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. 2026 Sep 14;148(38):41673–41685. doi: 10.1021/jacs.6c16940

Potential Driven Spin-Crossover Synergized with Hydrogen-Bond Engineering in a Molecular Catalyst for Selective H2O2 Electrosynthesis

Libo Sun †, Yanjie Zhai †, Zhiying Wu †, Dongxue Yu †, Zhiqiang Liang ‡, Zhen-An Qiao ‡, Hua Zhang †,§,∥,⊥, Xin Wang †,⊥,*
PMCID: PMC13632549  PMID: 42937837

Abstract

The electrochemical two-electron oxygen reduction reaction (2e– ORR) provides a sustainable route for hydrogen peroxide (H2O2) production. However, its efficiency is fundamentally constrained by the spin-forbidden activation of triplet O2 and the subsequent proton-coupled electron-transfer steps required to form singlet H2O2. Herein, we report a pyrazine-functionalized nickel phthalocyanine catalyst (NiPNPC) that overcomes these constraints and achieves exceptional selectivity for H2O2 (up to 97.15%). In situ spectroscopic and computational studies reveal that the pyrazine units within the macrocyclic ligand promote a dynamic spin-crossover at the Ni center from a low-spin to a high-spin under cathodic polarization for O2 activation, thereby resolving the intrinsic spin mismatch. Concurrently, the pyrazine units facilitate the reorganization of a well-defined hydrogen-bonding network at the electrolyte-catalyst interface. This network ensures efficient proton delivery to the active center and thereby efficient H2O2 formation. The synergy between dynamic spin-state modulation and interfacial hydrogen-bond engineering provides a mechanistic understanding for selective H2O2 formation and establishes a new design paradigm for advanced molecular electrocatalysts in sustainable synthesis.

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Introduction

Hydrogen peroxide (H2O2) is a vital oxidant with extensive industrial applications. − Currently, its large-scale production is dominated by the energy-intensive anthraquinone process, which faces challenges such as complex operations, environmental issues, and high costs associated with the catalysts. These drawbacks have created a growing demand for more efficient and sustainable alternatives. − The electrochemical two-electron oxygen reduction reaction (2e– ORR) has emerged as a promising route for H2O2 synthesis. − However, achieving high efficiency and selectivity remains a major challenge, primarily due to the competing four-electron pathway that produces water. − Overcoming this selectivity bottleneck requires the development of advanced ORR catalysts. − Therefore, a fundamental understanding of the reaction mechanism and the design of rational catalysts are crucial for advancing this sustainable production technology. −

A fundamental challenge in efficient 2e– ORR lies in its spin-forbidden character, where the ground-state molecular oxygen (3O2) is in a triplet, and H2O2 is in a singlet. − This spin mismatch creates an inherent barrier to the 2e– ORR pathway. Molecular catalysts, such as metal phthalocyanines, serve as an ideal platform to address this issue due to their tunable structures. − Currently, conventional design strategies have primarily focused on optimizing static properties, such as the choice of the metal center or the use of electron-withdrawing/donating functional groups to decorate the macrocyclic ligands, etc. , In contrast, the dynamic evolution of the molecular catalyst’s geometric and electronic structure and spin state during catalysis, especially how ligand modifications influence this dynamic reaction process, remains poorly understood. ,

Beyond the spin challenge, the overall selectivity towards H2O2 is further dictated by subsequent proton-coupled electron transfer (PCET) steps. − The efficiency of these PCET processes is highly dependent on the local reaction environment, especially the hydrogen-bonding network at the catalyst-electrolyte interface. Engineering the macrocyclic ligand, for example, by incorporating hydrogen-bonding motifs onto the backbone, offers a viable strategy to tailor this interfacial microenvironment. An optimized hydrogen-bonding network can facilitate proton delivery, thereby aiding the formation and stabilization of H2O2. − Nonetheless, a fundamental question persists about how such engineered interfacial hydrogen-bonding networks cooperate with the dynamic spin and electronic states of the active sites to drive the 2e– ORR pathway. This mechanistic interplay remains a pivotal yet underexplored aspect of molecular catalysts.

Herein, we demonstrate that the combined strategy of facilitating dynamic spin-crossover and engineering an interfacial hydrogen-bonding network in a molecular catalyst drives highly selective H2O2 electrosynthesis. Using a pyrazine-functionalized nickel phthalocyanine derivative (NiPNPC) as the model catalyst, we achieve H2O2 selectivity up to 97.15%. In situ spectroscopic and theoretical analyses reveal that the pyrazine units in NiPNPC allow the nickel site, initially in a low-spin state in the pristine catalyst, to undergo a facilitated dynamic transition to a high-spin state to activate triplet O2. This spin-crossover facilitates the formation of a superoxide intermediate, thereby overcoming the spin-forbidden nature of O2 reduction. Concurrently, the pyrazine units in the ligand framework facilitate the formation of a tailored hydrogen-bonding network at the catalyst-electrolyte interface. This network enables efficient proton delivery during subsequent PCET steps and steers the reaction toward H2O2. Our work elucidates a cooperative mechanism in which dynamic spin-state transition activates triplet O2 to form a superoxide intermediate, while an engineered hydrogen-bonding microenvironment facilitates the crucial protonation steps. This insight advances the catalyst design paradigm from static electronic and geometric tuning toward the active co-regulation of spin states and interfacial microenvironments, providing a new strategy for developing molecular electrocatalysts for sustainable synthesis.

Results and Discussion

Building on the recognition that nickel phthalocyanine (NiPC) derivatives are promising candidates for the 2e– ORR, our previous work primarily explored static ligand modifications to influence the Ni active site. To advance beyond this strategy and address the dynamic and interfacial factors highlighted in the above section, we turned to pyrazine as a functional unit. Pyrazine provides structural rigidity, electronic tunability, and the ability to mediate both metal center properties and intermolecular interactions. The incorporation of pyrazine into the NiPC framework serves a dual purpose. First, it modulates the electron density at the Ni center, potentially influencing its dynamic spin state under reaction conditions. Second, the nitrogen atoms within the pyrazine ring offer sites to reorganize the hydrogen-bonding network at the catalyst-electrolyte interface. This integrated design targets the simultaneous regulation of dynamic spin states and the local proton transfer microenvironment.

Guided by this design principle, we synthesized a series of NiPC derivatives functionalized with pyrazine units, including NiNPC and NiPNPC, alongside the control counterpart NiPhPC, which lacks this unit (Figure b). We first investigated their electronic structures through computational methods. Analysis of the calculated electrostatic potential (ESP) maps reveals that the pyrazine unit significantly alters the molecular surface electrostatic potential (Figure c). In NiNPC and NiPNPC, the pyrazine regions appear blue, indicating a high electron density and an electron-rich state. This feature suggests a strong affinity for the partially positive hydrogen atoms of surface water molecules. Furthermore. Molecular orbital calculations further demonstrate a narrowing of the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) in the order of NiNPC > NiPNPC > NiPhPC (Figure d). The difference in the HOMO-LUMO gap implies different electron transfer capabilities. These computational results confirm that the incorporation of pyrazine effectively tunes the electronic properties of the Ni active site and promotes surface water reorganization at the molecular level.

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(a) Illustrating the triplet state O2 and the singlet state H2O2. (b) Illustrating the structure of NiNPC and NiPNPC. (c) Calculated electrostatic potentials (ESP) for the NiPC derivatives. (d) Calculated HOMO–LUMO orbitals.

Following the computational design, the target NiPC derivatives (NiNPC, NiPNPC, and NiPhPC) were successfully synthesized (see Experimental Section for details), and their molecular structures were confirmed by high-resolution mass spectrometry (HRMS, Figure S1). The electronic structures were further corroborated by UV–vis spectroscopy (Figure S2). All compounds display the characteristic absorption profiles of methallophthalocyanines, with a B-band (Soret band) around 290–320 nm and a Q-band around 550–700 nm, corresponding to a π–π* transitions. Notably, NiPNPC exhibits a slight red shift in its Q-band absorption compared to NiNPC, indicating a reduced HOMO–LUMO gap and facilitated π–π* transition. NiPhPC exhibits a further red shift than NiPNPC. This observation aligns well with the trend predicted by the frontier orbital calculations.

