Impact Statement
Hydrogen peroxide is a key oxidant for water treatment, disinfection, selective oxidation, and solar chemical processes. Conventional centralized production is energy- and solvent-intensive, can involve metal catalysts and associated contamination concerns, and requires the storage and transport of concentrated H2O2, creating decomposition and safety risks. Organic photoactive interfaces provide low-metal or metal-free routes to generate H2O2 directly from water, O2/air, and sunlight at or near the point of use. Their molecular structures and interfacial microenvironments can be tuned to coordinate selective oxygen reduction, compatible hole consumption, and rapid product release. Practical impact should therefore be evaluated beyond batch concentration using areal or volumetric productivity, solar-to-chemical efficiency, catalyst lifetime, H2O2 decomposition rate, extraction efficiency, and on-site utilization. Progress against these metrics could reduce downstream concentration, storage, and transport demands and enable safer distributed oxidant production.
1. Introduction
Photocatalytic H2O2 production provides a direct route to convert water, O2, and sunlight into a useful oxidant [Reference Zhang, Ma and Wang1–Reference Hayat, Ajmal and Alzahrani6]. Organic photoactive materials have emerged as versatile platforms for this purpose because their electronic structures, intermolecular interactions, and interfacial environments can be tailored through molecular design [Reference Yan, Shen and Shen7,Reference Zhao, Zhang and Yang8]. Supramolecular photocatalysts offer flexible control over molecular packing, protonation, hydrogen bonding, and local polarization, although their assemblies may respond sensitively to the reaction medium [Reference Freese, Meijer, Feringa and Beil9,Reference Zhang, Pan and Bian10]. Conjugated polymers allow broad tuning of light absorption and redox-active units, but structural disorder can introduce heterogeneous transport and trapping pathways [Reference Wei, Chang and Li3]. COFs provide ordered pores and spatially programmable catalytic units, while their performance depends on balancing framework conjugation, interlayer transport, and active-site accessibility [Reference Liu, Chen and Yu11,Reference Chen, Liu and Guo12,Reference Yong and Ma13]. Despite these structural differences, the decisive factor is not the material category itself, but how effectively the material organizes photogenerated charges, reactants, catalytic sites, and transport pathways at the interface (Figure 1).
From charge separation to interfacial regulation in photocatalytic H2O2 production.
Figure 1. Long description
A top banner contains three chevron-shaped arrows pointing right, labeled Absorption, Charge Separation and Migration, and Reaction Pathway Regulation.
Underneath the first two chevrons, a large blue sphere represents a photocatalyst. A red wavy arrow labeled hv(light energy) strikes the sphere. Inside the sphere, a yellow vertical arrow points from the VB (Valence Band) at the bottom to the CB (Conduction Band) at the top. The VB contains four yellow circles with h+(holes), and the CB contains four gray circles with e- (electrons).
To the left of the sphere, O2 molecules enter the CB and H2O molecules enter the VB. To the right of the sphere, three pathways emerge:
1. A blue arrow from the CB leads to a green box labeled Selective Reduction to H2O2, showing a ball-and-stick model of hydrogen peroxide.
2. A purple arrow from the VB leads to a purple box labeled Oxidation Half-reaction.
3. A dashed gray arrow from the center leads to a gray dashed box labeled Charge Recombination Loss.
Underneath the third chevron, Reaction Pathway Regulation, four chemical structures are listed vertically, each paired with a functional label:
1. A circular molecular framework labeled COFs-R corresponds to Functional Group.
2. A phenyl-acetylene chain with a subscript n corresponds to Charge Storage.
3. A complex fused heterocyclic aromatic structure corresponds to Radical Intermediate.
4. A 3D molecular model showing spatial distribution corresponds to D-A Spatial Separation.
A bottom red dashed box is labeled Hydrogen Peroxide Decomposition. A legend at the bottom left defines a blue arrow as Electron Pathway (Reduction), a purple arrow as Hole Pathway (Oxidation), and a dashed gray arrow as Recombination Pathway.
