NaOH溶液中碱浓度、氧气压力以及温度对Pt电极上氧气还原反应的影响

摘要

In this study, the influences of alkali concentration, oxygen partial pressure, and temperature on the oxygen reduction reaction (ORR) were examined in detail, using a special y designed electrochemical cell, by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) in NaOH solutions. It was found that the ORR pathway is dependent on the solution alkalinity, and is transformed from a two-electron reduction by forming HO2-in dilute solutions to a one-electron reduction by forming stable O2-in concentrated solutions. The process was significantly suppressed by decreases in the oxygen solubility and increases in the media viscosity. The oxygen pressure had a significant influence on the ORR, substantial y promoting the ORR in alkaline solutions as a result of the greatly increased solubility of oxygen in the solutions. We obtained the Henry′s constants of oxygen in NaOH solutions with different concentrations. The temperature had a clear dual effect on the ORR, as shown by the existence of an optimal temperature for the ORR in a given alkaline solution. These observations are discussed in terms of the oxygen reaction activity, oxygen solubility, and diffusion coefficient.%设计制作一种新型耐压电化学池并采用循环伏安(CV)和线性扫描伏安(LSV)技术系统研究了碱浓度、氧气压力以及温度对NaOH溶液中氧气还原反应(ORR)的影响。研究结果表明，碱浓度、氧气压力和温度对ORR动力学和热力学都有很大的影响。随着碱浓度增大， ORR过程逐渐由2电子(生成HO2-)转为1电子(生成O2-)反应，并且由于氧气溶解度减小和体系粘度增大ORR过程受到很大抑制。增大压力可以明显增加氧气溶解度，从而从动力学上促进ORR过程；同时计算得到了氧气在不同浓度NaOH溶液中的亨利系数。随着介质温度升高，由于氧气反应活性增强、扩散系数增大和溶解度减小的共同作用，表现出在给定浓度下存在一最佳温度使得ORR峰电流达到最大。