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. Through integration of high throughput experimental and theoretical techniques, CuO‐V2O5 is established as the most prominent composition system for oxygen evolution reaction photoelectrocatalysts. Four photoelectrocatalyst phases are discovered and structure–property relationships are developed using a strategic combination of combinatorial synthesis, high throughput screening, and detailed electronic structure calculations.