Visible‐Light Photooxidation of Water to Oxygen at Hybrid TiO2–Polyheptazine Photoanodes with Photodeposited Co‐Pi (CoOx) Cocatalyst

A cobalt oxide-based oxygen-evolving cocatalyst (Co-Pi) is photodeposited by visible-light irradiation onto nanocrystalline TiO2–polyheptazine (TiO2–PH) hybrid photoelectrodes in a phosphate buffer. The Co-Pi cocatalyst couples effectively to photoholes generated in the surface polyheptazine layer of the TiO2–PH photoanode, as evidenced by complete photooxidation of water to oxygen under visible-light (λ>420 nm) irradiation at moderate bias potentials. In addition, the presence of the cocatalyst also reduces significantly the recombination of photogenerated charges, particularly at low bias potentials, which is ascribed to better photooxidation kinetics resulting in lower accumulation of holes. This suggests that further improvements of photoconversion efficiency can be achieved if more effective catalytic sites for water oxidation are introduced to the surface structure of the hybrid photoanodes.