A Composite of Hematite and Cerium-Doped Metal–Organic Framework for Stable Photoelectrochemical Water Splitting

Abstract

Hematite (α-Fe₂O₃) is a promising semiconductor for photoelectrochemical (PEC) water splitting because of its favorable band gap. However, the challenge of improving PEC performance by constructing effective and stable cocatalysts on the surface of α-Fe₂O₃ persists. This study presents a simple approach for fabricating active α-Fe₂O₃ photoanodes coated with cerium-doped metal–organic framework (MOF) films. By adjustment of the Fe and Ce compositions of the MOFs, it was feasible to enhance the band gaps and band positions of the α-Fe₂O₃/MOF heterojunction. X-ray absorption spectroscopy (Fe K-edge XANES and EXAFS and Ce L₃-edge XANES), along with X-ray photoelectron spectroscopy, was employed to investigate the oxidation states of Fe and Ce, as well as their local structural environments in the MOF, providing insights into the enhanced water oxidation performance. The α-Fe₂O₃/MIL-53(Fe): x Ce thin film exhibited a photocurrent density of 2.3 mA cm⁻² at 1.23 V vs RHE, up to four times that of the pristine α-Fe₂O₃ photoanode. The MIL-53(Fe) catalyst, loaded with 2.7% Ce, exhibits enhanced PEC activity, relating to the reduced recombination of photogenerated carriers, increased active sites, and improved charge separation and transfer efficiency. This study offers novel views of the advancement of MOF-based composites for PEC water oxidation.