Effect of preparation conditions and Co–Pi groups as a noble metal-free redox mediator and hole extractor to boost the photoelectrochemical water oxidation for 1D nanorod α-Fe2O3

Abstract

Photoelectrochemical water splitting for hydrogen production is an ideal method for solar energy utilization. Herein, α-Fe₂O₃ was prepared by a hydrothermal process and the precursor concentration, calcination temperature and hydrothermal time were optimized. The Co–Pi groups were deposited on the surface by two-step dipping process. The preparation conditions and loading capacity of CoPi were optimized. SEM showed that the morphology of α-Fe₂O₃ was short nanorods. XPS indicated that CoPi was successfully deposited on the surface of Fe₂O₃. TEM and XRD showed that CoPi was amorphous. The photocurrent density of Fe₂O₃/CoPi increased to 1.95 mA cm⁻² at 1.23 V_RHE, which was 1.91 times that of bare Fe₂O₃. After CoPi modification, the initial potential shifted negatively by 70 mV. It could be inferred that CoPi acted as an effective water oxidation co-catalyst to reduce the activation energy of the oxygen evolution reaction. The chopping I–t curve showed that the transient anodic spike of Fe₂O₃ decreased after CoPi deposition. This indicated that CoPi acted as a hole extractor and redox mediator to reduce the charge accumulation on the Fe₂O₃ surface. Through calculation, the ABPE of Fe₂O₃/Co–Pi was 2.1 times that of Fe₂O₃. The charge injection efficiency of Fe₂O₃/Co–Pi at 1.23 V_RHE was 1.6 times that of Fe₂O₃. This study presented a richer understanding on the functions and promotional effects of the preparation conditions and CoPi groups for Fe₂O₃ photoanodes.