Stoichiometric water splitting using a p-type Fe2O3 based photocathode with the aid of a multi-heterojunction

Fe2O3-based photocathodes are one of the least expensive options for hydrogen generation by water splitting. Although p-type N, Zn-doped Fe2O3 (N, Zn-Fe2O3) has been reported to possess a negative conduction band minimum position sufficient for photocathodic hydrogen generation, the efficiency and stability of the resulting H-2 production is low and the reaction is sacrificial. In the present work, analysis by hard X-ray photoelectron spectroscopy (HAXPES) showed that these negative characteristics result from the self-redox reaction of p-type Fe2O3. Based on this result, a TiO2 layer was introduced onto the surface of p-type N, Zn-Fe2O3 to passivate surface defects. In addition, to ensure efficient electron transfer, a thin Cr2O3 layer was also inserted between N, Zn-Fe2O3 and a bottom side conductive oxide layer to generate a favorable band alignment for hole transfer. The resulting Pt/TiO2/N, Zn-Fe2O3/Cr2O3 electrode exhibits a highly stable, significantly enhanced cathodic photocurrent during H-2 production under AM 1.5 irradiation. The mechanism providing this improvement was investigated by combining electrochemical impedance spectroscopy, open-circuit voltage decay analysis and scanning tunneling electron microscopy-energy dispersive X-ray spectroscopy. Stoichiometric water splitting without an external electrical bias was also demonstrated by connecting the Fe2O3-based photocathode to an ntype SrTiO3-x photoanode, representing the first-ever example of stoichiometric overall water splitting using an Fe-based photocathode.