Guiding charge transfer kinetics into cocatalyst for efficient solar water splitting

Abstract

The combination of transition metal-based cocatalysts with semiconductors is a promising route to improve the photoelectrochemical performance in solar water splitting. However, it is difficult to evaluate the catalytic ability for cocatalysts quantitatively. Herein, we use kelvin probe force microscopy technique, combining with Mott-Schottky method, to investigate the cocatalysts from the point of surface potential and Femi level. Through synthesis the nickel/cobalt oxide nanoparticles and nanoporous bismuth vanadate (BiVO4), the result indicates the surface potential of NiCoO2 coated BiVO4 is lower than pristine BiVO4 and BiVO4 coated by NiO and CoO cocatalysts respectively. The lower surface potential means a more upward band bending structure at the interface of electrode and electrolyte, which can promote the separation of electron-hole pairs and enhance the charge transfer kinetics. Thus, the NiCoO2/BiVO4 photoanode achieve a remarkable photocurrent density of 2.34 mA/cm2 for water oxidation, and the charge separation and oxidation kinetics efficiencies are 61.9% and 72.7% respectively. In all, our studies provide a new mechanistic insight into cocatalysts for solar energy conversion.