Two-electron Oxidation Of Water Research Articles

Membrane-free Electrolysis Production of Hydrogen Peroxide on Low-Cost Metal-Free Electrocatalysts for Dye Degradation.

The efficient production of hydrogen peroxide (H2O2) solution was achieved by combining cathodic two-electron oxygen reduction (2e- ORR) and anodic two-electron water oxidation (2e- WOR) in two half-reaction cells. h-BN loaded on carbon fibers (h-BN@C) is prepared and employed as an anode material to catalyze 2e- WOR, while sulfonated commercial BP-2000 carbons (BP-2000-SO3H) were prepared as the cathode materials for 2e- ORR. In a 2 M KHCO3 solution, an overall Faradaic efficiency of 97% and a total H2O2 production rate of 1872 mmol g-1 h-1 over metal-free electrodes were accomplished in a membrane-free flow cell. The dilute H2O2 solution could be directly used to degrade cationic Rhodamine B or methyl orange and anionic methylene blue dyes in water. This work proved low-cost production of dilute H2O2 solution in simple membrane-free flow cells with single electrolyte and on-site utilization for efficient dye degradation.

Al-N3 Bridge Site Enabling Interlayer Charge Transfer Boosts the Direct Photosynthesis of Hydrogen Peroxide from Water and Air.

Manipulating the electronic environment of the reactive center to lower the energy barrier of the rate-determining water oxidation step for boosting the direct generation of H2O2 from water, air, and sunlight is fascinating yet remains a grand challenge. Driven by a first-principles screening across a series of metal single atoms in carbon nitride, we report a class of an Al-N3 bridge site enabling interlayer charge transfer in carbon nitride nanotubes (CNNT-Al) for the highly efficient photosynthesis of H2O2 directly from water, oxygen, and sunlight. We demonstrate that the interlayered Al-N3 bridge site in CNNT-Al is able to activate the neighboring surface N atom for promoting the rate-determining step of the two-electron water oxidation to H2O2. It is also able to act as a bridge for enhancing the vertical interlaminar charge transfer due to the hybridization between the 3s and 3p states of the interstitial Al atom and the conduction band of two adjacent carbon nitride layers. Collectively, these factors lead to a highest photocatalytic mass activity of 1410.2 μmol g-1 h-1 (with a photocatalyst concentration of 1 g L-1) for direct photosynthesis of H2O2 out of all CN-based photocatalysts and a 7-fold higher solar-to-chemical conversion efficiency (0.73%) compared to that of the natural photosynthesis of typical plants (∼0.1%). Most importantly, the CNNT-Al-based flow reactor can steadily produce H2O2 for 200 h and be directly used for the on-site degradation of organic dye in water. The CNNT-Al-based flow reactor can also kill a 10 times higher concentration of bacteria in deionized water than that in natural water with 100% efficiency, which makes our design economically appealing for practical water treatment.

Enhancement of Charge Separation in the Photochemical Two-Electron Water Oxidation by Sn-Porphyrins Covalently Bound through Silylation with Flexible Bridging Moieties on SnO2 Nanoparticles

Enhancement of Charge Separation in the Photochemical Two-Electron Water Oxidation by Sn-Porphyrins Covalently Bound through Silylation with Flexible Bridging Moieties on SnO₂ Nanoparticles

Advances in Two-Electron Water Oxidation Reaction for Hydrogen Peroxide Production: Catalyst Design and Interface Engineering.

Hydrogen peroxide (H2O2) is a versatile and zero-emission material that is widely used in the industrial, domestic, and healthcare sectors. It is clear that it plays a critical role in advancing environmental sustainability, acting as a green energy source, and protecting human health. Conventional production techniques focused on anthraquinone oxidation, however, electrocatalytic synthesis has arisen as a means of utilizing renewable energy sources in conjunction with available resources like oxygen and water. These strides represent a substantial change toward more environmentally and energy-friendly H2O2 manufacturing techniques that are in line with current environmental and energy goals. This work reviews recent advances in two-electron water oxidation reaction (2e-WOR) electrocatalysts, including design principles and reaction mechanisms, examines catalyst design alternatives and experimental characterization techniques, proposes standardized assessment criteria, investigates the impact of the interfacial milieu on the reaction, and discusses the value of in situ characterization and molecular dynamics simulations as a supplement to traditional experimental techniques and theoretical simulations, as shown in Figure 1. The review also emphasizes the importance of device design, interface, and surface engineering in improving the production of H2O2. Through adjustments to the chemical microenvironment, catalysts can demonstrate improved performance, opening the door for commercial applications that are scalable through tandem cell development.

