Research On Degradation Mechanism Of Membrane Electrode Performance Based On Pt/C Catalyst With Graphitized Carbon Support

In recent years,Proton Exchange Membrane Fuel Cell(PEMFC)has made great progress in the transportation field,especially in the commercial vehicle industry such as bus and logistics.However,it still faces high costs,insufficient lifespan,and infrastructure.Issues such as imperfections.Through the scale of the fuel cell industry and the adoption of new low platinum and non-platinum catalysts,the cost will be significantly reduced and fundamentally solved.Membrane electrode(MEA)is the core component of PEMFC.The development of long-lasting,high-performance membrane electrode plays a key role in the cost,life and reliability of fuel cells.Therefore,studying the performance degradation mechanism of MEA is important for the development of long-life PEMFC has important meaning.In this paper,by studying the structure-activity relationship between the degree of graphitization of carbon supports prepared at different temperatures and the activity,attenuation and durability of carbon-supported platinum catalysts,the"hundred-gram level"preparation of high-performance and anti-fading catalysts was realized.Based on the problems of low performance of the membrane electrode prepared by scraping the graphitized carbon support Pt/C catalyst(self-made Pt/GC),the structure of the catalyst layer is difficult to control,which greatly improves the potential cycle,reverse polarity,and high potential tolerance of the MEA.It slows down the attenuation rate of polarization characteristics,effectively suppresses the performance attenuation of MEA under dynamic load conditions,and has been applied and verified on k W-level stacks.The specific research results are as follows:(1)The physical properties of Graphitic Carbon(GC)prepared at different heat treatment temperatures were studied.Pt/C catalysts were prepared based on graphitized carbon supports prepared by heat treatment at four temperatures of 1600?,1800?,1900?and 2200?.It was found that the catalytic components of the four samples were all nanoparticles,which were well dispersed on the carrier,and the particle size was about 5nm,and increase as the carrier heat treatment temperature increases.The ORR activity of Pt/GC samples decreases with the increase of graphitization degree,but is still higher than the commercial Pt/C(Johnson Matthey,JM)on the market.After accelerated catalyst decay test,it was found that the electrochemically active area(ECSAs)of Pt/GC-1600,Pt/GC-1800,and Pt/GC-1900 catalysts decreased by 8.9%,6.8%and 5.7%respectively compared with the initial value.The ECSAs of the Pt/GC-2200 sample did not decrease but increased by 5%.It can be seen that the Pt/C catalyst prepared by the self-made graphitized carbon support has better anti-fading performance,which will help to improve the life of the fuel cell.Through process optimization and amplification,the"100g-level"preparation of high-performance and anti-fading catalysts was realized,laying the foundation for the application and verification of kilowatt-level stacks.(2)Research on MEA based on Pt/C catalyst prepared by self-made graphitized carbon support.First,a high-pressure homogenizer was used to disperse the catalyst ink,and the influence of different technical parameters(temperature,dispersion time,and dispersion pressure)on the dispersion effect,stability and rheology of the ink was explored,and the ionomer-carbon(I/C))ratio is the decisive factor influencing the Zeta potential of the catalyst ink,and the water-alcohol ratio is the main influencing factor of the rheological properties of the catalyst ink and the construction of the later catalyst layer.The optimal ink preparation temperature is 10?,time is 40 minutes and the pressure is 1200 bar.The slit extrusion method is used for coating,and the thickness of the catalyst layer and surface cracks are controlled.Standard MEA with active areas of25cm² and 340cm² were prepared.The single cell test results showed that the cell voltage reached 0.806 V at a current density of 300 m Acm^-2,0.734 V at a current density of 1000 m Acm^-2,and at 2000 m Acm^-2 The current density reaches 0.623 V,which shows that the MEA prepared by the self-made catalyst performs well in the activation polarization,ohmic polarization and concentration polarization control regions of the fuel cell,which fully reflects the preparation process of the graphitized Pt/C catalyst in this paper.Methods,research on high-stability anti-sedimentation slurry and research on catalytic layer construction are advanced.In the durability verification of the single cell,it was found that the MEA prepared by the self-made catalyst,after maintaining a high potential of 1.5V for 60 minutes,the monomer voltage attenuationwas only 2.9%at a current density of 1000 m Acm^-2,while the MEA prepared with a commercial JM catalyst attenuated The rate reached 14.8%.Secondly,when a reverse current of 5A(200 m Acm^-2)was applied to simulate the reverse polarity state,the membrane electrode prepared with commercial JM catalyst reached-2V in 13 min,while the membrane electrode prepared with a self-made highly graphitized carbon-supported platinum catalyst,The time to reach-2V is more than 200min,which shows that the self-made Pt/GC catalyst has greatly improved the anti-reverse ability of the fuel cell.Finally,during the 506h NEDC dynamic load cycling condition,the polarization performance of the single cell did not decay.This fully demonstrates that through the use of self-made graphitized Pt/C catalyst,anti-settling slurry and new catalytic layer research,the prepared MEA has excellent anti-fading performance.(3)In order to further evaluate the performance of the self-made Pt/GC catalyst in the fuel cell stack,a 1k W full-size metal bipolar plate stack was assembled,and the durability test was carried out based on the NEDC operating conditions that simulate the actual driving state of the vehicle.First,through the condition sensitivity test under different current densities,find the best operating conditions under dynamic conditions,and then based on the best operating conditions,verify the steady-state operation under different currents of 106A,166A,233A,333A,and 400A.During the durability test,as the experiment time continues to lengthen,the performance of the stack gradually decreases.Before 800 h,the stack performance was relatively stable,the average battery voltage fluctuated up and down,but basically there was no change,the attenuation rate was only 10?V h^-1,and the attenuation rate was 1.38%;however,after800h,the average cell voltage of the stack There was a continuous rapid drop in voltage,and by 1000h,the total attenuation rate was 5.21%.Combining the polarization data and high-frequency impedance data during the experiment,the physical and electrochemical characterization after disassembly of the stack was carried out.It was found that the attenuation mechanism of the membrane electrode prepared based on the graphitized support Pt/C catalyst was mainly as follows::1)The high potential at the idling point of vehicle-mounted operating conditions will accelerate the corrosion of the carbon carrier and the dissolution/dissolution process of Pt particles;2)The dynamic cyclic changes of temperature/humidity/pressure with variable load conditions will cause pores in the catalytic layer The collapse of the structure increases the water/gas molecular mass transfer resistance,which will accelerate the decay rate at high current densities;3)The failure of the membrane electrode frame seal will aggravate the hydrogen crossover,which will accelerate the local degradation of the proton exchange membrane and cause the hydrogen ion mass transfer resistance.Increase causes performance degradation.(4)Using AVL CFD software FIRE M,a three-dimensional attenuation model of the PEMFC membrane electrode was established,and the evolution process of the key material characteristic parameters of the membrane electrode was simulated and analyzed.Through systematic comparison and analysis of the changes in the characteristic physical quantities of the catalytic components,carbon supports,and ionomers of the membrane electrode model based on porous carbon materials and graphitized carbon materials during power generation,the evidence for the attenuation mechanism of fuel cells is completed.