Multistability, nonlinear response and wave propagation in self-humidified PEM fuel cells

A simple tanks-in-series model is presented, which allows for the understanding of the basic physics behind complex spatiotemporal behaviors observed in self-humidified polymer electrolyte membrane (PEM) fuel cells. Our approach is focused on how the intrinsically nonlinear dynamics of water formation couples with water transport, leading to multistability, inhomogeneous steady state current profiles through the cell and other nonlinear phenomena. We show in particular how the operating parameters determine the location of high current spots and the subsequent propagation of current waves throughout the cell during the ignition procedure. We also reproduce and explain transient current increases seen during the extinction of the cell and the unusual aspect of the polarization curves. Implications for the efficiency of self-humidified PEM fuel cells are highlighted, and possible ways to improve their performances are discussed on these bases.