Novel electrocatalyst with abundant oxygen vacancies enabling efficient two-electron water oxidation reaction for H2O2 synthesis

In the realm of electrocatalytic two-electron water oxidation reaction, the quest for efficient and selective catalysts poses a significant challenge in balancing productivity and activity, hindering the decentralized generation of hydrogen peroxide (H2O2) through electrochemical means. Addressing this hurdle, our study introduces a novel approach to crafting an effective and stable electrocatalyst for the two-electron water oxidation reaction (2e-WOR). Through the synthesis of magnesium stannite tungstate from a mixture of MgSnO3 and WO3, the engineer of a material with abundant oxygen vacancies is crucial for catalytic activity. This catalyst demonstrates exceptional performance, ascribed to its distinctive oxygen vacancies proximal to the active center Sn and electronic modulation by tungsten. Notably, Mg1-xSnWO6-x700 exhibits a remarkably low overpotential of 70 mV at 10 mA cm−2, coupled with a high faradic efficiency of 84 % for 2e- WOR at 2.6 V vs. RHE, maintaining consistent performance over 35 h. Furthermore, the formation of oxygen vacancies and the associated electronic transfer underscore the novelty and promise of our material in advancing the field of two-electron WOR. In sum, our electrocatalyst presents a cost-efficient and selective solution for water oxidation, offering potential avenues for enhancing H2O2 production.

Photoelectrochemical Synthesis of Hydrogen Peroxide from Saline Water via the Two-Electron Water Oxidation Reaction.

Hydrogen peroxide (H2O2) production on the anode is more valuable than oxygen and chlorine evolution for photoelectrochemical saline water splitting. In this work, by the introduction of bicarbonate (HCO3-), H2O2 is produced from saline water (2 M KHCO3 + 0.5 M NaCl aqueous solution) via the two-electron water oxidation reaction by a photoanode of bismuth vanadate (BiVO4). Furthermore, the Faradaic efficiency (FE) and accumulation for H2O2 are improved by coating antimony tetroxide (Sb2O4) on BiVO4. A H2O2 FE of 26% at 1.54 V vs RHE is obtained by Sb2O4/BiVO4 and 49 ppm of H2O2 is accumulated after a 135 min chronoamperometry. Similar to that in KHCO3 pure water solution, infrared spectroscopy and electrochemical analysis confirm that HCO3- plays a surface-mediating role in the formation of H2O2 in KHCO3 saline water solution. The presence of HCO3- in the electrolyte is able to not only increase the photocurrent density but also effectively inhibit the chlorine evolution reaction.

Metal Supported Metal Oxide Catalysts for Hydrogen Peroxide Production Via Water Splitting

The two-electron water oxidation reaction (WOR) has drawn recent attention as an efficient, simple method of producing on-site hydrogen peroxide through electrochemical water splitting. However, finding electrocatalysts with high activity and stability in the reaction’s harsh oxidizing environment is challenging. This is made especially difficult due to the competing four-electron and one-electron WOR, which necessitate a catalyst material with high selectivity towards the hydrogen peroxide production pathway. Here, we utilize metal/metal oxide coupling interactions to tune metal oxide catalysts to be active for 2 e- WOR via the creation of a Mott-Schottky junction. Metal/metal oxide interactions have been well studied for supported metal catalysts, but their behavior has been less investigated for catalysts where the metal oxide provides the active sites, called inverse catalysts. In this case, the difference in work functions between the metal support and metal oxide semiconductor catalyst drives electron transfer between the two, facilitating electronic interactions which can modulate the binding energy of reaction intermediates at the interface and thus tune the catalytic ability of the metal oxide. In this work, we investigate a variety of metal oxide catalyst and metal support materials and find that a thin layer of indium tin oxide (ITO) supported by a layer of platinum (Pt) has excellent catalytic ability towards 2 e- WOR. The activity, selectivity, and stability of the ITO/Pt catalyst shows significant improvement over the unsupported ITO catalyst and yields hydrogen peroxide production rates greater than those reported in literature using other standard catalysts for this reaction. This method of catalyst engineering also provides a future pathway to create new catalysts for this electrochemical reaction. Figure 1

