Abstract:

The effect of ZnO concentration on the electrochemical behaviors of ChCl-urea-ZnO deep eutectic solvents (DES) system were examined with electric conductivity tests and cyclic voltammetry. The results of electric conductivity tests indicate that the conductivity of ChCl-urea-ZnO DES increases with an increase in ZnO concentration as ZnO concentration is below 0.24 mol·L^-1. When ZnO concentration exceeds 0.24 mol·L^-1, the conductivity of ChCl-urea-ZnO DES tends to be roughly constant. The conductivity of ChCl-urea-ZnO DES increases with the increasing of temperature. The relation between conductivity and temperature is consistent with Kohlraush empirical formula. The results of voltammetry tests indicate that the reduction of Zn(Ⅱ) is a quasi-reversible process, which is controlled by diffusion step. The diffusion coefficient of zinc ion is about 1.2×10^-7 cm²·s^-1. Furthermore, with an increase in ZnO concentration, deposition potential of Zn shifts positively and reduction peak current increases gradually, indicating that the higher concentration of ZnO is helpful to the electrodeposition of zinc. In addition, the electrodeposition of Zn-ChCl-urea DES containing different concentration of ZnO was performed at 2.2 V and 343 K. The surface morphology and phase structure of Zn deposits were characterized by X-ray diffraction (XRD) and scanning electron microscopic (SEM), respectively. ZnO concentration is found to play central role on the morphology of deposited Zn. Different shapes of Zn deposits including rod-like and square, can be electrodeposited from ChCl-urea DES by controlling the ZnO concentration.

Key words: deep eutectic solvents, zinc oxide, electrochemistry, reduction, znic

摘要：

研究了ChCl-urea-ZnO低共熔溶剂（DES）体系的电化学行为与ZnO浓度的相互关系。电导率测定结果表明，ChCl-urea-ZnO体系的电导率随ZnO浓度的增加而增大，但当ZnO浓度超过0.24 mol·L^-1，体系电导率趋于稳定。随着温度的升高，ChCl-urea-ZnO的电导率增大，电导率与温度的关系符合Kohlraush经验公式。循环伏安测试结果表明，在ChCl-urea-ZnO低共熔体系中，Zn（Ⅱ）还原为金属锌是受扩散控制的准可逆过程，Zn（Ⅱ）的扩散系数约为1.2×10^-7 cm²·s^-1。而且金属锌的析出电位随ZnO浓度的增加而正移，峰值电流明显增大，说明增大ZnO浓度有利于锌的沉积。此外，ZnO浓度对锌沉积层的形貌有明显影响，不同ZnO浓度下得到锌沉积物的形貌各不相同，有短棒状、方形等。

关键词: 低共熔溶剂, 氧化锌, 电化学, 还原, 锌