Through-Plane Proton Transport Resistance of Membrane and Ohmic Resistance Distribution in Fuel Cells

Ohmic losses in fuel cells contain both ionic (mainly protonic) and electronic contributions. In this work, we developed a method to distinguish the resistance contributions from individual components. Proton transport resistance of proton exchange membranes (PEMs) in the through-plane direction, the major proton transport direction in in situ fuel cells, was measured using electrochemical impedance spectroscopy combined with compression-controlled fuel cell hardware. Membrane resistance was obtained by subtracting the nonmembrane contributions from the total resistance. Proton conductivities of PEMs with different equivalent weights, calculated from through-plane resistance measurements at various relative humidity conditions, were compared with good agreement to the in-plane measurements. Fuel cell electronic resistance and membrane-electrode interfacial resistance were also evaluated using both ex situ and in situ methods. The membrane-electrode interface resistance was nearly constant over a range of relative humidity conditions. The effects of test procedure and cell build strategy were investigated and had a significant impact on the membrane resistance measurements.