Stable production of hydrogen peroxide over zinc oxide @ zeolitic imidazolate Framework-8 composite catalysts

A promising method of producing hydrogen peroxide (H2O2) is the electrochemical two-electron water oxidation reaction (2e− WOR). In this process, it is important to design electrocatalysts that are both earth abundant and environmentally friendly, as well as offering high stability and production rates. The research of WOR catalysts, such as the extensively used transition metal oxides, is mainly focused on the modification of transition metal elements. Few studies pay attention to the protective heterostructure of metal oxides. Here, we demonstrate for the first time an organometallic skeleton protection strategy to develop highly stable WOR catalysts for H2O2 generation. Unlike the pure ZnO and zeolite imidazole framework-8 (ZIF-8) catalysts, ZnO@ZIF-8 enabled the production of hydrogen peroxide at high voltages. The experimental results demonstrate that the ZnO@ZIF-8 catalyst stably generates H2O2 even under a high voltage of 3.0 V vs. RHE, with a yield reaching 2845.819 μmolmin−1 g−1. ZnO@ZIF-8 shows a relatively low overpotential, with a current density of 10 mA cm−2 and an overpotential of 110 mV. The ZnO@ZIF-8 catalyst’s maximal FE value was 4.72 %. Moreover, the ZnO@ZIF-8 catalyst exhibits remarkable durability even after an extended 60-hour stability test. Operando Raman and theoretic calculation analyses reveal that the metal–organic skeleton being encapsulated on the metal oxide surface synergizes with each other, not only expanding the electrochemical surface area, but also adjusting the catalyst metal sites’ adsorption capacity. A novel approach to the modification of 2e− WOR metal oxide catalyst is presented in this work.

Molybdenum oxide catalyst for wastewater treatment studied by faradaic efficiency

The measurements of gas volumes evolved during electrochemical wastewater treatment provide the information on the process faradaic efficiency. This work demonstrates how it enables identification of the water oxidation pathway (2 or 4 electron) in flow electrolysis process through the application of the formulae suggested in the study. This way, the real wastewater oxidation strength, i.e. production of hydrogen peroxide can be determined based on calculations. These provide more accurate results than direct measurements of accumulated hydrogen peroxide concentration after the electrolysis process, as its instability may lead to its immediate decomposition and false results. As an example provided in the paper, the application of MoO3 as a catalyst in the carbon composite electrode indicates almost no hydrogen peroxide detected after the process, whereas its oxidative properties owing to production of hydroxyradicals demonstrate complete decomposition of wastewater analogue (methylene blue). The calculations point to high production of H2O2. Using pure carbon material without the catalyst in the same experiment, decomposition occurs at much lower rate. The possible mechanisms behind the processes are discussed. The approach presented in the work can aid to efficient development of catalysts towards two-electron water oxidation.

Bioinspired Tetranuclear Manganese Cubane Complex as an Efficient Molecular Electrocatalyst for Two-Electron Water Oxidation Towards Hydrogen Peroxide.

Stable homogeneous two-electron water oxidation electrocatalysts are highly demanded to understand the precise mechanism and reaction intermediates of electrochemical H2O2 production. Here we report a tetranuclear manganese complex with a cubane structure which can electrocatalyze water oxidation to hydrogen peroxide under alkaline and neutral conditions. Such a complex demonstrates an optimal Faradaic efficiency (FE) of 87 %, which is amongst (if not) the highest FE(H2O2) of reported homogeneous and heterogeneous electrocatalysts. In addition, active species were identified and co-catalysts were excluded through ESI-MS characterization. Furthermore, we identified water binding sites and isolated one-electron oxidation intermediate by chemical oxidation of the catalyst in the presence of water substrates. It is evident that efficient proton-accepting electrolytes avoid rapid proton building-up at electrode and substantially improve reaction rate and selectivity. Accordingly, we propose a two-electron catalytic cycle model for water oxidation to hydrogen peroxide with the bioinspired molecular electrocatalyst. The present work is expected to provide an ideal platform to elucidate the two-electron WOR mechanism at the atomic level.

Tandem Fields Facilitating Directional Carrier Migration in Van der Waals Heterojunction for Efficient Overall Piezo-Synthesis of H2O2.

