Simultaneously Producing H₂ and H₂O₂ by Photocatalytic Water Splitting: Recent Progress and Future

The solar-driven overall water splitting (2H₂O→2H₂ + O₂) is considered as one of the most promising strategies for reducing carbon emissions and meeting energy demands. However, due to the sluggish performance and high H₂ cost, there is still a big gap for the current photocatalytic systems to meet the requirements for practical sustainable H₂ production. Economic feasibility can be attained through simultaneously generating products of greater value than O₂, such as hydrogen peroxide (H₂O₂, 2H₂O→H₂ + H₂O₂). Compared with overall water splitting, this approach is more kinetically feasible and generates more high-value products of H₂ and H₂O₂. In several years, there has been an increasing surge in exploring the possibility and substantial progress has been achieved. In this review, a concise overview of the importance and underlying principles of PIWS is first provided. Next, the reported typical photocatalysts for PIWS are discussed, including commonly used semiconductors and cocatalysts, essential design features of these photocatalysts, and connections between their structures and activities, as well as the selected approaches for enhancing their stability. Then, the techniques used to quantify H₂O₂ and the operando characterization techniques that can be employed to gain a thorough understanding of the reaction mechanisms are summarized. Finally, the current existing challenges and the direction needing improvement are presented. This review aims to provide a thorough summary of the most recent research developments in PIWS and sets the stage for future advancements and discoveries in this emerging area.