p-n heterojunction constructed by γ-Fe 2 O 3 covering CuO with CuFe 2 O 4 interface for visible-light-driven photoelectrochemical water oxidation.

FeO is a promising n-type semiconductor as the photoanode of photoelectrochemical water-splitting method due to its abundance, low cost, environment-friendly, and high chemical stability. However, the recombination of photogenerated holes and electrons leads to low solar-to-hydrogen efficiency. In this work, to overcome the recombination issue, a p-type semiconductor, CuO, is introduced underneath the γ-FeO to synthesize γ-FeO/CuO on the FTO substrate. Along with the formation of p-n heterojunction, CuFeO is in situ generated at the interface of γ-FeO and CuO. The existence of CuO in CuO and CuFeO promotes the charge transfer from CuO to γ-FeO and within CuFeO, respectively, resulting in creating an internal electric field in γ-FeO/CuO and leading to the conduction band of CuO bending up and γ-FeO bending down. Additionally, Cu(II) in CuFeO contributes to fast electron capture. Consequently, the charge transfer efficiency and charge separation efficiency of photo-generated holes are promoted. Hence, γ-FeO/CuO exhibits an enhanced photocurrent density of 13.40 mA cm (1.9 times higher than γ-FeO). The photo corrosion resistance of CuO is dramatically increased with the protection of CuFeO, resulting in superior high chemical stability, i.e. 85% of the initial activity remains after a long-term test.