Proton Conducting Membranes Filled With Functionalized Graphene Oxide And Covalent Organic Frameworks

Proton exchange membranes(PEMs),as the key component of proton exchange membrane fuel cells(PEMFCs),determine the efficiency and operation stability of PEMFCs.Under low humidity conditions(<50%RH),Nafion^?membranes,the most commonly used PEMs,would suffer from a sharp decrease of proton conductivity.What's more,the prices of Nafion^?membranes are pretty high.For low-cost alternative membranes,such as sulfonated polyether ether ketone(SPEEK),the restrictive relationship between proton conductivity and dimensional stability,limits its practical application.To solve the problems above,the functionalized graphene oxide(GO)and covalent organic frameworks(COFs)were introduced into the polymer matrix to optimize the chemical and physical environments within the membrane,thus enhancing the proton conductivity under low humidity.Imidazolium-based ionic liquids(IMD-Si)were grafted on GO nanosheet to obtain m GO,and then phosphotungstic acid was loaded on m GO nanosheet through the electrostatic interaction with imidazole groups to obtain P-m GO nanosheet.Then P-m GO was introduced into SPEEK matrix to prepare SPEEK/P-m GO composite membranes.GO has a two-dimensional lamellar and phosphotungstic acid has a good proton conductivity under high temperature.The addition of P-m GO could locally construct continuous two-dimensional proton transport channels within the membranes.At 65°C and 40%relative humidity(RH),SPEEK/P-m GO-4 had a proton conductivity of 5.0 m S cm^-1,which was 31.3 times higher than the pure SPEEK membrane.Compared with GO nanosheet,imidazolium-based COF has an ordered one-dimensional channel,providing an additional pathway for proton transportation.The proton conducting COF(P-COF)were obtained by loading phosphotungstic acids into COF.And P-COF was blending with SPEEK matrix to prepare SPEEK/P-COF composite membranes.At 65°C and 40%RH,SPEEK/P-COF-15 had a proton conductivity of 6.2 m S cm^-1,which was 36.5 times higher than the pure SPEEK membrane.Zwitterion-functionlized COF(Z-COF)was synthesized by grafting zwitterions on the SNW-1 network and doped into Nafion matrix to prepare Nafion/Z-COF composite membranes.The introduction of Z-COF into Nafion matrix renderred enhanced water retention property.Under 80°C and 40%RH,Nafion/Z-COF-10 had a proton conductivity of 10.9 m S cm^-1,which was 7.3 times higher than recast Nafion membrane.