The Dynamics of Platinum Precipitation in an Ion Exchange Membrane

Microscopy of polymer electrolyte membranes (PEMs) that have undergone operation under fuel cell conditions, have revealed a well defined band of platinum in the membrane. Here, we propose a physics based model that captures the mechanism of platinum precipitation in the polymer electrolyte membrane. While platinum is observed throughout the membrane, preferential growth of the platinum at the band of platinum is dependent on the electrochemical potential distribution in the membrane. In this paper, the location of the platinum band is calculated as a function of gas concentration at the cathode and anode, gas diffusion coefficients, and solubility constants of the gases in the membrane, which are functions of relative humidity. Potential cycling the PEM fuel cell under conditions that resulted in the platinum band is near the cathode-membrane interface. As the oxygen concentration in the cathode gas stream increases and/or the hydrogen concentration in the anode gas stream decreases, the band moves toward the anode. The model developed in this paper agrees with the set of experimental data on the platinum band location and the platinum particle distribution and size.