Durability Study Of Membrane Electrode Assembly For Proton Exchange Membrane Fuel Cell

The main hurdle of large-scale commercialization of proton exchange membrane fuel cell(PEMFC)are short durability and high cost.As the key component of PEMFC,membrane electrode assembly(MEA)play a decisive role in the performance and durability of PEMFC.Therefore,studying the degradation mechanisms of MEA can provide a significate affect during developing long durability PEMFC.Accelerated stress tests are the common methods to investigate the durability of MEA.It can not only indicate the real degradation mechanisms of MEA in actual application,but also save test time and reduce test cost.There are some methods that load cycling operation,potential cycling operation,open circuit voltage(OCV)operation,relative humidity cycling operation to study the durability of MEA.In this paper,durability of MEA were investigated under OCV operation and relative humidity cycling operation.First,the influence of proton exchange membrane on the durability of MEA has investigated under OCV operation.The proton exchange membrane of Nafion 212 and PTFE/PFSA membrane are choosed.The performance of PEMFC during the OCV operation were characterized with the help of in situ electrochemical measurements,such as polarization curves,electrochemical impedance spectroscopy(EIS)and linear sweep voltage scans(LSV).Postmortem analyses such as scanning electron microscopy,and ion chromatography were applied to identify the MEA degradation mechanisms during the OCV operation.The open circuit voltage of Nafion 212 MEA declined from 1.013V to 0.794V after 115 h of OCV operation.However,the open circuit voltage of PTFE/PFSA MEA is 0.88 V after 500 h of OCV operation.The results indicated that Nafion 212 MEA degradation more severe.Next,the mechanical degradation of the membrane has studied under relative humidity cycling operation.The performance of MEA during the relative humidity cycling operation were characterized with the help of in situ electrochemical measurements,such as EIS and LSV.Postmortem analysis such as scanning electron microscopy was applied to identify the MEA degradation mechanisms during the relative humidity cycling operation.The on-line electrochemical measurements results show that the ohmic resistance and hydrogen crossover increase during the whole relative humidity cycling operation,while the short resistance decrease along with the relative humidity cycling operation.Scanning electron microscope result shows that proton exchange membrane becomes thinner after relative humidity cycling operation.In the end,the influence of backpressure on the durability of MEA has investigated under OCV operation.Backpressure can improve the open circuit voltage by increase the theoretical potential,in addition,backpressure can reduce the open circuit voltage decreasing rate.The performance of MEA during the OCV operation were characterized with the help of in situ electrochemical measurements,such as EIS and LSV.The results of in situ electrochemical measurements results show that the ohmic resistance and hydrogen crossover of exist backpressure MEA are lower than that no backpressure after OCV operation.The results indicate that backpressure can reduce the proton exchange membrane chemical degradation rate.