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

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.