Summary Hydrogen crossover has an important effect on the performance and durability of the polymer electrolyte membrane fuel cell (PEMFC). Severe hydrogen crossover can accelerate the degradation of membrane and thus increase the possibility of explosion. In this study, a two‐phase, two‐dimensional, and multiphysics field coupling model considering hydrogen crossover in the membrane for PEMFC is developed. The model describes the distributions of reactant gases, current density, water content in membrane, and liquid water saturation in cathode electrodes of PEMFC with intrinsic hydrogen permeability, which is usually neglected in most PEMFC models. The conversion processes of water between gas phase, liquid phase, and dissolved water in PEMFC are simulated. The effects of changes in hydrogen permeability on PEMFC output performance and distributions of reactant gases and water saturation are analyzed. Results showed that hydrogen permeability has a marked effect on PEMFC operating under low current density conditions, especially on the open circuit voltage (OCV) with the increase of hydrogen permeability. On the contrary, the effect of hydrogen permeability on PEMFC at high current density is negligible within the variation range of hydrogen permeability in this study. The nonlinear relations of OCV with hydrogen diffusion rate are regressed.

Subzero start-up of the polymer electrolyte membrane fuel cell (PEMFC) is one of the most challenging tasks to be solved before commercialization. During the subzero start-up process, water generated in the oxygen reduction reaction at the cathode side of PEMFC is susceptible to freeze，which makes active sites covered by the ice and gases failed to reach the surface of the catalyst layer (CL), leading to a substantial decay and even ending up with a failure of the start-up. Given that many factors affect the cold start process, the relative contribution of the essential factors on the cold start process is independently analyzed using first-order finite-difference sensitivity analysis from −20 C to −30 C. The effect of essential parameters on the cold start process is quantified. The investigated parameters include the ratio of bipolar plate (BP) thickness to that of the CL (R BP/CL), the starting voltage (V ini), stoichiometry ratios, inlet gas temperature (T in), the porosity of the CL (ε CL), initial membrane water content (λ ini), membrane thickness (θ mem), the volume fraction of ionomer (ω CL) in CLs, and the heat capacity of the BP (ρc pBP). Results show that the cold start process is most sensitive to R BP/CL and λ ini. Significant improvement of cold start performance can be achieved by appropriately adjusting R BP/CL , λ ini , T in , and ε CL. Appropriately increasing the V ini also can be a method to improve cold start performance, especially for the cold start from −30 C. Besides, optimized ω CL in CLs, proper θ mem , and lower ρc pBP can contribute to better performance, especially for the cold start from −20 C.

Summary Cold start is one of the urgent problems to be solved in the process of commercialization for the polymer electrolyte membrane fuel cell (PEMFC). In this study, cold start processes under constant power start‐up are simulated with a three‐dimensional transient model. Evolutions of voltage and current density under higher and lower current density under this mode are elucidated. The water accumulation location in the PEMFC is analyzed and effects of important parameters on the process of cold start are quantified under constant power start‐up mode. The results show that the current density first increases and then decreases when the PEMFC starts from a higher current density under constant power start‐up mode, while it is reversed when the PEMFC starts from a lower current density. Ice first appears in the area near the membrane under the channel and the hottest area in the cell also appears below the channel. At the lower current density, the distribution of water in ionomer is more uniform. Under two different starting current densities, the changing trends of the conductivity of the membrane and the anode catalyst layer are different. The activational heat is the largest heat source in the cold start process under constant power start‐up mode and the utilization of ionomer water storage is higher when the PEMFC starts from a lower current density. The temperature of the inlet gas is most sensitive to the cold start process at lower current density. And initial content of membrane water and membrane thickness have important impacts on the cold start performance when PEMFC starts from a higher current density due to the redistribution of potential.

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