Photocatalytic H2 O2 Generation Reaction with a Benchmark Rate at Air-Liquid-Solid Joint Interfaces

A compendium of all-in-one solar-driven water splitting using ZnIn2S4-based photocatalysts: guiding the path from the past to the limitless future

Photocatalytic water splitting represents a leading approach to harness the abundant solar energy, producing hydrogen as a clean and sustainable energy carrier. Zinc indium sulfide (ZIS) emerges as one of the most captivating candidates attributed to its unique physicochemical and photophysical properties, attracting much interest and holding significant promise in this domain. To develop a highly efficient ZIS-based photocatalytic system for green energy production, it is paramount to comprehensively understand the strengths and limitations of ZIS, particularly within the framework of solar-driven water splitting. This review elucidates the three sequential steps that govern the overall efficiency of ZIS with a sharp focus on the mechanisms and inherent drawbacks associated with each phase, including commonly overlooked aspects such as the jeopardising photocorrosion issue, the neglected oxidative counter surface reaction kinetics in overall water splitting, the sluggish photocarrier dynamics and the undesired side redox reactions. Multifarious material design strategies are discussed to specifically mitigate the formidable limitations and bottleneck issues. This review concludes with the current state of ZIS-based photocatalytic water splitting systems, followed by personal perspectives aimed at elevating the field to practical consideration for future endeavours towards sustainable hydrogen production through solar-driven water splitting.

Reinforcing oxygen reduction reaction and accelerating charge migration kinetics on In4SnS8 by polypyrrole for photocatalytic hydrogen peroxide production

Solar light-driven hydrogen peroxide (H2O2) production through the two-electron oxygen reduction reaction (ORR) from the earth-abundant O2 and water is a potential alternative to the energy-consuming anthraquinone oxidation process, although the activity of the common photocatalysts is still insufficient to satisfy the industrial demands. Poor accessibility of O2 to surface/interface and fast carrier recombination is the limiting-factor for catalytic systems. Herein, we develop a nanohybrid photocatalysts by introducing 1D conducting polymer of polypyrrole (PPy) nanotube on In4SnS8 to promote H2O2 evolution under visible light, obtaining up to 254.8 μM in 2 h, which is 2.4- and 13-fold larger than that of individual In4SnS8 and PPy. The detailed characterizations of hybrid structure, O2 adsorption behaviors, charge carrier dynamics over PPy/In4SnS8 in conjunction with computational calculations corroborate that the modification of PPy could enlarge the amount of O2 adsorption amount, expedite the cycle of O2 adsorption/desorption and accelerate the transportation of electrons from In4SnS8 to the interface, eventually speeding up H2O2 photoproduction via indirect 2e- ORR pathway. This work establishes a paradigm of regulating the interfacial microenvironment by polymer for boosting H2O2 photogeneration through high selectivity of ORR.

Robust Covalent Organic Frameworks for Photosynthesis of H2O2: Advancements, Challenges and Strategies

Since 2020, covalent organic frameworks (COFs) are emerging as robust catalysts for the photosynthesis of hydrogen peroxide (H2O2), benefiting from their distinct advantages. However, the current efficiency of H2O2 production and solar-to-chemical energy conversion efficiency (SCC) remain suboptimal due to various constraints in the reaction mechanism. Therefore, there is an imperative to propose efficiency improvement strategies to accelerate the development of this reaction system. This comprehensive review delineates recent advances, challenges, and strategies in utilizing COFs for photocatalytic H2O2 production. It explores the fundamentals and challenges (e.g., oxygen (O2) mass transfer rate, O2 adsorption capacity, response to sunlight, electron-hole separation efficiency, charge transfer efficiency, selectivity, and H2O2 desorption) associated with this process, as well as the advantages, applications, classification, and preparation strategies of COFs for this purpose. Various strategies to enhance the performance of COFs in H2O2 production are highlighted. The review aims to stimulate further advancements in utilizing COFs for photocatalytic H2O2 production and discusses potential prospects, challenges, and application areas in this field.

