Bismuth vanadate (BiVO4) is one of the most promising semiconductor materials for the conversion of sunlight into chemical fuels by water splitting. Tremendous efforts have been devoted to improving the photocatalytic activity of BiVO4 photoanodes, such as doping with foreign elements, engineering of heterojunction structures, and deposition of cocatalysts. However, the underlying physical–chemical mechanisms behind the photoelectrochemical performance of this material (J-V response) are still poorly understood. In this study we prepared BiVO4 photoanodes by a cathodic electrodeposition procedure. Photoelectrochemical impedance spectroscopy were employed to study the photoelectrochemical properties of this material under water-splitting conditions. We first observed two surface states at the semiconductor/liquid interface of BiVO4 photoanodes where holes accumulate (Figure 1a). The first surface state (SS1) is located near the onset potential (~0.45 VRHE), while the second surface state (SS2) sits near the water oxidation potential (~1.05 VRHE). The strong correlation between the charging of this state with the charge transfer resistance and the photocurrent onset provides new evidence of the accumulation of holes in surface states at the semiconductor/electrolyte interface, which are responsible for water oxidation. According to the cyclic voltammetry (CV) results (Figure 1b), the charging of this surface state under illumination is also associated with the intrinsic reversible redox process of V4+/V5+. These findings provide deeper insights into the impact of surface properties of BiVO4 electrodes upon the photoelectrochemical performance by utilizing a simple impedance spectroscopy measurement.

Direct observation of two surface states in a BiVO4 photoanode during photoelectrochemical water splitting

ACS Spring Meeting 2021

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