Current progress remains limited by mismatches across the photocatalytic cycle. Efficient charge separation is an important prerequisite but an insufficient predictor of H2O2 selectivity. Electrons may undergo selective two-electron oxygen reduction (2e− ORR) or competing one-electron and secondary H2O2 conversion pathways, whereas insufficiently consumed holes may recombine with electrons, oxidize the photocatalyst, or decompose the product. In addition, H2O2 may be formed efficiently but accumulate poorly if its desorption and diffusion are slower than its interfacial degradation. These limitations are fundamentally both spatial and temporal. Spatially, electron-rich domains, O2-binding sites, and proton- or water-accessible environments must be locally coordinated, while hole-consuming regions and product-release pathways should be separated from processes that promote recombination or H2O2 decomposition. Temporally, carrier generation and migration must be synchronized with O2 activation, proton-coupled electron transfer, hole consumption, and product release (Figure 2).
Precise coupling of photogenerated charges and chemical reaction sites across spatiotemporal scales.
Figure 2. Long description
A multi-panel diagram divided by a central vertical dashed line labeled Interface.
* At the top, a bridge-like structure is labeled spatiotemporal matching.
* A central horizontal orange arrow serves as a timeline with markers for fs, ps, ns, us, ms, and s.
* To the left of the interface is the Charge Transfer zone (ps to mu s). It features a vertical Excitation arrow pointing from a blue Valence Band (VB) containing h super plus holes to a red Conduction Band (CB) containing e super minus electrons. A dashed green arrow labeled Recombination points back down. Curved black arrows show charge movement toward the interface.
* At the interface, a blue and grey shaded region is labeled Adsorption forward slash Desorption.
* To the right of the interface is the Surface Reactions zone (ms to s). It shows molecular models of water and oxygen interacting with the surface. Three dashed boxes highlight specific mechanisms.
* The top box, Surface Charge, shows blue spheres accumulating on a surface.
* The middle box, Interfacial Field, shows Electrostatic Interaction between a surface-bound molecule and external black spheres.
* The bottom box, Reaction Energe Barrier, shows molecular clusters on a surface with one cluster containing a large black sphere.
* Temporal matching is highlighted on the left and Spatial matching on the right.
In this perspective, we propose spatiotemporal matching at organic photoactive interfaces as a unified framework for understanding and designing solar H2O2 photosynthesis. Rather than treating charge separation as the ultimate goal, this framework focuses on whether photogenerated carriers can be delivered to the appropriate reactants and catalytic sites within chemically relevant time windows. We discuss how supramolecular photocatalysts, conjugated polymers, and COFs regulate spatiotemporal matching through interfacial organization and transport. This perspective aims to move the field beyond empirical structure–performance relationships toward more predictive structure–matching–pathway relationships.
2. Charge Separation and Interfacial Regulation for H2O2 Selectivity
Charge separation is indispensable for photocatalytic H2O2 synthesis. In organic photocatalysts, exciton binding energies are often substantial, and the formation of mobile or long-lived charge carriers can be more difficult than in many inorganic semiconductors. Donor–acceptor molecular design, heteroatom substitution, framework conjugation, local polarization, and supramolecular aggregation have therefore been used to promote exciton dissociation and charge migration [Reference Zhang, Ma and Wang1,Reference Yan, Shen and Shen7,Reference Zhang, Pan and Bian10,Reference Zhang, Su and Cui14–Reference Li, Jiao and Tang17]. These strategies generally enhance photocatalytic activity by increasing the supply of charge carriers. However, once photogenerated charge carriers reach the reaction interface, they encounter multiple competing reaction pathways, including 2e− ORR, 4e− ORR, hydrogen evolution reaction (HER), water oxidation reaction (WOR), and subsequent H2O2 decomposition processes.
Charge separation primarily determines the availability of reactive charge carriers, whereas interfacial catalytic regulation governs their reaction pathways and utilization efficiency. Therefore, achieving highly selective photocatalytic H2O2 synthesis requires not only efficient generation and migration of photogenerated carriers but also precise coordination among photogenerated electrons, oxygen molecules, proton sources, and catalytic active sites. For example, Yang and co-workers confined H3PO4 molecular networks within the nanochannels of a covalent organic framework, constructing a hydrogen-bond-mediated proton transport network to optimize proton delivery at the reaction interface. This study demonstrated that enhanced interfacial proton transfer can significantly promote photocatalytic H2O2 production, revealing that efficient coupling between electron transfer and proton supply is crucial for improving charge utilization efficiency and facilitating interfacial catalytic reactions (Figure 3a) [Reference Lin, Zou and Wu18]. Furthermore, Zhang and co-workers introduced polyethyleneimine (PEI) onto the surface of g-C3N4 to achieve synergistic regulation of charge carrier behavior and oxygen reduction pathways [Reference Zeng, Liu and Kang19].This strategy not only promoted photogenerated electron–hole separation and enhanced interfacial electron availability but also modulated the local electronic structure and O2 adsorption characteristics, thereby favoring the selective 2e− ORR and significantly improving H2O2 production performance (Figure 3b). This system further demonstrates that simply increasing the number of photogenerated electrons is insufficient to guarantee efficient H2O2 synthesis; instead, the key lies in directing electrons toward selective reaction pathways at appropriate interfacial active sites.
