Study On The Effect Of Purge And Microporous Layer Material On Cold Start Performance Of PEMFC

The difficulty of starting proton exchange membrane fuel cell(PEMFC)in cold environments is one of the main obstacles to their commercialization.The main reason for the difficulty of cold start of PEMFC is that water will be generated inside the fuel cell when it works.When the temperature of the fuel cell is below 0℃,the water inside the fuel cell will freeze,hindering the transmission of reaction gases,resulting in the failure of PEMFC start-up and even damage to the membrane electrode of the fuel cell.Given that in low temperature environment,the water in the fuel cell will affect its performance,in this paper,by purge the PEMFC after shut down,the initial water content of the PEMFC during cold start is reduced,and the probability of freezing is reduced,thereby improving the cold start performance of fuel cells.Besides,because the microporous layer(MPL)plays an important role in the transport of water and gas in fuel cells,but the MPL made of polytetrafluoroethylene(PTFE)is expensive and the preparation process is complicated.Therefore,polyphenylene sulfide(PPS)was used in this paper to make MPL,and the effects of PPS content and particle size on the properties of MPL were tested.The main content and results of this paper are as follows:1.Purge conditions affect the cold start performance of fuel cells.In this paper,the effect of purge conditions on cold start performance was investigated by changing the purge time and purge flow rate of dry nitrogen.The experimental results found that the purging before cold start(or after shutdown)is not the longer the purge time or the larger the gas flow rate,the better the cold start performance.2.The assembling bolts torque affect cold start performance of PEMFC.In this paper,the cold start experiments of PEMFCs with assembling bolts torque of 1 N·m and 4 N·m were carried out.The experimental results show that the purge effect and subsequent cold start performance are different due to the influence of porosity and water redistribution.The fuel cell with assembling bolts torque of 1 N·m shows better performance.3.There is high frequency resistance relaxation after purge.In this paper,the high frequency resistance changes with different purge gas flow rate and different purge temperature are investigated.The experimental results show that the stable value of the high frequency resistance decreases with the increase of the gas flow rate,and the time required to reach the stable value also increases with the increase of the gas flow rate,and the temperature also has an effect on the relaxation phenomenon.4.The material of MPL affects the cold start performance of PEMFC.In this paper,the properties of MPL with PTFE and PPS as hydrophobic agents are compared,and the operation performance of fuel cells equipped with two kinds of MPL at 70℃ and-10℃ were tested respectively.The fuel cell equipped with MPL made of PPS were found to operate slightly worse than those made of PTFE at normal temperatures,but exhibited good performance at-10℃.5.The content and particle size of PPS affect the performance of MPL.By comparing the MPL with the PPS mass fraction of 10%,20% and 30%,it was found that the MPL with the PPS mass fraction of 20% showed the best performance;By comparing the MPL with the PPS particle size of 10 μm and 30 μm,it is found that when the PPS particle size is 10 μm,that is,the PPS particle size is smaller,the MPL shows better performance.