Effect of Sn-self diffusion via H2 treatment on low temperature activation of hematite photoanodes

Abstract

The objective of this study was to report the preparation of a highly efficient hematite nanorod photoanode by H₂ treatment of the β-FeOOH nanorod with subsequent quenching in air at lower temperature activation for photoelectrochemical (PEC) water oxidation. The hematite nanorod photoanode (H650) prepared by thermally treating the β-FeOOH nanorod at 360 °C for 1 h under H₂ flow and quenching at 650 °C for 10 min in air exhibited a remarkable photocurrent of 1.17 mA cm⁻² at 1.23 V vs. RHE, which was 20 times higher than that of hematite quenched at the same temperature without H₂ treatment. Such enhanced PEC performance was attributed to high Sn⁴⁺ diffusion from the fluorine doped SnO₂ (FTO) substrate via H₂ treatment and Sn⁴⁺ doping by subsequent lower temperature quenching. Our density functional theory (DFT) calculation supports our experimental results and proposed mechanism in that the Sn replacement reaction of magnetite (Fe₃O₄, H₂-reduced β-FeOOH) occurs at a lower temperature and requires a smaller energy than that of akaganeite (β-FeOOH).