Research progress on efficient and selective transition metal oxides for photoelectrochemical seawater splitting

Abstract

Harnessing solar energy through photochemical processes in seawater offers a promising path toward sustainable hydrogen production. Photoelectrochemical (PEC) seawater splitting combines light-driven charge separation with abundant water resources to generate hydrogen fuel. This review highlights recent progress in transition metal oxide (TMO) photoanodes and nickel (Ni)-based cocatalysts, focusing on the interplay of light absorption, charge transport, surface coordination chemistry, and catalytic selectivity. Representative TMOs, including titanium dioxide (TiO₂), tungsten trioxide (WO₃), hematite (Fe₂O₃), and bismuth vanadate (BiVO₄), are evaluated for optoelectronic properties, stability, and performance limitations. TiO₂ exhibits excellent photochemical stability but limited visible-light response (<1 mA cm⁻²). WO₃ and Fe₂O₃ extend light absorption, reaching ∼6 and ∼4 mA cm⁻², respectively, though both face charge recombination and stability challenges. BiVO₄ with a 2.4 eV bandgap, currently shows the best balance, achieving 4–7 mA cm⁻² at 1.23 V vs. RHE when coupled with protective layers and cocatalysts. Meanwhile, NiMo- and NiFe-based cocatalysts offer cost-effective enhancement of interfacial charge transfer and corrosion resistance. By adopting a coordination-chemistry-centered perspective, this review links defect structures, surface electronic states, and interfacial pathways to PEC performance, highlighting strategies to improve durability, selectivity, and scalability for practical seawater hydrogen production.