p-n heterojunction constructed by γ-Fe2O3 covering CuO with CuFe2O4 interface for visible-light-driven photoelectrochemical water oxidation

Fe 2 O 3 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-Fe 2 O 3 to synthesize γ-Fe 2 O 3 /CuO on the FTO substrate. Along with the formation of p-n heterojunction , CuFe 2 O 4 is in situ generated at the interface of γ-Fe 2 O 3 and CuO. The existence of Cu 2 O in CuO and CuFe 2 O 4 promotes the charge transfer from CuO to γ-Fe 2 O 3 and within CuFe 2 O 4 , respectively, resulting in creating an internal electric field in γ-Fe 2 O 3 /CuO and leading to the conduction band of CuO bending up and γ-Fe 2 O 3 bending down. Additionally, Cu(II) in CuFe 2 O 4 contributes to fast electron capture. Consequently, the charge transfer efficiency and charge separation efficiency of photo-generated holes are promoted. Hence, γ-Fe 2 O 3 /CuO exhibits an enhanced photocurrent density of 13.40 mA cm −2 (1.9 times higher than γ-Fe 2 O 3 ). The photo corrosion resistance of CuO is dramatically increased with the protection of CuFe 2 O 4 , resulting in superior high chemical stability, i.e. 85% of the initial activity remains after a long-term test.