Effects of operating parameters on the transient response of proton exchange membrane fuel cells subject to load changes

Water management is critical to the steady state and transient performance of proton exchange membrane (PEM) fuel cell systems. The dynamic behavior of PEM fuel cells is profoundly related to the dynamics of water transport in the fuel cell system, which include electro-osmotic drag and back-diffusion of water through membrane and rate at which water is generated, supplied and removed from the electrodes. In particular, for low humidity operations, water transport dynamics plays a dominant role in determining the time taken to reach steady state. Toward an understanding of the fuel cell dynamics for dry operations, numerical simulations are carried out for a single channel polymer electrolyte (PEM) fuel cell undergoing step change in cell voltage over wide range of operating conditions. A detailed model-based parametric study is carried out to analyze the effects of operating conditions on membrane water content and the time taken by the single cell system to reach steady state. Based on the studies, design windows are presented that limit the time taken to reach steady state to a desired value. Optimum parameter combinations that minimize the transient time are also identified from the studies.