Cobalt as a sacrificial metal to increase the photoelectrochemical stability of CuBi2O4 films for water splitting.

Abstract

CuBi2O4 is an excellent photocathode candidate in water-splitting photoelectrochemical cells. However, its poor photoelectrochemical stability caused by the reduction of Cu2þ to Cu metal limits its use. Here, we show a strategy to decrease the reduction of Cu2þ to Cu using cobalt as a sacrificial metal. Co-doped CuBi2O4 films were prepared by spray pyrolysis using Co2þ salt as the precursor. Co2þ ions replace Cu2þ in the CuBi2O4 structure, and subsequent heat treatment at 500 C leads to partial oxidation of Co2þ to Co3þ. As the reduction potential of Co3þ/Co2þ is higher than that of Cu2þ/Cu, Cu2þ reduction can be minimized. Comparatively, about 72% of the photocurrent produced by the CuBi2O4 film is lost in the first few minutes of illumination. In the Co-doped CuBi2O4 film, the photocurrent drops by less than 7%. Thus, the Co-doping can increase the CuBi2O4 photostability and be helpful for the fabrication of more stable photocathodes.