Water Oxidation Reaction Research Articles

Decomposition of a manganese complex loaded on TiO2 nanoparticles under photochemical reaction

Water splitting, through electrochemical and photochemical methods, is a promising approach for large-scale hydrogen production. However, the efficiency of these methods is hindered by the water-oxidation reaction (WOR). A variety of Mn complexes have been explored as potential models for water-oxidizing complex in Photosystem II. Among different Mn complexes, [H2O(terpy)MnIII(μ-O)2MnIV(terpy)H2O](NO3)3 (1, terpy = 2,2’:6′2″-terpyridine) has been extensively studied under WOR conditions. In this study, the reactivity of 1 is investigated when loaded onto TiO2 nanoparticles and subjected to photochemical conditions. Our main goal was to identify possible products that could arise from the conversion of 1 given the specified conditions. After conducting various analytical methods, it was determined that the reaction yielded MnOx and Mn(II) species as the resulting reaction products. These findings offer valuable insights into the progress of advanced WOR catalysts and the underlying mechanism of efficient water splitting for energy storage.

Heterojunction and co-catalyst engineering of bismuth vanadate by nickel molybdenum oxide and carbon quantum dot decorations for photoelectrochemical water splitting

Improving the charge diffusion length and water oxidation kinetics of bismuth vanadate (BiVO4) is essential to achieve better photoelectrochemical catalytic ability for water oxidation. Establishing heterojunctions and incorporating co-catalysts with BiVO4 create facile charge transfer paths and generate more water oxidation reactions. In this work, nickel molybdenum oxide (NM) and carbon quantum dot (CQD) are firstly deposited on BiVO4 by hydrothermal and soaking processes to design an efficient co-catalyst/photocatalyst system for water oxidation. The depositing amount of CQD is optimized to balance contributions of CQD and NM as the hole sink and the light-to-electron generator, respectively. The highest photocurrent densities of 2.2 and 3.9 mA/cm2 are achieved for BiVO4/NM/CQD in the electrolyte without and with hole scavenger, respectively. The BiVO4 electrode only shows a photocurrent density of 1.2 mA/cm2 in the electrolyte without hole scavenger. The best photoelectrochemical catalytic ability of BiVO4/NM/CQD is approached by the reduced charge-transfer resistance and charge recombination as well as the enhancement on carrier densities. The excellent long-term stability with the photocurrent retention of 90% under illumination for 24 h is also obtained for BiVO4/NM/CQD. This study opens a blueprint on designing efficient catalysts for water oxidation by incorporating heterojunction and co-catalyst materials simultaneously.

Carboxamide Fe(III) complex as the electrocatalyst of water oxidation reaction: WNA and I2M O–O bond formation pathways

A single-site Fe(III) carboxamide complex, [Fe(HbpH) (Cl)2] (1), (HbpH‾ = N,N′-Bis(picolinoyl)hydrazine) anion), was synthesized and used as the electrocatalyst of water oxidation reaction. Complex 1 catalyzes the oxidation of water to O2 at the pH of 8 in phosphate buffer solution with the onset of a catalytic wave at about 0.45 V versus RHE with the turnover frequency (TOF) of 5.8 s−1 at room temperature. The stability of the catalyst in water oxidation processes by electrochemical and UV–vis measurements, demonstrated the realistic molecular electrocatalysis of 1. Differential pulse voltammetry (DPV) of 1 in different pH values showed the dependency of oxidation potential to the pH of the environment, establishing the fact that the catalytic cycle involves the proton-coupled electron transfer (PCET) process. Density functional theory (DFT) calculations on the mechanism of water oxidation process of 1 shows that the oxygen evolution reaction is carried out through the water nucleophilic attack (WNA) to the metal center ion, resulted to the formation of FeIV(O) species. Also, DFT calculations showed that the formation of an O–O bond proceeds through the interaction two molecular mechanism (I2M), which compete with the WNA mechanism following from experimental analysis. The electroactivity of the metal centre and carboxamide ligand and the ability of the ligand to stabilize the high oxidation numbers of the metal-ion centre during the oxidation process, provide different oxidation pathways for an OER process.

Going around the Kok cycle of the water oxidation reaction with femtosecond X-ray crystallography.

