Relating the N-shaped polarization curve of a PEM fuel cell to local oxygen starvation and hydrogen evolution

In this work, we use the polarization curve of a polymer electrolyte membrane (PEM) fuel cell to investigate the inter-connected transport processes in its electrodes. The investigation is based on a segmented (7 by 7) PEM fuel cell. A local N-shaped negative differential resistance (N-NDR) branch was measured in the steady state polarization curve of the cell near its oxygen outlet. This phenomenon was also observed in a much more pronounced manner for highly-transient polarization curves on all segments. In this study, we show that even despite the cell running under normal conditions, in the case of oxygen starvation, a hydrogen evolution takes place in the cathode catalyst layer. This theory is illustrated through experimental measurements.