Separation Method for Oxygen Mass Transport Coefficient in Gas and Ionomer Phases in PEMFC GDE

A novel method to determine the oxygen mass transport coefficient and its separation into gas and ionomer contributions was developed and validated. The method is based on the use of a limiting current density distribution mathematical model and different diluent gases with varying molecular weights. A linear relationship between the inverse overall mass transport coefficient and the diluent molecular weight was revealed. Because the use of different gas diluents with different molecular weights only affects the mass transport coefficient in the gas phase, an extrapolation to a zero diluent weight gives the O2 mass transport coefficient in the ionomer phase. The gas phase mass transport coefficient is then calculated using the additive relation between the overall mass transport coefficient and its components. The O2 mass transport coefficient in the electrolyte phase was found to be equal to 0.01284 m s−1, while in an N2 diluent, the coefficient is 0.02727 m s−1. Effects of selected operating conditions (temperature, O2 concentration) and membrane/electrode assembly materials (cathode Pt loading and gas diffusion layer) on the O2 mass transport coefficient were studied and discussed.