Subsurface Engineering Induced Fermi Level De‐pinning in Metal Oxide Semiconductors for Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting is a promising approach for renewable solar light conversion. However, surface Fermi level pinning (FLP), caused by trap states, severely restricts the PEC activities. Theoretical calculations indicate subsurface oxygen vacancy (sub-Ov) could release FLP and retain active structure. A series of metal oxide semiconductors with sub-Ov were prepared through precisely regulated spin-coating calcination. Etching X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), energy loss spectra (EELS) demonstrated Ov located at sub ∼2–5 nm region. Mott–Schottky open circuit photovoltage results confirmed states elimination de-pinning. Thus, superior performances 5.1, 3.4, 2.1 mA cm−2 1.23 V vs. RHE achieved on BiVO4, Bi2O3, TiO2 outstanding stability 72 h, outperforming most reported works under identical conditions.