Dynamics of photogenerated holes in surface modified α-Fe203 photoanodes for solar water splitting.

This paper addresses the origin of the decrease in the external elec-trical bias required for water photoelectrolysis with hematite photoanodes, observed following surface treatments of such elec-trodes. We consider two alternative surface modifications: a cobalt oxo/hydroxo-based (CoOx) overlayer, reported previously to func-tion as an efficient water oxidation electrocatalyst, and a Ga203 overlayer, reported to passivate hematite surface states. Transient absorption studies of these composite electrodes under applied bias showed that the cathodic shift of the photocurrent onset observed after each of the surface modifications is accompanied by a similar cathodic shift of the appearance of long-lived hematite photoholes, due to a retardation of electron/hole recombination. The origin of the slower electron/hole recombination is assigned primarily to enhanced electron depletion in the Fe203 for a given applied bias. [ABSTRACT FROM AUTHOR]