Cold Start of PEMFC using Alternating Hydrogen Pump: Part I. Mechanistic Modeling

Cold start impedes the diffusion of fuel cell vehicles in regions with sub-zero temperatures. The alternating hydrogen pump (AHP) method has the advantages of fast, efficient and reliable startup without concerns for failure or degradation due to freezing of the product water. However, puzzling phenomena, including the variation of current in each half-cycle and the hook-shaped change of high frequency resistance (HFR), are observed during the AHP under constant voltage mode. These phenomena affect the efficiency and speed of cold starts, but are poorly understood. Herein, we develop a one-dimensional transient model, in which a mechanistic description of the water vapor transport enhanced by H ₂ convection is contemplated. The model is parameterized and validated using experiments under isothermal and adiabatic boundary conditions, respectively. The simulation results show that the puzzling phenomena are caused by the changes in the content and distribution of the water in the membrane, which in turn are induced by water transport in the membrane and water vapor removal from the membrane. The model has the potential to be applied in the optimization of the cold start process.