(a) Efficient proton transfer and charge separation within covalent organic frameworks via hydrogen-bonding network. Reprinted from Ref. [Reference Lin, Zou and Wu18] with Copyright (2024) American Chemical Society. (b) Plausible mechanism for the boosted H2O2 production by PEI/C3N4 photocatalysis. Reprinted from Ref. [Reference Zeng, Liu and Kang19] with Copyright (2020) American Chemical Society. (c) The behaviors of excitons, polarons and charge carriers in 3D photocatalysts. Reprinted from Ref. [Reference Huang, Shen and Yan22] with Copyright (2024) Springer Nature. (d) H2O2 yields through ORR at AQ moieties. Reprinted from Ref. [Reference Huang, Shen and Yan22] with Copyright (2024) Springer Nature.
Figure 3. Long description
Panel a shows a hexagonal COF lattice with a hydrogen bonding network. Light triggers the movement of H super plus protons and e super minus electrons, labeled as Boosting PCET, leading to the conversion of O2 into H2O2.
Panel b displays the chemical structure of PEI and its integration with C3N4 nanosheets. A zoomed-in section shows light-induced electron excitation from the valence band to the conduction band, where electrons react with O2 to form superoxide radicals and eventually H2O, while PEI amine groups facilitate proton transfer.
Panel c illustrates exciton and polaron behaviors in a 3D photocatalyst. It identifies six pathways: 1 Transformation of Electrons into Polarons, 2 Interlayer Diffusion of Polarons, 3 Electrons Directly Reacting with Absorbed O2, 4 Ultrafast Storage of Electrons at AQ, 5 Interlayer Diffusion of Electrons, and 6 Recombination. A callout box highlights the potential manifestation within the CPs interior involving electron-donor D and electron-acceptor A moieties.
Panel d is a dual-axis line and bar graph. The x-axis represents Time in minutes from 0 to 90. The left y-axis shows H2O yield in micromoles per gram, and the right y-axis shows H2O2 concentration in micromolar. Under Light in Ar, the yield increases linearly from 0 to 60 minutes. Under Dark in O2 from 60 to 90 minutes, the yield continues to rise at a slower rate, reaching approximately 3800 micromoles per gram. Insets show the ORR andWOR chemical cycles at A Q and alkynyl moieties.
Conversely, some semiconductor photocatalytic systems with strong charge-generation capability and high redox activity still fail to achieve efficient H2O2 accumulation [Reference Wen, Huang and Meng20]. For example, although TiO2-based photocatalysts exhibit favorable photogenerated carrier generation and strong redox properties, the lack of precise regulation of interfacial reaction pathways allows the produced H2O2 to undergo further reduction or oxidation by photogenerated electrons and holes, thereby limiting its effective accumulation [Reference Yi, Bahrini, Schoemaecker, Fittschen and Choi21]. This comparison further demonstrates that charge separation primarily determines the availability of reactive carriers, whereas the interfacial reaction environment governs the ultimate utilization pathways of these carriers and the resulting product selectivity. Therefore, rather than merely optimizing charge transport processes, achieving precise spatiotemporal matching among photogenerated carrier migration, oxygen activation, and proton-coupled electron transfer processes is critical for improving the efficiency and selectivity of photocatalytic H2O2 synthesis.