The oxidation state and local coordination environment of nickel in the synthesized derivatives were elucidated by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) spectroscopy. The Ni 2p XPS spectra (Figure a) for NiNPC, NiPNPC, and NiPhPC all show characteristic peaks of 2p3/2 and 2p1/2 at around 855.4 and 872.8 eV, confirming a nearly Ni­(II) oxidation state. The subtle variations in these spectral profiles indicate that the different functional groups modulate the electronic structure of these Ni centers. This finding is further supported by Ni K-edge XANES (Figure b). The edge positions for all derivatives align closely with those of the commercial NiPC, confirming a slightly less than +2 oxidation state. These results verify the successful synthesis of the target molecular structures, consistent with the HRMS and UV–vis data. Fourier-transform extended X-ray absorption fine structure (FT-EXAFS) spectra (Figure e) further show a prominent first-shell peak at around 1.4 Å (phase-uncorrected) for NiNPC, NiPNPC, NiPhPC, and commercial NiPC, attributable to Ni–N scattering. The complete absence of a Ni–Ni scattering path (around 2.2 Å) across all series unequivocally verified the isolation status of Ni sites. This conclusion was further corroborated by wavelet transform (WT) analysis (Figure c), which displayed only a single maximum at around 6.9 Å–1 and around 1.4 Å in the (k, R) space, corresponding to Ni–N coordination. Importantly, no characteristic signals of Ni–Ni metallic bonds were detected across the entire k-space range, particularly around 8.1 Å–1. Quantitative EXAFS fitting afforded the precise local coordination parameters (Figure S7 and Table S2). The fitting yielded an average Ni–N bond length of around 1.9 Å and a coordination number of around 4, confirming the four-coordinate configuration of our designed molecular catalysts.

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(a) XPS spectra for Ni 2p3/2 and 2p1/2 peaks. (b) Ni K-edge XANES data. (c) Wavelet transform (WT) contour maps of the extended EXAFS spectra at the Ni K-edge. (d) Raman spectra after immobilization. (e) Fourier-transformed (FT) k3-weighted χ­(k) function of the EXAFS spectra. (f) Illustration of transmission electron microscopy (TEM) images of NiPNPC. Inset: AC HAADF-STEM image of NiPNPC. (g–j) Energy-dispersive X-ray spectroscopy mapping images of NiPNPC.

To enable efficient electrocatalytic testing, the molecular NiPC catalysts were heterogenized by immobilizing them on multi-walled carbon nanotubes (CNTs) via π-π stacking interactions. The successful loading was first evidenced by Raman spectroscopy (Figure d). The intensity ratio of the I D/I G follows the order NiNPC­(CNT) > NiPhPC­(CNT) > NiPNPC­(CNT). This trend indicates that the functionalized derivatives, particularly NiPNPC and NiPhPC, integrate more effectively with the CNT graphitic surface, promoting a more ordered composite structure. The morphology and distribution of the supported catalysts were further examined by electron microscopy (Figures f, and S3–S4). Taking the optimal NiPNPC as an example, high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images (Figure f and inset) confirm the uniform dispersion of NiPNPC molecules on the CNT scaffold without observable aggregation. Elemental mapping via energy-dispersive X-ray spectroscopy (EDS) within the scanning electron microscope (Figure g–j) visually demonstrates the homogeneous distribution of Ni, N, and C elements, corroborating the successful and uniform immobilization. Besides, after immobilization on CNT, the Ni 2p3/2 binding energies of NiPhPC, NiNPC, and NiPNPC all converge to approximately 856 eV, indicating similar electronic environments at the Ni centers (Figure S5). Meanwhile, EXAFS fitting confirms that all three catalysts retain the four-coordinate Ni–N4 structure on the CNT support (Figures S6 and S8, Table S2). , These results suggest that the CNT support does not selectively perturb the Ni centers in a way that would distinguish the three catalysts, and the distinct catalytic behavior likely arises primarily from the molecular structure of the ligands. ,

The electrocatalytic performance of the NiPC derivatives for the 2e– ORR was evaluated using a rotating ring-disk electrode (RRDE). All potentials are reported versus the reversible hydrogen electrode (RHE). Linear sweep voltammetry (LSV) curves were recorded in O2-saturated 0.1 M KOH at a rotation rate of 1600 rpm (Figure a). The disk current densities (j disk) correspond to O2 reduction, while the ring current (j ring) arises from the oxidation of generated H2O2. Among the series, NiPhPC­(CNT) showed higher disk current and a relatively lower ring current over most potential windows, indicating it may also facilitate 4e‑ pathway to H2O, consistent with its poorer selectivity for H2O2. In contrast, NiPNPC­(CNT) exhibited a more positive onset potential for both disk and ring currents relative to the other catalysts, suggesting superior intrinsic activity associated with pyrazine units.

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(a) Electrocatalytic LSV curves at the ring-disk electrodes. (b) Calculated selectivity for production of H2O2. (c) Calculated electron transfer numbers. (d, e) LSV and selectivity comparison of NiPNPC in O2 atmosphere, air atmosphere, and with the addition of KSCN. (f) LSV comparison of NiPNPC and bare CNT electrode. (g–i) LSV, selectivity, and n transfer comparison of FePNPC, CoPNPC, and NiPNPC.

The corresponding H2O2 selectivity and electron transfer number (n) were derived from the RRDE data and are presented in Figure b,c. Remarkably, NiPNPC­(CNT) maintains high H2O2 selectivity (>90%) across a broad potential window (0.1 to 0.7 V vs RHE), reaching a maximum value of 97.15%, significantly higher than the others and bare CNT (Figure S10). Concurrently, its electron transfer number remains below 2.2 over this range, confirming the dominant 2e– pathway. These results confirm NiPNPC to as the the most intrinsic catalyst for 2e– ORR among the series. Meanwhile, the reaction kinetics of these catalysts were studied (Figure S13), where NiPNPC exhibits the lowest Tafel slopes for both disk (55 mV dec–1) and ring electrodes (62 mV dec–1), indicating that NiPNPC possesses the fastest ORR and H2O2 generation kinetics among these catalysts. To further probe the role of proton transfer in the rate-determining step, we performed Tafel analysis in both H2O and D2O electrolytes (0.1 M KOH vs 0.1 M KOD, Figure S14). For NiPNPC, the Tafel slope increased from 62 mV dec–1 in KOH to 84 mV dec–1 in KOD, while for NiPhPC it increased from 81 mV dec–1 to 103 mV dec–1. The kinetic isotope effect (k H/k D) for NiPNPC reached approximately 1.5–2 at cathodic potentials below 0.4 V, significantly higher than that for NiPhPC (approximately 1.5 across almost the entire potential range). This confirms that proton transfer plays a more pronounced role in the rate-determining step for NiPNPC, consistent with the enhanced proton delivery enabled by the pyrazine-reorganized hydrogen-bonding network. The smaller KIE for NiPhPC further supports that its proton transfer is less efficient.

To assess the practicality of NiPNPC under more realistic conditions, we evaluated its performance in an air atmosphere (Figure d,e). Although the absolute current densities decreased due to the lower O2 concentration, the H2O2 selectivity remained high (>80%, with a maximum of 90.10%), demonstrating its robust performance in ambient air. To identify the active site, we performed a poisoning experiment by introducing KSCN into the electrolyte (Figures d,e and S15). , The marked decrease in both current densities and H2O2 selectivity upon the addition of SCN– ions, which are known to block the metal sites, confirms the involvement of Ni in the catalytic process. The activity could be almost fully recovered after thoroughly washing the catalyst, elucidating the crucial role of Ni sites in the ORR process. Furthermore, to rule out catalytic decomposition of the produced H2O2, we conducted control experiments by scanning the potential in an N2-saturated electrolyte containing H2O2. The NiPNPC electrode showed decreased current for H2O2 reduction compared to bare CNT (Figure f), indicating that the H2O2 produced is not easily decomposed on the catalyst surface.

To underscore the unique advantage of the Ni center in NiPNPC, we synthesized and evaluated analogous Fe- and Co-based phthalocyanines with pyrazine (FePNPC, CoPNPC) and phenyl (FePhPC, CoPhPC) substituents for comparison. , As shown in Figures g–i and S16, their catalytic behavior differs markedly. Both FePNPC and FePhPC promote the 4e‑ ORR pathway to water and pooer 2e– ORR pathway to H2O2, consistent with the known properties of Fe centers. In contrast, the Co-based analogues (CoPNPC and CoPhPC) favor the 2e– ORR pathway. Notably, both FePNPC and CoPNPC show higher 2e– ORR activity than their phenyl-substituted counterparts FePhPC and CoPhPC, suggesting that pyrazine unit functionalization is an effective strategy for promoting the 2e– ORR across these molecular catalysts. However, the H2O2 selectivity of FePNPC and CoPNPC is consistently and significantly lower than that achieved by NiPNPC across the entire potential range. This comparative study clearly establishes NiPNPC as the optimal catalyst within this series for highly selective H2O2 production via 2e– ORR. The superior performance of NiPNPC thus provides a suitable platform for investigating the mechanistic origin of the high selectivity.

