Photocatalytic Coproduction of H 2 and H 2 O 2 : Mechanistic Insights, Material Design, and Challenges in the Two‐Electron Water Oxidation Reaction

Photocatalytic coproduction of hydrogen (H 2 ) and hydrogen peroxide (H 2 O 2 ) from pure water via the two‐electron water oxidation reaction (2e − ‐WOR) represents a novel approach toward sustainable solar‐to‐chemical energy conversion. This enables the parallel generation of two high‐added‐value products, offering a promising alternative to conventional systems. This review summarizes the latest advancements obtained using this approach and heterogeneous semiconductor photocatalysts. After introducing the fundamentals of photocatalysis, the thermodynamics, kinetics and mechanisms of water reduction and oxidation are discussed, accounting for the distinct competing pathways. Energetics and selectivity of H 2 O 2 production are assessed using free‐energy descriptors and volcano plot analysis. Stability of H 2 O 2 under photocatalytic conditions is examined, considering thermal, photochemical, and surface‐mediated decomposition processes. Material design strategies to promote photocatalytic H 2 /H 2 O 2 coproduction are critically analyzed and discussed. These include doping, defect engineering, morphology control, cocatalyst integration, and heterojunction formation. The aim of this review is to provide general guidelines for designing new efficient nanomaterials for photocatalytic H 2 /H 2 O 2 coproduction, minimizing H 2 O 2 degradation. Finally, it offers a critical assessment of reported approaches, providing insights into the current level of progress in this field: the experimental evidence underlying mechanism assignment is examined and organized into a hierarchy, against which the surveyed systems are classified.