Cobalt as a sacrificial metal to increase the photoelectrochemical stability of CuBi 2 O 4 films for water splitting

CuBi 2 O 4 is an excellent photocathode candidate in water-splitting photoelectrochemical cells. However, its poor photoelectrochemical stability caused by the reduction of Cu 2+ to Cu metal limits its use. Here, we show a strategy to decrease the reduction of Cu 2+ to Cu using cobalt as a sacrificial metal. Co-doped CuBi 2 O 4 films were prepared by spray pyrolysis using Co 2+ salt as the precursor. Co 2+ ions replace Cu 2+ in the CuBi 2 O 4 structure, and subsequent heat treatment at 500 °C leads to partial oxidation of Co 2+ to Co 3+. As the reduction potential of Co 3+ /Co 2+ is higher than that of Cu 2+ /Cu, Cu 2+ reduction can be minimized. Comparatively, about 72% of the photocurrent produced by the CuBi 2 O 4 film is lost in the first few minutes of illumination. In the Co-doped CuBi 2 O 4 film, the photocurrent drops by less than 7%. Thus, the Co-doping can increase the CuBi 2 O 4 photostability and be helpful for the fabrication of more stable photocathodes.