We further employed in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and in situ Raman spectroscopy to monitor the formation and evolution of reaction intermediates in real time. As shown in Figures S17–S18, NiPNPC and NiPhPC were compared. , The superoxide (O2 •–) signal (1110 cm–1) is much weaker for NiPNPC compared to NiPhPC throughout the potential range, underscoring the faster turnover and consumption of O2 •– on the former catalyst. , In 0.1 M KOD, the O2 •– signal for NiPNPC is stronger than in 0.1 M KOH, suggesting hydrogenation with proton transfer plays a more important role in the H2O2 production. In situ Raman studies reinforce these observations. Based on the benchmark study by Dong et al., which identified *OOH (∼732 cm–1), *OH (∼1080 cm–1), and O2 •– (∼1150 cm–1) using D2O and 18O2 isotope experiments, we assign our observed bands accordingly. Under an Ar atmosphere (Figure b), only the characteristic D and G bands of the CNT support and molecular catalyst are observed. Upon introducing O2 and applying a cathodic potential, new peaks emerge simultaneously (Figure a). The peak at about 740 cm–1 is assigned to the *OOH intermediate, the band at about 1087 cm–1 is assigned to the *OH species, and the peak at about 1147 cm–1 is attributed to the O–O stretching vibration of adsorbed O2 •–. This assignment is further supported by our D2O isotope experiments (Figure c, 0.1 M KOD vs 0.1 M KOH), where the ∼740 cm–1 and ∼1087 cm–1 bands exhibited slight red shifts (to ∼724 and ∼1080 cm–1, respectively), confirming the presence of exchangeable protons, while the ∼1147 cm–1 band remained unchanged, consistent with a proton-free O2 •– species.

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In situ Raman spectra of NiPNPC under (a) O2, (b) Ar atmosphere, and (c) 0.1 M KOD. (d) In situ Raman spectra of the O–H stretching vibrational mode of NiPNPC and NiPhPC. (e) Calculated ratio of the interfacial water. (f) The EPR signals of O2 •– radicals under different potentials. (g) The EPR signals of H radicals for NiPhPC and NiPNPC under Ar and O2 atmospheres. (h) The EPR signals of the NiPNPC electrodes under different potentials. (i) The measurement of effective magnetic moments for NiPNPC and NiPhPC.

To probe the reaction pathway and identify key intermediates, we employed in situ electron spin resonance (ESR) spectroscopy using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin-trap agent for NiPNPC under operating potentials. ,, As shown in Figure f, characteristic signals corresponding to superoxide radicals (O2 •–) are detected with negative potentials, , which aligns with the in situ ATR-SEIRAS and in situ Raman results. Considering that efficient hydrogenation also plays a key role in the formation of H2O2, the characteristic hydrogen radical was further examined. As shown in Figure g, NiPNPC exhibits a stronger hydrogen radical signal than that of NiPhPC under an Ar atmosphere. Indicating NiPNPC is superior to NiPhPC for hydrogen radical generation. However, such signals can be consumed under an O2 atmosphere, suggesting the existence of hydrogenation and consumption of hydrogen radicals to produce H2O2 during the reaction.

The observation of a stronger active hydrogen signal for NiPNPC than for NiPhPC prompted us to investigate the structure of interfacial water, as the structure of interfacial water, which mediates proton delivery to the active site, is crucial for the hydrogenation steps. To probe the interfacial water structure, we performed in situ Raman spectroscopy in the O–H stretching region (around 3000–3800 cm–1) (Figures d,e, and S21–S28). ,, The spectra were deconvoluted into three components, the free water (ca. 3600 cm–1), moderately H-bonded water (2HB·H2O, ca. 3450 cm–1), and strongly H-bonded water (4HB·H2O, ca. 3200 cm–1), following established literature protocols. ,, As shown in Figure e, NiPNPC exhibits the highest proportion of 2HB·H2O and the lowest proportion of 4HB·H2O among all catalysts, indicating that pyrazine functionalization reorganizes the interfacial water network into a more dynamic hydrogen-bonding configuration that facilitates proton transfer. ,, Control experiments (Figures S21–S28) reveal that CNT alone also exhibits a relatively high 2HB·H2O population, attributed to oxygen-containing functional groups on the CNT surface that attract water. However, CNT lacks Ni sites for O2 activation and shows poor H2O2 selectivity, confirming that water reorganization alone is insufficient for selective 2e– ORR. NiPhPC shows the highest 4HB·H2O population, reflecting a rigid water network that impedes proton delivery, consistent with its lower H2O2 selectivity. ZnPNPC (which contains the same pyrazine units as NiPNPC but d10 Zn with no spin crossover) shows increased 2HB·H2O compared to NiPhPC, confirming the hydrogen-bonding role of pyrazine. However, ZnPNPC exhibits poor H2O2 selectivity, further confirming that the Ni-centered spin crossover is essential for high catalytic activity. The observed higher 2HB·H2O population, the enhanced hydrogen radical signal, and the observed KIE (>1) all correlate with the accelerated proton transfer enabled by the reorganized interfacial water network and higher H2O2 selectivity for NiPNPC than NiPhPC.

After examining the surface and interfacial behavior of the catalysts, we turned to probe the metal sites during reactions. As exhibited in Figures h, S32 and S33, the pristine NiPNPC shows a negligible EPR signal at OCP due to its low-spin state. Upon cathodic polarization, however, an obvious potential-dependent response emerges, irrespective of the atmosphere (Ar or O2), indicating that unpaired electrons respond to the applied potential. Control experiments (Figure S32) with CNT, NiPhPC, NiNPC, metal-free ligand, and ZnPNPC confirm that this potential-dependent EPR signal originates from the Ni center, while ligand-centered radicals and CNT defects do not contribute. Magnetic moment tests further exclude a static high-spin state for both NiPNPC and NiPhPC (calculated to be ca. 2.83 for a high-spin state). The observation that NiPNPC shows almost no signal at OCP but a clear signal under cathodic polarization, despite a low-spin ground state, provides direct evidence for a potential-driven spin crossover at the Ni site. To verify this dynamic spin-state transition, we performed operando X-ray emission spectroscopy (XES) measurements (Figures a,b, and S34). XES is highly sensitive to spin state. The evolution of the Kβ′ emission line under applied potential provides a direct spectral characteristic of the Ni spin state. Operando XES analysis, calibrated against NiPC (low-spin) and NiO (high-spin) references, reveals a potential-driven transition of the Ni center from low-spin to high-spin under cathodic polarization. The high-spin fraction shows a clear potential-dependent increase, reaching approximately 50% at 0.3 V vs RHE (semi-quantitative estimate based on linear interpolation between the OCP and 0 V spectra). The spectral features of NiPNPC shift with applied potential under both Ar and O2 atmospheres (Figure S34), confirming that the spin transition is primarily potential-driven. The spin crossover is attributed to the introduction of pyrazine units to the macrocyclic ligand, which lowers the energy barrier for spin crossover, as supported by DFT calculations (Figure S40). This spin state change aligns with the EPR signals of the NiPNPC electrode under applied potentials. In contrast, the change in the XES spectra for NiPhPC was much smaller than that of NiPNPC under different applied potentials (Figure S34), confirming a relatively weak spin state change when combined with the magnetic measurement. These results indicate that the high-spin Ni species critically contributes to the 2e– ORR on NiPNPC.

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(a) Operando Ni Kβ’ XES spectra for NiPNPC. (b) Normalized intensity comparison of Kβ’ signal at around 8253 eV. (c) Operando Ni K-edge XANES of NiPNPC under O2 atmosphere. (d) The orbital interactions between low-spin (LS) and high-spin (HS) Ni sites and the triplet O2 molecule for NiPNPC. (e) Operando Fourier-transformed k-space of NiPNPC under O2 atmosphere. (f–h) Calculated 2e– and 4e– ORR reaction pathway. (i) Molecular dynamics simulation results of the interfacial structure for NiPNPC. (j) Relative concentration of water along the z-axis of NiPNPC and NiPhPC. (k) Calculated H-bond between water and molecules.

Operando X-ray absorption near-edge structure (XANES) spectroscopy tests were performed for NiPNPC to obtain further insights into the oxidation state and coordination environment of the Ni atom during the reaction. Under an O2 atmosphere, Figure c displays the normalized Ni K-edge XANES spectra. The operando XANES spectra reveal that the oxidation state of Ni under all applied potentials are close to +2. The coordination environment was also investigated from the characteristic 1s–4p peak, where a clear peak at around 8338 eV, indicative of four-coordinate Ni centers, is observed under different potentials. Operando Fourier-transform extended X-ray absorption fine structure spectra (Figure e) with prominent first-shell peaks and a fitted coordination number of approximately 4 (Figure S35) are observed with no Ni–Ni bond detected, confirming that Ni remains in a 4-coordinated, atomically dispersed state during reactions. The different behaviors of high-spin and low-spin state Ni can be further understood through orbital analysis. The orbital interactions between Ni sites with different spin states and the triplet O2 molecule were analyzed. As shown in Figure d, the oxygen molecule is more readily captured by high-spin Ni than by low-spin Ni because of a higher bond order resulting from the spin-orbital interactions between high-spin Ni and O2, thus ensuring effective activation of the triplet O2 molecule. It should be noted that, after O2 end-on adsorption, NiPNPC may decrease from a D4h to C 4v symmetry. Under this symmetry, the d z 2 orbital with A1 irreducible representation (irrep) is symmetry-matched to the O2 σ-type orbital (A1), while the d xz /d yz orbitals (E) match the O2 π* orbitals (E). The d x 2–y 2 (B1) and d xy (B2) orbitals have zero overlap with O2σ and π* when considering the point group symmetry, although they indirectly influence the overall electron-donating properties of the metal. The present qualitative analysis provides a simplified model of the bond order and orbital interactions.

