H2O O2 Research Articles

Colloid-Chemical Mechanisms of the Formation of Ultra- and Nanosize Iron Oxide/Hydroxide Phases Obtained in the Fe0(St3)–H2O–O2 System and Their Electrokinetic Properties. I. Preparation and Formation Mechanisms of Ultradisperse Phases of [Fe(II)–Fe(III)] LDH, Magnetite, Cobalt-Ferrous Ferrite, Lepidocrocite, and Goethite in the Fe0(St3)–H2O–O2 System

Colloid-Chemical Mechanisms of the Formation of Ultra- and Nanosize Iron Oxide/Hydroxide Phases Obtained in the Fe0(St3)–H2O–O2 System and Their Electrokinetic Properties. I. Preparation and Formation Mechanisms of Ultradisperse Phases of [Fe(II)–Fe(III)] LDH, Magnetite, Cobalt-Ferrous Ferrite, Lepidocrocite, and Goethite in the Fe0(St3)–H2O–O2 System

Polydopamine-coated hollow carbon nitride as a full-spectral response photocatalyst for efficient H2O2 production via redox dual pathways

Achieving rapid and highly selective photocatalytic production of H2O2 from H2O and O2 over carbon nitride (CN) continues to pose a significant challenge. Here, a polydopamine (PDA) cover-layer modified hollow carbon nitride (HCP) is prepared to address this issue. Incorporating PDA not only introduces active site for O2 reduction, but also optimizes the Gibbs free energy for the formation of *OH intermediate during H2O oxidation. Additionally, the excellent light absorption and electronic mobility properties of PDA also contribute to the optimized features of HCP-24, resulting in a broad response across the spectrum and efficiently facilitates the generation of H2O2 through both O2 reduction and H2O oxidation pathways. Notably, HCP-24 demonstrates a significantly enhanced H2O2 evolution rate, achieving 5.5 times higher production (116.25 μmol g−1 h−1) compared to pristine CN (20.95 μmol g−1 h−1). This research provides valuable insights for the advancement of efficient catalysts for the photocatalytic generation of H2O2.

Sustainable photocatalytic hydrogen peroxide production over octonary high-entropy oxide

The direct utilization of solar energy for the artificial photosynthesis of hydrogen peroxide (H2O2) provides a reliable approach for producing this high-value green oxidant. Here we report on the utility of high-entropy oxide (HEO) semiconductor as an all-in-one photocatalyst for visible light-driven H2O2 production directly from H2O and atmospheric O2 without the need of any additional cocatalysts or sacrificial agents. This high-entropy photocatalyst contains eight earth-abundant metal elements (Ti/V/Cr/Nb/Mo/W/Al/Cu) homogeneously arranged within a single rutile phase, and the intrinsic chemical complexity along with the presence of a high density of oxygen vacancies endow high-entropy photocatalyst with distinct broadband light harvesting capability. An efficient H2O2 production rate with an apparent quantum yield of 38.8% at 550 nm can be achieved. The high-entropy photocatalyst can be readily assembled into floating artificial leaves for sustained on-site production of H2O2 from open water resources under natural sunlight irradiation.

Engineering of Single-Atomic Sites for Electro- and Photo-Catalytic H2O2 Production.

Direct electro- and photo-synthesis of H2O2 through the 2e- O2 reduction reaction (ORR) and H2O oxidation reaction (WOR) offer promising alternatives for on-demand and on-site production of this chemical. Exploring robust and selective active sites is crucial for enhancing H2O2 production through these pathways. Single-atom catalysts (SACs), featuring isolated active sites on supports, possess attractive properties for promoting catalysis and unraveling catalytic mechanisms. This review first systematically summarizes significant advancements in atomic engineering of both metal and nonmetal single-atom sites for electro- and photo-catalytic 2e- ORR to H2O2, as well as the dynamic behaviors of active sites during catalytic processes. Next, the progress of single-atom sites in H2O2 production through 2e- WOR is overviewed. The effects of the local physicochemical environments on the electronic structures and catalytic behaviors of isolated sites, along with the atomic catalytic mechanism involved in these H2O2 production pathways, are discussed in detail. This work also discusses the recent applications of H2O2 in advanced chemical transformations. Finally, a perspective on the development of single-atom catalysis is highlighted, aiming to provide insights into future research on SACs for electro- and photo-synthesis of H2O2 and other advanced catalytic applications.

