Electrochemical Characterization of Proton Diffusion during Discharge and Cycling of γ-MnO2

Abstract

In this work step potential electrochemical spectroscopy (SPECS) and electrochemical impedance spectroscopy (EIS) are used to examine the γ-MnO2 electrode and provide two distinct measurements of proton diffusivity during the discharge and cycling of γ-MnO2. This is carried out by modeling the electrochemical data assuming solid-state spherical diffusion (in the case of SPECS) and by using an equivalent circuit approach (in the case of EIS). In both cases an outline of the model employed and the details of the fitting process are included. The resulting A√D values are then considered and any changes noted during discharge or cycling, along with the variation observed between the two techniques, are explained in terms of the structural and morphological changes which the material undergoes. A key finding from these studies is that SPECS characterizes bulk diffusional processes, while EIS focuses on near-surface (<1 nm deep) processes.