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

Hematite (alpha-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 alpha-Fe2O3 to increase the atomic ratio of Fe to O on the surface. Subsequently, oxygen vacancy (VO) and hydrogen (H) impurity defects were introduced to further control the chemical composition of Fe2O3. The introduction of VO can increase the charge carrier density, while the charge transport mobility is reduced due to the low hopping process of small polarons induced by VO. To address the problem, we show that shallow-level defects are created via H doping, which extracts the trapped electrons out of the VO-induced trap states. Due to the formation of homogeneous distribution of Fe and O, introduction of VO and incorporation of shallow-level defects by H impurity, charge separation efficiency was markedly improved. Consequently, the photocurrent density of the alpha-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. In this work, oxygen vacancy (VO) and hydrogen (H) impurity defects were introduced to control the chemical composition of alpha-Fe2O3. Our work verifies the relationship between the semiconductor electrode performance and its composition and provides effective guidance for further optimization.