Thermal stability of MDM and oxidative decomposition mechanism under the condition of air infiltration: A combined experimental, ReaxFF-MD and DFT study

When siloxanes are used as the working fluids of organic Rankine cycle systems, there is a possibility of air infiltration due to the large vacuum present in the condenser. To address this issue, experimental and simulation studies were conducted on the thermal stability and pyrolysis product characteristics of octamethyltrisiloxane (MDM) in the presence of air. The results indicated that air significantly promotes the decomposition of MDM at the temperatures above 250 °C. Air was helpful in increasing the formation of CH2O, CO, and CO2, and also enhanced polymerization of decomposition product of siloxane, leading to higher yields of MD2M, MD3M, MD4M, D3, D4, and D5. By combining reactive force field molecular dynamics (ReaxFF-MD) simulations with density functional theory (DFT) calculations, the microscopic mechanisms of MDM's oxidative decomposition by O2 in air and H2O under humid conditions were elucidated. O2 can easily combine with unsaturated Si atoms to form Si-O bonds, combine with CH3 radicals to form C-O bonds, and undergoes hydrogen extraction reactions to initiate decomposition. H2O mainly undergoes initial decomposition through CH3 radical hydrogenation and binding with unsaturated Si atoms. The generated O2H, O, and OH radicals tend to bind with Si atoms in molecules and radicals, facilitating polymerization reactions.

Hypochlorous acid electrosynthesis and service life assessment of a Ti|Ti–Ru–Ir-oxides anode assembled in a flow electrolyzer: Understanding the influence of the concurrent O2 bubbling flow

This paper addresses the influence of bubbling flow and service life of the Ti|Ti–Ru–Ir-oxides anode during the electrosynthesis of HClO in a laboratory-scale filter-press-type electrolyzer. The electrolyzer was assembled in a flow plant in recirculation mode. Polarization curves in rotating disk electrode (RDE) revealed the coexistence of the oxygen evolution reaction (OER) during HClO electrosynthesis in diluted chloride solutions (containing 35 mM NaCl at pH 3). CFD simulations of the two-phase (O2–H2O) flow were obtained by solving simultaneously the Navier-Stokes and charge conservation equations using a finite element method code. The O2–H2O simulations show the efficient gas release in the electrolyzer provoked by the continuous phase (H2O) inertia and the well-engineered cell design. The moderated O2 dispersion caused a quasi-homogeneous current distribution along the anode. However, the current efficiency during HClO electrosynthesis gave values of ∼32% provoked by the OER on the anode. The HClO accumulations (from 3.02 to 6.64 mM) showed excellent agreement with CFD simulations. The accelerated life tests revealed that the Ti | Ti–Ru–Ir-oxides anode has a lifetime of at least 26 years during the HClO electrosynthesis in diluted chloride solutions.

