Understanding the electrochemical impedance of a proton exchange membrane fuel cell

Electrochemical Impedance Spectroscopy (EIS) may provide a tool to understand electrode structure and membrane resistance of a PEMFC Membrane Electrode Assembly (MEA). This dissertation presents studies of the reproducibility of EIS measurements, the impedance caused by the distribution of ionomer in the electrodes, and the impedance caused by hydrogen crossover through a PEMFC membrane.; To characterize the reproducibility of impedance measurements, the impedance of N2/N2 Proton Exchange Membrane (PEM) systems was measured for Gore(TM) PRIMEA(c) 5510 MEAs at 70°C and the effects on the data from system inductance, RH, and reaction area were analyzed. The impedance of the MEAs was tested at 11%, 19%, 38% and 48% RH with reaction areas of 9, 16, and 23 cm2. The variation in the impedance was approximately 10% for all humidities. Reproducibility studies indicated that EIS measurements could be made on standard 25 cm 2 laboratory PEMFCs without significant measurement errors.; A baseline ionomer distribution in the electrodes of a new Gore(TM) 5510 MEA was investigated using Electron Probe MicroAnalysis (EPMA). The effects of ionomer distribution on the EIS spectra were investigated using 1-D porous electrode simulations with variable ionomer conductivity through the electrode. The effect of relative humidity on the impedance with similar ionomer profiles are shown for 11%, 19%, 38% and 48% RH. The developed porous electrode model that used the experimentally measured ionomer profile in the electrodes predicts the N2/N2 EIS data for varying RH conditions.; The effect of hydrogen crossover in a Gore(TM) 5510 MEA was investigated for varying RH conditions using polarization and EIS experiments. A model of the crossover as a function of RH was developed. The model fit well at high cathode H2 concentrations, but had 16% error at 19 vol% H 2 and 19% RH. It was shown that the assumption of a small cathodic current density accounts for the differences between the experimental and model impedance. The developed EIS model allows analysis of the hydrogen diffusion coefficient in the membrane using in-situ H2/N2 EIS data and predicts the hydrogen crossover directly from the impedance data.