The water oxidation reaction in photosystem II (PS II) produces most of the molecular oxygen in the atmosphere, which sustains life on Earth, and in this process releases four electrons and four protons that drive the downstream process of CO2 fixation in the photosynthetic apparatus. The catalytic center of PS II is an oxygen-bridged Mn4Ca complex (Mn4CaO5) which is progressively oxidized upon the absorption of light by the chlorophyll of the PS II reaction center, and the accumulation of four oxidative equivalents in the catalytic center results in the oxidation of two waters to dioxygen in the last step. The recent emergence of X-ray free-electron lasers (XFELs) with intense femtosecond X-ray pulses has opened up opportunities to visualize this reaction in PS II as it proceeds through the catalytic cycle. In this review, we summarize our recent studies of the catalytic reaction in PS II by following the structural changes along the reaction pathway via room-temperature X-ray crystallography using XFELs. The evolution of the electron density changes at the Mn complex reveals notable structural changes, including the insertion of OX from a new water molecule, which disappears on completion of the reaction, implicating it in the O-O bond formation reaction. We were also able to follow the structural dynamics of the protein coordinating with the catalytic complex and of channels within the protein that are important for substrate and product transport, revealing well orchestrated conformational changes in response to the electronic changes at the Mn4Ca cluster.

Impact of Varying the Photoanode/Catalyst Interfacial Composition on Solar Water Oxidation: The Case of BiVO4(010)/FeOOH Photoanodes.

Photoanodes used in a water-splitting photoelectrochemical cell are almost always paired with an oxygen evolution catalyst (OEC) to efficiently utilize photon-generated holes for water oxidation because the surfaces of photoanodes are typically not catalytic for the water oxidation reaction. Suppressing electron-hole recombination at the photoanode/OEC interface is critical for the OEC to maximally utilize the holes reaching the interface for water oxidation. In order to explicitly demonstrate and investigate how the detailed features of the photoanode/OEC interface affect interfacial charge transfer and photocurrent generation for water oxidation, we prepared two BiVO4(010)/FeOOH photoanodes with different Bi:V ratios at the outermost layer of the BiVO4 interface (close to stoichiometric vs Bi-rich) while keeping all other factors in the bulk BiVO4 and FeOOH layers identical. The resulting two photoanodes show striking differences in the photocurrent onset potential and photocurrent density for water oxidation. The ambient pressure X-ray photoelectron spectroscopy results show that these two BiVO4(010)/FeOOH photoanodes show drastically different Fe2+:Fe3+ ratios in FeOOH both in the dark and under illumination with water, demonstrating the immense impact of the interfacial composition and structure on interfacial charge transfer. Using computational studies, we reveal the effect of the surface Bi:V ratio on the hydration of the BiVO4 surface and bonding with the FeOOH layer, which in turn affect the band alignments between BiVO4 and FeOOH. These results explain the atomic origin of the experimentally observed differences in electron and hole transfer and solar water oxidation performance of the two photoanodes having different interfacial compositions.

Exploring the potential of calcined nanolayered manganese oxides for water-oxidation reaction

Large-scale electrochemical and photochemical hydrogen production methods from water splitting are limited by the water-oxidation reaction (WOR). This study investigates the influence of calcination temperatures on the WOR efficiency of layered Mn oxides, which are known for their stability and high catalytic activity. The Mn oxides were synthesized via thermal decomposition of KMnO4 and characterized using various techniques including scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, thermal gravimetric analysis, and Raman spectroscopy. The results indicate that even after calcination at high temperatures (≥400 °C), layered Mn oxides remain effective catalysts for WOR. Notably, the calcined sample at 800 °C in cerium (IV) ammonium nitrate at concentrations of 0.30 M shows maximum turnover frequency and turnover number of 6.7 × 10−6/s and 8.6 × 10−3 mol (O2)/mol (Mn) (for 1300 s), respectively.

Coordination engineering regulating metal single-atom anchored on n-doped carbon as a bifunctional catalyst for H2O2 production via dual channels

Electrochemical synthesis of hydrogen peroxide (H2O2) via two-electron oxygen reduction reaction (2e- ORR) or two-electron water oxidation reaction (2e- WOR), parades great prospects in substituting traditional anthraquinone process. However, the low efficiency and selectivity hinders its practical utilization. Exploration of a bifunctional catalyst capable of simultaneously driving the 2e- WOR and 2e- ORR is crucial for thoroughly improving H2O2 conversion efficiency. Herein, by means of first principles calculation, the 2e- ORR and 2e- WOR activities of metal-nitrogen doped carbon (M−NC, M = Mn, Fe, Co, Ni, Ru, In, and Pt) are investigated. Combining the pyrrole nitrogen coordination regulation, the best sample (RuN(Po)4) is screened from forty single atom configurations, which exhibits ultra-low overpotentials (0.02 V/0.04 V) and excellent inhibition on 4e- ORR/WOR side reactions. In-depth study further verifies its low reaction energy barrier and high thermodynamic stability for H2O2 synthesis in two pathways. Our work is expected to provide useful understanding for designing highly-efficient bifunctional catalysts for H2O2 production.

