantial built-in electric field strength of |E| ≈ 4.53 × 105 V m-1, providing a powerful, pre-existing driving force for charge separation. This built-in electric field governs charge separation across the heterojunction. Beyond the primary interfacial field, the unique marigold-like superstructure itself introduces an additional level of order that actively promotes directional charge transport. KPFM mapping across individual lamellar units reveals a well-defined internal potential gradient (Δ ≈ 14 mV) along the radially arranged petals (Supplementary Fig. 34). This secondary, intra-structure electric field functions as a built-in directional guide, efficiently channeling the initially separated electrons along the ultrathin lamellae directly toward the catalytic sites, thereby substantially minimizing random diffusion and bulk recombination losses. The synergistic integration of this multi-scale electric field architecture — which combines the strong interfacial field (primary driver) with the ordered intra-structure gradient (secondary director) — collectively ensures vectorial charge separation and rapid transport across the entire hierarchical system. The functional role of this field under operational conditions was captured by in-situ characterizations. In-situ KPFM under illumination shows a significant decrease in the interfacial CPD from 215.2 mV (dark) to 149.8 mV (light) (Fig. 6e, Supplementary Fig. 35). This reduction signifies a relative increase in electron density on the “CS alveoli” side, directly visualizing the light-induced, field-driven electron transfer. Most definitively, in-situ XPS under illumination provides atomically resolved chemical-state evidence (Fig. 6f-h). Upon irradiation, the Co 2p binding energy decreases, confirming electron accumulation on the Co sites within “CS alveoli”. Concurrently, the binding energies of N and O species increase, indicating electron depletion from the TP-TDS framework. These complementary shifts offer unambiguous spectroscopic proof that photogenerated electrons are driven from TP-TDS to the “CS alveoli” by the built-in electric field. The integration of static interfacial analysis (UPS, charge density difference, dark KPFM) with dynamic operando probes (in-situ KPFM, in-situ XPS) establishes a coherent and quantitative charge-transfer mechanism. The charge dynamics are governed by a multi-scale electric field architecture: first, a strong, pre-formed interfacial electric field, originating from Fermi-level equilibration, provides the primary driving force for charge separation; second, the ordered intra-structure potential gradient within the marigold-like superstructure acts as a directional guide, channeling the separated electrons efficiently toward the catalytic Co-S sites. This synergistic design ensures that photogenerated electrons are not only effectively separated but also rapidly and directionally transported from the light-harvesting TP-TDS to the catalytic centers in the “CS alveoli”, minimizing bulk recombination losses. This directed fast charge flow is the cornerstone of the efficient hydrogen evolution observed in CT-35.

Density functional theory (DFT) calculations provide fundamental insights into the electronic structure and reaction energetics of the system (the atomic coordinates of the optimized computational models are provided in Supplementary Data 1). The bare “CS alveoli” exhibits metallic character, while the TP-TDS COF has a computed band gap of 1.51 eV (Fig. 7a, b) － smaller than the experimental value of 2.08 eV — which is typical for the PBE functional due to its known tendency to underestimate band gaps.48 The projected density of states (PDOS) reveals that the electronic states near the Fermi level are overwhelmingly dominated by Co 3d and S 3p orbitals (Fig. 7c). This pinpoints the Co-S unit as the electronic origin of the catalytic activity. This functional role is structurally anchored by the preserved Co-S coordination motif, as independently confirmed by EXAFS. The reaction energetics provide independent and quantitative validation. The calculated hydrogen adsorption free energy (ΔG ) for the pristine TP-TDS COF is 0.76 eV, indicating excessively strong intermediate adsorbed hydrogen (H*) binding. In striking contrast, the “CS alveoli” unit exhibits a near-optimal ΔG of 0.53 eV (Fig. 7d), which thermodynamically favors efficient H release. These results suggest the Co-S moiety within the “CS alveoli” as the primary and superior active site for the hydrogen evolution reaction. Integrating all spectroscopic, electrochemical, and theoretical evidence, we propose a refined photocatalytic mechanism governed by atomically defined interfacial synergy within a multi-scale electric field architecture (Fig. 7e). The process is initiated by photoexcitation of the TP-TDS semiconductor. The favorable interfacial energy alignment (UPS) provides the thermodynamic driving force, while the strong, pre-formed interfacial electric field (primary driver, KPFM) directs the initial charge separation. The photogenerated electrons are then rapidly channeled through a dual pathway: (i) along the ordered intra-structure potential gradient (secondary director, KPFM) within the marigold-like lamellae, and (ii) across atomic-scale Co-N/O coordination bridges — whose formation is directly evidenced by XPS and EXAFS — toward the “CS alveoli”. DFT calculations are consistent with the interpretation that these bridges function not as new active sites but as essential electronic conduits and modulators, delivering and tuning the electron density at the Co-S catalytic center to lower the kinetic barrier for proton reduction (optimal ΔG ). Concurrently, the photogenerated holes are efficiently scavenged.

Collectively, this mechanism elucidates a cascaded synergy across scales: the Co-N/O bridges ensure directional charge delivery at the atomic level, while the Co-S sites provide optimized catalytic function at the molecular level, all housed within a biomimetic superstructure that maximizes light-harvesting and mass transport. Therefore, the exceptional performance of the “alveoli-on-lamina” architecture demonstrates a powerful design paradigm: the conscious integration of high-density atomic dispersion, atomic-scale charge-transfer highways, and biomimetic hierarchical structuring through precise interfacial engineering is a decisive strategy for constructing next-generation photocatalytic systems.

Methods
Reagents
Cobalt (II) nitrate hexahydrate (Co(NO ) ·6H O, 99.9%), 2-methylimidazole (2-MIM, 98%), methanol (CH OH, ≥ 99.9%), thiacetamide (TAA, 99%), absolute ethanol (C H OH, ≥ 99.8%), glacial acetic acid (CH COOH, ≥ 99.7%), 1, 4 dioxane (C H O , ≥ 99.5%), mesitylene (C H , 98%), tetrahydrofuran (C H O, ≥99.9%), acetone (C H O, ≥99.5%), ascorbic acid (C H O , ≥99%) and anhydrous sodium sulfate (Na SO , ≥99%) were purchased from Tianjin Zhiyuan Chemical Reagent Co., Ltd. 2, 4, 6- triformylphloroglucinol (TP, 97%), and 3, 7-diaminodibenzo [b,d] thiophene-5, 5-dioxide (TDS, 95%) were supplied by Aladdin and Shanghai Hao Hong biological medicine Technology Co., Ltd., respectively. All nitrates were lyophilized for 12 hours prior to use.

Synthesis of photocatalysts
Synthesis of ZIF-67 Precursor: ZIF-67 was synthesized according to a modified procedure. Typically, cobalt(II) nitrate hexahydrate (4 mmol, 0.73 g) was dissolved in 50 mL of methanol (denoted as Solution A), and 2-methylimidazole (16.9 mmol, 1.622 g) was separately dissolved in another 50 mL of methanol (denoted as Solution B). Both solutions were stirred individually for 10 minutes at room temperature. Subsequently, Solution A was rapidly poured into Solution B under vigorous stirring. The resulting mixture was stirred for an additional 30 minutes and then allowed to age statically at room temperature for 24 hours. The purple precipitate formed was collected by centrifugation, washed thoroughly with methanol (6 × 4 mL), and dried at 60 °C for 16 hours in air49.

