Protecting hydrogenation-generated oxygen vacancies in BiVO4 photoanode for enhanced water oxidation with conformal ultrathin amorphous TiO2 layer

Introducing appropriate amount of oxygen vacancies by hydrogenation treatment is a simple and efficient way to improve the photoelectrochemical performance of nanostructured oxide photoanodes. However, the hydrogenation effect is often not durable due to the gradual healing of oxygen vacancies at or close to surface of photoanodes. Herein, we tackled the problem by conformal coating the hydrogenated nanoporous BiVO 4 (H-BiVO 4 ) photoanode with an ultrathin layer of amorphous TiO 2 . Photoelectrochemical measurements showed that a 4   nm-thick TiO 2 layer could significantly improve the stability of H-BiVO 4 photoanode for repeated working test, with negligible influence on the initial photocurrent compared to the uncoated one. Mott–Schottky and linear sweep voltammetry measurements showed that donor density and photocurrent density of the H-BiVO 4 electrode almost decayed to the values of pristine BiVO 4 electrode after 3   h test, while the amorphous TiO 2 -coated electrode only degraded by 6% and 5% of the initial values respectively in the same period. The investigation thus suggested that the amorphous TiO 2 layer did protect the oxygen vacancies in H-BiVO 4 photoanode by isolating these oxygen vacancies from environmental oxygen, while at the same time not impeding the interfacial charge transfer to water molecules due to its leaky nature.