3. Temporal Matching between Charge Dynamics and Interfacial Reactions
Temporal matching refers to the compatibility between the kinetic timescales of photoinduced charge generation, migration, separation, and interfacial reaction processes. In this context, temporal matching does not simply indicate prolonged carrier lifetime, but requires that the lifetime of reactive charge states exceeds the characteristic timescale of interfacial electron/proton transfer and product-release processes. It ensures that photogenerated electrons can effectively participate in O2 reduction within their lifetimes, while photogenerated holes are simultaneously consumed through oxidation processes. In organic photocatalysts, photoexcitation and ultrafast charge redistribution generally occur on femtosecond-to-picosecond timescales. Subsequently, exciton migration and charge separation proceed on picosecond-to-nanosecond timescales. In contrast, interfacial catalytic processes, including O2 adsorption, proton-coupled electron transfer (PCET), *OOH intermediate formation, H2O2 desorption, and subsequent oxidation reactions, typically occur over much longer timescales ranging from microseconds to seconds (Figure 2). The relevant lifetime is therefore not a single carrier lifetime, but the overlap among exciton migration, charge localization, interfacial electron transfer, proton transfer, hole removal, and product release.
Charge storage provides a kinetic bridge between ultrafast photoinduced processes and relatively sluggish interfacial reactions. Nevertheless, its effectiveness depends on whether the stored charge states can be continuously activated and involved in subsequent catalytic cycles. Ouyang and co-workers achieved temporal matching through the integration of charge storage and structural regulation in a three-dimensional self-supported TPC-AQ conjugated polymer [Reference Huang, Shen and Yan22]. In this system, anthraquinone (AQ) served as a reversible electron reservoir, while the three-dimensional triptycene (TPC) framework facilitated oxygen transport. Femtosecond transient absorption (fs-TA) spectroscopy identified three electron transfer pathways: intramolecular transfer directly involved in O2 reduction (τ1 = 0.90 ps), electron storage in reduced AQ (τ2 = 15.92 ps), and interlayer transfer toward surface reaction sites (τ3 = 206.60 ps, Figure 3c). The dominant intramolecular pathway (82.2%) indicated that AQ-based electron storage effectively enhanced electron utilization. Light–dark switching experiments further demonstrated that stored electrons could sustain H2O2 production for approximately 20 min after light removal, bridging transient photoexcitation and dark-state ORR processes (Figure 3d).
Recently, Zhu and co-workers achieved temporal matching through radical stabilization by regulating the conjugated structure (Figure 4a) [Reference Han, He and Liu23].The introduction of tetraphenylmethane (TPM) nodes weakened long-range π-conjugation, promoting electron localization at carbonyl sites and the formation of stable carbonyl radical anions (Figure 4b). fs-TA measurements revealed that TPM-DADK exhibited a long-lived component (τ3) of 1839 ps in air, over five times longer than the untreated system (353 ps). Meanwhile, TRPL analysis showed accelerated interfacial electron transfer after structural regulation, with the excited-state lifetime decreasing from 4.37 ns to 2.03 ns (Figure 4c). In situ infrared and EPR analyses further suggested that stabilized radical intermediates not only stored electrons but also facilitated dynamic exfoliation and exposure of additional O2 activation sites (Figure 4d). The continued H2O2 generation after light removal confirmed that these long-lived intermediates effectively coupled photoinduced electron generation with dark-state oxygen reduction.
(a) Schematic diagram of anion radical intermediate DADK•− and protonated anion intermediate DADKH• formation via photogenerated electron transfer and reduction. Reprinted from Ref. [Reference Han, He and Liu23] with Copyright (2025) Springer Nature. (b) Rational design and functional tuning of DADK-based frameworks from full conjugation to segmented π-systems via node modulation. Reprinted from Ref. [Reference Han, He and Liu23] with Copyright (2025) Springer Nature. (c) PL decay dynamics of TPM-DADK before and after photo-exfoliation under Ar with an excitation wavelength of 420 nm. Reprinted from Ref. [Reference Han, He and Liu23] with Copyright (2025) Springer Nature. (d) In situ FTIR spectra of TPM-DADK during irradiation in a 2-propanol aqueous solution with saturated oxygen. Reprinted from Ref. [Reference Han, He and Liu23] with Copyright (2025) Springer Nature.
Figure 4. Long description
A multi-panel figure containing four sections labeled a through d.
Panel a: A chemical reaction scheme showing the transformation of DADK into DADK dot minus via h v and e minus, then into DADKH dot via H plus. The structures show the reduction of a carbonyl group to an oxyanion and then to a hydroxyl group.