Preparation of “CS Alveoli” derived from ZIF-67: The cobalt sulfide “CS alveoli” were synthesized via a solvothermal sulfurization of ZIF-67. In a typical procedure, ZIF-67 (0.34 g) and thioacetamide (TAA, 0.38 g) were dispersed in absolute ethanol (60 mL) under vigorous stirring for 30 minutes to form a homogeneous suspension. This suspension was then charged into a 100 mL Teflon-lined stainless-steel autoclave, which was sealed and maintained at 120 °C for 6 hours. After the reaction, the autoclave was allowed to cool naturally to room temperature. The resulting black product was collected by filtration, sequentially washed with deionized water and absolute ethanol (six times with 4 mL each), and finally dried at 60 °C overnight50.

Synthesis of TP-TDS COF: TP (0.08 mmol, 16.8 mg) and TDS (0.12 mmol, 29.6 mg) were added to a 10 mL Pyrex tube containing a mixed solvent of mesitylene (1.5 mL) and 1,4-dioxane (1.5 mL). Glacial acetic acid (6 M aqueous solution, 0.3 mL) was then added dropwise as a catalyst. After sonication for 10 min to achieve a homogeneous dispersion, the tube was purged with N for 15 min and sealed. The reaction mixture was heated at 120 °C in an oil bath for 3 days. After cooling to room temperature, the precipitate was collected by centrifugation and washed sequentially with tetrahydrofuran and acetone (three times each). The product was subsequently soaked in acetone for 24 h with solvent renewal every 5 h. Finally, the resulting red solid was dried at 60 °C for 12 h to obtain the TP-TDS COF.

Synthesis of CS@TP-TDS-x (CT-x) Heterojunctions: The CT-x heterojunctions were synthesized following a modified procedure based on the TP-TDS COF synthesis. In a typical process for CT-35, TDS (0.12 mmol, 29.6 mg) and pre-synthesized “CS alveoli” (35 mg) were first dispersed in 1,4-dioxane (1.5 mL) and stirred for 1 h. Then, TP (0.08 mmol, 16.8 mg) and mesitylene (1.5 mL) were added to the mixture. After stirring for an additional 20 min, glacial acetic acid (6 M aqueous solution, 0.3 mL) was introduced, followed by sonication for 10 min. Subsequent steps — N purging, sealing, solvothermal reaction at 120 °C for 3 days, cooling, product collection, washing with tetrahydrofuran/acetone, solvent soaking, and drying at 60 °C — were performed analogously to the TP-TDS COF synthesis. Products with different “CS alveoli” loadings (15, 25, 35, or 45 mg) were similarly prepared and are denoted as CT-x, where x represents the mass (in mg) of “CS alveoli” used.

Synthesis of control samples: To elucidate the specific roles of the interfacial coordination bonds and synthesis pathway, the following control samples were prepared:
CS-NH : The synthesis was halted after stirring TDS with “CS alveoli” in 1,4-dioxane for 1 h. The black intermediate was collected by centrifugation, washed six times with ethanol, and dried overnight at 60 °C.
CoCl @TP-TDS: This sample was prepared following the CT-35 procedure but with “CS alveoli” replaced by an an equal mass of CoCl .
Milled CT-35: Pre-synthesized “CS alveoli” (35 mg) and TP-TDS COF were manually ground together in a mortar for 20 min to achieve physical mixing without chemical bonding.
Milled CoCl /TP-TDS: Pre-synthesized TP-TDS COF and CoCl powder (35 mg) were manually ground together in a mortar for 20 min.
These two milled samples were synthesized exclusively via physical mixing, physical proximity while deliberately avoiding the solvothermal conditions required for coordination chemistry to occur.
Traditional CT-35: “CS alveoli” (35 mg), TP (0.08 mmol, 16.8 mg), and TDS (0.12 mmol, 29.6 mg) were directly mixed in a solvent mixture of mesitylene (1.5 mL) and 1,4-dioxane (1.5 mL). After sonication to dissolve the organic precursors and disperse the “CS alveoli”, glacial acetic acid (6 M aqueous solution, 0.3 mL) was added. The subsequent steps (sonication, N purging, sealing, solvothermal reaction, washing, and drying) were identical to those described in the section for the synthesis of TP-TDS COF.

Measurement of Photocatalytic Hydrogen Evolution
Photocatalytic hydrogen evolution reactions were performed in a 100 mL three-neck quartz reactor containing 50 mL of an aqueous ascorbic acid solution (0.1 M, pH = 2.5) as a sacrificial agent. Catalyst (2 mg) was dispersed in the solution via ultrasonication for 20 minutes. The system was then purged with N for 40 minutes to completely remove air. The reaction was carried out under visible light irradiation (300 W Xe lamp with a 420 nm cutoff filter) and simulated sunlight (AM 1.5G) with continuous stirring. The intensity was calibrated to 100 mW/cm2 at the sample position using a certified silicon photodiode power meter (CEL-FZ-A, Beijing Zhongjiaojinyuan Technology Co., Ltd.). The evolved hydrogen gas was quantified using an on-line gas chromatograph (GC-7900, TCD detector, N carrier gas). The CT-35 sample, which exhibited the highest photocatalytic activity, was selected for stability testing by repeating the reaction over ten consecutive cycles.We calculated the apparent quantum yield (AQY) of the samples as follows:
number of product obtained
AQY (%) = × 100%
number of incident photons
= 
np× NA
× 100%
P × S × t × λ
h × c
= 
np × NA × h × c
× 100%
P × S × t × λ
where n is the mole number of product obtained (mol), N is the Avogadro constant (6.022 × 1023 mol−1), P is the optical density (W cm-2), S is the light irradiation area (cm2), t is the light irradiation time (s), λ is the monochromatic light wavelength (m), h is Planck’s constant (6.626 × 10−34 J s), and c is the speed of light (3 × 108 m s−1).

