Photoelectrochemical Water Oxidation Using Cobalt Phosphate-Modified Nitrogen-Doped Titania Nanotube Arrays

The synthesis of cobalt phosphate (CoPi)-modified, nitrogen-doped TiO₂ nanotube arrays (N-TNAs) for photoelectrochemical (PEC) oxygen evolution under visible light is reported. Because of the nitrogen doping, the N-TNAs exhibit enhanced visible-light activity toward the PEC water oxidation reaction. However, the performance is diminished as a result of self-oxidation by photogenerated holes in the valence band of the N-TNAs. Compared with the N-TNAs, the CoPi/N-TNAs prepared under optimal conditions show a twofold improvement in photocurrent generation and are also sensitive to light with wavelengths as long as 580 nm. Stable oxygen evolution with a Faradaic efficiency approaching unity is demonstrated using the CoPi/N-TNA photoanodes under simulated sunlight for at least 2 h of operation.