Composition modulation of a hematite photoanode for highly efficient photoelectrochemical water oxidation

Abstract

Hematite (α-Fe₂O₃) has emerged as a promising candidate for photoelectrochemical (PEC) water oxidation. Modulating its composition is pivotal for obtaining highly efficient PEC performance. However, an oxygen-rich surface is formed from the FeOOH precursor, resulting in poor surface charge transfer. In this work, for the first time, Fe nanoparticles were deposited on the surface of α-Fe₂O₃ to increase the atomic ratio of Fe to O on the surface. Subsequently, oxygen vacancy (V_O) and hydrogen (H) impurity defects were introduced to further control the chemical composition of Fe₂O₃. The introduction of V_O can increase the charge carrier density, while the charge transport mobility is reduced due to the low hopping process of small polarons induced by V_O. To address the problem, we show that shallow-level defects are created via H doping, which extracts the trapped electrons out of the V_O-induced trap states. Due to the formation of homogeneous distribution of Fe and O, introduction of V_O and incorporation of shallow-level defects by H impurity, charge separation efficiency was markedly improved. Consequently, the photocurrent density of the α-Fe₂O₃ photoanode was increased from 0.76 to 1.71 mA cm⁻² at a potential of 1.23 V versus the reversible hydrogen electrode. Our work verifies the relationship between the PEC performance of the semiconductor photoanode and its composition and provides promising opportunities for further optimization.