p‑Type CuRhO₂ as a Self-Healing Photoelectrode for Water Reduction under Visible Light

Polycrystalline CuRhO₂ is investigated as a photocathode for the splitting of water under visible irradiation. The band edge positions of this material straddle the water oxidation and reduction redox potentials. Thus, photogenerated conduction band electrons are sufficiently energetic to reduce water, while the associated valence band holes are energetically able to oxidize water to O₂. Under visible illumination, H₂ production is observed with ∼0.2 V underpotential in an air-saturated solution. In contrast, H₂ production in an Ar-saturated solution was found to be unstable. This instability is associated with the reduction of the semiconductor forming Cu(s). However, in the presence of air or O₂, bulk Cu(s) was not detected, implying that CuRhO₂ is self-healing when air is present. This property allows for the stable formation of H₂ with ca. 80% Faradaic efficiency.