Panel b: A schematic for the rational design of frameworks. At the top left, DADK redox units are combined with a linkage and different node units labeled Py, Flu, and TPM via Suzuki-Miyaura Coupling. This leads to three framework types: Py-DADK with full conjugation, Flu-DADK with partial conjugation, and TPM-DADK with a conjugation break. A vertical arrow indicates weakened pi-pi stacking from top to bottom. A text box lists drawbacks for Py and Flu-DADK, while another lists advantages for TPM-DADK. Below this, a three-step illustration shows 3D-TPM-DADK layers undergoing irradiation and electron storage to form ketyl radical anions, followed by exfoliation and sonication into individual nanosheets due to repulsion.
Panel c: PL decay dynamics graph for TPM-DADK. The x-axis is Time in ns from 0 to 50. The y-axis is Counts. Two data series are shown: As-synthesized (orange circles) with tau equals 4.37 ns, and After Photo-exfoliation (blue triangles) with tau equals 2.03 ns. The blue curve shows a faster decay rate.
Panel d: In situ FTIR spectra of TPM-DADK. The x-axis is Wavenumber in inverse centimeters from 1300 to 900. The y-axis is Intensity in arbitrary units. Six stacked spectra are shown from bottom to top: Dark 10 min, Dark 20 min, Light on 10 min, Light on 20 min, Light off 10 min, and Light off 20 min. Peaks are identified for O-Oad between 1200 and 1050, and O-O at approximately 950. The peaks increase in intensity during the light-on phases.
The TPC-AQ system extends electron utilization through the synergistic effects of electron storage and three-dimensional transport, whereas the TPM-DADK system improves electron conversion efficiency through radical stabilization and exposure of interfacial active sites. These strategies provide effective approaches for regulating carrier utilization in photocatalytic H2O2 synthesis. However, temporal matching alone is insufficient to ensure efficient catalysis. The generation, migration, and consumption of photogenerated carriers must also occur at appropriate spatial locations.
4. Spatial Matching for Selective H2O2 Formation
Spatial matching refers to the spatial coordination between the generation, migration, and localization of photogenerated charge carriers and the adsorption sites of key reactants. Spatial matching requires sufficient spatial overlap between carrier localization regions, reactant adsorption domains, and catalytic active sites, while maintaining spatial separation from undesired side-reaction sites. Such regulation enables electrons to rapidly reach O2-activation sites while holes are consumed in spatially separated regions, thereby suppressing charge recombination and side reactions. On the reduction side, electron-rich regions, O2 adsorption or activation sites, and proton or water-accessible domains should be positioned in close proximity to facilitate electron-O2-proton coupling and the formation of intermediates such as *OOH. Meanwhile, holes should be directed to spatially separated oxidation regions and consumed promptly to suppress charge recombination and H2O2 oxidation. Product desorption, diffusion, and extraction are also integral to spatial design, because prolonged residence of H2O2 near redox-active sites may lead to further reduction, oxidation, or decomposition. Thus, spatial matching relies on the local colocalization of beneficial components and the spatial separation of mutually interfering processes [Reference Cheng, Lv and Cheng16,Reference Zhao, Wang and Yin24].
Supramolecular photocatalysts offer a molecular-level approach to regulating interfacial spatial matching [Reference Zhu, Jia and Liu25]. Zhu and co-workers constructed the anthrazoline-based supramolecular photocatalyst SA-SADF-H+ through unsymmetric protonation, revealing how molecular polarization governs reductive-side spatial matching. Unsymmetric protonation breaks molecular symmetry and reorganizes the interfacial charge distribution, while the enhanced molecular dipole and built-in electric field drive photogenerated electrons toward the reactive interface. Meanwhile, protonation improves the hydrophilicity of the material and creates adjacent N–H+/C–H dual sites for Yeager-type O2 adsorption, thereby enabling the local coordination of electron supply, O2 adsorption and activation, and proton/water delivery. In situ diffuse reflectance infrared Fourier-transform spectroscopy detected endoperoxide and *HOOH intermediates, while no pronounced •O2− signal was observed, indicating that such interfacial colocalization favors the selective formation of H2O2 through a direct one-step 2e− ORR pathway. Consistent with this spatially coordinated interface, SA-SADF-H+ achieved an H2O2 production rate of 9333.4 μmol g−1 h−1 and a solar-to-chemical conversion efficiency of 1.35% (Figure 5a) [Reference Li, Han and Liu26].
