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.

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.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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