Diffusion Model and Filling Mechanism of Proton in Alkaline γ ‐ MnO2 Electrode

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Abstract
The electrochemical behavior of electrodes at different reduction degrees and different temperature was studied by a potential step technique and the variations of the peak‐current and the charge with reduction degree ( , curve) was obtained. Considering the crystal structure of , we proposed a double plane model for proton diffusion in and derived its mathematical expression. The evaluation of three models (linear semi‐infinite diffusion model, spherical model, and double plane model) has been tried using the method of “curve fitting in a small region and extended to the whole area” and the superiority of the double plane model was confirmed. Treating the original data (current‐time curve) with this model we obtained the proton diffusion coefficient and diffusion activation energy at different reduction degree ( , curve). The curves of , as well as those of , show an obvious discontinuity around and support Maskell's double solution theory. Further studies on the experimental results and the double solution theory suggest that there is a possibility of existing “the three types of proton filling ways” in cathodic reduction process of .

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