Mechanisms of Ni Dissolution from Ni-Rich Cathode in Li-Ion Batteries

Nickel-rich cathodes are the most promising candidates for realizing high-energy-density Li-ion batteries because of the high theoretical capacity. However, their structural instability detrimentally affects the battery performance during cell cycling, which restricts its large-scale commercial application. One impediment to their commercialization is the dissolution of transition metal ions, which can diffuse to the anode, corrupt the solid electrolyte interphase (SEI) films protecting the anode, and accelerate battery capacity fading. Here, we use ab initio molecular dynamics (AIMD) simulations to investigate the mechanism of Ni dissolution from the LiNiO2 cathode surfaces. Our calculations identified that the proton-transfer reactions between electrolytes and cathode surfaces cause the reduction of surface Ni atoms from Ni3+ to Ni2+, which weakened the Ni-O bonding. As the LiNiO2 cathode surface gets delithiated, more surface protonation reactions were observed, and the reduced Ni atoms were found to be dissolved from the cathode surfaces in the form of NiOOH, which is the fundamental origin of phase transition of LiNiO2 cathode from a layered to electrochemically inactive spinel-like structure, accompanied by H2O elimination and O2 evolution. Besides, we also studied the impact of various factors on Ni dissolution rates such as the presence of fluorine attachment and the coordination of Ni atoms and electrolyte species. These findings help inform future design of protective coatings, electrolytes, additives, and interfaces for Ni-rich cathode.

Synthesis and bio-medical applications of multifunctional phosphorester cyclic amide anchored sterculia network

The main focus of the present research is to design network hydrogels derived from natural polymers to promote a sustainable future. Multifunctional hydrogels were prepared by combining sterculia gum (SG), phosphorester -cyclic amide polymers for bio-medical applications including drug delivery (DD). The antibiotic drug ceftriaxone was incorporated into hydrogels to enhance wound healing potential. The surface morphology of copolymers was investigated by using FESEM and AFM techniques. FTIR and 13C NMR spectroscopic techniques provided insight into the formation of network structures. In FTIR analysis, distinctive bands were identified: at 1649 cm−1 attributed to CO stretching of the cyclic amide of PVP, at 1147 cm−1 and 974 cm−1 representing PO stretching and P-O-C of poly(BMEP), respectively. In the 13C NMR spectrum, a prominent peak at 63.272 ppm revealed the presence of (O-CH2) linkage of poly(BMEP). XRD demonstrated amorphous characteristics of hydrogels. The interactions of copolymer with blood, bio-membrane and encapsulated drug illustrated their biocompatibility, bio-adhesion and controlled DD properties. The dressings expressed a hemolytic index value of 2.58 ± 0.03 %. The hydrogels exhibited mucoadhesive character, revealed from the adhesion force of 50.0 ± 5 mN needed to separate polymer dressing from the mucosa. Dressings exhibited antioxidant properties and displayed 33.73 ± 0.3 % radical scavenging in the DPPH assay. Protein adsorption test of copolymer illustrated 9.48 ± 0.970 % of albumin adsorption. The tensile strength of the dressing was found 0.54 ± 0.03 N mm−2 while the burst strength 9.92 ± 0.27 N was observed. The sustained release of the drug was provided by supra-molecular interactions. Drug release followed a non-Fickian diffusion mechanism and the release profile was best described by the Higuchi kinetic model. Additionally, hydrogel dressings revealed permeability to H2O vapors and O2 and antimicrobial activity. These findings suggest the suitability of sterculia gum-based hydrogels for DD uses.

Strongly active and environmentally friendly WO3/C3N4 photocatalysts for converting cyclohexane to cyclohexanone under ambient conditions

C–H bond activation under mild conditions remains a great challenge in the chemical industry, while catalytic cyclohexane oxidation is inefficient and often requires organic solvents and strong oxidants. This study constructed a C3N4/WO3 Z-type heterojunction catalyst to efficiently convert cyclohexane into cyclohexanone and cyclohexanol (KA oil) through aqueous phase oxidation by O2 under visible light irradiation. With strong redox performance and high photogenerated carrier separation ability, the proposed composite catalyst can produce the key active species for cyclohexane oxidation in the H2O–O2 system. The reaction mechanism was clarified through experiment and DFT theory calculation. Cyclohexane was converted into cyclohexyl radical under the action of ·OH, and ·O2− converted most products into cyclohexanone. The catalyst can be recycled under optimized process conditions while reaching a KA oil yield of 139.73 μmol g−1 h−1 and a selectivity of 93.1%.