(a) Schematic diagram for fabrication of SA-SADF-H+ hydrogel via unsymmetric protonation-driven self-assembly, accompanied by electrostatic potential distribution maps and molecular dipole for SADF and SADF-H+. Reprinted from Ref. [Reference Li, Han and Liu26] with Copyright (2025) John Wiley and Sons. (b) A hexavalent 2D covalent organic framework with spatially segregated donor and acceptor columns and engineered hydraulically active 1D channels. Reprinted from Ref. [Reference Chen, Liu and Guo12] with Copyright (2024) Springer Nature. (c) Brief illustration of photo-self-Fenton reactions. Reprinted from Ref. [Reference Zhang, Wang and Xiao29] with Copyright (2022) Elsevier. (d) Biphasic fluid system that enables continuous H2O2 photosynthesis, separation, and extraction. The colors yellow, blue, and pink represent the photocatalyst, water phase, and oil phase, respectively. Reprinted from Ref. [Reference Shao, Yu and Ji30] with Copyright (2024) Springer Nature. (e) Schematic mechanism of photocatalytic H2O2 production by TTT-COF. Reprinted from Ref. [Reference Yang, Zhao and Liu31] with Copyright (2025) Springer Nature.
Figure 5. Long description
Panel a: A molecular transformation flowchart. On the left, SADF is shown as a hydrophobic molecule with a dipole of 2.923 Debye and red-blue electrostatic maps. A purple arrow labeled 1 Protonation and 2 Unsymmetric Deprotonation leads to SADF-H super plus on the right, which is hydrophilic with a 7.491 Debye dipole and segregated delta plus and delta minus regions.
Panel b: Two 3D structural models of a COF. The left model shows a hexagonal pore with blue donor columns and green/red acceptor columns. O2 enters and H2O2 exits. The right model shows a detailed molecular lattice with blue central units and tan peripheral units, highlighting WOR and ORR active sites.
Panel c: A schematic of a photo-self-Fenton system. A sun icon illuminates a polymer lattice between a VB and CB. Electrons e minus reduce O2 to H2O2, while a cyclic Fe3+ to Fe2+ reaction generates hydroxyl radicals.
Panel d: A process flow diagram for continuous photosynthesis. From left to right: H2O and catalyst in oil phase are pumped into a coiled reactor for H2O2 photosynthesis. The mixture enters a separation tank where the oil phase settles at the bottom for recycling, and the H2O solution is extracted for disinfection, healthcare, and wastewater treatment.
Panel e: A mechanism diagram for TTT-COF. Light excites electrons from the VB to the CB. In the reduction reaction, O2 is converted to H2O2 via superoxide radicals. In the oxidation reaction, holes h plus convert H2O to O2 or oxidize organic alcohols to aldehydes.
COFs provide a structurally defined platform for interfacial spatial matching through the programmable organization of their π-skeletons and pores [Reference Liu, Chen and Yu11,Reference Li, Lv and Xue27,Reference Cheng, Wu and Zhang28]. Jiang and co-workers constructed a series of hexavalent donor–acceptor alternating COFs in which triphenylene knots serve as electron-donating water-oxidation sites, whereas diphenylbutadiyne linkers act as electron-accepting oxygen-reduction sites [Reference Chen, Liu and Guo12]. The donor and acceptor units form spatially segregated columns for hole and electron transport, directing the two carriers toward the WOR and ORR sites, respectively, while suppressing charge recombination. In parallel, hydrophilic pore walls create one-dimensional molecular-transport channels that deliver water and dissolved O2 to the catalytic centers through capillary action. This dual-channel architecture couples charge transport with reactant delivery: electrons, O2, and ORR sites are locally matched at the linkers, whereas holes, water, and WOR sites are spatially coordinated at the knots. The optimized TP-DPBD3O-COF achieved an H2O2 production rate of 7200 μmol g−1 h−1, a maximum apparent quantum yield of 18.0%, and a solar-to-chemical conversion efficiency of 0.91% (Figure 5b). Together, these examples show that spatial matching extends beyond charge separation alone: it requires the deliberate colocalization of electrons, reactants, and reduction sites, together with the spatial segregation of oxidation processes and efficient reactant transport, to steer the overall photocatalytic cycle toward selective and stable H2O2 formation.
