Durability Study Of PTFE Reinforced Membrane Electrode In Proton Exchange Membrane Fuel Cell For Automotive Application

Proton exchange membrane fuel cell(PEMFC),an efficient and environmentally friendly device which can convert the chemical energy of hydrogen and oxygen into electric energy directly,is seen as a promising application commercially.PEMFC have attracted attention from various fields such as transportations,portable devices and stationary electric power plant and so on.At present,cost and durability set obstacles on the way to PEMFC's commercialization.The durability of membrane electrode assembly(MEA)which is the crucial component of PEMFC plays a decisive role in the durability of PEMFC.Investigating the degradation mechanisms of MEA can provide us with a better understanding of relative materials,and in return facilitate the refinement of relative materials.Accelerated stressor tests(ASTs)are the general approaches that are employed to conduct the durability tests.It can not only save us plenty of time,but also reduce the cost markedly.Nowadays,the ASTs are based on the standard durability-evaluation protocols established by Department of Energy(DOE)of United States including electro-catalyst cycle,electro-catalyst support cycle,MEA chemical stability and membrane mechanical cycle.Currently,researchers combine the standard durability-evaluation protocols and the conditions of automotive applications such as frequent load cycling,relative humidity or temperature cycling,gas supply and so on,to analyze the degradation mechanisms of PEMFC comprehensively.In this work,we utilized three types of ASTs to study the durability of platinum,carbon,and the chemical durability of membrane,corresponding to potential cycling,high potential holding and open circuit voltage(OCV)holding.According to potential cycling experiment,platinum nanoparticles grew and agglomerated under accelerated conditions.Besides,platinum also dissolved and reduced by permeable hydrogen,depositing in the membrane and forming "Pt band".Both Pt agglomeration and dissolution/redeposition contributed to the loss of electrochemical surface area(ESA),and subsequently,resulted in the loss of cell performance.Pt dissolution/redeposition was considered as a time-dependent process.At the beginning of potential cycling test,it was believed that Pt degradation was due to nanoparticle growth and agglomeration.As test processed,Pt dissolution/redeposition became considerable.During high potential holding test,durability of carbon support was analyzed.Carbon support corroded under high potential conditions,generating CO which would absorb on Pt.Further,carbon support corrosion generated various carbon-oxygen groups which strengthened the hydrophilia of carbon surface and reduced hydrogen crossover subsequently.Simultaneously,carbon support corrosion caused Pt degradation like Pt agglomeration and physical loss.In addition,OCV test was employed to investigate the influence of membrane thickness on membrane degradation and Pt agglomeration.Hydrogen crossover increased as membrane thickness decreased,resulting in severer OCV decay which can be demonstrated by F+ concentration test and SEM images.During OCV test,permeable hydrogen reacted with oxygen at the cathode side,generating H2O2 which further decomposed into radicals ·OH and ·OOH.These radicals attacked the membrane and caused chemical degradation.Different permeable hydrogen influenced Pt agglomeration differently.As membrane thickness decreased,more permeable hydrogen would react with oxygen directly at the cathode side,generating huge heat and forming "hot point".The high temperature locally facilitated Pt agglomeration and leaded to the uneven distribution of Pt particle size.