A Study On MEA Materials And Structures Of PEMFC

Proton exchange membrane fuel cells（PEMFCs）are expected to find wide application as portable electronics,distributed stationary power stations and electric vehicles.PEMFCs possess outstanding advantages,such as zero/low emission,high efficiency,high power density,and rapid start-up.Limited by materials cost and unsatisfactory performance of membrane electrode assembly（MEA）,PEMFC’s commercialization is hindered.In this dissertation,we studied the materials and structures of membrane electrode assembly（MEA）,aiming to reduced the MEA cost and enhance the mass transfer process.A novel SPEEK membrane of high sulfonation degree,high dimensional stability and high mechanical strength was prepared.A facile post treatment was carried out by successive immersing SPEEK membrane in NaBH₄ and H2SO4 solutions,which afforded the membrane with gradient crosslink structure.At 80°C,SPEEK-RC exhibited a high proton conductivity of 0.11S·cm-1 and swelled up to only 38.6%,while pristine SPEEK can be 31% swollen at 30°C and dissolve at elevated temperatures.Additionally,the post treatment enhanced membrane mechanical strength greatly（46.6MPa vs.15.1MPa）.According to 1H-NMR and ATR-FTIR spectra,we found NaBH₄ reduces certain benzophenone moieties on SPEEK into benzhydrol groups,which later react with sulfonic acid groups on SPEEK in H2SO4 solution to form crosslinks between the polymer chains.With the combination of experiment and molecular simulation,we systematically studied the synthesis process of high-performance Pt/GNPs catalyst（Pt loaded on graphite nanoplatelets）in pyrene derivate/EG-H2 O solution.Following are the conclusions.First,PCA（pyrenecarboxylic acid）or AP（pyrenamine）could be adsorbed onto GNPs surface and slide readily,enabling PCA or AP to exfoliate GNPs into thinner layers under sonication.Second,bonded onto Pt nanoparticle surface,as “molecular spacer” between Pt nanoparticles,PCA and AP can preventing Pt nanoparticles from aggregation.Third,with the presence of PCA or AP,Pt nanoparticles grew mainly via Oswald ripening,resulting in narrow size distribution of Pt particles.Finally,Pt nanoparticles were finally loaded onto GNPs evenly distributed,since PCA and AP can interact with both GNPs and Pt.For the first time,we prepared aligned Pt/GNPs catalyst layer via direct electrophoresis.The alignment shortened the mass transfer path within the cathode and enhanced the Pt utilization（97%）at the same time.The results indicated that the aligned structure was stabilized by support among Pt/GNPs platelets.The electrochemical surface area of the aligned catalyst layer could be as high as 135.9m2·g-1,by electrophoresis of 0.001mg·mL-1 Pt/GNPs dispersion in CCl4,under 8V·cm-1,10 Hz alternating electric field.Post treated SPEEK and aligned Pt/GNPs catalyst layer was hot-pressed to prepare membrane electrode assembly and packed into a single cell.After optimization,a maximal power density of 843mW·cm-2 was obtained at 80°C,equivalent to a gravimetric power density of 7.92kW/g Pt.