Piezo-synthesis of H2O2 utilizing sustainable mechanical energy as well as earth-abundant water and oxygen is a green, cost-effective, and promising approach. However, achieving simultaneous two-electron water oxidation reaction (2e- WOR) and two-electron oxygen reduction reaction (2e- ORR) faces huge challenges due to insufficient synergistic active sites and slow/messy carrier transfer. Herein, a novel 2D/2D van der Waals heterojunction consisting of BiOIO3 and carbon nitride (BIO/CN) is elaborately designed for highly efficient overall H2O2 piezo-synthesis. Theoretical/experimental results reveal that a Z-scheme electron transfer is formed and facilitated by the tandem interfacial electric field and the bulk piezo-polarization field. On this basis, the carriers are efficiently separated while the oxidation/reduction capacity is preserved, thus providing the strong driving force for the 2e- WOR and 2e- ORR on BIO and CN, respectively. Furthermore, the kinetic and thermodynamic processes of WOR and ORR for H2O2 synthesis improve remarkably. Therefore, BIO/CN exhibits an excellent H2O2 yield of 259.8µM within 30min in pure water and air atmosphere (without any sacrificial agents and aeration). This study provides a new idea on strategically controlling electron transfer toward high-efficiency H2O2 piezo-synthesis and expands the avenue for developing effective environmental purification materials.

Photocatalytic H2O2 production and fuel cell performance based on PDI nanobelts enhanced by surface plasmon resonance of gold nanoparticles

The photocatalytic hydrogen peroxide (H2O2) fuel cell represents an innovative self-powered apparatus amalgamating the production and conversion of H2O2 to supply electricity. Using efficient photocatalyst as photoanode to realize two-electron water oxidation to produce H2O2 is considered as a key factor to improve the performance of fuel cell. In this study, perylene imide nanobelts decorated with gold nanoparticles (Au/PDI) were synthesized and subsequently employed as the photoanode to construct a photocatalytic H2O2 fuel cell. This cell can produce H2O2 under irradiation and store it, subsequently utilizing the stored H2O2 to generate electricity in the absence of light. The maximum power density of Au/PDI-based cell could reach 1.07 mW·cm−2 under AM 1.5 G solar light, which has around 1.7 times enhancement compared to PDI-based cell. Meanwhile, a specific capacitance of 5661 mF·cm−2 was obtained after 3 h irradiation. After operating the cell for 12 h, the specific capacitance remained at 50.2 % of its initial value. It is indicated that PDI-based photocatalysts hold considerable promise in water oxidation for H2O2 production. The incorporation of noble nanometals has shown effective enhancement in photocatalytic H2O2 production through the localized surface plasmon resonance (LSPR) effects, thereby enriching the photoanode materials designed for H2O2 fuel cell application.

Characterization and H2O2 production mechanisms study on self-oxidized graphite during the two-electron water oxidation electrochemical process

The 2e− water oxidation process is an eco-friendly way to produce H2O2 using water as the raw material. It avoids the low solubility of oxygen in water, unlike traditional oxygen reduction methods. However, electrocatalysts always suffer from self-oxidation during the oxidation reaction, leading to decreased activity. We solved this by using non-metal graphite electrocatalysts that undergo an evolution process to oxidized carboxylated graphite, which is even more active. A defect forms on the graphite surface that facilitates HCO3− adsorption. The –COOH group easily forms a –COOOH intermediate, which is advantageous for hydrogen peroxide generation. The hydrogen peroxide generation rate is 4.55 times higher than that of initial graphite. Graphite is an environmentally friendly catalyst that avoids the release of metal ions, making it more suitable for large-scale applications.

Nanostructured boron-doped diamond electrodes for two-electron water oxidation to produce hydrogen peroxide

Boron-doped diamond (BDD) electrodes have been widely used in water treatment, e.g., degradation of antibiotics and pigments for water purification. Hydrogen peroxide production by two-electron electrochemical oxidation of water is a green and attractive method that has the potential to replace the conventional anthraquinone autoxidation (AO) process. In this study, BDD films were prepared on single-crystal silicon wafers by using hot-filament chemical vapor deposition (HFCVD) technique. Then, dense tubular nanostructure (nanotubes) arrays were prepared on the BDD films employing inductively coupled plasma (ICP) etching. Energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) proved the formation of oxygen-terminated nanostructures, which was ascribed to the oxygen plasma and the self-masking. The length of diamond nanotubes as well as the root diameter increased gradually and non-linearly with the increase of etching time. It was indicated by cyclic voltammetry (CV) analysis that the effective active area of the electrodes increased after etching, and variations of resulting reaction performance were observed. The oxygen-terminated and nanostructured BDD electrode obtained by etching with the optimized parameters features better electrocatalytic performance, with reduced oxidation potential and 46.8 % higher Faraday Efficiency (FE) for hydrogen peroxide production, compared to the original BDD sample. Therefore, the manufacturing of nanostructures is an effective method to improve the efficiency of BDD water oxidation for the production of hydrogen peroxide.