(Photo)electrochemical Measurements
(Photo)electrochemical analyses, including electrochemical impedance spectroscopy (EIS) and photocurrent response (i-t) measurements, were conducted on an electrochemical workstation using a standard three-electrode system. A Pt plate and an Ag/AgCl electrode (0.197 V vs. NHE) served as the counter and reference electrodes, respectively. The i-t measurements were performed at a constant applied potential of 0.60 V vs. Ag/AgCl, and the applied potential was iR-corrected automatically by the workstation. All potentials in this study have been converted to the reversible hydrogen electrode (RHE) scale for consistency with the literature. The conversion was performed using the equation: E = E + 0.059 × pH + E , where E = 0.197 V vs. NHE. With the electrolyte pH of 6.8 ± 0.1, the conversion factor is approximately +0.60 V. The working electrode was prepared by dispersing 5 mg of the photocatalyst in a mixture of 0.25 mL ethanol, 0.25 mL ethylene glycol, and 0.04 mL Nafion solution, followed by sonication for 1 hour. The resulting suspension was drop-cast onto conductive glass and dried at 60 °C for 12 hours. Measurements were performed in 0.5 M Na SO (pH = 6.8 ± 0.1) electrolyte under simulated sunlight (AM 1.5G, 100 mW cm-2) where applicable.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This manuscript proposes a biomimetic \"alveoli-on-lamina\" structure, which uses \"CS alveoli\" to accommodate high-density active sites and acts as an efficient photothermal nano-reactor, thereby significantly improving the HER performance under Pt-free conditions. However, the explanations regarding the structure-activity relationship and the transfer mechanism of photogenerated electrons/holes seem to lack sufficient evidence and description. I suggest that this manuscript would benefit from substantial revisions, followed by resubmission for further consideration.\n1. The title is cumbersome. It is suggested to remove \"534.6 mmol g-1 h-1\". This information is not appropriate to be included in the title.\n2. In Figure 1f, the author mentions that the same daisy-like morphology indicates the formation of Co-N/O coordination. However, the macroscopic morphology control seems insufficient to explain the role of Co-site coordination. Please provide other supporting information to demonstrate the connection between Co-site coordination and structure control.\n3. Please remove the \"AC\" from \"AC-HAADF-STEM\". The author did not obtain clear atomic phases using STEM with aberration correction.\n4. In page 9, Please remove the sentence \"but also significantly enhances charge carrier dynamics.\" This part is a structural characterization and cannot lead to any conclusions regarding the dynamics.\n5. The N 1s XPS spectra (Fig. 2b) of TP-TDS show small zigzags in the contour line between 402-404 eV, which seems not to occur during the fitting process. Please explain this. Additionally, the Co 2p XPS spectra (Fig. 2a) have too many noise points. Please provide more clear and reliable data.\n6. Page 11: “As shown in Fig. 2d……indicating a unique coordination geometry consistent with atomically dispersed Co sites”. The coordination form in atomically dispersion cannot be determined by XANES analysis. It needs to be judged based on the r-space of EXAFS. Please revise this part.\n7. In Table S2, the bond distance is 2.06 Å. However, the author mentioned in the manuscript that the bond length is 1.65 Å. Please confirm this again.\n8. The authors claim that these atomic-scale structural features drives the exfoliation into lamellae and establishes electron-transfer pathways. Please provide sufficient evidence to support this viewpoint.\n9. The author claims that the marigold petal-like superstructures can facilitate directional and rapid electron transfer. Please provide sufficient evidence or diagrams.\n10. The Eb values of TP-TDS and CT-35 are not significantly different. Is such a close numerical difference sufficient to indicate the difference in the intensity of carrier interactions?\n11. The author states that the changes in the in-situ XPS spectra imply that the light excitation accelerated the interface electron transfer from TP-TDS to \"CS alveoli\". Please provide sufficient evidence to demonstrate the connection between the binding energy and the electron transfer during HER.\n12. Please provide the structural model of the transition state for TP-TDS in HER (showing the adsorption and desorption process of H).\n13. In the introduction section, please enhance the description of the advantages of COF/MOF photocatalysis. Such as: 10.1002/adma.202504808; 10.1021/jacs.3c07047; 10.1039/D4QI01578A.\n14. Some formatting issues: (1) The font in Figure 2 is somewhat compressed. Please re-adjust and re-layout it to make the entire picture more aesthetically pleasing. (2) The proportions in Figure 6f need to be adjusted to make the combination with the other pictures more aesthetically pleasing.", "reviewer_2": "Title: High-density atomically dispersed cobalt sites anchored on biomimetic alveoli-engineered COF laminae drive Pt-free solar H2 production with a rate of 534.6 mmol g-1 h-1\nThis manuscript presents a highly innovative and meticulously characterized study on a biomimetic photocatalytic architecture. The reported hydrogen evolution performance is exceptional and would be of significant interest to the readership of Nature Communications. The work is generally well-executed and supported by extensive characterization. However, several key points require clarification and additional evidence to fully substantiate the authors' claims and strengthen the manuscript to the high standard expected for this journal.\n1.While AC-HAADF-STEM beautifully confirms atomic dispersion, the term \"high-density\" requires quantitative support.\n2.The authors have provided evidence for the presence of Co-N/O bonds in the final CT-35 composite. However, to unequivocally demonstrate that these bonds represent newly formed coordination between the “CS alveoli” and the TP-TDS COF—rather than partially retaining the original Co-N coordination from the ZIF-67 precursor—a more quantitative analysis of the cobalt coordination environment is necessary.\n3.The localized heating effect is proposed as a key synergistic mechanism. To quantify its specific contribution to the record H2 evolution rate, a control experiment is highly recommended.\n4.The UPS/XPS data provide excellent indirect evidence for interfacial electron transfer. However, more direct proof of light-induced spatial charge separation across the heterojunction would significantly strengthen the mechanism discussion.\n5.The claim of coordination-induced exfoliation, transforming the morphology from a “coral polyp-like” network to “marigold-like petals”, is primarily supported by representative SEM images. To make this argument more statistically robust, a quantitative analysis of the COF lamellae thickness is necessary.\n6.The authors use the CoCl2@TP-TDS control sample to convincingly argue that cobalt species are essential for inducing the morphological transformation from a 3D coral-like network to 2D marigold-like petals. This is a well-designed experiment. However, to definitively rule out the possibility that this transformation is simply caused by the physical adsorption or intercalation of Co2+ ions (rather than the formation of specific Co-N/O coordination bonds), a supplementary control experiment is necessary.\n7.The introduction highlights the merits of dibenzothiophene-S,S-dioxide (TDS) for its rapid hole transfer. However, in the heterojunction, the “CS alveoli” are the proposed electron acceptors and HER sites. What is the specific advantage of using TDS-based COF over other COFs with similar light absorption but different electronic properties? A control experiment with a different COF would help isolate the contribution of the specific COF electronic structure.