Atomically Resolved Transition Pathways of Iron Redox.

The redox transition between iron and its oxides is of the utmost importance in heterogeneous catalysis, biological metabolism, and geological evolution. The structural characteristics of this reaction may vary based on surrounding environmental conditions, giving rise to diverse physical scenarios. In this study, we explore the atomic-scale transformation of nanosized Fe3O4 under ambient-pressure H2 gas using in-situ environmental transmission electron microscopy. Our results reveal that the internal solid-state reactions dominated by iron diffusion are coupled with the surface reactions involving gaseous O or H species. During reduction, we observe two competitive reduction pathways, namely Fe3O4 → FeO → Fe and Fe3O4 → Fe. An intermediate phase with vacancy ordering is observed during the disproportionation reaction of Fe2+ → Fe0 + Fe3+, which potentially alleviates stress and facilitates ion migration. As the temperature decreases, an oxidation process occurs in the presence of environmental H2O and trace amounts of O2. A direct oxidation of Fe to Fe3O4 occurs in the absence of the FeO phase, likely corresponding to a change in the water vapor content in the atmosphere. This work elucidates a full dynamical scenario of iron redox under realistic conditions, which is critical for unraveling the intricate mechanisms governing the solid-solid and solid-gas reactions.

Dual Channel H2O2 Photosynthesis in Pure Water over S-Scheme Heterojunction Cs3PMo12/CC Boosted by Proton and Electron Reservoirs.

Dual channel photo-driven H2O2 production in pure water on small-scale on-site setups is a promising strategy to provide low-concentrated H2O2 whenever needed. This process suffers, however, strongly from the fast recombination of photo-generated charge carriers and the sluggish oxidation process. Here, insoluble Keggin-type cesium phosphomolybdate Cs3PMo12O40 (abbreviated to Cs3PMo12) is introduced to carbonized cellulose (CC) to construct S-scheme heterojunction Cs3PMo12/CC. Dual channel H2O2 photosynthesis from both H2O oxidation and O2 reduction in pure water has been thus achieved with the production rate of 20.1mmolL-1gcat. -1h-1, apparent quantum yield (AQY) of 2.1% and solar-to-chemical conversion (SCC) efficiency of 0.050%. H2O2 accumulative concentration reaches 4.9mmol L-1. This high photocatalytic activity is guaranteed by unique features of Cs3PMo12/CC, namely, S-scheme heterojunction, electron reservoir, and proton reservoir. The former two enhance the separation of photo-generated charge carriers, while the latter speeds up the torpid oxidation process. In situ experiments reveal that H2O2 is formed via successive single-electron transfer in both channels. In real practice, exposing the reaction system under natural sunlight outdoors successfully results in 0.24mmol L-1 H2O2. This work provides a key practical strategy for designing photocatalysts in modulating redox half-reactions in photosynthesis.

Sub-Band Assisted Z-Scheme for Effective Non-Sacrificial H2O2 Photosynthesis.

Photosynthesis of H2O2 from earth-abundant O2 and H2O molecules offers an eco-friendly route for solar-to-chemical conversion. The persistent challenge is to tune the photo-/thermo- dynamics of a photocatalyst toward efficient electron-hole separation while maintaining an effective driving force for charge transfer. Such a case is achieved here by way of a synergetic strategy of sub-band-assisted Z-Scheme for effective H2O2 photosynthesis via direct O2 reduction and H2O oxidation without a sacrificial agent. The optimized SnS2/g-C3N4 heterojunction shows a high reactivity of 623.0µmolg-1h-1 for H2O2 production under visible-light irradiation (λ>400nm) in pure water, ≈6 times higher than pristine g-C3N4 (100.5µmolg-1h-1). Photodynamic characterizations and theoretical calculations reveal that the enhanced photoactivity is due to a markedly promoted lifetime of trapped active electrons (204.9ps in the sub-band and >2.0ns in a shallow band) and highly improved O2 activation, as a result of the formation of a suitable sub-band and catalytic sites along with a low Gibbs-free energy for charge transfer. Moreover, the Z-Scheme heterojunction creates and sustains a large driving force for O2 and H2O conversion to high value-added H2O2.

