Photodeposition of Co-Based Oxygen Evolution Catalysts on α-Fe2O3 Photoanodes

Cobalt-based oxygen evolution catalysts contain-ing phosphates (Co-Pi OEC) were photochemically deposited onto the surface of n-type α-Fe2O3 electrodes to enhance solar O2 production. α-Fe2O3 films used in this study were prepared by electrodepositing Fe films followed by thermal oxidation at 500 °C. The use of a nonaqueous plating solution made it possible to deposit adherent and uniform Fe films, which is difficult to achieve in an aqueous medium. Photodeposition of Co-Pi OEC was carried out by using photogenerated holes in the valence band of α-Fe2O3 to oxidize Co2+ ions to Co3+ ions in a phosphate buffer solution, which resulted in the precipitation of Co-Pi OEC on the α-Fe2O3 surface. Two different deposition conditions, open circuit (OC) and short circuit (SC) conditions, were studied comparatively to understand their effect on the growth and composition of Co-Pi OEC deposits. The results showed that the SC condition where the photoreduction reaction is physically separated from the photo-oxidation ...