Study On The Pretreatment Process Of Membrane Electrode Assembly To Improve The Performance Of PEMFC

The cost competitiveness of the Proton Exchange Membrane Fuel Cell(PEMFC)relative to existing energy sources is the key to its successful commercialization.Optimizing the Membrane Electrode Assembly(MEA)can improve the performance of the MEA,which can reduce the amount of platinum(Pt)catalyst used in the membrane electrode and achieve the purpose of reducing costs.The pretreatment process is one of the ways to optimize MEA,and the MEA pretreatment process and its mechanism of action have not yet been extensively studied.This process method can improve the performance of MEA without increasing the Pt loading,and is not limited to the type of MEA catalyst,the preparation method of the catalytic layer,the type of membrane and even its application scenarios.Therefore,it is of great value to develop a new pretreatment process and explore its mechanism.This paper focuses on the pretreatment process of MEA to carry out related research,the specific content is as follows:(1)Developed a new type of MEA pretreatment process——Isopropanol/Water solution(IPA/Water)soaking pretreatment process,and explored the reasons for its optimization.The peak power density of the optimized MEA can reach 3034 mW/cm2.According to the peak power density,the performance of the optimized MEA is improved by about 12%compared with that of the original process.A "cave model" was proposed to explain the mechanism of the pretreatment process:there will be a large number of areas in the catalyst layer that cannot be infiltrated—karst caves.The addition of isopropyl alcohol changed the surface tension of the isoaking solution,which made the solution wetting the cave area,thus expanding the proton transport channel inside the MEA,forming a new three-phase interface,and improving the utilization rate of the catalyst.The use of MEA vacuum soaking pretreatment achieved a similar optimization effect,and indirectly demonstrated the rationality of the cave model.(2)The IPA/Water soaking pretreatment process was optimized,and an optimal pretreatment procedure was obtained.With a fixed soaking time of 30 s,the performance of the MEA soaked under different concentration gradients of the soaking solution was tested.Compared with the conventional MEA,the performance of all MEAs has been improved,especially at high current density.The IPA/Water concentration changes from 5%?10?15%,and the electrochemical properties of MEA gradually increase.When the concentration of the soaking solution continues to increase,the swelling loss is too obvious,and the performance of MEA begins to decline.The optimization effect of the vacuum soaking-IPA/Water saoking double pretreatment process and the IPA/Water soaking pretreatment process on the optimization of MEA are compared,and it is concluded that the IPA/Water soaking pretreatment has the key effect of reducing the proton resistance in addition to wetting the cave.Subsequently,a "Transmission-Line Equivalent Circuit Model of Catalyst Layer Impedance" was established to explain the reasons for the changes in ohmic resistance,and to summarize the law of MEA ohmic impedance changes with or without swelling.The slope of the ohmic impedance curve is closely related to the number of MEA three-phase points/the area of the three-phase interface.(3)The effect of IPA/Water soaking pretreatment process on different types of platinum carbon(Pt/C)catalysts was compared,and the relationship between the cavern effect and the properties of carbon supports and the number of carbon supports was explored.The results show that the high specific surface area of carbon black has a large number of micro-nano structures in the catalyst layer,which is likely to cause a strong cave effect,resulting in a low catalyst utilization rate.The more the number of carbon loading,the more obvious the cave effect will be.Correspondingly,the IPA/Water soaking pretreatment process has a more obvious effect on improving the performance of MEA with strong cave effect.Finally,the IPA/Water soaking pretreatment process is combined with the sulfuric acid boiling treatment process,which changes the properties of the carbon support and further improves the performance of MEA to 3170 mW/cm2(peak power density),which is an increase of about 17%compared with the original process.