First-principles Calculation Of BiVO₄ Water Oxidation

The photocatalytic water splitting based on a semiconductor particle can achieve the green conversion from solar energy to hydrogen energy,which is a promising new energy technology.Among many semiconductor materials,BiVO₄has received great attentions due to its advantages such as high stability,low-cost and ideal band gap.There are many researches on BiVO₄water oxidation in theoretical calculation and simulation.However,these calculation researches did not take into account the effects of defects and solution environment and cannot be compared with the experimental system.Further,the active site of BiVO₄water oxidation is currently considered to be the Bi site,and whether V site can be used as the catalytic site of water oxidation still need to be explored.Furthermore,there is still insufficient research on how to promote the conduction band of BiVO₄so that it can achieve photocatalytic water splitting.Therefore,the following researches are carried out in this paper:（1）First-principles study on the effect of water and oxygen vacancy on the surface water oxidation properties of BiVO₄.By using the method of DFT,the water oxidation processes of BiVO₄（001）and（101）crystal surfaces in vacuum and aqueous solution and oxygen vacancy were calculated respectively.It can be seen from the calculation results that the different environment and the oxygen vacancy will affect the water oxidation performance.The OER overpotential of BiVO₄（001）crystal surface in aqueous solution is lower than that in vacuum environment,and the OER overpotential in aqueous solution is higher than that in vacuum after adding oxygen vacancy.The OER overpotential of BiVO₄（101）crystal surface in aqueous solution is higher than that in vacuum environment with or without oxygen vacancy.The presence of oxygen vacancy reduces the OER overpotential of BiVO₄in vacuum and increases the OER overpotential in aqueous solution.（2）First-principles study of BiVO₄water oxidation active sites.In this chapter,we explore the water oxidation active sites of 11 different BiVO₄crystal slabs.The results showed that only Bi site could be exposed on the surface of BiVO₄as the water oxidation active site,while most of V sites could not be exposed.Even if there are individual V sites exposed,it is found through calculation that the overpotential of water oxidation reaction at the V sites is very large,which is not suitable to be used as the water oxidation active site.Therefore,only Bi site on the surface of BiVO₄is the water oxidation active site.（3）Density functional theory study of the quantum size and spin-orbit coupling effects of BiVO₄and their effects on photocatalytic water splitting.In this chapter,we investigated the effects of the quantum size and spin-orbit coupling effects on the band structure of BiVO₄and their effects on photocatalytic water splitting.When the thickness of BiVO₄layer is about 0.64～1.28 nm,affected by the quantum size and spin-orbit coupling effect,the conduction band edge of BiVO₄upshifts above the equilibrium redox potentials for H₂/H₂O,and the water splitting can be achieved without the overpotential of HER.However,the hydrogen evolution calculation shows that the hydrogen evolution reaction of BiVO₄（001）and（101）crystal slabs within this thickness has a large overpotential.Therefore,it is still very difficult to achieve the water splitting of BiVO₄,and may be reduction cocatalyst is also needed.