Solar-Driven Photocatalytic H₂O₂ Production: Mechanistic Foundations, Catalyst Design, Performance Benchmarking, and...

Hydrogen peroxide (H₂O₂) is a clean oxidant, disinfectant, and candidate liquid energy carrier, yet its industrial manufacture remains dominated by the energy-intensive anthraquinone process. Solar photocatalytic H₂O₂ synthesis offers a decentralized alternative that could combine water, molecular oxygen, and sunlight under ambient conditions. The field now spans inorganic semiconductors, graphitic carbon nitride (g-C₃N₄), covalent organic frameworks (COFs), heterojunctions, and other porous frameworks. This review connects reaction mechanisms, catalyst design, performance testing, and emerging applications across these major platforms. We examine the two-electron oxygen reduction reaction (2e^- ORR), two-electron water oxidation reaction (2e^- WOR), and dual-channel photosynthesis. We then assess how intrinsic electronic and structural properties govern O₂ adsorption, intermediate stabilization, proton-coupled electron transfer, selective two-electron conversion, product release, and H₂O₂ loss. Performance is interpreted together with the water matrix, donor use, O₂ supply, illumination, normalization basis, and analytical method. Finally, we consider collected H₂O₂ production, in situ utilization, coupled synthesis, and multiscale optimization from molecular sites to reactors. Mechanistic verification, long-term stability, mass transfer, and transparent reporting remain the central challenges for practical solar H₂O₂ production.