Correlations between the Electronic Structure and Energetics of the Catalytic Steps in Homogeneous Water Oxidation Catalysis.

The development of an efficient electrocatalyst for the water oxidation reaction is limited by unfavorable scaling relations between catalytic intermediates, resulting in an overpotential. In contrast to heterogeneous catalysts, the electronic structure of homogeneous catalysts can be modified to a great extent due to a tailored ligand design. However, studies utilizing the tunability of organic ligands have rarely been conducted in a systematic manner and, as of yet, have not produced catalytic paths that avoid the aforementioned unfavorable scaling relations. To investigate the influence of electron-donating groups (EDGs) or electron-withdrawing groups (EWGs) on elementary steps in electrochemical water oxidation catalysis, cis-[Ru(bpy)2(H2O)]2+ (bpy = 2,2'-bipyridine) was selected as the scaffold that was modified with methyl, methoxy, chloro, and trifluoromethyl groups. This catalyst can undergo several electron transfer (ET), proton transfer (PT), and proton-coupled electron transfer (PCET) steps that were all probed experimentally. In this systematic study, it was found that PCET steps are relatively insensitive with respect to the presence of EDGs or EWGs, while the decoupled ET and PT steps are more heavily affected. However, the influence of the substituents decreases with an increasing oxidation state of Ru due to a lack of d-electrons available at the Ru center for π-backbonding to the bipyridine ligand. Therefore, the RuV/VI redox couple appears to be relatively unaffected by the substituent. Nevertheless, the implementation of EWGs can shift all oxidation events to a very narrow potential window. Not only do our findings illustrate how electronic substituents affect the entire potential energy landscape of the catalytic water oxidation reaction, but they also show that the cis-[Ru(bpy)2(H2O)]2+ compounds follow different design rules and scaling relations, as has been reported for every other oxygen evolution catalyst thus far.

BiVO4 Heterojunctions as Efficient Photoanodes for Photoelectrochemical Water Oxidation

AbstractPhotoelectrochemical (PEC) water splitting has attracted strong interest as sustainable technology by converting solar energy into hydrogen. The semiconductor photoelectrodes play an important role to increase the solar‐to‐hydrogen conversion efficiency. Bismuth vanadate (BiVO4) is an excellent candidate as a photoanode material for PEC water oxidation because of its visible light absorption, suitable band edge location, high stability and low cost. However, BiVO4 alone may undergo short carrier diffusion length, rapid recombination of photo‐induced charge carriers and photocorrosion. The heterojunction strategy established by combining two or more materials has provided an outstanding technique to address these issues. This Review focuses on recent important works with respect to BiVO4 heterojunction photoanodes for PEC water oxidation reactions, including interface junction and surface functional junction formation. Additionally, challenges faced and prospects for future research on BiVO4 heterojunction photoanodes in the field of solar‐to‐hydrogen conversion are proposed.

Triggering the high catalytic activity of Ni-based catalyst for urea and urine electrolysis by adding Fe and constructing the CoFeP@Ni3S2 heterostructure

For effective hydrogen production, urea oxidation reaction (UOR) with much lower potential has been used to replace the water oxidation reaction (OER), while fulfilling the wastewater treatment. Development of bifunctional electrocatalysts is the crucial link in urea-assistant water electrolysis. Here, a novel composite consisting of the bimetallic phosphide nanosheets and porous Ni3S2 nanospheres was prepared by a hydrothermal-electrodeposition method. It proves that the NF/CoFeP@Ni3S2 electrode exhibits an outstanding performance for HER/UOR (HER overpotential is 173 mV and EUOR is 1.358 V, 100 mA cm−2). As for a two-electrode system taking NF/CoFeP@Ni3S2 as cathode and anode in urea medium, the voltage at 100 mA cm−2 is just 1.454 V. Even in human urine electrolyte, just only a slight current decrease is observed. Both in urea and urine, the voltage of NF/CoFeP@Ni3S2 remain stable during a 50-hour continuous operation. The formation of heterostructures between the bimetallic phosphides and Ni3S2, and Fe addition realize the gradual improvement in activity from the pristine CoP to CoFeP and then to the CoFeP@Ni3S2. This strategy provides a practical hetero-structured catalyst design form considering the structure properties of urea molecule for the efficient water-hydrogen conversion synchronous sewage treatment.

