潘 振華

Photocatalysis provides a direct solar‐driven route for addressing two urgent global needs, clean water and clean energy. Classical research treats pollutant degradation and hydrogen production as separate domains, with environmental photocatalysis focused on mineralization and hydrogen studies centered on water splitting. This perspective reframes photocatalytic systems as dual‐function redox platforms in which pollutants serve not only as electron donors but as reactive substrates capable of selective transformation while supporting hydrogen evolution. We established the mechanistic basis for this coupling, examining band energetics, hole‐driven oxidation, and the kinetic competition between proton reduction and oxygen reduction. Real water matrices introduce additional pathways shaped by natural organic matter, common anion/cations, turbidity, and microbial activity, which shift redox balance and influence selectivity. Recent advances in catalyst design, co‐catalyst engineering, and structured reactors have created new opportunities for guided oxidative pathways and stable hydrogen evolution. Building on these developments, we highlight emerging co‐valorization strategies that produce hydrogen while also converting wastewater‐borne organics into useful intermediates such as aldehydes and acids. Finally, we propose evaluation metrics that capture redox partitioning, product selectivity, and performance under realistic conditions. This integrated perspective positions dual‐function photocatalysis as a promising foundation for circular water–energy systems.

ABSTRACT Solar‐powered CO ₂ reduction through photoelectrochemical (PEC) approaches to produce hydrocarbon fuels, such as methane (CH ₄ ), is one of the most promising paths for supplying sustainable fuels. However, the limited light absorption capability and sluggish kinetics restrict the photocatalytic rate and selectivity for hydrocarbon production. Here, we introduce tandem catalysts on photocathodes designed to enhance controlled sequential reactions involving intermediates and thus the selectivity of CO ₂ reduction. Specifically, when mounted on Cu/Ag‐Cu bilayer catalysts, the p‐type Si photocathode with a pyramid‐structured surface dramatically improves CO ₂ ‐to‐CH ₄ conversion, achieving a selectivity of 60.2 ± 3.4% and a working current density of −32.9 ± 1.9 mA cm ⁻² at −1.1 V vs. RHE. As identified by operando Raman and synchrotron‐radiation Fourier transform infrared spectroscopy and Density Functional Theory, the bottom layer of the Cu/Ag‐Cu catalysts comprises Ag and Cu nanoparticles, which catalyse the initial reduction of CO ₂ to form *CO and the creation of *H species dissociated from H ₂ O, respectively. The top Cu layer subsequently enables the protonation of *CO to *CHO, ultimately yielding CH ₄ . This design of tandem catalysts, coupled with a thorough investigation of the reaction mechanisms, offers a powerful approach toward high‐performance and selective pathways for solar‐powered CO ₂ reduction to targeted products.