Having established the dynamic behaviors of both the interfacial water network and the Ni spin state, we next examined their interplay across the potential range. Notably, EPR measurements reveal the presence of superoxide radicals across a wide potential range, indicating that O2 activation occurs continuously throughout the operating window. Meanwhile, operando XES shows that the spin-state signal evolves progressively with applied potential, confirming that the Ni center maintains its spin-crossover capability. Concurrently, the population of weakly H-bonded water (2HB·H2O), which is established at higher potentials, is consumed as the potential shifts negatively, consistent with its role in supplying protons for hydrogenation. These observations support the conclusion that spin crossover and hydrogen-bond network engineering operate in a concerted manner. Triplet O2 is adsorbed and activated on the in situ generated high-spin Ni site, leading to electron transfer and the formation of a superoxide intermediate (as verified by DFT, Figures S40–S41). Simultaneously, the pyrazine-reorganized hydrogen-bonding network facilitates proton delivery and promotes the protonation of the superoxide intermediate to form the key *OOH intermediate, and the subsequent hydrogenation step then yields H2O2. This dynamic picture, in which spin-crossover enables O2 activation and an engineered hydrogen-bonding network governs selective protonation, provides a fundamental explanation for the superior performance of NiPNPC.

Density functional theory (DFT) calculations were performed to gain deeper insights into the mechanism. Geometry optimization reveals a slightly longer average Ni–N bond length in the NiPNPC macrocycle (1.920 Å) compared to NiPhPC (1.911 Å). Crystal orbital Hamiltonian population (COHP) analysis yields integrated COHP values of −1.162 eV for NiPNPC and −1.163 eV for NiPhPC (Figure S42), which are nearly identical. This indicates that the pyrazine substitution induces only a minor electronic perturbation at the Ni center. The primary electronic effect of pyrazine is better captured by the operando XES and spin-crossover energy calculations (Figures S40–S41), which show a significantly reduced energy difference for the low-spin to high-spin transition in NiPNPC. We then computed the free energy profiles for the 2e– ORR pathway (Figures f–h, and S38–S39). For NiPNPC in its low-spin state, the potential-determining step (PDS) for *OOH formation has an energy difference of 0.490 eV. Crucially, when accounting for the in situ generated high-spin state identified by XES, this energy difference drops significantly to 0.223 eV. In contrast, the PDS energy difference for NiPhPC is calculated to be 0.705 eV. This large difference (approximately 0.480 eV) in the activation energy rationalizes the superior H2O2 selectivity of NiPNPC. Finally, molecular dynamics (MD) simulations were conducted to probe the interfacial structure (Figures i–k and S45). The water molecules around the catalyst show a distinct peak near 5 Å, corresponding to the relative concentration between water and the catalyst. As shown in Figure j, the intensity of the peak is substantially higher for NiPNPC than for NiPhPC, demonstrating that the pyrazine N atoms indeed promote the accumulation and reorganization of water at the interface, thereby leading to a changed hydrogen-bonding network at the interface. From the calculation, it is found that NiPNPC could form more hydrogen bonds with water layers compared to that of NiPhPC (Figure k), which aligns with our in situ spectroscopic observations observed from Figure e. Thereby, the decoration of the pyrazine unit could disrupt the tetrahedral water network of the interface, leading to a weakened rigid 4HB·H2O network and enhanced 2HB·H2O population. This MD-derived picture is consistent with the Raman spectral deconvolution and is further supported by the enhanced hydrogen radical signal in EPR and the kinetic isotope effect observed in D2O electrolyte. The convergence of computational and experimental evidence confirms that pyrazine-induced water reorganization facilitates proton transfer, thereby promoting the selective formation of H2O2.

Traditional H-cell systems for H2O2 production usually require electrolytes that contain inorganic salts, raising both production expenses and downstream purification costs. To circumvent this limitation, we used a porous solid electrolyte (PSE) reactor with a design that allows deionized water to replace conventional electrolyte solutions (Figure S47). , In this setup, protons formed at the anode travel through a proton exchange membrane (PEM) into the middle porous solid electrolyte layer, while HO2 – generated at the cathode passes through an anion exchange membrane (AEM) into the same layer, the two species then combine to form pure H2O2. We evaluated NiPNPC in this PSE reactor under galvanostatic operation, with current densities ranging from 10 to 200 mA cm–2 (Figure a–c). Across the entire range, the cell maintained a Faradaic efficiency (FE) for H2O2 above 80%, reaching a maximum of approximately 95.04% at 10 mA cm–2 and remaining around 84.42% at 200 mA cm–2. At the highest current density, the production rate reached 3.15 mmol cm–2 h–1 with a cell voltage below 2.99 V. These results indicate that the high selectivity observed in fundamental RRDE measurements translates effectively to a more practical system. The PSE reactor also showed robust durability with NiPNPC (Figure d). At an industrially relevant current density of 100 mA cm–2, the Faradaic efficiency remained above 88% for at least 100 h of continuous operation. Over this period, the outlet H2O2 concentration stayed above 3400 ppm at a flow rate of 0.5 mL min–1. Taken together, integrating the NiPNPC cathode catalyst with the PSE reactor enables H2O2 collected from the water-fed PSE stream with high selectivity and long-term durability, demonstrating the practical potential of our molecular design strategy.

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(a) I–V curve for H2O2 production of NiPNPC in the porous solid electrolyte reactor. (b) Faradaic efficiency of H2O2. (c) H2O2 production rate. (d) Stability test. (e) The molecules used for biomass conversion with H2O2 to produce formate. (f) The selectivity to yield formate for Glycerol with H2O2 produced under different current densities. (g) The selectivity comparison of Glycerol, Erythritol, Xylitol, and Glucose to yield formate.

Motivated by the exceptional 2e– ORR selectivity in both RRDE and PSE, we further evaluated the practical potential of NiPNPC by assembling it into a gas diffusion electrode (GDE) and testing it in a flow cell reactor (Figure S48). ,− As shown in Figure S49, the H2O2 production rate increases with applied current density, reaching a high yield rate of 19.31 mol g–1 h–1 at 200 mA cm–2. A long-term stability test at 50 mA cm–2 (Figure S50) demonstrates stable operation over 52 h, accumulating H2O2 at a concentration of 1.71 wt % in the electrolyte. The SEM and XPS data before and after stability tests confirm the good stability of NiPNPC under reaction conditions (Figures S51 and S52). Considering the challenges associated with H2O2 separation and storage, we further investigated its direct utilization in a tandem electrochemical and chemical process for biomass transformation (Figure e). ,, Using the in situ generated H2O2, glycerol was selectively oxidized to formate in the alkaline electrolyte. As shown in Figure f, a formate selectivity of approximately 89.08% was achieved at a current density of 75 mA cm–2. This tandem strategy was successfully extended to other biomass-derived polyols, including erythritol, xylitol, and glucose (Figure g). Among them, erythritol afforded the highest formate selectivity (up to 93.53%), highlighting the versatility of this integrated approach for producing valuable chemicals from renewable sources.

Conclusions

In summary, we have demonstrated a synergistic molecular design that integrates dynamic spin-state regulation with interfacial hydrogen-bond engineering to achieve highly selective H2O2 electrosynthesis. In the pyrazine-functionalized NiPC catalyst (NiPNPC), O2 adsorption is triggered by a potential-driven spin-crossover at the Ni center from low-spin to high-spin, which resolves the spin mismatch and facilitates the formation of a superoxide intermediate. Concurrently, the pyrazine units trigger the assembly of an optimized hydrogen-bonding network at the catalyst-electrolyte interface, ensuring efficient proton delivery for the formation of *OOH intermediate and the selective formation of H2O2 (up to 97.15%). Advanced in situ techniques, accompanied by computational techniques, explained the spin-state transformation, intermediate pathway, and the optimized *OOH. This work shifts the design paradigm for molecular electrocatalysts from static electronic and geometric tuning toward the active co-regulation of dynamic spin states and the local reaction microenvironment. The strategy of combining spin-crossover motifs with functional units that tailor interfacial networks represents a broadly applicable blueprint for the rational design of advanced catalysts across diverse proton-coupled electron transfer processes

Supplementary Material

ja6c16940_si_001.pdf (7.5MB, pdf)

Acknowledgments

This project was supported by the grants from the City University of Hong Kong (grant no. 9020005, 9610663, and 7020103), the ITF-RTH–Global STEM Professorship (9446008), the Hong Kong Branch of National Precious Metals Material Engineering Research Center–ITC Fund, and General Research Fund (CityU 11300924) from the Research Grants Council of Hong Kong SAR, China. The research work described in this paper was conducted in the JC STEM Lab of Electrocatalysis and Electrosynthesis (9228006) funded by The Hong Kong Jockey Club Charities Trust. This research project (Development of advanced catalysts for electrochemical carbon abatement, Project Code: 370184872) is part of the CREATE Thematic Programme in Decarbonisation and is supported by the National Research Foundation, Prime Minister’s Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) programme.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacs.6c16940.

