Photoelectrochemical Water Oxidation by Cobalt Catalyst ("Co-Pi")/α-Fe2O3 Composite Photoanodes: Oxygen Evolution and Resolution of a Kinetic Bottleneck

A cobalt-phosphate water oxidation catalyst ("Co-Pi") has been electrodeposited onto mesostructured alpha-Fe2O3 photoanodes. The photoelectrochemical properties of the resulting composite photoanodes were optimized for solar water oxidation under frontside illumination in pH 8 electrolytes. A kinetic bottleneck limiting the performance of such photoanodes was identified and shown to be largely overcome by more sparse deposition of Co-Pi onto the alpha-Fe2O3. Relative to alpha-Fe2O3 photoanodes, a sustained 5-fold enhancement in the photocurrent density and O-2 evolution rate was observed at +1.0 V vs RHE with the Co-Pi/alpha-Fe2O3 composite photoanodes. These results demonstrate that integration of this promising water oxidation catalyst with a photon-absorbing substrate can provide a substantial reduction in the external power needed to drive the catalyst's electrolysis chemistry.