\n8.The BET data shows an increase in the pore size of CT-35 (4.9 nm) compared to pristine TP-TDS (3.5 nm), which the authors attribute to a \"pillaring effect\" from the CS alveoli. This is a reasonable hypothesis. To provide direct structural evidence for this claim, I recommend performing layer spacing measurements via high-resolution TEM (HRTEM) on the exfoliated COF lamellae in CT-35.", "reviewer_3": "The manuscript presents a novel biomimetic \"alveoli-on-lamina\" heterostructure based on a COF and ZIF-67-derived cobalt sulfide for photocatalytic hydrogen evolution. The reported HER rate of 534.6 mmol g⁻¹ h⁻¹ and AQY of 90.2% are exceptionally high and, if robustly substantiated, would be of significant interest to the field. The multi-faceted characterization to prove atomic dispersion and interfacial bonding is a strength. However, several major concerns regarding the experimental methodology, data interpretation, and claims must be addressed before the manuscript can be considered for publication.\n1. The concentration of the sacrificial agent (ascorbic acid, SA) is not stated. The performance of a photocatalyst is highly dependent on the concentration and type of sacrificial agent. This information is critical for comparing the activity with other systems in the literature. Furthermore, the pH of the reaction solution, which can drastically influence the HER kinetics, is not mentioned. The light source intensity (in mW/cm²) should also be provided and calibrated.\n2. The claim of a significant photothermal effect (reaching 144.1°C) is intriguing but requires more rigorous proof. The IR thermal image (Fig. 4f) shows the temperature of the solid catalyst under light in air, which may not reflect the actual temperature at the solid-liquid interface within the aqueous reaction mixture. The bulk solution temperature during catalysis must be measured and reported to substantiate the claim that localized heating is a major contributor to the performance.\n3. To decouple the photothermal effect from the electronic effects (charge separation), a control experiment should be performed where the reaction is conducted under external heating to the claimed localized temperature (~144°C) in the dark. If the HER rate under these conditions is negligible, it would confirm that the photothermal effect primarily serves to lower the activation barrier rather than drive the reaction thermally, strengthening the \"photocatalytic\" claim.\n4. While the AC-HAADF-STEM images (Fig. 1h,i) show isolated Co atoms, the fields of view are limited. To convincingly demonstrate \"high-density\" atomic dispersion throughout the entire CT-35 composite, larger-area HAADF-STEM images and corresponding elemental maps are needed to rule out the presence of any Co-based clusters or nanoparticles that are not shown.\n5. The term \"biomimetic alveoli\" is used extensively. The analogy to lung alveoli, based on hollow structures for gas exchange, is interesting. However, the manuscript should more clearly articulate the specific structural and functional parallels beyond the simple \"hollow cavity\" morphology to justify the use of this strong biomimetic claim.\n6. The \"CS alveoli\" are claimed to be the primary active site based on DFT calculations (optimal ΔG_H*). However, the EXAFS data (Fig. 2e, S7) indicates the Co in CT-35 is coordinated with N/O, suggesting the Co electronic structure is significantly altered from the pristine Co₃S₄. The authors should discuss whether the active site is the original Co in the sulfide or the newly formed Co-N/O moiety. The proposed mechanism (Fig. 6f) oversimplifies this.\n7. The stability test (Fig. 3g) is commendable. However, post-recycling characterization should be more comprehensive. ICP-OES analysis of the reaction solution after cycling should be performed to check for Co and S leaching. Additionally, XPS or XAFS on the used catalyst would provide critical information on whether the atomic-level coordination environment (Co-N/O) remains intact after prolonged irradiation and exposure to the reaction medium.\n8. The KPFM data (Fig. 5c,d) shows a contact potential difference, but a more quantitative analysis of the surface potential shift at the interface would strengthen the claim of efficient charge transfer. Furthermore, the in-situ XPS data under illumination is mentioned but not shown; this critical data should be presented in the main text or supplementary information to directly support the proposed light-induced charge redistribution.\n9. The quality of some schematics (e.g., Scheme 1, 2) could be improved for a journal of this caliber.\n10. The text on pages 6-7 contains a large block of seemingly random numbers, which appears to be a formatting error and must be corrected.\nThe description of the DFT-calculated band gap for TP-TDS should explicitly acknowledge the known limitation of the PBE functional to manage reader expectations.\nThe work presents a potentially groundbreaking photocatalytic system. However, the major concerns listed above, particularly regarding the experimental details and the evidence for the proposed mechanisms, must be thoroughly addressed. Additional control experiments and more rigorous data are required to fully support the extraordinary claims and to meet the high standard of proof expected for Nature Communications."}, "author_response": "We thank the reviewer for this excellent suggestion. We agree that a concise and clear title is more appropriate for Nature Communications. Accordingly, we have revised the title by removing the specific numerical value as suggested. The new title is now more streamlined and focuses on the core discovery of our work (see page 1).\n2. In Figure 1f, the author mentions that the same daisy-like morphology indicates the formation of Co-N/O coordination. However, the macroscopic morphology control seems insufficient to explain the role of Co-site coordination. Please provide other supporting information to demonstrate the connection between Co-site coordination and structure control.\nResponse: We agree that morphological similarity alone cannot conclusively establish the formative role of atomic-level coordination bonds. Our initial comparison with the in-situ synthesized CoCl @TP-TDS control sample was indeed indicative but not definitive in isolating coordination bonding as the key structural determinant. To address this unambiguously, we have designed and performed a decisive control experiment specifically aimed at decoupling the effects of in-situ coordination bond formation from those of simple physical mixing. We prepared two additional control samples under conditions that preclude coordination bond formation: (1) milled CoCl /TP-TDS: prepared by grinding pre-synthesized TP-TDS COF with CoCl powder; (2) milled CT-35: prepared by grinding pre-synthesized TP-TDS COF with pre-synthesized CS powder.\nThese samples were synthesized exclusively via physical mixing (solid-state grinding for 20 minutes), physical proximity while deliberately avoiding the solvothermal conditions required for coordination chemistry to occur. They were systematically compared with the original in-situ synthesized samples.\n(1) Morphological Analysis (SEM): As shown in (Fig. 1a-b), both physically mixed samples exhibit only featureless, irregular aggregates, completely lacking any defined morphology. In stark contrast, the in-situ synthesized CoCl @TP-TDS (Fig. 1c) and the CT-35 catalyst (Fig. 1d) both display well-defined marigold-like structures. This stark morphological contrast demonstrates that the well-defined marigold-like superstructure is not a trivial consequence of physical mixing, but arises specifically from the in-situ coordination-directed assembly process during synthesis.\n(2) Chemical State Analysis (XPS): As presented in Fig. 2, the XPS spectra of the milled CT-35 sample show no characteristic peaks for Co-N/O coordination bonds. These signature peaks are present exclusively in the samples where in-situ coordination synthesis was possible. This provides direct proof that the intended atomic-scale Co-N/O coordination bonds are exclusively formed under specific synthesis conditions and are essential for the development of the distinct morphology.\n(3) Microstructure and Layer Thickness Analysis (AFM): To probe the origin of the structural differences, we performed AFM measurements (Fig. 3). In-situ synthesized CT-35: Forms ultrathin lamellae with a uniform thickness of only ~6.4 nm, indicating highly ordered exfoliation and assembly. Milled CT-35: Appears as highly irregular aggregates with large thickness variations, featuring a typical height of ~132.7 nm. The order-of-magnitude difference (approximately 20-fold) in structural order and thickness quantitatively confirms that the precise exfoliation and ordered assembly of the COF lamellae in CT-35 are exactly mediated by the coordination bonds formed in-situ, not by physical interactions.