Solar photoelectrochemical generation of fuel is a promising energy technology yet the lack of an efficient, robust photoanode remains a primary materials challenge in the development and deployment of solar fuels generators. Metal oxides comprise the most promising class of photoanode materials, but no known material meets the demanding requirements of low band gap energy, photoelectrocatalysis of the oxygen evolution reaction (OER), and stability under highly oxidizing conditions. Here, the identification of new photoelectroactive materials is reported through a strategic combination of combinatorial materials synthesis, high‐throughput photoelectrochemistry, optical spectroscopy, and detailed electronic structure calculations. Four photoelectrocatalyst phases, α‐Cu2V2O7, β‐Cu2V2O7,γ‐Cu3V2O8, and Cu11V6O26, are reported with band gap energy at or below 2 eV. The photoelectrochemical properties and 30 min stability of these copper vanadate phases are demonstrated in three different aqueous electrolytes (pH 7, pH 9, and pH 13), with select combinations of phase and electrolyte exhibiting unprecedented photoelectrocatalytic stability for metal oxides with sub‐2 eV band gap. Through integration of experimental and theoretical techniques, new structure‐property relationships are determined and establish CuO–V2O5 as the most prominent composition system for OER photoelectrocatalysts, providing crucial information for materials genomes initiatives and paving the way for continued development of solar fuels photoanodes.

The solar-driven synthesis of fuel, which is performed by coupling the oxygen evolution reaction (OER) with fuel-forming hydrogen evolution or carbon dioxide reduction reactions, is a promising strategy for generating renewable energy.1 Chemical fuels offer high energy density and facile distribution, and photoelectrochemical (PEC) cells with tandem light absorbers and liquid-semiconductor junctions are being developed into efficient solar fuels generators. 2Widespread deployment of PEC solar fuels technology is impeded by several technological challenges, most notably the development of a stable photoanode that enables efficient photoelectrocatalysis of the OER. 2,3The coupling of solar light absorption with electrocatalysts enables efficient fuel generation but also poses substantial challenges with respect to the electrochemical stability of active components, particularly in the acidic or alkaline media that yield the highest device efficiencies. 4 A corresponding challenge for solar fuels research is the discovery of OER photoelectrocatalysts that exhibit stable operation in as high of a concentration of base as possible. Traditionally, with the notable exception of a-Fe 2 O 3 , the stability of low-band gap (below 2.5 eV) metal oxides has proved problematic. 5 In particular, compound metal oxide semiconductors such as bismuth vanadate (BiVO 4 ) suffer from rapid corrosion via anodic dissolution of V species. 6 In the present work we demonstrate that V corrosion is mitigated in copper vanadates through self-passivation. A primary strategy for protection of light absorbers in aqueous electrolytes is the application of an inert, protective coating, which often lowers efficiency due to increases in electrical resistance and recombination rates.