Active layer of the cathode of a fuel cell with a solid polymer electrolyte: The effect of the Nafion concentration on the overall characteristics

A computer-aided simulation of the structure of the active layer of the cathode of a fuel cell with a solid polymer electrolyte (Nafion) is performed under the assumption about equidimensionalness of dimensions of grains of the substrate (with platinum crystallites in them) and grains (agglomerates of molecules) of Nafion. It is analyzed how the Nafion concentration affects principal parameters, which include the specific surface area, in the vicinity of which electrochemical process goes on; the effective ionic electroconductivity, and the effective diffusion coefficient of a gas. It is demonstrated how one can determine the Nafion concentration at which the overall current takes on a maximum value. Dependences of the optimum value of the overall current and the thickness of the active layer and the weight of platinum, which correspond to it, on the Nafion concentration are calculated. It is demonstrated that there in principle cannot exist one individual optimum concentration of Nafion, which is suitable for all techniques used for the preparation of the active layer. The mutual relationship between values of the effective diffusion coefficient of a gas and the effective ionic electroconductivity of Nafion determines the value of the optimum of the Nafion concentration.