Controllable synthesis of hexagonal h-WO3 microflowers for water oxidation reaction

Tailoring the morphology and crystalline phase of metal oxides induces the variation in structure and surficial microenvironment, in turn influencing their catalytic activity. To date, metastable hexagonal phase WO3 is nearly inactive in electrochemical water oxidation reaction owing to the poor conductivity. Here, we report a facile route to precisely fabricate hexagonal WO3 microflowers with the nanosheet building blocks. In comparison to WO3·0.33H2O microflowers, h-WO3 microflowers could significantly catalyze the transformation of H2O to O2 via water oxidation reaction with high activity of 276 mV at 10 mA/cm2. The synthesized h-WO3 microflowers exhibit superior oxygen evolution efficiency than WO3·0.33H2O microflowers and commercial IrO2. Coordinative unsaturated W sites and hexagonal channels enable them to greatly activate and dissociate the O–H bond into O2 in alkaline electrolyte.

Self-Transformation of Atomically Precise Alloy Nanoclusters to Plasmonic Alloy Nanocrystals: Evaluating Photosensitization in Solar Water Oxidation.

Atomically precise alloy nanoclusters (NCs) inherit the advantages of homometal NC counterparts such as atomic stacking fashion, quantum confinement effect, and enriched catalytic active sites and simultaneously possess the advantageous physicochemical properties such as significantly enhanced photostability, ideal photosensitization efficiency, and favorable energy band structure. Nevertheless, elucidation of the roles of alloy NCs and alloy nanocrystals (NYs) in boosting solar water oxidation has so far not yet been reported owing to the deficiency of applicable alloy NC photosystems. Herein, utilizing the generic thermal-induced self-transformation of alloy NCs to alloy NYs, we comprehensively explore the photosensitization properties of glutathione (GSH)-capped alloy NCs (AgxAu1-x@GSH and CuxAu1-x@GSH) and the corresponding alloy NY (AgAu and CuAu) counterparts in solar water oxidation reaction. The results imply that photoelectrons of alloy NCs surpass the hot electrons over plasmonic alloy NYs in stimulating the PEC water oxidation reaction. The photoelectrons of alloy NCs demonstrate lower interfacial charge-transfer resistance, longer carrier lifetime, and a more enhanced photosensitization effect with respect to the plasmonic alloy NYs, contributing to the significantly boosted photoelectrochemical water oxidation activities. Moreover, we found that our result is universal.

Fabrication of MIL‐101(Fe) on UiO‐66 as an Electrocatalyst for Enhanced Overall Water Splitting

AbstractThe water‐splitting process is an attractive avenue for manufacturing hydrogen gas (a green and renewable energy source). However, this process requires efficient and economical electrocatalysts to lessen the high energy barrier of water oxidation and hydrogen evolution reactions. MOF‐on‐MOF hybrid structures assembled by unifying two or more MOF units are being explored as electrocatalysts with promising results. In this study, a novel electrocatalyst nanostructure of an iron‐based MOF on a zirconium‐based MOF denoted as MIL‐101(Fe)/UiO‐66 was prepared by hydrothermal synthesis. MIL‐101(Fe) offers abundant active sites with higher surface area for catalytic activity, while UiO‐66 acts as a support to enhance stability and conductivity. It was observed that compared to the individual MOFs, hybrid (MIL‐101(Fe)/UiO‐66) exhibited significantly enhanced catalytic efficiency towards overall water‐splitting. This was evidenced by the higher current densities and lower overpotentials observed for the hybrid. The MIL‐101(Fe)/UiO‐66 showed an overpotential of 185 mV for HER and 290 mV for OER @ η10 in an alkaline electrolyte solution. Moreover, it was stable for over 24 hours with a very small decrease in activity. With MIL‐101(Fe)/UiO‐66 as the cathode and anode, the unified water‐splitting cell attained a low overall required potential of 1.58 V @ η10 demonstrating good performance of overall water splitting. It offers an appealing strategy for creating high‐performance electrocatalysts for energy‐related applications, in particular water splitting, by combining the advantages of different MOFs through facile fabrication methods.

