Effect of substitution doping and surface adsorption of Al atoms on photocatalytic decomposition of water and oxygen from BiVO₄ (010) crystal surface

Abstract

Using solar photoelectrochemical decomposition of water to produce hydrogen and oxygen is one of the most feasible approaches to obtaining renewable energy. Compared with hydrogen-evolution reaction (HER), the oxygen-evolution reaction (OER) is very complex, there are four sluggish proton-coupled electron transfer processes. It is critical to improve OER performance. The BiVO₄ (010) facet possesses low surface energy, strong visible absorption, and good activity for OER, and is considered as one of the most suitable PEC catalysts. However, its poor electron conductivity, low charge carrier mobility, and high charge recombination rates significantly limit its practical applications. To achieve highly active OER photocatalysts, we modify BiVO₄ (010) facet by substitutial doping with Al atom and surface adsorption with Al atom. According to density functional theory calculations, we compare OER performances of these two modified BiVO₄ (010) facets. The results show that both approaches can effectively regulate the electronic structure of BiVO₄ and then tune OER activity resulting from the change of the structure. Though Al substitutional doping reduces the band gap of the (010) facet and enhances the visible light absorption, the improvement of OER performance is not significant because the doping site is inside and has little influence on the surface active site. Importantly, the surface adsorption of Al atom is considered as an efficient means to improve the OER activity on BiVO₄ (010) facet due to the combined action between surface adsorbed Al and active site Bi atoms. Al adsorbed (010) facet exhibits excellent OER catalytic activity: 1) the induction of localized states and the reduction of band gap are conducive to the electronic transition, optical absorption, thus increasing the electrical conductivity; 2) there is lower hole effective mass, and thus effectively enhancing the ability to transfer from anode surface to electrolyte surface, thereby increasing the difference between the effective mass ratio of electron−hole pairs and 1 and effectively reducing the electron-hole recombination; 3) the nteraction between the active sites and oxygen-containing intermediates is reinforced in the OER process, therefore the potential determining step of OER decreases effectively. This work provides an important reference for designing efficient and stable two-dimensional semiconductor-based photocatalysts for OER. We believe that it will arouse great interest of the BiVO₄ community and motivate numerous experimental researches.