Toward Integrated Solar Fuel Platforms: Advances in Oxide‐Based Photoelectrochemical Water Splitting and CO 2 Reduction

Photoelectrochemical (PEC) solar‑fuel production has emerged as a compelling route to carbon‑neutral energy. Yet, its practical deployment remains limited by the intrinsic constraints of metal‑oxide semiconductors, restricted visible‑light absorption, short carrier diffusion lengths, sluggish interfacial kinetics, and low CO 2 ‑reduction selectivity. This review provides a comprehensive assessment of advances in oxide‑based PEC materials for solar water splitting and CO 2 reduction, highlighting how nanoscale engineering has reshaped performance. We examine fundamental thermodynamic and kinetic requirements for PEC operation, including band‑edge alignment, charge‑carrier dynamics, and redox selectivity, and critically evaluate how morphology control, bandgap tuning, defect/dopant engineering, heterojunction design, surface passivation, and plasmonic activation collectively overcome long‑standing bottlenecks. We compare material‐specific progress in TiO 2 , ZnO, Fe 2 O 3 , WO 3 , BiVO 4 , Cu 2 O/CuO, and mixed‑oxide systems through reported photocurrent density, Faradaic efficiency, product selectivity, and stability. At the device scale, we discuss how membrane selection, photoelectrode architecture, and advanced reactor designs, including flow‑cell CO 2 ‑reduction systems, translate material innovations into practical performance gains. Finally, we outline techno‐economic and life‐cycle considerations, emphasizing durability, resource sustainability, and the growing role of machine‐learning‐driven material discovery. With continued progress in oxide nano‐engineering and system integration, PEC platforms are now approaching the > 10% solar‐to‐hydrogen efficiency needed for scalable solar‐fuel generation.