Bifunctional Electrode Design Targeting Co‐Enhanced Kinetics and Mass Transport for Hydrogen and Water Oxidation Reactions (Adv. Funct. Mater. 40/2023)

Bifunctional Electrode Design Targeting Co‐Enhanced Kinetics and Mass Transport for Hydrogen and Water Oxidation Reactions (Adv. Funct. Mater. 40/2023)

Extremely low onset potential of modified Fe2O3 photoanode for water oxidation

The photoelectrochemical (PEC) performance of hematite (α-Fe2O3)-based photoanodes is still far from its theoretical value because they are constrained by serious charge recombination and sluggish water oxidation kinetics. Herein, we developed a heterostructural photoanode by coating boron doped graphite carbon nitride nanolayers onto an Fe2O3 nanoarray (BCN/Fe2O3), followed by modification with NiCo(OH)x cocatalyst. The constructed NiCo(OH)x/BCN/Fe2O3 demonstrates a significantly improved photocurrent density of 2.7 mA cm−2 at 1.23 VRHE (V versus reversible hydrogen electrode), which is 3.2 times higher than that of pristine Fe2O3. Additionally, it exhibits an extremely negative onset potential of 0.60 VRHE. Detailed studies reveal that the BCN/Fe2O3 heterojunction endows a driving force for charge separation and establishes a direct pathway for their transport, while NiCo(OH)x acts as a cocatalyst to accelerate the surface water oxidation reaction.

Iron Cobalt Phosphonate Derived Heteroatom Doped Metal Oxides as Superior Electrocatalysts for Water Oxidation Reaction

AbstractThe development of low cost‐effective and highly efficient heterogeneous electrocatalysts is most appreciable in the research community. A newly designed microporous organic‐inorganic hybrid iron cobalt phosphonate (FeCoDPAM) is synthesized using diphenylphosphinamide as an organophosphorus ligand through a hydrothermal pathway without any template. To synthesize N, P‐codoped bimetallic oxides (NP/FeCoO350, NP/FeCoO550, and NP/FeCoO750), the as‐synthesized material FeCoDPAM has undergone pyrolysis at three different temperatures, i. e., 350, 550, 750 °C, respectively. The high specific surface area and a regular microporous array of N, P‐codoped iron cobalt oxide (NP/FeCoO350) material provide excellent oxygen evolution reaction (OER) activity. The NP/FeCoO350 material catalyzes OER with the overpotential of 331 mV at a current density of 10 mAcm−2 and Tafel slope of 56.7 mV dec−1 in 1.0 M KOH solution. The inclusion of iron in the cobalt phosphonate framework can change the electronic structure, and electron transfer can be feasible to the d‐orbital of cobalt. Due to the doping of heteroatoms such as N and P into the bimetallic oxide matrix, a synergistic effect can occur, which is the driving force for the efficient electrocatalytic OER activity. Also, the FeCoO350 displays stability with outstanding oxidative current up to 50 h time in chronoamperometry measurement.

Anchoring (fullerol‐)Ru‐based‐complex onto TiO2 for Efficient Water Oxidation Catalysis

AbstractRuthenium polypyridine complexes are the most effective catalysts for the water oxidation reaction (WOR), but the catalytic activity still has a large room for improvement. Herein, a fullerol‐based ruthenium complex was prepared by the covalent grafting of the polypyridyl ruthenium complex of water oxidation catalyst (WOC) with fullerol, and the (fullerol)‐Ru‐based WOCs anchored on the surface of nano‐TiO2 were prepared through a sensitization strategy. The synthesized heterogeneous nano‐catalysts are fully characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), infrared spectroscopy (IR), Brunauer–Emmett–Teller (BET) specific surface area and pore size distribution, and diffusion reflection ultraviolet‐visible spectrum (DRS). The chemical oxygen evolution experiments reveal that the WOR catalyzed by the catalyst is a first‐order reaction with respect to Ce (NH4)2(NO3)6 (denoted as CAN) concentration when using CAN as the sacrificial oxidant under acidic conditions. The anchoring of Ru‐based WOC to TiO2 result in a decrease in the redox potentials of RuIV/III couples, which decrease the barrier of the crucial O−O bond‐forming step, and the heterogeneous nano‐catalyst exhibit a high catalytic activity with a turnover frequency of 13.4 s−1 and more excellent stability with a 15‐min‐turn over number of 1054 for TiO2‐fullerol‐based ruthenium complex WOC.

