Modeling And Performance Analysis Of Proton Exchange Membrane Fuel Cell Under Subzero Cold Start Condition

The development of zero discharge proton exchange membrane fuel cell(PEMFC)is the highland of technology competition in the field of automobile industry.It is also the core measure to implement the national "double carbon" strategy.However,under complex environmental conditions and operating conditions,PEMFC still generally faces multiple challenges such as stability,reliability and durability,which are essential factors limiting its rapid development.Among them,the cold start problem in cold regions is a common challenge for PEMFCs with different power levels.Therefore,it is of great significance to study the multi-variable interaction law and dynamic change process of PEMFC ice-water-gas-heat under subzero environment,and to reveal the key parameters affecting the PEMFC cold start,so as to improve its cold start performance.The work of this paper mainly includes the following aspects.Firstly,the mass transfer,transmission and phase transition of PEMFC working process are analyzed,such as electrochemical reaction of membrane electrode,water absorption and desorption of proton exchange membrane,freezing and melting of water in electrode pores,and evaporation and condensation of water.Furthermore,by designing and solving the control equations,the heat and mass transfer law and electrical output performance of fuel cell are calculated and determined.Finally,based on the COMSOL analysis platform,a three-dimensional multi-parameter and multi-physics coupling transient simulation model suitable for PEMFC cold start performance analysis was designed and verified by experiment,which laid a foundation for subsequent research work.In order to clarify the influence of important operating parameters and structural parameters such as ambient temperature,cathode inlet relative humidity,initial membrane water content and proton exchange membrane thickness on the cold start performance of PEMFC,the effects of the above parameters on the output performance,temperature change and internal icing distribution of PEMFC under different cold start conditions were analyzed.The variation of ice distribution in the cathode catalyst layer during the cold start-up of PEMFC was revealed,and the dynamic process of ice crystal encroachment and the critical value of ice volume fraction were determined.It is clear that the ambient temperature and initial membrane water content have a significant effect on the output performance of PEMFC at the initial stage of cold start.Higher ambient temperature and lower initial membrane water content help to stabilize the output performance of the cold start process,delay icing,and prolong the survival time of the cold start condition.The PEMFC achieved 96 s self-starting at-7℃.The relative humidity of the cathode inlet air is determined to be a non-sensitive parameter.The inlet air humidification has limited improvement in the performance of fuel cell power generation and heat generation,but it will increase the risk of icing accumulation.Under different humidification schemes,the difference in the maximum temperature rise of PEMFC during the start-up process is only0.24℃.The influence of membrane thickness was revealed.Although the increase of membrane thickness can improve the water storage capacity and prolong the cold start duration,excessive thickness of membrane is not conducive to the heat capacity and temperature rise efficiency.In contrast,the maximum temperature rise of 0.127 mm membrane scheme is 15.6% higher than that of 0.183 mm membrane scheme,the former is more suitable for PEMFC cold start.Finally,in order to systematically study the influence of multi-parameters such as ambient temperature,initial membrane water content and proton exchange membrane thickness on the cold start performance of PEMFC and further clarify the main effect and interaction effect characteristics of factors,a multi-factor and multi-level orthogonal test was designed and carried out.Comprehensive analyses show that,ambient temperature and membrane thickness are important factors that determine the consequence of PEMFC cold start,and the interaction effect of the two is quite significant.Initial membrane water content is not decisive to the consequence of cold start,but its level will greatly affect the survival time by interaction effect.Increase of membrane thickness and ambient temperature will significantly increase the cold start survival time.When membrane thickness is at medium and high level,the interaction effect between membrane thickness,ambient temperature and initial membrane water content is significant,while the interaction effect between factors are gradually weakened when thinner membrane is used.Temperature rise of PEMFC during startup is influenced by both ambient temperature and membrane thickness and the interaction effect between them is notable,while the interaction effect of membrane thickness and initial membrane water content on the PEMFC temperature rise is not significant.