Boosting Photoelectrochemical Water Oxidation of Hematite by Surface States Modification

Abstract

State-of-the-art water-oxidation catalysts in acidic electrolyte usually contain expensive noble metals such as ruthenium and iridium. However, they are exceedingly expensive to be implemented broadly in semiconductor photoanodes for affordable photoelectrochemical (PEC) water splitting devices. Here, an Earth-abundant CoFe Prussian blue analogue (CoFe-PBA) is incorporated with core-shell Fe₂O₃Fe₂TiO₅ type II heterojunction nanowires as composite photoanodes for PEC water splitting. Those deliver a stable photocurrent of 1.25 mA cm-2 at 1.23 V vs. reversible reference electrode in acidic electrolyte (pH=1). The enhancement arises from the synergic behavior between the successive decoration of the hematite surface with nanolayers of Fe₂TiO₅ and then, CoFe-PBA. The underlying physical mechanism of performance enhancement through formation of the Fe₂O₃Fe₂TiO₅ CoFe-PBA heterostructure reveals that the surface states electronic levels of hematite were modified such that an interfacial charge transfer becomes kinetically favorable. These findings open new pathways for the future design of cheap and efficient hematite-based photoanodes.

Keywords: Photoelectrochemical (PEC) water splitting, hematite, surface states, Fe2TiO5, CoFe Prussian blue analogue, photoanodes, water oxidation, nanowires, acidic electrolyte