\n(4) Atomic Local Structure Analysis (EXAFS): As indicated by the EXAFS fitting parameters in Table 1, atomic-scale Co-N/O coordination bonds are unambiguously confirmed in CT-35 (the coordination number is fitted to be 0.7 ± 0.4). This distinct coordination environment is absent in the pristine CS sample. This provides the ultimate, atomic-scale confirmation of the coordination structure at the Co sites in the target catalyst, offering the fundamental explanation for all the macro- and microscopic observations described above. The value of ~0.7, while lower than typical integer values for bulk coordination complexes, is highly significant in this context. It definitively confirms the presence of a distinct, ordered Co-N/O coordination environment in CT-35, which is entirely absent in the pristine CS control sample. The non-integer CN likely reflects the heterogeneous and potentially defective nature of the coordination sites within the porous COF framework, where not all Co atoms are identically coordinated, or some may be partially accessible/unsaturated. Critically, this fitted parameter is derived from a clearly identifiable peak in the Fourier-transformed EXAFS spectrum of CT-35 that is absent in the controls, confirming the formation of the coordination structure.\nIn summary, these targeted experiments establish a clear causal relationship: The development of the hierarchical marigold-like superstructure is strictly dependent on the in-situ formation of Co-N/O coordination bonds during synthesis. These bonds act as indispensable structure-directing agents, orchestrating cross-scale assembly from atomic coordination to macroscopic morphology.\nWe have revised the manuscript to incorporate these critical findings and to clarify the formative role of coordination bonding, moving beyond mere correlation to establishing causation. We are grateful for the reviewer's comment, which has significantly strengthened this aspect of our work. (see page 6, 9-11 in the revised manuscript and Fig. S2-5, S12, Table S4 in the SI)\nFig.1 The SEM of (a) milled CT-35 and (b) milled CoCl /TP-TDS; (c) CoCl @TP-TDS and (d) CT-35\nFig.2 The XPS of (a) CS; (b) milled CT-35 and (c) CT-35.\nFig. 3 AFM height sensor images of (a) the TP-TDS, (c) CT-35 and (f) milled CT-35; The corresponding profile spectra of (b) the TP-TDS, (e) CT-35 and (h) milled CT-35; Corresponding amplitude images (d) CT-35 and (g) milled CT-35.\nFig.4 (a) XANES spectra; (b) Fourier transformation of Co K-edge EXAFS spectra in R space of CS, CT-35 and reference samples (Co-foil, CoO, CoPc, CoS).\nTable 1. EXAFS fitting parameters at the Co K-edge for various samples. (Ѕ 2=0.75)\nSample Shell CNa R(Å)b σ2(Å2)c ΔE (eV)d R-range/Å R factor\n0\nCS Co-S 4.0±0.3 2.24±0.01 0.0054 -1.4±2.1 3.0-10.3 1.0-2.3 0.0135\nCo-N/O 0.7±0.4 1.95±0.06 0.0002\nCT-35 -4.2±0.9 3.0-10.3 1.0-3.0 0.0096\nCo-S 3.9±0.4 2.25±0.02 0.0029\naN: coordination numbers; bR: bond distance; cσ2: Debye-Waller factors; d ΔE : the\n0\ninner potential correction. R factor: goodness of fit.\n3. Please remove the “AC” from “AC-HAADF-STEM”. The author did not obtain clear atomic phases using STEM with aberration correction.\nResponse: We thank the reviewer for this critical and correct observation. We sincerely apologize for the oversight in our initial description. The reviewer is absolutely right that the images we obtained did not achieve the resolution necessary to resolve clear atomic phases. Therefore, to ensure the technical accuracy of our manuscript, we have followed the reviewer’s suggestion and removed the “AC” prefix from all instances in the text and figures. The technique is now correctly referred to as HAADF-STEM (see page 6-7 in the revised manuscript and page 9 in the SI).\n4. In page 9, Please remove the sentence “but also significantly enhances charge carrier dynamics.” This part is a structural characterization and cannot lead to any conclusions regarding the dynamics.\nResponse: We agree with the reviewer’s valid point. The mentioned sentence in the structural characterization section did overreach by implying a direct conclusion about charge carrier dynamics, which should be supported by subsequent experimental evidence. To maintain logical rigor and ensure that claims are appropriately supported by the data at hand, we have removed the indicated sentence (see page 6 in the revised manuscript).\n5. The N 1s XPS spectra (Fig. 2b) of TP-TDS show small zigzags in the contour line between 402-404 eV, which seems not to occur during the fitting process. Please explain this. Additionally, the Co 2p XPS spectra (Fig. 2a) have too many noise points. Please provide more clear and reliable data.\nResponse: We are grateful to the reviewer for the thorough assessment of our XPS data quality. In response to the comments, we have completely re-measured the N 1s and Co 2p XPS spectra under optimized experimental conditions. The new data, now presented in the revised manuscript as Fig. 5, show significant improvements in both spectral quality and fitting reliability. For the N 1s region, the previously observed irregular baseline features between 402-404 eV have been eliminated in the new measurements. The current spectrum displays a smooth baseline that allows unambiguous peak fitting and chemical state identification. For the Co 2p region, we have obtained data with substantially improved signal-to-noise ratio, enabling clear resolution of the Co 2p and Co 2p spin-orbit components along with their satellite 3/2 1/2 features. The high-quality data confirm our original assignment of chemical states while providing more robust support for the proposed coordination environment. We thank the reviewer for suggesting these important improvements, which have strengthened the evidence presented in our study (see Fig. 2a-b in the revised manuscript).\nFig. 5 The XPS of (a) Co 2p; (b) N1s.\n6. Page 11: “As shown in Fig. 2d……indicating a unique coordination geometry consistent with atomically dispersed Co sites”. The coordination form in atomically dispersion cannot be determined by XANES analysis. It needs to be judged based on the r-space of EXAFS. Please revise this part.\nResponse: We sincerely thank the reviewer for pointing out this imprecision in our XANES analysis. The reviewer is correct that detailed coordination geometry (e.g., bond distance, coordination number) is primarily derived from the R-space fitting of EXAFS data, while XANES is more sensitive to electronic structure and average oxidation state.\nTo address this, we have revised the text on Page 9-10 (red section). The original statement, which overinterpreted the XANES data, has been removed. The discussion now more accurately frames the XANES findings as follows:\n“Critically, the Fourier-transform EXAFS spectrum shows no detectable Co-Co coordination path (Fig. 2d, Table S4), providing definitive bulk-sensitive evidence that Co species exist in an atomically dispersed state, consistent with the STEM observations. Quantitative fitting of the EXAFS data reveals the precise local structure: the Co center in CT-35 maintains a primary coordination shell of S atoms (Co-S coordination number, CN = 3.9 ± 0.4; bond distance, R = 2.25 ± 0.02 Å), analogous to pristine “CS alveoli”. Concurrently, a distinct secondary coordination shell corresponding to Co-N/O bonds is identified (CN = 0.7 ± 0.4; R = 1.95 ± 0.06 Å). This non-integer CN reflects the heterogeneous yet definitive presence of these interfacial linkages. Wavelet-transform analysis further validates the atomic dispersion of Co and the specific coordination geometry32 (Fig. 2e-f).”\nThis revision ensures that the claims made from each technique are technically accurate and appropriately supported. We thank the reviewer again for helping us improve the rigor of our discussion.\n7. In Table S2, the bond distance is 2.06 Å. However, the author mentioned in the manuscript that the bond length is 1.65 Å. Please confirm this again.