Intriguing photo-electrochemical characteristics of BiVO₄ photoelectrodes studied in pH-neutral aqueous solutions are reported herein. Indeed, we have observed photocurrent polarity switching, as put in evidence by cyclic voltammetry under chopped illumination conditions. Such unusual behavior was analyzed in detail using Intensity Modulated Photocurrent Spectroscopy (IMPS). At potentials where positive photocurrent was observed, the expected shape of IMPS was recorded, starting in quadrant (IV) at high-frequency (HF) and reaching quadrant (I) at low-frequency (LF) with two well defined semicircles. Surprisingly, in the negative photocurrent region, IMPS started in quadrant (II) at HF and ended in quadrant (III) at LF. Such highly infrequent features were interpreted here as the rotation of the IMPS spectra around the origin of the plot, due to the sign switch of the photocurrent. A model that takes into account the existence of in-band energy states at the surface of BiVO₄ has been used in order to account for the experimental results. It was found that (i) the surface state capacitance; (ii) the relaxation time constant associated to surface states; and (iii) the density of in-gap surface states, were all showing a well-marked maximum in the nearby value of the switch potential. This suggests that surface states are more influent in the nearby where photocurrent switch occurs.

有趣的BiVO _4的光电化学特性本文报道了在pH中性水溶液中研究的光电极。确实，我们已经观察到光电流极性的切换，这在斩波照明条件下通过循环伏安法得到了证明。使用强度调制光电流谱（IMPS）对这种异常行为进行了详细分析。在观察到正光电流的电势下，记录了IMPS的预期形状，从高频（HF）的象限（IV）开始，到低频（LF）的象限（I），有两个定义明确的半圆。令人惊讶的是，在负光电流区域，IMPS在HF的象限（II）开始，在LF的象限（III）结束。由于光电流的符号开关，这种极少出现的特征在这里被解释为IMPS光谱围绕图原点的旋转。为了说明实验结果已经使用了图₄。发现：（i）表面状态电容；（ii）与表面状态有关的弛豫时间常数；（iii）间隙内表面态的密度在开关电位附近均显示出明显的最大值。这表明在发生光电流转换的附近，表面状态的影响更大。