Effect of annealing atmosphere on the performance of TiO₂ nanorod arrays in photoelectrochemical water splitting

TiO₂ nanorod arrays grown on a fluorine-doped tin oxide coated glass substrate with a hydrothermal technique were annealed under different atmospheres (oxygen, air, nitrogen and argon) and used as the photoanode in photoelectrochemical (PEC) water splitting. The effects of the annealing atmosphere on the structure, surface chemical state and PEC performance were investigated. The TiO₂ nanorod samples all showed the same rutile phase structure but different PEC activities. The sample annealed in argon exhibited the highest photocurrent density among the others of 0.978 mA cm⁻² at a bias of 1.23 V versus the reversible hydrogen electrode (RHE), achieving an increase of 124.8% in comparison with the sample annealed in oxygen. The oxygen vacancy densities within the samples were examined with the X-ray photoelectron spectroscopy and the electron spin resonance techniques. Generally, the density of oxygen vacancy in the TiO₂ samples increases with the decrease of the oxygen content in the annealing atmosphere. The increased oxygen vacancy concentration enhances the visible light absorption which facilitates the generation of electrons and holes, as well as increases the electron conductivity and thus inhibits the recombination of the charge carriers.