  • Detailed synthesis, characterization and DFT calculation methods; HRMS, UV–vis, EXAFS fitting data, additional electrocatalytic data, in situ ATR-SEIRAS, in situ Raman, EPR, Operando XES, Operando XAFS, additional DFT calculations, PSE and flow cell setup, additional flow cell data (PDF)

The authors declare no competing financial interest.

References

  1. Perry S. C., Pangotra D., Vieira L., Csepei L.-I., Sieber V., Wang L., Ponce de León C., Walsh F. C.. Electrochemical synthesis of hydrogen peroxide from water and oxygen. Nat. Rev. Chem. 2019;3(7):442–458. doi: 10.1038/s41570-019-0110-6. [DOI] [Google Scholar]
  2. Lee K., Mehrgardi M. A., Zare R. N.. Interfacial Curvature, not Simply Size, Controls Spontaneous Hydrogen Peroxide Formation in Water Microdroplets. J. Am. Chem. Soc. 2025;147(36):33240–33247. doi: 10.1021/jacs.5c11575. [DOI] [PubMed] [Google Scholar]
  3. Sun Y., Fan K., Li J., Wang L., Yang Y., Li Z., Shao M., Duan X.. Boosting electrochemical oxygen reduction to hydrogen peroxide coupled with organic oxidation. Nat. Commun. 2024;15(1):6098. doi: 10.1038/s41467-024-50446-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Campos-Martin J. M., Blanco-Brieva G., Fierro J. L. G.. Hydrogen Peroxide Synthesis: An Outlook beyond the Anthraquinone Process. Angew. Chem., Int. Ed. 2006;45(42):6962–6984. doi: 10.1002/anie.200503779. [DOI] [PubMed] [Google Scholar]
  5. Jung E., Shin H., Hooch Antink W., Sung Y.-E., Hyeon T.. Recent Advances in Electrochemical Oxygen Reduction to H2O2: Catalyst and Cell Design. ACS Energy Lett. 2020;5(6):1881–1892. doi: 10.1021/acsenergylett.0c00812. [DOI] [Google Scholar]
  6. Shi X., Back S., Gill T. M., Siahrostami S., Zheng X.. Electrochemical Synthesis of H2O2 by Two-Electron Water Oxidation Reaction. Chem. 2021;7(1):38–63. doi: 10.1016/j.chempr.2020.09.013. [DOI] [Google Scholar]
  7. Hwang Y. L., Ma S., Zuo P., Duan J., Hou B.. Recent Progress of Electrochemical Production of Hydrogen Peroxide by Two-Electron Oxygen Reduction Reaction. Adv. Sci. 2021;8(15):2100076. doi: 10.1002/advs.202100076. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Wang Y., Waterhouse G. I. N., Shang L., Zhang T.. Electrocatalytic Oxygen Reduction to Hydrogen Peroxide: From Homogeneous to Heterogeneous Electrocatalysis. Adv. Energy Mater. 2021;11(15):2003323. doi: 10.1002/aenm.202003323. [DOI] [Google Scholar]
  9. Wen Y., Zhang T., Wang J., Pan Z., Wang T., Yamashita H., Qian X., Zhao Y.. Electrochemical reactors for continuous decentralized H2O2 production. Angew. Chem. 2022;134(35):e202205972. doi: 10.1002/ange.202205972. [DOI] [PubMed] [Google Scholar]
  10. Kang Y., Tan Y., Tian W., Zhang H., Chen Q., Wang J., Henrotte O., Kammerer D., Akkerman Q. A., Fan C.. et al. Promoting Formation and Suppressing Decomposition of H2O2 via Photocarrier Flow at Au@TiO2 Interfaces. J. Am. Chem. Soc. 2025;147(51):47244–47254. doi: 10.1021/jacs.5c14650. [DOI] [PubMed] [Google Scholar]
  11. Zhang X., Zhou Q., Li C., Su H., Chen T., Cui P., Ban C., Tao Y., Wang J., Jiang Y.. et al. Thermodynamic and Kinetic Modulation of Artificial H2O2 Photosynthesis via Spatial Control of Redox Catalytic Sites. J. Am. Chem. Soc. 2026;148(10):11068–11080. doi: 10.1021/jacs.5c22625. [DOI] [PubMed] [Google Scholar]
  12. Jia Y., Xue Z., Yang J., Liu Q., Xian J., Zhong Y., Sun Y., Zhang X., Liu Q., Yao D., Li G.. Tailoring the Electronic Structure of an Atomically Dispersed Zinc Electrocatalyst: Coordination Environment Regulation for High Selectivity Oxygen Reduction. Angew. Chem., Int. Ed. 2022;61(2):e202110838. doi: 10.1002/anie.202110838. [DOI] [PubMed] [Google Scholar]
  13. Zhang E., Tao L., An J., Zhang J., Meng L., Zheng X., Wang Y., Li N., Du S., Zhang J.. Engineering the local atomic environments of indium single-atom catalysts for efficient electrochemical production of hydrogen peroxide. Angew. Chem. 2022;134(12):e202117347. doi: 10.1002/ange.202117347. [DOI] [PubMed] [Google Scholar]
  14. Zhang Z., Chen W., Chu H. K., Xiong F., Zhang K., Yan H., Meng F., Gao S., Ma B., Hai X.. et al. Fe–O4 Motif Activated Graphitic Carbon via Oxo-Bridge for Highly Selective H2O2 Electrosynthesis. Angew. Chem., Int. Ed. 2024;63(39):e202410123. doi: 10.1002/anie.202410123. [DOI] [PubMed] [Google Scholar]
  15. Fan Y., Chen Y., Ge W., Dong L., Qi Y., Lian C., Zhou X., Liu H., Liu Z., Jiang H., Li C.. Mechanistic Insights into Surfactant-Modulated Electrode–Electrolyte Interface for Steering H2O2 Electrosynthesis. J. Am. Chem. Soc. 2024;146(11):7575–7583. doi: 10.1021/jacs.3c13660. [DOI] [PubMed] [Google Scholar]
  16. Ramaswamy N., Tylus U., Jia Q., Mukerjee S.. Activity Descriptor Identification for Oxygen Reduction on Nonprecious Electrocatalysts: Linking Surface Science to Coordination Chemistry. J. Am. Chem. Soc. 2013;135(41):15443–15449. doi: 10.1021/ja405149m. [DOI] [PubMed] [Google Scholar]
  17. Chen S., Luo T., Chen K., Lin Y., Fu J., Liu K., Cai C., Wang Q., Li H., Li X.. et al. Chemical identification of catalytically active sites on oxygen-doped carbon nanosheet to decipher the high activity for electro-synthesis hydrogen peroxide. Angew. Chem. 2021;133(30):16743–16750. doi: 10.1002/ange.202104480. [DOI] [PubMed] [Google Scholar]
  18. Tian Y., Li M., Wu Z., Sun Q., Yuan D., Johannessen B., Xu L., Wang Y., Dou Y., Zhao H., Zhang S.. Edge-hosted Atomic Co– N4 Sites on Hierarchical Porous Carbon for Highly Selective Two-electron Oxygen Reduction Reaction. Angew. Chem. 2022;134(51):e202213296. doi: 10.1002/ange.202213296. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Tian Z., Zhang Q., Thomsen L., Gao N., Pan J., Daiyan R., Yun J., Brandt J., López-Salas N., Lai F.. et al. Constructing interfacial boron-nitrogen moieties in turbostratic carbon for electrochemical hydrogen peroxide production. Angew. Chem. 2022;134(37):e202206915. doi: 10.1002/ange.202206915. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Zhang C., Shen W., Guo K., Xiong M., Zhang J., Lu X.. A Pentagonal Defect-Rich Metal-Free Carbon Electrocatalyst for Boosting Acidic O2 Reduction to H2O2 Production. J. Am. Chem. Soc. 2023;145(21):11589–11598. doi: 10.1021/jacs.3c00689. [DOI] [PubMed] [Google Scholar]
  21. Sheng H., Janes A. N., Ross R. D., Kaiman D., Huang J., Song B., Schmidt J. R., Jin S.. Stable and selective electrosynthesis of hydrogen peroxide and the electro-Fenton process on CoSe2 polymorph catalysts. Energy Environ. Sci. 2020;13(11):4189–4203. doi: 10.1039/D0EE01925A. [DOI] [Google Scholar]
