Determination of the in-plane components of the electrical conductivity tensor in PEM fuel cell gas diffusion layers

The in-plane components of the electrical conductivity tensor for gas diffusion layers (GDLs) used in polymer electrolyte membrane fuel cells were measured using an alternative method that has not previously been applied to GDLs. This method uses a square electrode configuration, which offers many practical and theoretical advantages over conventionally used linear four point probe methods. Results obtained using this method were in excellent agreement with reported values where applicable. Pronounced anisotropy was found in the in-plane electrical conductivity for all samples, in agreement with other findings. Conductivity measurements were also performed on samples rotated relative to a fixed axis to determine the full extent of anisotropy, assumed to be due to fiber alignment, allowing the intrinsic components of the conductivity tensor to be found. The maximum and minimum conductivities were found at a rotation angle different from the main directions of the GDL sheet from which the tested samples were cut. The average in-plane conductivity of GDL samples was independent of rotation angle. Because the direction of maximum conductivity was found to differ from the main sheet axis, the measured conductivity tensor was rotated to yield the corrected 2-dimensional tensor relative to the main GDL axis. The method for performing this correction is discussed and an experimental method for measuring the necessary data from only a single sample is proposed.