| Direct methanol fuel cells?DMFCs?,have recently received considerable attention and research due to their high conversion efficiency,convenient fuel supply,quick start times,zero emission levels ect..The proton exchange membrane is the heart of a fuel cell,and its performance directly determines the efficiency of the fuel cell.At present,the commercial proton exchange membrane is the perfluorosulfonic acid membrane,which possess excellent proton conductivity,chemical stability and mechanical properties,but also there are obvious disadvantages,such as poor water retention capacity at high temperature,high methanol permeability and environmental pollution.Recently,researchers have developed sulfonated polyaromatic polymers that can replace Nafion membranes such as sulfonated poly?ether ether ketone?,sulfonated poly?aryl ether sulfone?and sulfonated poly?aryl ether nitrile?.Typically,sulfonated polyaromatic polymer membranes achieve high proton conductivity only at high IEC values.However,high IEC values often impair methanol resistance,dimensional stability and mechanical properties.When polymer with a low IEC value,it shows excellent properties besides proton conductivity.In order to balance the proton conductivity and methanol permeability,the researchers have developed many methods including:chemical crosslinking,organic-organic composite and organic-inorganic composite.Among thoese,organic-inorganic composite is considered to be the simplest and most effective method to improve the comprehensive performance of proton exchange membrane.In this paper,The composite proton exchange membranes were prepared by solution blending with functionalized graphene as an inorganic filler and sulfonated poly?arylene ether nitrile??SPEN?as a matrix.The specific works are as follows:?1?Graphene oxide was prepared by improved Hummers method,and two different functionalized graphenes were prepared by chemical grafting:sulfonated graphene oxide?SGO?and aminated graphite oxide?NGO?,then blending with SPEN to obtained single-doped?S,N?and co-doped composite membranes?S/N-1,S/N-2,S/N-3?.The results show that all composite membranes exhibit excellent thermal stability,mechanical properties and dimensional stability.Meanwhile,the performance of co-doped composite membranes is superior to that of single-doped membranes.Among all the membranes,S/N-3 composite membrane exhbit the best performance.The proton conductivity of S/N-3 composite membrane can reach 0.064 S·cm-1 at 20°C,0.21 S·cm-1 at 80°C,and the selectivity can reach 4.48×105 S·cm-3·s,which is nearly 10 times higher than that of Nafion117(0.45×105 S·cm-3).?2?A novel amino-sulfo bifunctionalized GO?NSGO?was designed and synthesized by a simple aryl diazonium salt.A series of NSGO/SPEN composite membranes were prepared by incorporating NSGO into the SPEN matrix.The results show that the modified graphene has excellent compatibility and dispersibility in the matrix.And the water uptake,swelling ratio and methanol permeability of the composite membrane firstly decreased and then increased with the increase of the content,while the proton conductivity appeared to increase first and then decrease.Among thoses membranes,the NSGO/SPEN-2 composite membrane display the best performance.The proton conductivity of NSGO/SPEN-2 can reach 0.056 S·cm-1 and the methanol permeability is1.41×10-77 cm2·s-1 at 20°C.?3?A series of amino-sulfonated poly?aryl ether nitriles?with different amino contents were designed and synthesized via nucleophilic aromatic substitution reaction,and the AmSPEN-10 with the best comprehensive performance was selected as the polymer matrix.NSGO/AmSPEN composite membrane with various amounts were prepared by adding NSGO into the AmSPEN matrix.The results show that all the composite membranes have good dimensional stability,and the swelling ratio,which are only 10.82%-13.36%at 80°C.In addition,the methanol permeability of NSGO/AmSPEN-2 composite membrane is 0.68×10-7 cm2·s-1 and its selectivity is7.72×105 S·cm-3·s,which is nearly 17.2 times higher than that of commercial Nafion117.Furthermore,compared to NSGO/SPEN-2 membrane,it increased 94.5%. |
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