  22. Yang C., Bai S., Yu Z., Feng Y., Huang B., Lu Q., Wu T., Sun M., Zhu T., Cheng C.. et al. A newly-explored Pd-based nanocrystal for the pH-universal electrosynthesis of H2O2 . Nano Energy. 2021;89:106480. doi: 10.1016/j.nanoen.2021.106480. [DOI] [Google Scholar]
  23. Zhou Z., Kong Y., Tan H., Huang Q., Wang C., Pei Z., Wang H., Liu Y., Wang Y., Li S.. et al. Cation-Vacancy-Enriched Nickel Phosphide for Efficient Electrosynthesis of Hydrogen Peroxides. Adv. Mater. 2022;34(16):2106541. doi: 10.1002/adma.202106541. [DOI] [PubMed] [Google Scholar]
  24. Liu C., Yu Z., She F., Chen J., Liu F., Qu J., Cairney J. M., Wu C., Liu K., Yang W.. et al. Heterogeneous molecular Co–N–C catalysts for efficient electrochemical H2O2 synthesis. Energy Environ. Sci. 2023;16(2):446–459. doi: 10.1039/D2EE02734H. [DOI] [Google Scholar]
  25. Sun W., Tang L., Ge W., Fan Y., Sheng X., Dong L., Zhang W., Jiang H., Li C.. Anionic Surfactant-Modulated Electrode–Electrolyte Interface Promotes H2O2 Electrosynthesis. Adv. Sci. 2024;11(36):2405474. doi: 10.1002/advs.202405474. [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. Jiang K., Zhao J., Wang H.. Catalyst Design for Electrochemical Oxygen Reduction toward Hydrogen Peroxide. Adv. Funct. Mater. 2020;30(35):2003321. doi: 10.1002/adfm.202003321. [DOI] [Google Scholar]
  27. Long Y., Lin J., Ye F., Liu W., Wang D., Cheng Q., Paul R., Cheng D., Mao B., Yan R.. et al. Tailoring the Atomic-Local Environment of Carbon Nanotube Tips for Selective H2O2 Electrosynthesis at High Current Densities. Adv. Mater. 2023;35(46):2303905. doi: 10.1002/adma.202303905. [DOI] [PubMed] [Google Scholar]
  28. Xia B., Du J., Li M., Duan J., Chen S.. Pseudo-Jahn–Teller Effect Breaks the pH Dependence in Two-Electron Oxygen Electroreduction. Adv. Mater. 2024;36:2401641. doi: 10.1002/adma.202401641. [DOI] [PubMed] [Google Scholar]
  29. Yang X., Zeng Y., Alnoush W., Hou Y., Higgins D., Wu G.. Tuning Two-Electron Oxygen-Reduction Pathways for H2O2 Electrosynthesis via Engineering Atomically Dispersed Single Metal Site Catalysts. Adv. Mater. 2022;34(23):2107954. doi: 10.1002/adma.202107954. [DOI] [PubMed] [Google Scholar]
  30. Chen S., Luo T., Li X., Chen K., Fu J., Liu K., Cai C., Wang Q., Li H., Chen Y.. et al. Identification of the Highly Active Co–N4 Coordination Motif for Selective Oxygen Reduction to Hydrogen Peroxide. J. Am. Chem. Soc. 2022;144(32):14505–14516. doi: 10.1021/jacs.2c01194. [DOI] [PMC free article] [PubMed] [Google Scholar]
  31. Liu T., Meng J., Qin H., Zhang M., Sun N., Mei B., Li H., Zhang X.-P., Li J., Cao R.. Mechanistic Studies of Catalytic O2-to-H2O2 Conversion at a Single Cobalt Site. J. Am. Chem. Soc. 2025;147(26):22322–22328. doi: 10.1021/jacs.5c04848. [DOI] [PubMed] [Google Scholar]
  32. Mtangi W., Tassinari F., Vankayala K., Vargas Jentzsch A., Adelizzi B., Palmans A. R. A., Fontanesi C., Meijer E. W., Naaman R.. Control of Electrons’ Spin Eliminates Hydrogen Peroxide Formation During Water Splitting. J. Am. Chem. Soc. 2017;139(7):2794–2798. doi: 10.1021/jacs.6b12971. [DOI] [PMC free article] [PubMed] [Google Scholar]
  33. Thorning F., Jensen F., Ogilby P. R.. Modeling the Effect of Solvents on Nonradiative Singlet Oxygen Deactivation: Going beyond Weak Coupling in Intermolecular Electronic-to-Vibrational Energy Transfer. J. Phys. Chem. B. 2020;124(11):2245–2254. doi: 10.1021/acs.jpcb.0c00807. [DOI] [PubMed] [Google Scholar]
  34. Lu C., Hu C., Lyu L.. Nonexpendable H2O2 induces rapid molecular oxygen activation over micropotential Cu-modulated zinc oxide. Cell Rep. Phys. Sci. 2025;6(2):102431. doi: 10.1016/j.xcrp.2025.102431. [DOI] [Google Scholar]
  35. Rice D. B., Wong D., Weyhermüller T., Neese F., DeBeer S.. The spin-forbidden transition in iron­(IV)-oxo catalysts relevant to two-state reactivity. Sci. Adv. 2024;10(26):eado1603. doi: 10.1126/sciadv.ado1603. [DOI] [PMC free article] [PubMed] [Google Scholar]
  36. Smith P. T., Kim Y., Benke B. P., Kim K., Chang C. J.. Supramolecular tuning enables selective oxygen reduction catalyzed by cobalt porphyrins for direct electrosynthesis of hydrogen peroxide. Angew. Chem. 2020;132(12):4932–4937. doi: 10.1002/ange.201916131. [DOI] [PubMed] [Google Scholar]
  37. Chen Y., Zhen C., Chen Y., Zhao H., Wang Y., Yue Z., Wang Q., Li J., Gu M. D., Cheng Q.. et al. Oxygen Functional Groups Regulate Cobalt-Porphyrin Molecular Electrocatalyst for Acidic H2O2 Electrosynthesis at Industrial-Level Current. Angew. Chem., Int. Ed. 2024;63(34):e202407163. doi: 10.1002/anie.202407163. [DOI] [PubMed] [Google Scholar]
  38. Sun L., Jin X., Su T., Fisher A. C., Wang X.. Conjugated Nickel Phthalocyanine Derivatives for Heterogeneous Electrocatalytic H2O2 Synthesis. Adv. Mater. 2024;36(17):2306336. doi: 10.1002/adma.202306336. [DOI] [PubMed] [Google Scholar]
  39. van Langevelde P. H., Hetterscheid D. G. H.. Selective electrochemical H2O2 production by a molecular copper catalyst: A crucial relation between reaction rate and mass transport. Chem. Catal. 2024;4(8):101069. doi: 10.1016/j.checat.2024.101069. [DOI] [Google Scholar]
  40. Liu C., Zhang D., Chen J., She F., Liu F., Yu Z., Zheng Z., Levine M. S., Sessler J. L., Chen Y.. et al. Coordination-Dependent Oxygen Reduction Reaction Activity of Single Atom Co–Nx–C Electrocatalysts. J. Am. Chem. Soc. 2026;148(6):6569–6582. doi: 10.1021/jacs.5c20980. [DOI] [PubMed] [Google Scholar]
  41. Peng J., Mai J., Chen J., Yu Z., Yu J., Li H., Yue X., Zhang L.. Unraveling the Mechanism of Coordination Engineering in Ni-N2O2 Heterogeneous Molecular Catalysts for H2O2 Electrosynthesis. Adv. Funct. Mater. 2026;36(31):e27905. doi: 10.1002/adfm.202527905. [DOI] [Google Scholar]
  42. Moges E. A., Chang C.-Y., Huang W.-H., Angerasa F. T., Lakshmanan K., Hagos T. M., Edao H. G., Dilebo W. B., Pao C.-W., Tsai M.-C.. et al. Heteroatom-Coordinated Palladium Molecular Catalysts for Sustainable Electrochemical Production of Hydrogen Peroxide. J. Am. Chem. Soc. 2024;146(1):419–429. doi: 10.1021/jacs.3c09644. [DOI] [PubMed] [Google Scholar]
  43. Sun L., Su T., Fisher A. C., Shan J., Chen W., Zhang H., Wang X.. Dynamic protonation of ligand sites in molecular catalysts enhances electrochemical CO2 reduction. Sci. Adv. 2025;11(17):eadu6915. doi: 10.1126/sciadv.adu6915. [DOI] [PMC free article] [PubMed] [Google Scholar]
  44. Zeng Y., Zhao J., Wang S., Wang W., Lu Y.-R., Xi S., Xu W., Yoda Y., Masuda R., Li X.. et al. Unraveling the Dynamic Low-Spin State Evolution of Single-Fe-Atom Sites for Efficient CO2 Electroreduction. J. Am. Chem. Soc. 2025;147(46):42539–42548. doi: 10.1021/jacs.5c13466. [DOI] [PubMed] [Google Scholar]