Photosynthesis of H2O2 in pure water over 2D metal-organic frameworks film by co-doping Ga and porphyrin

Hydrogen peroxide (H2O2) is a clean oxidizing agent and potential energy carrier. Photocatalytic H2O2 production has garnered increased attention due to its green and energy-saving process. However, existing photocatalysts face several challenges, such as limited response to visible light, the requirement for sacrificial reagents, and complications in powder recycling. In this work, we synthesized two-dimensional (2D) NH2-MIL-53(Al) films co-modified with Ga and tetrakis (4-carboxyphenyl) porphyrin (TCPP) with enhanced photocatalytic activity of 268.7 µmol∙g−1∙h−1 from only O2 and pure H2O, reaching 3.5 times higher than pure NH2-MIL-53(Al). Notably, in comparison with other reported MOF photocatalysts, NMA-Ga5%-L30 stands out with the highest photocatalytic H2O2 generation activity in a pure water system under visible light. Moreover, this sample film was readily recovered from a photocatalytic system and exhibits significant cycling stability. The heightened photocatalytic activity is attributed to the dual modification, which not only reduces the photogenerated band gap but also promotes the charge carrier’s separation and transfer. This work provides a strategy for the design of MOFs-based photocatalysts with easy recycle properties for artificial photosynthesis of H2O2.

Trends on barrier characteristics improvement of emerging biopolymeric composite films using nanoparticles - A review

BackgroundBio-based films have wide applications in various areas, including medical, packaging, biosensor design, and environmental remediation. Unfortunately, their associated features restricted the application windows for these bio-based films. Barrier properties, such as H2O permeability, O2 permeability, and UV-barrier properties, are among the typical qualities important in designing packaging films because they safeguard food safety and extend shelf life. MethodsEnhancing the barrier qualities has been imperative in recent years owing to its significant impact on food preservation and the valorization of natural biopolymers. The most innovative method is adding metal and metal oxide nanoparticles to the biopolymer with carefully regulated loads and parameters. This review aims to examine the barrier performance as well as their enhancement methods using metal, metal-oxide, and the synergetic effects of nanoparticles. Significant findingsThe review concludes that incorporating metallic and metallic oxide NPs into films has improved their barrier quality. The current and future materials in the property improvement field include metallic and metallic oxide nanoparticles, such as Ag, ZnO, GO, and TiO2, as well as their binary effects. Improvements to the barrier characteristics of bio-based films address the environmental and socioeconomic problems brought on by using petro-based films.

Spatially- and time-resolved measurements of HO2 radicals in a ns pulse atmospheric pressure plasma jet

The absolute, spatially-resolved, and time-resolved number density of the hydroperoxyl radical is measured in a quasi-two-dimensional, atmospheric pressure ‘curtain’ plasma jet powered by a train of ns discharge pulses. The spatial distribution of HO2 is measured across the shorter dimension of the jet. The measurements are made in two different configurations, (a) H2O–O2–He jet impinging on a copper foil target, and (b) O2–He jet incident on the liquid water surface. In the first configuration, the water vapor is added to the O2–He flow in a bubbler filled with distilled, deionized water. The measurements are made using the previously developed pulsed cavity ring down spectroscopy diagnostic near 1.5 μm. The ring-down cavity is formed between two high-reflectivity mirrors placed at the ends of the stainless steel ‘arms’ purged with dry air, with the plasma jet placed in the gap between the arms. The objectives of this work are to use the HO2 number density to assess the accuracy of the modeling predictions using a previously developed ‘global’ reaction mechanism, and to estimate the efficiency of hydrogen peroxide generation in the ns pulse discharge plasma. HO2 was detected only in the first configuration, most likely due to the rapid decay of the metastable He atoms and O atoms generated in the plasma, which prevents the generation of H atoms (dominant HO2 precursors) in the evaporation/mixing layer. Both the water vapor in the jet and HO2 generated in the plasma have been measured. The results exhibit a rapid accumulation of HO2 during the ns pulse discharge burst, followed by the decay in the afterglow on a ms time scale. The kinetic model overpredicts the quasi-steady-state HO2 number density, as well as the HO2 decay rate after the discharge is turned off. The relatively slow HO2 decay in the afterglow suggests that it may be affected by diffusion, along with the surface adsorption and desorption of radicals. The present approach demonstrates the utility of a 2D curtain plasma jet for the line-of-sight absorption spectroscopy measurements of radicals and excited species present in small concentrations in ambient plasma environments.