5. Product Stabilization Closes the Catalytic Cycle
H2O2 photosynthesis does not end at product formation. Net productivity depends on the competition among formation, desorption, decomposition, extraction, and use. The generated H2O2 can disproportionate, undergo further reduction, be oxidized by holes, react with •OH or other reactive oxygen species, or enter Fenton-like pathways (Figure 5c) [Reference Zhang, Wang and Xiao29]. These processes are consequences of how the product is positioned relative to redox-active sites and how long it remains at the illuminated interface.
Several forms of mismatch can consume the product. Spatial mismatch occurs when H2O2 forms too close to hole-rich or strongly oxidative regions. Temporal mismatch occurs when product residence at the interface exceeds the interval between oxidative or reductive events. Redox mismatch occurs when the same catalyst that forms H2O2 also has sufficient driving force to decompose it. Mass-transport mismatch occurs when desorption, extraction, or downstream use is slower than decomposition. These scenarios explain why high initial ORR activity may not translate into high net accumulation.
Recent COF studies have begun to treat product handling as part of catalyst design. Perfluoroalkyl-modified COFs enabled continuous photocatalytic H2O2 synthesis and extraction in a biphasic fluid system (Figure 5d), illustrating that product separation can be coupled to photocatalysis rather than performed only after reaction [Reference Shao, Yu and Ji30]. Homologous heteropolyaromatic COFs couple H2O2 production with aerobic oxidation, showing how reductive O2 activation and oxidative substrate transformation can be integrated within one organic framework platform (Figure 5e) [Reference Yang, Zhao and Liu31,Reference He, Dong and Zhao32]. For distributed oxidation chemistry, the most relevant systems may be those that balance formation, stabilization, extraction, and on-site utilization under continuous operation [Reference Wang, Zhang and Hsueh33,Reference Li, Yue and Huang34].
6. Outlook
Organic H2O2 photocatalysis is moving beyond simple performance comparisons. Higher yield remains important, but mechanistic progress will depend on linking molecular structure, supramolecular organization, and framework topology to the spatial location and temporal sequence of ORR, oxidative half-reactions, and H2O2 stabilization. Therefore, conventional descriptors, including band structures, photocurrent responses, and fluorescence quenching efficiencies, should be complemented by more physically informative kinetic and spatial parameters, such as charge transfer pathways, excited-state lifetimes, interfacial reaction timescales, and the spatial matching between active sites and reactants.
Developing a systematic descriptor framework for evaluating spatiotemporal matching will be essential for future studies (Supplementary Table S1). Spatially resolved experiments should identify where electrons and holes accumulate and where O2 activation, hole consumption, and product release occur [Reference Wang, Ding and Li35,Reference Wang, Zhang and Xing36]. Surface photovoltage, Kelvin probe force microscopy, spatially resolved spectroscopy, selective deposition, site blocking, and isotope labeling can provide complementary information. Time-resolved measurements should connect excitation, exciton separation, charge transport, radical or polaronic intermediates, PCET, and product formation. Transient absorption, time-resolved photoluminescence, operando EPR, in situ vibrational spectroscopy, and chopped-light kinetics are most informative when correlated with chemical rates rather than interpreted separately. Beyond conventional static descriptors, future studies should establish quantitative descriptors for spatiotemporal matching. The temporal compatibility between charge transfer and key reaction steps can evaluate whether carriers participate in interfacial reactions within their lifetimes, while the spatial overlap among charge distribution, oxygen diffusion pathways, and active sites can reveal the coupling efficiency between carriers, reactants, and catalytic centers. These descriptors, together with their corresponding characterization and computational methods, are summarized in Supplementary Table S1. These parameters may overcome the limitations of conventional static parameters, including band structures, surface areas, and adsorption energies, providing new guidelines for the rational design of organic photocatalysts.
Computation should also move beyond static O2 adsorption energies [Reference Zhou, Mao and Guo2,Reference Zhang, Tang, Cong and Wang37]. For organic interfaces, useful models should consider charge redistribution, adsorption geometry, proton source, explicit solvation, local electric fields, *OOH formation, water oxidation or alternative hole-consuming pathways, and H2O2 decomposition. Performance reporting should separate formation rate, selectivity, apparent quantum efficiency, solar-to-chemical efficiency, decomposition rate, long-term stability, and utilization efficiency. These quantities are needed to decide whether an improvement arises from faster formation, slower decomposition, better extraction, or more productive downstream chemistry.