\nResponse: We thank the reviewer for this careful observation regarding the bond distances. The apparent discrepancy arises from the distinction between the apparent distance in the Fourier-transformed (FT) spectrum and the actual fitted bond length. The value of ~1.65 Å is the apparent distance from the phase-uncorrected FT-EXAFS spectrum. Due to the photoelectron scattering phase shift, this value is consistently shorter than the true bond distance. In contrast, the value of 2.06 Å provided in Table S2 is the actual Co-N/O bond length obtained from the quantitative EXAFS fitting procedure, which applies the necessary phase correction to yield accurate distances. This is a standard practice in EXAFS analysis [1-4].\nTherefore, the data in the manuscript and SI are correct and self-consistent; the two values represent different stages of the standard EXAFS data processing pipeline. We have added a clarifying note to Table S4 in the revised SI to prevent any potential misunderstanding for readers.\nBuilding upon this valuable discussion and to ensure the utmost clarity and rigor, we took the opportunity to re-measure and perform a more comprehensive quantitative EXAFS analysis to ensure the highest data quality (Fig. 6 and Table 2). The renewed fitting for the CT-35 sample reveals a more nuanced local coordination environment. The Co center maintains a primary coordination shell of S atoms with a coordination number (CN) of 3.9 ± 0.4 and a bond distance (R) of 2.25 ± 0.02 Å. A secondary coordination shell is also identified, corresponding to Co-N/O bonds with a CN of 0.7 ± 0.4 and R = 1.95 ± 0.06 Å. This refined analysis provides a precise quantitative description of the local atomic structure around the Co center in the hybrid material. We have updated the manuscript with this improved EXAFS discussion and the new fitting parameters to reflect the enhanced rigor of our analysis.\nWe are grateful for the reviewer’s comment, which has strengthened the structural characterization in our work.\nFig. 6 (a) Co K-edge XANES spectra and (b) Fourier transformation of Co K-edge EXAFS spectra in R space of CS, CT-35 and the reference samples (Co-foil, CoO, CoPc, CoS).\nTable 2 EXAFS fitting parameters at the Co K-edge for various samples（Ѕ 2=0.75）\nSample Shell CNa R(Å)b σ2(Å2)c ΔE (eV)d R factor\n0\nÅ-1 Å\nCo foil Co-Co 12* 2.49±0.01 0.0062 7.1±0.3 3.0-12.3 1.0-3.0 0.0006\nCS Co-S 4.0±0.3 2.24±0.01 0.0054 -1.4±2.1 3.0-10.3 1.0-2.3 0.0135\nCo-N/O 0.7±0.4 1.95±0.06 0.0002\nCT-35 -4.2±0.9 3.0-10.3 1.0-3.0 0.0096\nCo-S 3.9±0.4 2.25±0.02 0.0029\naCN: coordination numbers; bR: bond distance; cσ2: Debye-Waller factors; d ΔE : the\n0\ninner potential correction. R factor: goodness of fit. Error bounds that characterize the structural parameters obtained by EXAFS spectroscopy were estimated as CN±20%; R ± 1%; σ2 ± 20%.\n* The apparent bond distance obtained directly from the Fourier-transformed EXAFS spectrum is phase-uncorrected and therefore shorter than the true bond length due to the photoelectron scattering phase shift. The accurate bond length, as reported in the fitting results table, is derived from phase-corrected EXAFS fitting, which is a standard practice for accurate structural determination\nReference:\n1 .Jiang, M. et al. Floatable organic-inorganic hybrid-TiO unlocks superoxide 2 radicals for plastic photoreforming in neutral solution. Nature Communications 16 (2025). https://doi.org/10.1038/s41467-025-59467-x\n2. Lee, W. H. et al. Polymeric stabilization at the gas–liquid interface for durable solar hydrogen production from plastic waste. Nature Nanotechnology 20, 1237-1246 (2025). https://doi.org/10.1038/s41565-025-01957-6\n3. Qiu, F. et al. Nickel-catalysed deuteration of benzylic C(sp3)–H bonds using D O. 2 Nature Synthesis 4, 1141-1150 (2025). https://doi.org/10.1038/s44160-025-00816-5\n4. Si, S. et al. Selective photoelectrochemical synthesis of adipic acid using single-atom Ir decorated α-Fe O photoanode. Nature Communications 16 (2025). 2 3 https://doi.org/10.1038/s41467-025-60506-w\n8. The authors claim that these atomic-scale structural features drives the exfoliation into lamellae and establishes electron-transfer pathways. Please provide sufficient evidence to support this viewpoint.\nResponse: We thank the reviewer for this important request for evidence linking atomic-scale coordination to the observed exfoliation and electronic properties. Our claim is supported by a clear mechanistic chain of evidence, from atomic bonding to nanoscale morphology and, finally, to macroscopic charge transport functionality.\n(1) Evidence for Coordination-Driven Exfoliation into Lamellae\nThe formation of atomic-scale Co-N/O coordination bonds, as confirmed by XAFS (Fig. 7a-b) and XPS (Fig. 7c-e), functions as both a structural modifier and an exfoliation driver. This role is directly and quantitatively demonstrated by AFM measurements (Fig. 8). In the CT-35 sample, where these coordination bonds are present, well-defined lamellae with a uniform thickness of ~6.4 nm are observed (Fig. 8c-e). This represents an order-of-magnitude reduction compared to the much thicker pristine TP-TDS (~71.5 nm, Fig. 8a-b). In stark contrast, the milled CT-35 control sample — which lacks properly formed coordination bonds — exhibits only irregular aggregates with large height variations (~132.7 nm, Fig. 8f-h). This clear dichotomy establishes that the in-situ formed coordination bonds are essential and sufficient for the controlled exfoliation into thin lamellae, thereby creating the nanoscale architecture necessary for efficient charge transport.\n(2) Evidence for Established Electron-Transfer Pathways\nTo directly demonstrate the establishment of efficient electron-transfer pathways by the atomic-scale coordination, we performed functional photoelectrochemical measurements. As shown in Fig. 9, CT-35 exhibits a significantly enhanced and stable photocurrent density compared to the milled control sample. This marked performance difference provides decisive functional evidence: the coordination network in CT-35 creates effective pathways that facilitate charge carrier generation, separation, and transport — processes that are severely hindered in the control sample lacking proper coordination. While time-resolved photoluminescence (TR-PL) analysis of the nearly non-emissive milled control was not feasible, the photocurrent response serves as a more direct and quantitative probe of the net electron-transfer outcome in operating conditions. The dramatic enhancement in CT-35 therefore unequivocally confirms that the Co–N/O coordination bonds not only drive structural exfoliation but also establish the essential electronic highways for efficient charge transfer.\nIn summary, the combination of atomic-scale spectroscopy (XAFS/XPS), nanoscale morphology quantification (AFM), and macroscopic functional testing (photocurrent) provides a coherent and multi-faceted evidence chain. It demonstrates that the Co-N/O coordination bonds (1) drive the exfoliation into thin lamellae and (2) concurrently establish efficient electron-transfer pathways within the resulting architecture, leading to the observed superior photoelectrochemical performance.\nWe believe this evidence robustly supports our proposed mechanism and have clarified this point in the revised manuscript (see page 7, 9-11 in the revised manuscript and Fig. S4-5, S12-18 in the SI).\nFig. 7 (a) XANES spectra; (b) Fourier transformation of Co K-edge EXAFS spectra in R space. The XPS of (c) CS; (d) milled CT-35 and (e) CT-35.\nFig. 8 AFM height sensor images of (a) the TP-TDS, (c) CT-35 and (f) milled CT-35; The corresponding profile spectra of (b) the TP-TDS, (e) CT-35 and (h) milled CT-35; Corresponding amplitude images (d) CT-35 and (g) milled CT-35.\nFig. 9 Transient photocurrent responses.\n9. The author claims that the marigold petal-like superstructures can facilitate directional and rapid electron transfer. Please provide sufficient evidence or diagrams.\nResponse: We thank the reviewer for raising this critical point regarding the functional role of the unique morphology. We agree that explicit evidence linking the marigold petal-like superstructure to directional and rapid electron transfer is essential. Our claim is supported by a combination of morphological, electrical, photophysical, and functional measurements that collectively delineate this structure-function relationship:\n(1) Structural Basis for Efficient Transfer: The superstructure is composed of ultrathin, radially arranged lamellae (6.4 nm thick, AFM Fig. 10a-c). This architecture inherently provides short and ordered pathways for electron transport, minimizing diffusion distances and random scattering — a prerequisite for both rapid and directional movement.