New Insights into Se/BiVO4 Heterostructure for Photoelectrochemical Water Splitting: A Combined Experimental and DFT Study

Monoclinic clinobisvanite BiVO4 is one of the most promising materials in the field of solar water splitting due to its band gap and suitable valence band maximum (VBM) position. We have carried out comprehensive experimental and periodic density functional theory (DFT) simulations of BiVO4 heterojunction with selenium (Se-BiVO4), to understand the nature of the heterojunction. We have also investigated the contribution of Se to higher performance by effecting morphology, light absorption, and charge transfer properties in heterojunction. Electronic properties simulations of BiVO4 show that its VBM and conduction band minimum (CBM) are comprised of 0 2p and V 3d orbitals, respectively. The Se/BiVO4 heterojunction has boosted the photocurrent density by 3-fold from 0.7 to 2.2 mA cm(-2) at 1.3 V vs SCE. The electrochemical impedance and Mott-Schottky analysis result in favorable charge transfer characteristics, which account for the higher performance in Se/BiVO4 as compared to the BiVO4 and Se. Finally, spectroscopic, photoelectrochemical, and DFT show that Se makes a direct Z-scheme (band alignments) with BiVO4 where the photoexcited electron of BiVO4 recombines with the VB of Se, ginving electron-hole separation at Se and BiVO4, respectively; as a result, enhanced photocurrent is obtained.