Study On Durability Of WML (Water Management Layer) For Fuel Cell By Accelerated Test

Gas diffusion layer(GDL)is the main part of MEA for proton exchange membrane fuel cell(PEMFC),which plays an important role in supporting the catalyst layer,conducting electrons,managing gas diffusion and water removal and transporting heat.Micro-porous layer as the key assembly of GDL mainly provides a better path for reactant gases transport to the catalyst layer and achieves a proper hydrophobicity for better water management.As more people have focused on freeze start from subzero temperature and development of stacks with low air pressure, especially the enhancing durability of stacks,the function and the durability of GDL become more and more important.The task of studying the durability of MPL is to study the variability of characteristic owned to MPL during the long operating process of PEMFC to a certain extent,i.e.thickness,pore structure,resistivity, permeability,contact angle and hydrophobicity/hydrophilicity et al..MPL with excellent durability acts as a significant effect in enhancing the activity of long-time PEMFC operating.So it is necessary and important to study durable activity of MPL for designing novel MPL and developing long-term PEMFC.In the present paper,the mechanical along with the chemical and electrochemical fading mechanism of MPL during the long-term PEMFC operating was modeled by accelerated experiments.Combined with the modem analysis method including SEM,XRD,XPS,FTIR and CV,the above characteristics of MPL were investigated in system,and then the effect to the management of gas transport and water removal and the activity fading mechanism of PEMFC were studied in detail.The main conclusions are drawn as follows:(1)The results of chemical accelerating experiments showed that MPL lapses after being boiled for 500h in 15%H₂O₂ solution at 70℃,which could cause an activity decrease by 10%of a single fuel cell.The analysis results of SEM,XRD,XPS and FTIR indicate that both carbon powder and PTFE could fall off the MPL during the accelerating experiments,while carbon powder fell more rapidly than PTFE did.Carbon powder was also observed to be oxidized and the membrane of PTFE splited.All of the above resulting to the weaking of MPL thickness,increasing of resistivity,increasing of permeability and monishing of contact angel.Finally,it brings to decreasing uniformity of the gas and water transport and increasing resistivity of electrons conducting.(2)The results of electro-chemical accelerating experiments demonstrated that VulcanXC-72R carbon power could be oxidized evidently under 1.2V vs.SCE for 2h in 1M H₂SO₄,while MPL appeared a oxygen-desorption peak after standing under 1.2V vs.SCE for 20 h in 1M H₂SO₄ in cyclic voltammogram.The MPL after standing under 1.2V vs.SCE for 60 h in 1M H₂SO₄ lower the activity of a single fuel cell greatly.This is mainly because of the oxidization of carbon powder leading to the high resistivity and permeability resulting in the unbalance of gas and water transport.(3)The results of mechanical accelerating experiments demonstrated that MPL wrecked remarkably under the pressure200 psi 30min for at 140℃.The MPL fading mechanism mostly results from the compact surface of MPL under high pressure,which leads to the destroying of structure of microspores and the pores proportion between hydrophobicity and hydrophilicity.This may bring on difficulty in management of gas/water transport during high current density.