\n(2) Multi-Scale Electric Field Architecture for Vectorial Charge Transport:\nImportantly, the unique marigold-like superstructure itself introduces an additional level of order that actively promotes directional charge transport. Kelvin probe force microscopy (KPFM) mapping across individual lamellar units reveals a well-defined internal potential gradient (Δ ≈ 14 mV) along the radially oriented “petals” (Fig. CPD 10d-g). This secondary, intra-structure electric field functions as a built-in directional guide, efficiently channeling the photogenerated electrons along the ultrathin lamellae directly toward the catalytic active sites. As a result, random diffusion and bulk recombination losses are substantially minimized. The synergistic integration of this multi-scale electric-field architecture — which combines the strong interfacial field (primary driver) with the ordered intra-structure gradient (secondary director) — collectively ensures highly efficient vectorial charge separation and rapid transport across the entire hierarchical system.\n(3) Quantitative Evidence for Rapid Charge Transfer Kinetics: Electrochemical impedance spectroscopy (Fig. 11a) provides direct quantitative support. The Nyquist plot of CT-35 exhibits a significantly smaller semicircle diameter than the control sample milled CT-35, indicating a dramatically lower charge-transfer resistance (R ). ct This reduction in interfacial resistance quantitatively confirms that the superstructure enables greatly accelerated electron transfer kinetics at the electrode/electrolyte interface.\n(4) Evidence for Suppressed Bulk Recombination: Time-resolved photoluminescence (TR-PL, Fig. 11b) shows that CT-35 exhibits a significantly extended charge carrier lifetime (4.43 ns) compared to its individual components (CS: 0.20 ns; TP-TDS: 0.49 ns). This orders-of-magnitude increase indicates that electron extraction and transfer within the integrated superstructure far outpace recombination, a direct consequence of the efficient pathways it provides.\n(5) Macroscopic Functional Validation: The photocurrent response (Fig. 11c) provides the ultimate functional proof. CT-35 generates a significantly higher and stable photocurrent compared to the disordered milled control, directly corroborating the efficient charge collection enabled by the synergistic effects above.\nThus, the marigold-like morphology creates radially aligned, ultrathin lamellae → establishes a multi-scale electric field architecture (interfacial + intra-structure) for synergistic, directional charge separation and transport → results in accelerated interfacial charge transfer (low R ) and suppressed bulk recombination (long τ) → ct culminates in significantly enhanced photocurrent output. This complete progression of evidence, from nanoscale morphology and multi-scale charge kinetics to macroscopic function, robustly supports our claim. We have strengthened this discussion in the revised manuscript as suggested (see page 7, 11, 17-18, Fig. 1g-h, Fig 3a in the revised manuscript and Fig. S4, S18-19 and S33 in the SI).\nFig. 10 (a) AFM height sensor image, (b) corresponding amplitude image and (c) the correspond line profile spectrum of the CT-35 sample; (d) KPFM height sensor image, (f) surface potential image and (e, g) the correspond line profile spectra of CT-35 sample.\nFig. 11 (a) Electrochemical impedance spectroscopy (EIS) Nyquist plots, (b) time-resolved photoluminescence (TR-PL) decay spectra and (c) Transient photocurrent responses\nFig. 12 Schematic illustration of the proposed photocatalytic mechanism for H 2 evolution over CT-x\n10. The Eb values of TP-TDS and CT-35 are not significantly different. Is such a close numerical difference sufficient to indicate the difference in the intensity of carrier interactions?\nResponse: We sincerely thank the reviewer for this insightful comment, which prompted us to re-examine our data. The reviewer is correct that the originally reported Eb values were too similar to conclusively indicate a difference in carrier interactions. Upon careful re-measurement, we have determined the accurate Eb value for CT-35 to be 34.9 meV (Fig. 13). We have updated all figures and data in the manuscript accordingly and apologize for the initial error. This revised value represents a ~52% reduction in Eb compared to TP-TDS, which is highly significant in exciton physics. It indicates a fundamental weakening of Coulombic interactions in CT-35, facilitating more efficient exciton dissociation into free charges. This conclusion is directly corroborated by the temperature-dependent PL measurements (figure inset), where CT-35 exhibits a markedly suppressed increase in PL intensity upon cooling compared to TP-TDS. This behavior is a direct manifestation of weakened carrier interactions, leading to more efficient exciton dissociation. The weakened carrier interaction directly explains CT-35’s enhanced charge separation efficiency and superior photocatalytic performance. We thank the reviewer again for their valuable critique, which has significantly strengthened our analysis. (please see page 13-14 and Fig. 4c in the revised manuscript)\nFig. 13 Temperature-dependent PL spectra of CT-35.\n11. The author states that the changes in the in-situ XPS spectra imply that the light excitation accelerated the interface electron transfer from TP-TDS to \"CS alveoli\". Please provide sufficient evidence to demonstrate the connection between the binding energy and the electron transfer during HER.\nResponse: We thank the reviewer for raising this pivotal question regarding the mechanistic link between spectroscopic shifts and functional electron transfer. To establish a direct, causal understanding, we have conducted a suite of complementary in-situ and ex-situ measurements. These data collectively delineate a clear mechanism where light excitation dynamically drives and accelerates interfacial electron transfer, creating the optimal catalytic state for the hydrogen evolution reaction (HER).\nUltraviolet photoelectron spectroscopy (UPS) provides the electronic context. The measured work functions (Ф = 2.95 eV, Ф = 3.08 eV; Fig. 14a-b) indicate that CS TP-TDS the Fermi level of CS is higher than that of TP-TDS. Their intimate contact in CT-35 establishes an interfacial band alignment favorable for charge exchange, setting the electronic stage for subsequent photoprocesses. Furthermore, the HER free-energy diagram (Fig. 14c) identifies the Co sites within the “CS alveoli” as intrinsically efficient with a near-optimal ΔG , establishing the functional imperative to deliver H* electrons precisely to these locations. In-situ Kelvin Probe Force Microscopy (KPFM) provides decisive, real-space evidence for the direction and light-dependence of the charge transfer. Upon illumination, the contact potential difference (Δ ) at the CPD interface decreases significantly (from 215.2 mV in dark to 149.8 mV under light; Fig. 14d-g). This decrease signifies a relative increase in electron density on the “CS alveoli” side, offering direct proof of directional electron flow from photoexcited TP-TDS to the CS units. High-resolution in-situ X-ray photoelectron spectroscopy captures the consequent chemical-state changes at the atomic scale. Under illumination, the Co 2p peaks shift to lower binding energy, confirming electron accumulation on the Co centers (Fig. 14h). Concurrently, the N 1s peak of TP-TDS shifts positively, indicating electron depletion from the donor framework (Fig. 14i). These complementary shifts are the definitive spectroscopic signature of electron transfer from TP-TDS to the Co sites in “CS alveoli”, perfectly aligning with the direction of charge flow visualized by KPFM. In summary, our evidence establishes a coherent and conclusive cascade that directly addresses the reviewer’s query: (i) A pre-aligned interface (UPS) channels photogenerated electrons toward intrinsically active sites (ΔG ). (ii) Light excitation directly triggers and accelerates directional H* electron transfer from TP-TDS to the CS alveoli, a process visually confirmed in real space and time by in-situ KPFM. (iii) This transferred charge populates the Co catalytic sites, a change atomically verified by the characteristic negative binding energy shift of Co 2p in in-situ XPS. (iv) The resulting electron-enriched state of the Co sites corresponds precisely to the theoretically optimal configuration for efficient HER.