Hydroxyl-Bonded Co Single Atom Site on Boroncarbonitride Surface Realizes Nonsacrificial H2O2 Synthesis in the Near-Infrared Region

Photocatalytic synthesis of hydrogen peroxide (H2O2) from O2 and H2O under near-infrared light is a sustainable renewable energy production strategy, but challenging reaction. The bottleneck of this reaction lies in the regulation of O2 reduction path by photocatalyst. Herein, the center of the one-step two-electron reduction (OSR) pathway of O2 for H2O2 evolution via the formation of the hydroxyl-bonded Co single-atom sites on boroncarbonitride surface (BCN-OH2/Co1) is constructed. The experimental and theoretical prediction results confirm that the hydroxyl group on the surface and the electronic band structure of BCN-OH2/Co1 are the key factor in regulating the O2 reduction pathway. In addition, the hydroxyl-bonded Co single-atom sites can further enrich O2 molecules with more electrons, which can avoid the one-electron reduction of O2 to •O2 -, thus promoting the direct two-electron activation hydrogenation of O2. Consequently, BCN-OH2/Co1 exhibits a high H2O2 evolution apparent quantum efficiency of 0.8% at 850 nm, better than most of the previously reported photocatalysts. This study reveals an important reaction pathway for the generation of H2O2, emphasizing that precise control of the active site structure of the photocatalyst is essential for achieving efficient conversion of solar-to-chemical.

Hydrophobic-treated yolk-shell SnS2@CSs Z-scheme confinement reactor for solar-electro-driven hydrogen peroxide production in neutral media

The diffusion and adsorption properties of the O2/H2O corpuscles at active sites play a crucial role in the fast photo-electrocatalytic reaction of hydrogen peroxide (H2O2) production. Herein, SnS2 nanosheets with abundant interfacial boundaries and large specific areas are encapsulated into hollow mesoporous carbon spheres (CSs) with flexibility, producing a yolk-shell SnS2@CSs Z-scheme photocatalyst. The nanoconfined microenvironment of SnS2@CSs could enrich O2/H2O in catalyst cavities, which allows sufficient internal O2 transfer, improving the surface chemistry of catalytic O2 to O2- conversion and increasing reaction kinetics. By shaping the mixture of SnS2@CSs and polytetrafluoroethylene (PTFE) on carbon felt (CF) using the vacuum filtration method, the natural air-breathing gas diffusion photoelectrode (AGPE) was prepared, and it can achieve an accumulated concentration of H2O2 about 12 mM after a 10 h stability test from pure water at natural pH without using electrolyte and sacrificial agents. The H2O2 product is upgraded through one downstream route of conversion of H2O2 to sodium perborate. The improved H2O2 production performance could be ascribed to the combination of the confinement effect of SnS2@CSs and the rich triple phase interfaces with the continuous hydrophobic layer and hydrophilic layer to synergistically modulate the photoelectron catalytic microenvironment, which enhanced the transfer of O2 mass and offered a stronger affinity to oxygen bubbles. The strategy of combining the confined material with the air-breathing gas diffusion electrode equips a wide practical range of applications for the synthesis of high-yield hydrogen peroxide.

A fingerprint-like supramolecular-assembled Ag3PO4/polydopamine/g-C3N4 heterojunction nanocomposite for enhanced solar-driven oxygen evolution in vivo

Biocompatible photocatalytic water-splitting systems are promising for tissue self-oxygenation. Herein, a structure-function dual biomimetic fingerprint-like silver phosphate/polydopamine/graphitic carbon nitride (Ag3PO4/PDA/g-C3N4) heterojunction nanocomposite is proposed for enhanced solar-driven oxygen (O2) evolution in vivo in situ. Briefly, a porous nitrogen-defected g-C3N4 nanovoile (CN) is synthesized as the base. Dopamine molecules are controllably inserted into the CN interlayer, forming PDA spacers (4.28 nm) through self-polymerization-induced supramolecular-assembly. Ag3PO4 nanoparticles are then in situ deposited to create Ag3PO4/PDA/CN. The fingerprint-like structure of PDA/CN enlarges the layer spacing, thereby accelerating mass transfer and increasing reaction sites. The PDA spacer roles as excellent light harvester, electronic-ionic conductor, and redox pair through conformational changes, resulting in tailored electronic band structure, optimized carrier behavior, and reduced electrochemical impedance. In physiological conditions, Ag3PO4/PDA/CN exhibits O2 evolution rate of 45.35 μmol⋅g-1⋅h-1, 9-fold of bulk g-C3N4. The biocompatibility and in vivo oxygen supply effectiveness for biomedical applications have been verified in animal models.

