First-principles study on ZnV2O6 and Zn2V2O7: Two new photoanode candidates for photoelectrochemical water oxidation

We used first principles calculations based on density functional theory with generalized gradient approximation to investigate and compare the structural, electronic and optical properties of two photoanode materials, ZnV2O6 and Zn2V2O7, for use in photocatalytic water splitting. After geometry optimization, the calculated structural parameters evince a satisfactory agreement with the reported experimental results indicating that the used method and conditions are suitable. The electronic structures demonstrate that both photocatalysts possess favorable band gaps (2.31 and 2.52 eV) and appropriate band edge positions for oxygen evolution reaction under solar radiation. The relatively light effective masses at the valence band maximum and conduction band minimum are expected to result in enhanced photocatalytic activity due to lower recombination probability of the photogenerated electrons and holes. The analysis of electronic density of states reveal that the higher coordination number of vanadium in ZnV2O6 with respect to Zn2V2O7 causes more delocalisation of bands owning to lower V-V and O-O distances in conduction and valence bands, respectively. Moreover, the origins of features that appear in solar energy harvesting characteristics (dielectric function and optical absorption coefficient) have been discussed for solar water splitting in detail.