Carbazole-containing covalent triazine frameworks for efficient hydrogen peroxide photosynthesis from natural sunlight

Hydrogen peroxide (H2O2) photosynthesis via polymer photocatalysts is an environmentally friendly and sustainable method for H2O2 production. However, their efficiency is currently unsatisfactory due to limited dissociation and insufficient migration of photogenerated charge carriers. Constructing donor–acceptor (D-A) type polymer photocatalysts has been demonstrated to be a promising approach to improve their optical and electronic properties related to charge carrier separation and migration. Herein, we design two donor–acceptor (D-A) type carbazole-containing covalent triazine frameworks (CTF-PCZs), namely CTF-BPCZ and CTF-TPCZ. These CTF-PCZs are found to reduce the exciton binding energy (Eb) and enhance charge carriers transfer ability compared to non-D-A type CTF-HUST-1. Remarkably, CTF-TPCZ exhibit excellent H2O2 photosynthesis performance, achieving a rate of up to 10331 μmol g−1 h−1 from pure water under solar simulator (AM 1.5G), and 6039 μmol g−1 h−1 from pure water under natural sunlight irradiation in scaled-up photocatalytic experiments, significantly surpass those of all previously reported polymer-based photocatalysts. In-situ experiments provide direct evidence for intermediates involved in the photocatalytic process. Both experiments and DFT calculations reveal that the triazine ring fragment plays a crucial role in H2O2 photosynthesis through a two-step single-electron oxygen reduction reaction (ORR) and the carbazolyl group plays a crucial role in one-step two-electron water oxidation reaction (WOR).

Study on Influence Factors of H2O2 Generation Efficiency on Both Cathode and Anode in a Diaphragm-Free Bath.

Electrosynthesis of H2O2 via both pathways of anodic two-electron water oxidation reaction (2e-WOR) and cathodic two-electron oxygen reduction reaction (2e-ORR) in a diaphragm-free bath can not only improve the generation rate and Faraday efficiency (FE), but also simplify the structure of the electrolysis bath and reduce the energy consumption. The factors that may affect the efficiency of H2O2 generation in coupled electrolytic systems have been systematically investigated. A piece of fluorine-doped tin oxide (FTO) electrode was used as the anode, and in this study, its catalytic performance for 2e-WOR in Na2CO3/NaHCO3 and NaOH solutions was compared. Based on kinetic views, the generation rate of H2O2 via 2e-WOR, the self-decomposition, and the oxidative decomposition rate of the generated H2O2 during electrolysis in carbonate electrolytes were investigated. Furthermore, by choosing polyethylene oxide-modified carbon nanotubes (PEO-CNTs) as the catalyst for 2e-ORR and using its loaded electrode as the cathode, the coupled electrolytic systems for H2O2 generation were set up in a diaphragm bath and in a diaphragm-free bath. It was found that the generated H2O2 in the electrolyte diffuses and causes oxidative decomposition on the anode, which is the main influent factor on the accumulated concentration in H2O2 in a diaphragm-free bath.

Oxygen vacancy based WO3/SnO2-x promote electrochemical H2O2 accumulation by two-electron water oxidation reaction and toxic uniform dimethylhydrazine degradation

The key to constructing an anodic electro-Fenton system hinges on two pivotal criteria: enhancing the catalyst activity and selectivity in water oxidation reaction (WOR), while simultaneously inhibiting the decomposition of hydrogen peroxide (H2O2) which is on-site electrosynthesized at the anode. To address the issues, we synthesized novel WO3/SnO2-x electrocatalysts, enriched with oxygen vacancies, capitalize on the combined activity and selectivity advantages of both WO3 and SnO2-x for the two-electron pathway electrocatalytic production of H2O2. Moreover, the introduction of oxygen vacancies plays a critical role in impeding the decomposition of H2O2. This innovative design ensures that the Faraday efficiency and yield of H2O2 are maintained at over 80 %, with a noteworthy production rate of 0.2 mmol h−1 cm−2. We constructed a novel electro-Fenton system that operates using only H2O as its feedstock and applied it to treat highly toxic uniform dimethylhydrazine (UDMH) from rocket launch effluent. Our experiments revealed a substantial total organic carbon (TOC) removal, achieving approximately 90 % after 120 mins of treatment. Additionally, the toxicity of N-nitrosodimethylamine (NDMA), a byproduct of great concern, was shown to be effectively mitigated, as evidenced by acute toxicity evaluations using zebrafish embryos. The degradation mechanism of UDMH is predominantly characterized by the advanced oxidative action of H2O2 and hydroxyl radicals, as well as by complex electron transfer processes that warrant further investigation.

