Photo-assisted electrodeposition of cobalt–phosphate (Co–Pi) catalyst on hematite photoanodes for solar water oxidation

A photo-assisted electrodeposition approach was used to deposit a cobalt-phosphate water oxidation catalyst ("Co-Pi") onto recently improved dendritic mesostructures of [small alpha]-Fe2O3. A comparison between this approach, electrodeposition of Co-Pi, and Co2+ wet impregnation showed that photo-assisted electrodeposition of Co-Pi yields superior [small alpha]-Fe2O3 photoanodes for photoelectrochemical water oxidation. Stable photocurrent densities of 1.0 mA cm-2 at 1.0 V and 2.8 mA cm-2 at 1.23 V vs. RHE measured under standard illumination and basic conditions were achieved. By allowing deposition only where visible light generates oxidizing equivalents, photo-assisted electrodeposition provides a more uniform distribution of Co-Pi onto [small alpha]-Fe2O3 than obtained by electrodeposition. This approach of fabricating catalyst-modified metal-oxide photoelectrodes may be attractive for optimization in conjunction with tandem or hybrid photoelectrochemical cells.