Enhancement in Photoelectrochemical Efficiency and Modulation of Surface States in BiVO4 through the TiO2 Outer Layer Using the Atomic Layer Deposition Technique

Abstract

Owing to several important properties, BiVO4 is the promising photoanode material for the photoelectrochemical (PEC) water oxidation reaction; however, the poor charge transfer and transport and slow surface catalytic activity limit to achieve the expected high theoretical efficiency. In the present investigation, thin films of TiO2 have been formed over the BiVO4 photoanode surface using the atomic layer deposition technique (ALD). Films are formed at 5, 50, and 150 nm thicknesses, and the PEC performances have been evaluated. Enhancement in the performance has been observed upon inclusion of the ALD/TiO2 films over BiVO4. The performance has been observed to be higher in the case of 50 nm ALD/TiO2 films. The ALD/TiO2 films have several important roles in the enhancement in the PEC efficiency other than only the enhancement of stability through retardation of the photocorrosion process. The intensity modulated photocurrent spectroscopy measurements have been carried out for the selective evaluation of the different modes of charge transfer processes upon excitation of the photoanode materials on photoexcitation. The enhancement in the charge transfer rate constant (kt) over the relative retardation of the charge recombination rate constant (kr) indicated the specific roles of modulation of the surface states. The investigation revealed the significant scopes of the modifications of surfaces using ALD techniques to selectively modulate the surface electronic states of materials in enhancing catalytic efficiency.