三价铬还原电沉积机理

Electrochemical Mechanism of Trivalent Chromium Electrodeposition

采用循环伏安法、极化曲线、恒电流阶跃、交流阻抗等电化学方法研究了Cr 在氯化物/N,N 二甲基甲酰胺(DMF)体系中的阴极还原机理。研究结果表明:Cr3+阴极还原分两步进行,其中第1步为不可逆过程,第2 步为准可逆过程;反应无前置转化过程;Cr3+ 还原的极化曲线符合Tafel方程;Cr3+ 还原受电化学控制;Cr3+ 在还原过程中,电活性中间产物在电极表面吸附,随溶液浓度增大,Cr3+ 的扩散系数减小,但电活性中间产物在电极表面的饱和吸附量却随之增大。

The reduction mechanism of Cr3+ in chloride/N, N-dimethylformamide (DMF) solution was studied using several kinds of electrochemical methods, such as cyclic voltammetry, steady polarization curve, chronopotentiometry, and alternating current impedance. The results show that Cr3+ gets three electrons in two steps, the first step is nonreversible, while the second step is quasi-reversible, and the trivalent Cr3+ does not undergo chemical transformation reaction before its reduction in the cathode. The steady polarization curve of Cr3+ reduction is fit to Tafel equation, and the calculated values of active energy indicate the reduction process is determined by electrochemical step. The middle product, which is electrochemically active and adsorptive, is formed in the first step. The values of diffusion coefficient of Cr3+ and saturated adsorption of middle product calculated from chronocoulometry method reveal that the greater the concentration of Cr3+, the smaller diffusion coefficient, and the more saturated adsorption of the middle product.