Solar Water Oxidation by Composite Catalyst/α-Fe2O3 Photoanodes

Electrodeposition of an amorphous cobalt catalyst layer over a high-surface-area alpha-Fe2O3 photoanode causes a more than 350 mV cathodic shift in the onset potential for photoetectrochemical water oxidation using this anode and simulated solar irradiation. The catalyst layer is shown to deposit conformally onto the mesostructured alpha-Fe2O3, leading to a large contact area at the interface between the two halves of the composite photoanode. Photoetectrochemical measurements show that the photocurrent generated from this composite photoanode still derives from alpha-Fe2O3 excitation but is now accessible at an external bias several hundred millivolts below what is typically required for alpha-Fe2O3 photoanodes alone, indicating a reduced external. bias would be needed to drive overall water splitting. These results demonstrate modification of this prototypical photoanode material with a conformal layer of a competent electrocatalyst to separate the tasks of photon absorption and redox catalysis, a strategy that may have important and general ramifications for solar photoelectrochemical hydrogen generation.