  45. Wang A., Xiang L., Wang G., Song X., Xu H., Wang L.. Bioinspired Construction of Proton-Coupled Electron Transfer Pathways in Covalent Organic Frameworks for Enhanced Photosynthesis of Hydrogen Peroxide. ChemSusChem. 2025;18(22):e202501760. doi: 10.1002/cssc.202501760. [DOI] [PubMed] [Google Scholar]
  46. Vos R. E., Sun P., Schauermann D., Javed H., Hanselman S. R., Fu G., Koper M. T. M.. CO2 electroreduction on Cu operates via an alternative chain growth mechanism to form C–C bonds at elevated temperature and pressure. Nat. Catal. 2025;8:1338–1347. doi: 10.1038/s41929-025-01451-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
  47. Chen J., Ma Q., Li X., Zhao J., Yu Z., Dong S.. Hydride-Mediated Hydrogen Activation on Cobalt-Alloyed Single-Atom Palladium Catalysts for Efficient H2O2 Synthesis. J. Am. Chem. Soc. 2026;148(13):14063–14071. doi: 10.1021/jacs.5c23128. [DOI] [PubMed] [Google Scholar]
  48. Cheng F., Liu Y., Zhao Z., Yang X., Zheng W., Yang B., Li Z., Zhang Q., Dong C.-L., Lei L.. et al. Enhanced proton-feeding kinetics of metal-organic framework toward industrial-level H2O2 electrosynthesis for sustainable bleaching. Nat. Commun. 2025;16(1):10183. doi: 10.1038/s41467-025-65276-z. [DOI] [PMC free article] [PubMed] [Google Scholar]
  49. Sang Z., Qiao Y., Chen R., Yin L., Hou F., Liang J.. Internal hydrogen-bond enhanced two-electron oxygen reduction reaction for π-d conjugated metal-organic framework to H2O2 synthesis. Nat. Commun. 2025;16(1):4050. doi: 10.1038/s41467-025-58628-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
  50. Ren G., Zhou M., Wang H.. Weakened Interfacial Hydrogen Bond Connectivity Drives Selective Photocatalytic Water Oxidation toward H2O2 at Water/Brookite-TiO2 Interface. J. Am. Chem. Soc. 2024;146(9):6084–6093. doi: 10.1021/jacs.3c13402. [DOI] [PubMed] [Google Scholar]
  51. Liu Y., Lu X., Wang J., Zhou Z., Xia Y., Zhang R., Fan X.. Hydrogen bond formation-modulated H2O2 generation under periodic local polarization piezoelectric electric field. Chem. Eng. J. 2025;522:167240. doi: 10.1016/j.cej.2025.167240. [DOI] [Google Scholar]
  52. Zhang J., Zeng H., He B., Liu Y., Xu J., Niu T., Pan C., Zhang Y., Lou Y., Wang Y.. et al. Suppressing the hydrogen bonding interaction with *OOH toward efficient H2O2 electrosynthesis via remote electronic tuning of Co-N4. Appl. Catal., B. 2024;358:124448. doi: 10.1016/j.apcatb.2024.124448. [DOI] [Google Scholar]
  53. Churakov A. V., Grishanov D. A., Medvedev A. G., Mikhaylov A. A., Vener M. V., Navasardyan M. A., Tripol’skaya T. A., Lev O., Prikhodchenko P. V.. Stabilization of hydrogen peroxide by hydrogen bonding in the crystal structure of 2-aminobenzimidazole perhydrate. CrystEngComm. 2020;22(16):2866–2872. doi: 10.1039/D0CE00096E. [DOI] [Google Scholar]
  54. Tung C.-W., Zhang W., Lai T. Y., Wang J., Chu Y.-C., Wang G.-B., Hsu C.-S., Liao Y.-F., Hiraoka N., Ishii H.. et al. Spin crossover-driven diiron electrocatalyst boosts sustainable water oxidation. Nat. Sustainability. 2025;8(7):793–805. doi: 10.1038/s41893-025-01571-3. [DOI] [Google Scholar]
  55. Li X., Feng Y., Fu S., Wu T., Liang P., Ma X., Iqbal R., Qian Y., Ma Y., Bonn M.. et al. Pyrazine-Embedded 2D Conjugated Metal–Organic Framework with Quasi-Honeycomb Lattice for High-Capacitance Lithium-Ion Storage. Angew. Chem., Int. Ed. 2025;64(27):e202502988. doi: 10.1002/anie.202502988. [DOI] [PMC free article] [PubMed] [Google Scholar]
  56. Zhang Y., Zhao J., Ku C., Xu T., Fang S., Huang T., Tang M., Chen F., Wang Z., Wang C.. Pyrazine units as electrochemical active centers for organic batteries. Sci. China Mater. 2025;68(11):3851–3868. doi: 10.1007/s40843-025-3566-3. [DOI] [Google Scholar]
  57. Lu T., Chen F.. Multiwfn: A multifunctional wavefunction analyzer. J. Comput. Chem. 2012;33(5):580–592. doi: 10.1002/jcc.22885. [DOI] [PubMed] [Google Scholar]
  58. Ren J., Su X., Zhang X., Yan X., Wang H.-G., Chen L.. A Pyrazine-Based Two-Dimensional Conjugated Metal–Organic Framework for Air Self-Charging Aqueous Zinc-Ion Batteries. CCS Chem. 2026;8:341–349. doi: 10.31635/ccschem.025.202505557. [DOI] [Google Scholar]
  59. Zhang X., Su H., Cui P., Cao Y., Teng Z., Zhang Q., Wang Y., Feng Y., Feng R., Hou J.. et al. Developing Ni single-atom sites in carbon nitride for efficient photocatalytic H2O2 production. Nat. Commun. 2023;14(1):7115. doi: 10.1038/s41467-023-42887-y. [DOI] [PMC free article] [PubMed] [Google Scholar]
  60. Jin C., Shen H., Li J., Guo X., Rao S., Yang W., Liu Q., Sun Z., Yang J.. Isolated Ni Atoms for Enhanced Photocatalytic H2O2 Performance with 1.05% Solar-to-Chemical Conversion Efficiency in Pure Water. Nano Lett. 2024;24(45):14484–14492. doi: 10.1021/acs.nanolett.4c04573. [DOI] [PubMed] [Google Scholar]
  61. Fan W., Duan Z., Liu W., Mehmood R., Qu J., Cao Y., Guo X., Zhong J., Zhang F.. Rational design of heterogenized molecular phthalocyanine hybrid single-atom electrocatalyst towards two-electron oxygen reduction. Nat. Commun. 2023;14(1):1426. doi: 10.1038/s41467-023-37066-y. [DOI] [PMC free article] [PubMed] [Google Scholar]
  62. Li Z., Jia J., Sang Z., Liu W., Nie J., Yin L., Hou F., Liu J., Liang J.. A Computation-Guided Design of Highly Defined and Dense Bimetallic Active Sites on a Two-Dimensional Conductive Metal–Organic Framework for Efficient H2O2 Electrosynthesis. Angew. Chem., Int. Ed. 2024;63(46):e202408500. doi: 10.1002/anie.202408500. [DOI] [PubMed] [Google Scholar]
  63. van Langevelde P. H., Ligthart N. E. G., van Duren P. G. J., Vermaas D. A., Hetterscheid D. G. H.. H2O2 Synthesis with Molecular Electrocatalysts Enables Substantial Current Densities in a Flow Cell Using Gas Diffusion Electrodes. ACS Electrochem. 2025;1(11):2326–2337. doi: 10.1021/acselectrochem.5c00179. [DOI] [PMC free article] [PubMed] [Google Scholar]
  64. Yu K., Guan S., Zhang W., Zhang W., Meng Y., Lin H., Gao Q.. Engineering Asymmetric Electronic Structure of Co–N–C Single-Atomic Sites Toward Excellent Electrochemical H2O2 Production and Biomass Upgrading. Angew. Chem., Int. Ed. 2025;64(19):e202502383. doi: 10.1002/anie.202502383. [DOI] [PubMed] [Google Scholar]
  65. Zhang C., Yuan L., Liu C., Li Z., Zou Y., Zhang X., Zhang Y., Zhang Z., Wei G., Yu C.. Crystal Engineering Enables Cobalt-Based Metal–Organic Frameworks as High-Performance Electrocatalysts for H2O2 Production. J. Am. Chem. Soc. 2023;145(14):7791–7799. doi: 10.1021/jacs.2c11446. [DOI] [PubMed] [Google Scholar]
