Mechanism of Charge Separation in Type II Heterostructure: CuBi₂O₄–BiVO₄ System

In this study, we explore the photoelectrochemical behavior of planar heterostructured FTO/CuBi2O4/BiVO4 electrode and tandem FTO/BiVO4 || FTO/CuBi2O4 photoelectrochemical cell in order to evaluate the mechanisms of charge separation and transfer in both systems. Both heterostructured and individual electrodes were characterized by SEM, XRD, XPS, and Kelvin probe methods to confirm the successful formation of a planar heterostructure. Evaluation of the band gap, conduction and valence band energy level positions, as well as the position of the Fermi level of individual components of the heterostructure infers the formation of the type II heterostructure with an ability to realize both conventional mechanism and Z-scheme mechanism of charge separation. It was demonstrated that the photoelectrochemical behavior of both the heterostructured electrode and the tandem photoelectrochemical cell depends on photoexcitation conditions. Particularly, photoexcitation of either both components in the heterostructured electrode or both the photoanode and photocathode in the tandem cell leads to dominating realization of Z-scheme mechanism of charge separation and transfer.