Atomic layer deposition of ZnO thin films using a liquid cyclopentadienyl-based precursor

A new compound, bis(n-propyltetramethylcyclopentadienyl)zinc [Zn(Cppm)2], was synthesized as a Zn precursor for atomic layer deposition (ALD) of ZnO films. The compound is a liquid at room temperature and is thermally stable below ∼230 °C. Although the vapor pressure of this precursor is low (1 Torr at 99 °C), it is sufficient for the material to be used in ALD. ZnO thin films were deposited on p-type Si(100) wafers at 200 °C by ALD using the precursor. Three types of ZnO films were grown using different oxidants: (a) O2 plasma, (b) H2O, and (c) H2O followed by O2 plasma. The growth rates expressed in the growth per cycle were (a) 0.13 nm/cycle, (b) 0.07 nm/cycle, and (c) 0.10 nm/cycle, respectively, and all of the resultant films had a hexagonal wurtzite structure. Cross-sectional transmission electron microscopy revealed that, although all of the ZnO films were crystalline. X-ray diffraction analysis determined that the (002) orientation was dominant when the oxidant was H2O, and that the (103) orientation was observed when O2 plasma was used. All of the obtained films were nearly stoichiometric. Using H2O as an oxidant, very small amounts of impurities remain in the film. However, high-purity ZnO films can be deposited using H2O followed by O2 plasma as oxidants.

Electron-donating five-membered heterocyclic modulated electronic states boosting visible-light-driven H2O2 production

Pyridyl-conjugated microporous polymers (CMPs) were synthesized and discovered that the catalyst with a five-membered heterocycle could facilitate O2 reduction and H2O oxidation into H2O2 under photo-irradiation. The electronic state structure of the CMPs was further modulated by incorporating aldehyde-based monomers containing five-membered heterocycles. It was observed that the introduction of an electron-donating thiophene ring (Th-CMP) or a furan ring (Fu-CMP) significantly increased the H2O2 production yield. Remarkably, the H2O2 yield from Th-CMP in pure water and O2, without the need for any sacrificial agents, achieved 855 μM h−1, which surpasses most of the reported organic polymer photocatalysts. Mechanism researchs indicated Thiophene groups not only expanded the range for visible light absorption, but also facilitates the separation and migration of charge carriers, thereby providing favorable conditions for H2O2 generation. This study presents a promising and innovative direction to designing cost-effective and efficient CMPs for the photocatalytic generation of H2O2.