Rational engineering WO3-X/CNTs@carbon fiber membrane for the high-efficient produce H2O2 via electrochemical two-electron water oxidation route

The electrochemical two-electron water oxidation reaction (2e-WOR) offers a promising avenue for hydrogen peroxide (H2O2) production. It is crucial to design electrocatalysts with high selectivity, yield, resource abundance, and environmental friendliness. In this paper, as a new generation 2e-WOR electrocatalyst, the WO3-X/CNTs@carbon fiber membrane nanostructure with abundant oxygen-rich vacancy (OV) has been discovered by a series of test techniques including XRD, FE-SEM, TEM, FT-IR, Raman and XPS, comprising interconnected carbon nanotubes and carbon fibers enveloped in WO3 nanorods with oxygen-rich vacancies. By comparing the specific surface area of WO3-x/CNTs@carbon fiber membrane at different temperatures, it was observed that the maximum value is 44.09 m2/g when the mass ratio of AMT to PAN was 3:2 at 600 °C. Furthermore, the WO3-X/CNTs@carbon fiber membrane can be directly utilized as an independent electrode. The electrochemical performance test revealed that the Faraday efficiency of the WO3-X/CNTs @CF-600-2 can reach 54 % (2.48 V vs RHE (reversible hydrogen electrode)), while the H2O2 yield can achieve 10.3 μmol· min−1·cm−2, nearly ten times higher than that of pure WO3. Furthermore, the stability testing demonstrated that after 12 h, the WO3-X/CNTs @CF-600-2 exhibited excellent stability with minimal change in its Faraday efficiency. This enhancement is attributed to the improved selectivity of WO3, excellent electrical conductivity, and mass transfer performance of carbon fiber. Finally, we proposed a mechanism for 2e-WOR and provided some perspectives on this reaction along with summarizing recent discoveries.

Factors Controlling the Photochemical Two-Electron Water Oxidation Initiated By One-Electron in the Molecular Catalyst Sensitized System for Artificial Photosynthesis

Factors Controlling the Photochemical Two-Electron Water Oxidation Initiated By One-Electron in the Molecular Catalyst Sensitized System for Artificial Photosynthesis

Efficient Photosynthesis of Hydrogen Peroxide by Cyano-Containing Covalent Organic Frameworks from Water, Air and Sunlight.

The insufficient exciton (e- -h+ pair) separation/transfer and sluggish two-electron water oxidation are two main factors limiting the H2 O2 photosynthetic efficiency of covalent organic frameworks (COFs) photocatalysts. Herein, we present an alternative strategy to simultaneously facilitate exciton separation/transfer and reduce the energy barrier of two-electron water oxidation in COFs via a dicyano functionalization. The in situ characterization and theoretical calculations reveal that the dicyano functionalization improves the amount of charge transfer channels between donor and acceptor units from two in COF-0CN without cyano functionalization to three in COF-1CN with mono-cyano functionalization and four in COF-2CN with dicyano functionalization, leading to the highest separation/transfer efficiency in COF-2CN. More importantly, the dicyano group activates the neighbouring C atom to produce the key *OH intermediate for effectively reducing the energy barrier of rate-determining two-electron water oxidation in H2 O2 photosynthesis. The simultaneously enhanced exciton separation/transfer and two-electron water oxidation in COF-2CN result in high H2 O2 yield (1601 μmol g-1 h-1 ) from water and oxygen without using sacrificial reagent under visible-light irradiation. COF-2CN can effectively yield H2 O2 in water with wide pH range, in different real water samples, in scaled-up reactor under natural sunlight irradiation, and in continuous-flow reactor for consecutively producing H2 O2 solution for water decontamination.