Recent developments in photocatalytic production of hydrogen peroxide

Hydrogen peroxide (H2O2), an environmentally friendly strong oxidant and energy carrier, has attracted widespread attention in photocatalysis. Artificial photosynthesis of H2O2 using water and oxygen as raw materials, solar energy as an energy source, and semiconductor materials as catalysts is considered a promising technology. In the past few decades, encouraging progress has been made in the photocatalytic production of H2O2. Therefore, we summarize the research achievements in this field in recent years. This review first briefly introduces the reaction pathway, detection techniques and evaluation metrics. Then, the recent advances in photocatalysts are highlighted. Furthermore, the existing challenges and possible solutions in this field are presented. At last, we look forward to the future development direction of this field. This review provides valuable insights and guidance for efficient photocatalytic H2O2 production.

Progress and Opportunities in Photocatalytic, Electrocatalytic, and Photoelectrocatalytic Production of Hydrogen Peroxide Coupled with Biomass Valorization

Hydrogen peroxide (H2O2) has been considered an energy carrier (fuel) and oxidizer for various chemical synthesis and environmental remediation processes. Biomass valorization can generate high-value-added products in a green and pollution-free way to solve the energy and environmental crisis. The biomass valorization coupled with H2O2 generation via photo-, electro-, and photoelectrocatalysis plays a positive role in sustainable targets, which can maximize energy utilization and realize the production of value-added products and fuel synthesis. Recently, catalyst design and mechanism studies in H2O2 generation coupled with biomass valorization are in the infancy stage. Herein, this review begins with a background on photo-, electro-, and photoelectrocatalytic techniques for H2O2 generation, biomass valorization, and the H2O2 generation couples with biomass valorization. Meanwhile, the progress and reaction mechanism are reviewed. Finally, the prospects and challenges of a synergistic coupled system of H2O2 synthesis and value-added biomass in achieving high conversion, selectivity, and reaction efficiency are envisioned.

Polyvinyl alcohol as solid proton donor to modify g-C3N4via hydrogen bonding enabling efficient photocatalytic H2O2 production from H2O and O2

Polyvinyl alcohol (PVA) was used as a solid proton donor to improve the photocatalytic performance of graphitic carbon nitride (CN) for hydrogen peroxide (H2O2) production. The modified CN (CN/PVA) was prepared by mixing CN and PVA at room temperature. The H2O2 production efficiency of CN/PVA was 5.65 times higher than that of CN in pure water. Photocurrent measurement, electrochemical impedance spectroscopy (EIS), and photoluminescence (PL) analysis proved that PVA increased charge separation of CN. X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared (FTIR) analyses further suggested that PVA acted as the proton donor during H2O2 production by interacting with CN via hydrogen bonds. The combination of the charge separation enhancer and proton donor from PVA promoted the sequential two-step single-electron reduction of O2 for H2O2 production. This study paves the way for the modification of g-C3N4 with hydroxyl-containing materials as solid proton donors for photocatalytic H2O2 production.

Controlled synthesis of 2D-2D conductive metal-organic framework/g-C3N4 heterojunctions for efficient photocatalytic hydrogen evolution

Designing photocatalysts with efficient charge separation and electron transport capabilities to achieve efficient visible-driven hydrogen production remains a challenge. Herein, 2D-2D conductive metal-organic framework/g-C3N4 heterojunctions were successfully prepared by an in situ assembly. Compared to pristine g-C3N4, the ratio-optimized Ni-CAT-1/g-C3N4 exhibits approximately 3.6 times higher visible-light H2 production activity, reaching 14 mmol g-1. Through investigations using time-resolved photoluminescence, surface photovoltage, and wavelength-dependent photocurrent action spectroscopies, it is determined that the improved photocatalytic performance is attributed to enhanced charge transfer and separation, specifically the efficient transfer of excited high-energy-level electrons from g-C3N4 to Ni-CAT in the heterojunctions. Furthermore, the high electrical conductivity of Ni-CAT enables rapid electron transport, contributing to the overall enhanced performance. This work provides a feasible strategy to construct efficient dimension-matched g-C3N4-based heterojunction photocatalysts with high-efficiency charge separation for solar-driven H2 production.