High-Temperature Corrosion of High- and Medium-Entropy Alloys CrMnFeCoNi and CrCoNi Exposed to a Multi-Oxidant Atmosphere H2O–O2–SO2

The high-temperature corrosion behaviors of the equimolar CrCoNi medium-entropy alloy and CrMnFeCoNi high-entropy alloy were studied in a gas atmosphere consisting of a volumetric mixture of 10% H2O, 2% O2, 0.5% SO2, and 87.5% Ar at 800 °C for up to 96 h. Both alloys were initially single-phase fcc with a mean grain size of ~ 50 μm and a homogeneous chemical composition. The oxide layer thickness of CrMnFeCoNi increased linearly with exposure time while it remained constant at ~ 1 μm for CrCoNi. A Cr2O3 layer and minor amounts of (Co,Ni)Cr2O4 developed on the latter while three oxide layers were detected on the former, i.e., a thin and continuous chromium rich oxide layer at the oxide/alloy interface, a dense (Mn,Cr)3O4 layer in the center and a thick and porous layer of Mn3O4 and MnSO4 at the gas/oxide interface. Additionally, a few metal sulfides were observed in the CrMnFeCoNi matrix. These results were found to be in reasonable agreement with thermodynamic calculations.

Triggering Dual Two‐electron Pathway for H2O2 Generation by Multiple [Bi−O]n Interlayers in Ultrathin Bi12O17Cl2 towards Efficient Piezo‐self‐Fenton Catalysis

AbstractPiezo‐self‐Fenton system (PESF) has been emerging as a promising water treatment technology but suffering from unsatisfied H2O2 production efficiency. Herein, we rationally design a Bi12O17Cl2 piezo‐catalyst with multiple [Bi−O]n interlayers towards highly efficient H2O2 production. The introduction of [Bi3O4.25] layers initiates dual two‐electron pathway for H2O2 generation by altering the interlayer properties. It is found that the additional [Bi3O4.25] layers not only enhance the polarization electric field but also serve as active sites for triggering dual pathways of two‐electron O2 reduction and H2O oxidation reaction for H2O2 production. Therefore, the Bi12O17Cl2 exhibits an ultrahigh rate of H2O2 generation (7.76 mM h−1 g−1) in pure water. Based on the adequate H2O2 yield, a PESF was constructed for acetaminophen (ACE) degradation with an apparent rate constant of 0.023 min−1. This work not only presents a potential strategy of tuning the activity of bismuth based piezo‐catalysts but also provides a good example on the construction of highly efficient PESF for environmental remediation by using natural mechanical energy.

Defective ZnIn2S4 Nanosheets for Visible-Light and Sacrificial-Agent-Free H2O2 Photosynthesis via O2/H2O Redox.

H2O2 photosynthesis has attracted great interest in harvesting and converting solar energy to chemical energy. Nevertheless, the high-efficiency process of H2O2 photosynthesis is driven by the low H2O2 productivity due to the recombination of photogenerated electron-hole pairs, especially in the absence of a sacrificial agent. In this work, we demonstrate that ultrathin ZnIn2S4 nanosheets with S vacancies (Sv-ZIS) can serve as highly efficient catalysts for H2O2 photosynthesis via O2/H2O redox. Mechanism studies confirm that Sv in ZIS can extend the lifetimes of photogenerated carriers and suppress their recombination, which triggers the O2 reduction and H2O oxidation to H2O2 through radical initiation. Theoretical calculations suggest that the formation of Sv can strongly change the coordination structure of ZIS, modulating the adsorption abilities to intermediates and avoiding the overoxidation of H2O to O2 during O2/H2O redox, synergistically promoting 2e- O2 reduction and 2e- H2O oxidation for ultrahigh H2O2 productivity. The optimal catalyst displays a H2O2 productivity of 1706.4 μmol g-1 h-1 under visible-light irradiation without a sacrificial agent, which is ∼29 times higher than that of pristine ZIS (59.4 μmol g-1 h-1) and even much higher than those of reported photocatalysts. Impressively, the apparent quantum efficiency is up to 9.9% at 420 nm, and the solar-to-chemical conversion efficiency reaches ∼0.81%, significantly higher than the value for natural synthetic plants (∼0.10%). This work provides a facile strategy to separate the photogenerated electron-hole pairs of ZIS for H2O2 photosynthesis, which may promote fundamental research on solar energy harvest and conversion.