  66. Chen Y., Li Z., Zhu Y., Sun D., Liu X., Xu L., Tang Y.. Atomic Fe Dispersed on N-Doped Carbon Hollow Nanospheres for High-Efficiency Electrocatalytic Oxygen Reduction. Adv. Mater. 2019;31(8):1806312. doi: 10.1002/adma.201806312. [DOI] [PubMed] [Google Scholar]
  67. Lim J. S., Woo J., Bae G., Yoo S., Kim J., Kim J. H., Lee J. H., Sa Y. J., Jang J.-W., Hwang Y. J.. et al. Understanding the preparative chemistry of atomically dispersed nickel catalysts for achieving high-efficiency H2O2 electrosynthesis. Chem. Sci. 2024;15(34):13807–13822. doi: 10.1039/D4SC03105A. [DOI] [PMC free article] [PubMed] [Google Scholar]
  68. Guo Q., Huang B., Bo G., Ma H., Wen Y., Long X., Qian X., Zhao Y.. Molecular Engineering of Wastewater Nickel into Single-Site Electrocatalysts for Hydrogen Peroxide Production with Industrial Level Current. Angew. Chem., Int. Ed. 2025;64(49):e202514519. doi: 10.1002/anie.202514519. [DOI] [PubMed] [Google Scholar]
  69. Song Z., Chi X., Dong S., Meng B., Yu X., Liu X., Zhou Y., Wang J.. Carboxylated Hexagonal Boron Nitride/Graphene Configuration for Electrosynthesis of High-Concentration Neutral Hydrogen Peroxide. Angew. Chem., Int. Ed. 2024;63(7):e202317267. doi: 10.1002/anie.202317267. [DOI] [PubMed] [Google Scholar]
  70. Dong J.-C., Zhang X.-G., Briega-Martos V., Jin X., Yang J., Chen S., Yang Z.-L., Wu D.-Y., Feliu J. M., Williams C. T.. et al. In situ Raman spectroscopic evidence for oxygen reduction reaction intermediates at platinum single-crystal surfaces. Nat. Energy. 2019;4(1):60–67. doi: 10.1038/s41560-018-0292-z. [DOI] [Google Scholar]
  71. Hu C., Huang H., Chen F., Zhang Y., Yu H., Ma T.. Coupling Piezocatalysis and Photocatalysis in Bi4NbO8X (X = Cl, Br) Polar Single Crystals. Adv. Funct. Mater. 2020;30(7):1908168. doi: 10.1002/adfm.201908168. [DOI] [Google Scholar]
  72. Wang Y., Wei P., Shen Z., Wang C., Ding J., Zhang W., Jin X., Vecitis C. D., Gao G.. O2-Independent H2O2 Production via Water–Polymer Contact Electrification. Environ. Sci. Technol. 2024;58(1):925–934. doi: 10.1021/acs.est.3c07674. [DOI] [PubMed] [Google Scholar]
  73. Tang Y.-Y., Luo X., Xia R.-Q., Luo J., Peng S.-K., Liu Z.-N., Gao Q., Xie M., Wei R.-J., Ning G.-H., Li D.. Molecular Engineering of Metal–Organic Frameworks for Boosting Photocatalytic Hydrogen Peroxide Production. Angew. Chem., Int. Ed. 2024;63(36):e202408186. doi: 10.1002/anie.202408186. [DOI] [PubMed] [Google Scholar]
  74. Xia R.-Q., Liu Z.-N., Tang Y.-Y., Wu T., Luo X., Deng Q.-M., Ning G.-H., Li D.. In Situ Exfoliation of Covalent Metal-Organic Frameworks for Enhancing Photocatalytic Hydrogen Peroxide Production. Angew. Chem. 2025;137(43):e202514091. doi: 10.1002/ange.202514091. [DOI] [PubMed] [Google Scholar]
  75. Li Y., Chen J., Ji Y., Zhao Z., Cui W., Sang X., Cheng Y., Yang B., Li Z., Zhang Q.. Single-atom iron catalyst with biomimetic active center to accelerate proton spillover for medical-level electrosynthesis of H2O2 disinfectant. Angew. Chem. 2023;135(34):e202306491. doi: 10.1002/ange.202306491. [DOI] [PubMed] [Google Scholar]
  76. Zhou S., Cao W., Shang L., Zhao Y., Xiong X., Sun J., Zhang T., Yuan J.. Facilitating alkaline hydrogen evolution kinetics via interfacial modulation of hydrogen-bond networks by porous amine cages. Nat. Commun. 2025;16(1):1849. doi: 10.1038/s41467-025-56962-z. [DOI] [PMC free article] [PubMed] [Google Scholar]
  77. Fang Y., Fan Y., Xie K., Ge W., Zhu Y., Qi Z., Song Z., Jiang H., Li C.. Boosting Hydrogen Peroxide Electrosynthesis via Modulating the Interfacial Hydrogen-Bond Environment. Angew. Chem. 2023;135(27):e202304413. doi: 10.1002/ange.202304413. [DOI] [PubMed] [Google Scholar]
  78. Liu Y., Li L., Li X., Xu Y., Wu D., Sakthivel T., Guo Z., Zhao X., Dai Z.. Asymmetric tacticity navigates the localized metal spin state for sustainable alkaline/sea water oxidation. Sci. Adv. 2025;11(22):eads0861. doi: 10.1126/sciadv.ads0861. [DOI] [PMC free article] [PubMed] [Google Scholar]
  79. Lee B.-H., Shin H., Rasouli A. S., Choubisa H., Ou P., Dorakhan R., Grigioni I., Lee G., Shirzadi E., Miao R. K.. et al. Supramolecular tuning of supported metal phthalocyanine catalysts for hydrogen peroxide electrosynthesis. Nat. Catal. 2023;6(3):234–243. doi: 10.1038/s41929-023-00924-5. [DOI] [Google Scholar]
  80. Xia C., Xia Y., Zhu P., Fan L., Wang H.. Direct electrosynthesis of pure aqueous H2O2 solutions up to 20% by weight using a solid electrolyte. Science. 2019;366(6462):226–231. doi: 10.1126/science.aay1844. [DOI] [PubMed] [Google Scholar]
  81. Zhang X., Zhao X., Zhu P., Adler Z., Wu Z.-Y., Liu Y., Wang H.. Electrochemical oxygen reduction to hydrogen peroxide at practical rates in strong acidic media. Nat. Commun. 2022;13(1):2880. doi: 10.1038/s41467-022-30337-0. [DOI] [PMC free article] [PubMed] [Google Scholar]
  82. Liu L., Kang L., Feng J., Hopkinson D. G., Allen C. S., Tan Y., Gu H., Mikulska I., Celorrio V., Gianolio D.. et al. Atomically dispersed asymmetric cobalt electrocatalyst for efficient hydrogen peroxide production in neutral media. Nat. Commun. 2024;15(1):4079. doi: 10.1038/s41467-024-48209-0. [DOI] [PMC free article] [PubMed] [Google Scholar]
  83. Zhang M.-D., Huang J.-R., Liang C.-P., Chen X.-M., Liao P.-Q.. Continuous Electrosynthesis of Pure H2O2 Solution with Medical-Grade Concentration by a Conductive Ni-Phthalocyanine-Based Covalent Organic Framework. J. Am. Chem. Soc. 2024;146(45):31034–31041. doi: 10.1021/jacs.4c10675. [DOI] [PubMed] [Google Scholar]
  84. Xia C., Kim J. Y., Wang H.. Recommended practice to report selectivity in electrochemical synthesis of H2O2 . Nat. Catal. 2020;3(8):605–607. doi: 10.1038/s41929-020-0486-1. [DOI] [Google Scholar]
  85. Liu X., Zhou T., Yuan B.-J., Shi Q., Zhou P., Wang Y., Li J., Zhang C., Shao M., Duan H.. Dynamic attraction of leached metal species enables durable glucose electrooxidation in a strong acid. Nat. Commun. 2026;17:7159. doi: 10.1038/s41467-026-73501-6. [DOI] [PMC free article] [PubMed] [Google Scholar]
  86. Song Y., Qian J., Li S., Zhao Z., Chen H., Zou K., Han Z., Li Z., Li H., Zhou H.. et al. Stabilizing Lattice Oxygen to Enable Durable MnO2 Electrocatalyst for Simultaneous Acidic Hydrogen Production and Biomass Valorization. Angew. Chem. 2025;137(25):e202502847. doi: 10.1002/ange.202582501. [DOI] [PubMed] [Google Scholar]

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