From a future development perspective, short-term efforts should focus on establishing spatiotemporal matching descriptors and quantifying them through multidimensional characterization. Medium-term studies should combine time-resolved and spatially resolved techniques to correlate carrier dynamics with interfacial reactions. In the long term, theoretical calculations and artificial intelligence-assisted design may enable the construction of predictable organic photocatalytic interfaces. Ultimately, organic photocatalytic H2O2 synthesis is expected to evolve from empirical structure–performance optimization toward rational design based on spatiotemporal matching, providing new opportunities for solar-driven chemical synthesis and efficient H2O2 utilization.
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Supplementary material
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Author Contributions
X.Z. conceived the topic and overall framework of the perspective. Y.L., X.H., and B.W. contributed to literature collection, organization of the manuscript structure, and preparation of the initial draft. W.C., X.T., and Y.C. contributed to literature analysis, figure preparation, and discussion of representative organic photocatalytic systems. Y.A. contributed to the refinement of the conceptual framework and critical revision of the manuscript. X.Z. supervised the work, revised the manuscript, and finalized the submission. All authors discussed the content, reviewed the manuscript, and approved the final version.
Financial Support
This work was supported by the National Natural Science Foundation of China (22672125), the Natural Science Basic Research Program of Shaanxi (2026JC-YXQN-049), and the Fundamental Research Funds for the Central Universities (GK202602008).
Competing Interests
The authors declare that they have no competing interests.
Data Availability Statement
No new experimental or computational data were generated or analyzed in this perspective article. The discussion is based on previously published literature, and all relevant sources are cited in the manuscript.
Open access
Comments
Dear Professor Zhang and Editors,
We are pleased to submit our Perspective manuscript entitled “Beyond Charge Separation: Spatiotemporal Matching at Organic Photoactive Interfaces for Solar H2O2 Photosynthesis” for consideration for publication in Cambridge Materials: Energy.
This submission follows the kind invitation from Professor Tierui Zhang to contribute a forward-looking article to this newly launched journal. We greatly appreciate the opportunity to contribute to a forum that connects rigorous materials research with renewable energy technologies and broader sustainability challenges.
Solar H2O2 photosynthesis from water and O2/air is an attractive route toward distributed oxidant production under mild conditions. Organic photocatalysts, including supramolecular assemblies, conjugated polymers, covalent organic frameworks and covalent triazine frameworks, provide highly tunable platforms for regulating molecular structure, packing, local polarity and interfacial chemistry. However, the field still often explains H2O2 activity primarily in terms of light absorption, band positions, photoluminescence quenching, photocurrent response or charge-separation efficiency.
In this Perspective, we argue that although charge separation is indispensable, it does not by itself determine H2O2 selectivity, product stability or catalytic durability. The central challenge is to convert transient photogenerated carriers into selective interfacial chemistry. We therefore propose spatiotemporal matching at organic photoactive interfaces as a design framework. Spatial matching emphasizes the proper arrangement of electron-rich O2-activation sites, proton/water environments, hole-consuming regions and H2O2 release pathways. Temporal matching emphasizes the kinetic overlap among photoexcitation, exciton and charge separation, charge transport, proton-coupled electron transfer, oxidative half-reactions, and H2O2 release or stabilization.
Rather than presenting a conventional materials-by-materials review, this Perspective seeks to connect photophysical descriptors with reaction-pathway selection and product handling. We believe this framework can help the field move from empirical structure–property correlations toward more predictive structure–matching–pathway relationships for solar H2O2 synthesis and utilization. The topic is closely aligned with the scope of Cambridge Materials: Energy, particularly its interest in renewable energy conversion, sustainable chemical production, and materials design with broader environmental relevance.
We confirm that this manuscript is original, has not been published previously, and is not under consideration elsewhere. All authors have approved the submission. We also confirm that there are no conflicts of interest to declare.
Thank you very much for considering our manuscript for publication in Cambridge Materials: Energy. We look forward to receiving your feedback.
Sincerely,
Xiaolin Zhu
School of Chemistry and Chemical Engineering
Shaanxi Normal University
Xi’an, China