Abstract
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 specially 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 O-2(-) 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, substantially 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.
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