\nWe have integrated this comprehensive analysis into the revised manuscript to provide a unequivocal and multi-faceted demonstration of the proposed mechanism. (see page 16,17, 19, Fig. 5, 6d in the revised manuscript and Fig. S32 and S34 in the SI)\nFig. 14 Ultraviolet photoelectron spectroscopy (UPS) spectra of (a) CS and (b) TP-TDS; (c) the diagram of calculated hydrogen adsorption free energy diagram for samples; (d, f) In-situ Kelvin probe force microscopy (KPFM) height sensor images and (e, g) corresponding line profiles of CT-35 under varying conditions. (h, i) High-resolution XPS spectra of (h) Co 2p and (i) N 1s core levels.\n12. Please provide the structural model of the transition state for TP-TDS in HER (showing the adsorption and desorption process of H).\nResponse: We sincerely thank the reviewer for this insightful comment, which allows us to clarify an important aspect of the HER mechanism and provide additional structural insight. In the context of photocatalytic HER under acidic conditions (using ascorbic acid as a sacrificial agent), the reaction kinetics are generally fast, and the activity is predominantly governed by the thermodynamics of hydrogen adsorption. Therefore, the widely accepted descriptor in the field is the Gibbs free energy of hydrogen adsorption (ΔG ) rather than a specific transition state energy barrier [1-3]. H* The process is effectively described by a three-state diagram (initial state → H*adsorbed intermediate → 1/2 H product), where the value of ΔG determines the 2 H* catalytic efficiency. Accordingly, our DFT analysis focused on calculating and comparing the ΔG values for the relevant sites, as presented in the manuscript. This H* approach is the standard methodology for assessing HER activity on such materials.\nTo further address the reviewer’s interest in the atomic-scale interaction and to bridge the process from adsorption to desorption, we have now included the optimized structure of the H* adsorption state on the TP-TDS framework in the Supplementary Information (New Figure S40). This structure directly underlies our ΔG calculation H and visually demonstrates the favorable binding configuration of the key reaction intermediate. We hope this explanation and the additional structural data fully address the reviewer’s query. Thank you again for raising this point, which has helped us enrich the discussion in our manuscript.\nFig. 15 The absortion H structure of TP-TDS.\nReference:\n1. Kresse, G. a. F. u., J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 54, 11169--11186 (1996). https://doi.org/10.1103/PhysRevB.54.11169\n2. Grimme, S., Ehrlich, S. & Goerigk, L. Effect of the damping function in dispersion corrected density functional theory. Journal of Computational Chemistry 32, 1456-1465 (2011). https://doi.org/10.1002/jcc.21759\n3. Reckien, W., Janetzko, F., Peintinger, M. F. & Bredow, T. Implementation of empirical dispersion corrections to density functional theory for periodic systems. Journal of Computational Chemistry 33, 2023-2031 (2012). https://doi.org/10.1002/jcc.23037\n13. In the introduction section, please enhance the description of the advantages of COF/MOF photocatalysis. Such as: 10.1002/adma.202504808; 10.1021/jacs.3c07047; 10.1039/D4QI01578A.\nResponse: We thank the reviewer for this constructive suggestion and for providing these highly relevant and recent references. In response, we have revised the introduction section and incorporated the suggested references (ref. 8, 13 and 18) to better illustrate their tunable functionalities, unique charge transfer mechanisms, and exceptional photocatalytic performance. We believe that these additions have improved the context and depth of our introduction. Thank you again for this valuable recommendation.\nReference:\n1. Yu, J. J. et al. Topology‐templated synthesis of dibenzo [g,p] chrysene‐based sp2 carbon‐linked covalent organic frameworks with kagome lattice for enhanced photocatalytic hydrogen evolution. Advanced Materials (2025). https://doi.org/10.1002/adma.202504808\n2. Huang, Z.-W. et al. Thermally induced orderly alignment of porphyrin photoactive motifs in metal–organic frameworks for boosting photocatalytic CO reduction. 2 Journal of the American Chemical Society 145, 18148-18159 (2023). https://doi.org/10.1021/jacs.3c07047\n3. Zhou, Z.-H. et al. Engineering uranyl sites into MOFs for efficient and highly selective photocatalytic CO reduction. Inorganic Chemistry Frontiers 11, 6493-6501 2 (2024). https://doi.org/10.1039/d4qi01578a\n14. Some formatting issues: (1) The font in Figure 2 is somewhat compressed. Please re-adjust and re-layout it to make the entire picture more aesthetically pleasing. (2) The proportions in Figure 6f need to be adjusted to make the combination with the other pictures more aesthetically pleasing.\nResponse: We thank the reviewer for their careful review and for pointing out these formatting issues. We agree that the clarity and aesthetic presentation of the figures are important. In response to the reviewer’s comments, we have carefully revised both figure. These changes have been made in the revised manuscript (see Fig. 2 and Fig. 6 in the revised manuscript). We believe the updated figures are now more aesthetically pleasing and easier to read. Thank you for helping us improve the presentation of our work.\nFig. 16 High-resolution XPS of (a) Co 2p; (b) N 1s for CS, CT-35 and TP-TDS, (c) Co K-edge XANES spectra and (d) Fourier transformation of Co K-edge EXAFS spectra in R space of CS, CT-35 and reference samples (Co-foil, CoO, CoPc, CoS); wavelet transform (WT) contour plots of the k2-weighted Co K-edge EXAFS of (e) CS, (f) CT-35.\nFig. 17 Partial density of states (PDOS) of (a) CS alveoli, (b) TP-TDS, (c) CT-x; (d) the diagram of calculated hydrogen adsorption free energy diagram for samples; (e) schematic illustration of the proposed photocatalytic mechanism for H evolution over 2 CT-x."}, {"round": 2, "reviewer_comments": {"reviewer_2": "After I carefully read the revised version, one critical question should be addreassed. I noticed there are some related references are missing, which are very important for the readers to understand the novelty.", "reviewer_4": "The authors replied in a very satisfactory way to all the raised concerns. The additional experimental proofs not only clarify the manuscript, but strongly strengthen it. The manuscript has green light for publication from my side.", "reviewer_5": "I have carefully examined the reviewer reports alongside the detailed rebuttal and revised figures. Overall, I find that the authors have made a substantial and serious effort to address Reviewer #3’s concerns, and in most cases have done so convincingly by adding new experiments, clarifying overstatements, and improving the rigor of structure–function correlations.\nOverall assessment: In my view, the authors have satisfactorily addressed Reviewer #3’s scientific concerns, both conceptually and experimentally. The revised manuscript now meets the standards of rigor, clarity, and mechanistic justification expected for Nature Communications. I see no fundamental issues that have been overlooked, and the remaining points are largely editorial's decision.", "reviewer_1": "This manuscript proposes a biomimetic “alveoli-on-lamina” structure, which uses “CS alveoli” to accommodate high-density active sites and acts as an efficient photothermal nano-reactor, thereby significantly improving the HER performance under Pt-free conditions. However, the explanations regarding the structure-activity relationship and the transfer mechanism of photogenerated electrons/holes seem to lack sufficient evidence and description. I suggest that this manuscript would benefit from substantial revisions, followed by resubmission for further consideration.\n1. The title is cumbersome. It is suggested to remove \"534.6 mmol g-1 h-1\". This information is not appropriate to be included in the title."}, "author_response": ""}]

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