image5_An Ordinary Differential Equation Model for Simulating Local-pH Change at Electrochemical Interfaces.tif

The local pH value at an electrochemical interface (pH^s) inevitably changes during redox reactions involving the transfer of H⁺ or OH⁻ ions. It is important to quantitatively estimate pH^s during polarization, as this parameter has a significant impact on the activity and selectivity of electrochemical reactions. Numerical simulation is an effective means of estimating pH^s because it is not subject to experimental constraints. As demonstrated in a number of studies, pH^s can be estimated by solving partial differential equations that describe diffusion process. In the present work, we propose a method to consider the process by using ordinary differential equations (ODEs), which can significantly reduce the computational resources required for estimating pH^s values. In the ODE-based model, the description of the diffusion process was achieved by considering the reaction plane in the diffusion layer over which the H⁺ and OH⁻ concentrations are balanced while assuming that the concentration profiles in the layer are in a steady state. The resulting model successfully reproduces experimental voltammograms characterized by local pH changes in association with the hydrogen evolution and hydrogen peroxide reduction reactions.