电化学还原预处理对BiVO_4薄膜电极光电化学氧化水性能的提高

在酸性水溶液中(pH=2.0),采用电化学还原(ER)方法对BiVO4薄膜电极进行预处理,并探讨了其对薄膜电极光电化学氧化水性能的影响.结果表明,这种预处理可显著提高电极的光电化学氧化水的性能,且具有良好的光电化学稳定性.利用扫描电子显微镜、X射线衍射、拉曼光谱、光电子能谱、紫外-可见漫反射光谱、荧光光谱、电化学阻抗谱及Mott-Schottky等方法对ER处理前后的电极进行了表征.结果表明,ER预处理使电极粗糙度增大,表面积增大约1.4倍;电极材料的晶型无明显变化,但V—O对称伸缩振动略有红移;表面Bi,V和O结合能变小,Bi3+部分被还原,Bi/V原子比增大;ER处理导致电极平带电位负移,光生载流子在薄膜电极/溶液界面转移速率加快,表面复合速率降低.这些变化和表面积增加是BiVO4电极光电化学性能提高的主要原因.

Enhanced the Performance of Photoelectrochemical Oxidation of Water over BiVO4 Film Electrodes by Electrochemical Reduction Pretreatment

BiVO4 thin film electrodes were pretreated by electrochemical reduction(ER) in acid aqueous solutions(pH=2), and its impact on the performance of photoelectrochemical oxidation of water was tested. The results show that this treatment enhances the photoelectrochemical oxidation of water over the BiVO4 thin film electrodes and the treated electrodes have a good photoelectrochemical stability. The untreated and ER treated electrode films were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, UV-Vis diffuse reflectance spectroscopy, photoluminescence, electrochemical impedance spectroscopy, Mott-Schottky measurements, etc. From a physical chemistry perspective, the ER pretreatment resulted an increase of the roughness of the electrode with increasing in surface area by a factor of 1.4; no detectable change in crystalline but a slightly red-shift in the V—O symmetric stretching; a decrease in binding energy for the surface Bi, V and O; partly reduction of Bi3+ with an increase in the atom ratio of Bi/V on the surface. From the view of photoelectrochemistry, due to ER treatment, the flatband potential for the electrode was negatively shifted, the charge-transfer rate of photocarriers at the electrode/solution interface was accelerated while the surface recombination rate was decreased. These changes and the increased surface area are the main reasons for the enhanced photoelectrochemical performance.