Study on the redistribution mechanism and secondary purge strategy of proton exchange membrane fuel cells

Abstract

Effective control of membrane water content is essential for increasing the space for ice formation during the cold start stage and enhancing the success rate of start-up. Shutdown purge can effectively lower the membrane water content following fuel cell operation. However, during the cooling and standing process after purge, the rapid change in saturated vapor pressure can result in the redistribution of membrane dissolved water, leading to an increase in its content and a reduction in the success rate of cold start. Therefore, this study establishes a multidimensional, multiphase simulation model to comprehensively and thoroughly analyze the redistribution mechanism after purging and investigates the relationship between membrane water content and cold start. This is achieved by identifying the maximum membrane water content boundary during the cold start process and ultimately improving the success rate of cold start through a secondary purge strategy. The research results indicate that the membrane water content of the fuel cell increases from 2.31 to 8.31 after redistribution. During the cold start stage, the cold start success of the fuel cell under different environmental temperatures exhibits relatively specific boundary conditions, with the cold start process being closely related to the load current density and initial membrane water content. After implementing the secondary purging strategy, the membrane water content of the fuel cell decreases again, displaying favorable cold start characteristics in the cold start stage and successfully starting at −10 °C. This study can provide a reliable basis for the development of purging strategies during shutdown and offer a theoretical foundation for the boundary identification process of cold start.