Concurrent oxygen reduction and water oxidation at high ionic strength for scalable electrosynthesis of hydrogen peroxide

Electrosynthesis of hydrogen peroxide via selective two-electron transfer oxygen reduction or water oxidation reactions offers a cleaner, cost-effective alternative to anthraquinone processes. However, it remains a challenge to achieve high Faradaic efficiencies at elevated current densities. Herein, we report that oxygen-deficient Pr1.0Sr1.0Fe0.75Zn0.25O4-δ perovskite oxides rich of oxygen vacancies can favorably bind the reaction intermediates to facilitate selective and efficient two-electron transfer pathways. These oxides exhibited superior Faradic efficiencies (~99%) for oxygen reduction over a wide potential range (0.05 to 0.45 V versus reversible hydrogen electrode) and current densities surpassing 50 mA cm−2 under high ionic strengths. We further found that the oxides perform a high selectivity (~80%) for two-electron transfer water oxidation reaction at a low overpotential (0.39 V). Lastly, we devised a membrane-free electrolyser employing bifunctional electrocatalysts, achieving a record-high Faradaic efficiency of 163.0% at 2.10 V and 50 mA cm−2. This marks the first report of the concurrent oxygen reduction and water oxidation catalysed by efficient bifunctional oxides in a novel membrane-free electrolyser for scalable hydrogen peroxide electrosynthesis.

Combining heterointerface/surface oxygen vacancies engineering of bismuth oxide to synergistically improve its solar water splitting performance

Solar-powered photoelectrochemical (PEC) water splitting is recognized as a strategy for addressing fossil resource and global warming concerns. The purpose of this paper is to demonstrate for the first time a facile method to fabricate dendritic nanostructured (DN) Bi:Bi2O3 heterointerface engineering junctions that possess abundant surface oxygen vacancies (OVs, DN Bi:Bi2O3-OVs/FTO), with outstanding PEC performance. The surface OVs serve as shallow donors and active reaction sites, whereas the Bi-metal bridges are used for fast electron transport. Furthermore, surface OVs can enhance the surface features of Bi:Bi2O3 heterointerfaces and boost their electrical conductivity and donor density. This greatly enhances electrolyte ion and electron mobility, resulting in rapid water oxidation reactions at the Bi:Bi2O3/electrolyte interfaces. By combining the Bi:Bi2O3 heterointerface junction and surface OVs, we are able to create an effective photoanode with 95 % charge injection efficiency, applied bias photon-to-current efficiency (ABPE) of 0.112 %, and a photocurrent response of 0.334 mA.cm−2 at 1.23 V vs. the reversible hydrogen electrode (RHE), which represents improvements of about 4.5 and 10 folds over that of pure DN Bi2O3 photoanode. It is possible to construct a variety of unique nanostructured electrodes with adjustable optical and electronic properties to be used in solar cells, energy storage, and PEC applications.

Embedding Carbon Quantum Dots into Crystalline Polyimide Covalent Organic Frameworks to Enhance Water Oxidation for Achieving Dual-Channel Photocatalytic H2O2 Generation in a Wide pH Range.

Photocatalytic technique is regarded as the cleanest approach for producing H2O2. Herein, two kinds of novel polyimide COFs decorated with CQDs (namely, MPa-COFs/CQDs and MNd-COFs/CQDs) were constructed by using the one-pot hydrothermal method. Due to the electron donor role of CQDs, the recombination of photoinduced electrons and holes was suppressed after the combination of polyimide COFs with CQDs. Importantly, the introduction of CQDs not only boosted the absorbing ability of polyimide COFs toward visible light but also reduced the impedance and improved the charge transfer efficiency. After CQDs were embedded into polyimide COFs, the surface hydrophilicity of catalysts was significantly improved, which provided convenience for the water oxidation reaction. Benefiting from the electron donor-acceptor interaction between polyimide COFs and CQDs, a step-by-step two-electron oxygen reduction reaction over polyimide COFs was enhanced. More interestingly, the embedding of CQDs can create a direct two-electron water oxidation reaction pathway, which played an important role in photocatalytic H2O2 generation. Meanwhile, H+ generated from water oxidation can also be used for the reduction of oxygen to form H2O2. Under the synergistic effects of water oxidation and oxygen reduction, as-prepared MPa-COFs/CQDs-2 displayed excellent performance in photocatalytic H2O2 generation, and its yield was as high as 540 μmol/g within 60 min. In short, the current work shared an effective strategy to improve the performance of polyimide COFs in photocatalytic H2O2 production.