Du Hao

Effect of Alkali Concentration, Oxygen Partial Pressure and Temperature on Oxygen Reduction Reaction on Pt Electrode in NaOH Solution

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 Henrys 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.

Structure and Diffusivity of Oxygen in Concentrated Alkali-Metal Hydroxide Solutions: A Molecular Dynamics Simulation Study

Molecular dynamics simulations of oxygen molecules in NaOH and KOH solutions at different temperatures (25-120 degrees C) and concentrations (1:100-1:5, molar ratios) were performed in this study. The interactions of oxygen molecules with the surrounding solvent and solute were clarified by considering the solvent-solvent, oxygen-solvent, and oxygen-solute radial distribution functions. The self-diffusion coefficients of the oxygen molecules and the solute were both determined by analyzing the mean-squared displacement (MSD) curves, using Einsteins relationship. It was concluded that at all concentrations, the diffusion coefficient of oxygen in NaOH solution is smaller than that in the corresponding KOH solution. The diffusion coefficients for hydroxide, Na+, and K+ decrease with increasing solute concentration, following similar trends to those of oxygen. The oxygen diffusion coefficient obtained in this study is in good agreement with the reported experimental value, suggesting that MSD is an attractive approach to study the oxygen diffusion behavior in strong alkaline solutions at elevated temperatures, which are experimentally extremely challenging.