Functionalized Graphene Oxide For Construction Of Nanocomposite Proton Exchange Membranes

Proton exchange membrane fuel cell(PEMFC)is a new type of clean energy conversion device that can directly convert hydrogen,methanol and other fuels into electrical energy through electrochemical reaction.With the advantages of zero emission,high energy conversion rate and environment-friendly,it may ease the energy crisis and environmental pollutioa To inprove proton conduction properties of sulfonated poly(ether ether ketone)(SPEEK),two types of functionalized graphene oxide were doped with it to prepare inorganic-organic nanocomposite proton exchange membranes(PEMs).By observing the micro structure of the conposite proton exchange membrane and testing its comprehensive performance,the extra proton transfer pathways inside of the membrane were proposed and the contribution of the functionalized graphene oxide in proton transfer process was studied.Sulfonated reduced graphene oxide(SRGO)has been synthesized and incorporated into random SPEEK in order to decrease the proton conduction barrier between isolated sulfonic acid groups in SPEEK and improve its conduction properties.SRGO was prepared by a facile arylation of reduced graphene oxide(RGO)with diazonium salt,which allowed the benzene sulfonate groups to be covalently bonded to the RGO layer.The conposite membranes with appropriate SRGO content exhibited considerably improved thermal stability,mechanical strength and dimensional stability.Since the sulfonic acid groups presented in SRGO promoted ion conduction,the composite membranes exhibited better proton conductivities(a),particularly at low relative humidity(RH)conditions.Taking SPEEK/SRGO-1.0 membrane as an example,its ? was as high as 8.6 mS cm-1 at 80 ?/50%RH,which is three times greater than that of the blank.To further study the influence of different functional groups on GO surface to the proton conductivity of composite PEMs,poly(2,5-benzimidazole)-grafted graphene oxide(ABPBl-GO)was synthesized through the reaction of 3,4-diaminobenzoic acid(DABA)with the carboxyl acid groups present on the GO surface and incorporated into SPEEK to fabricate nanocomposite membranes,which then were further doped with phosphoric acid(PA).The simultaneous incorporation of ABPBI-GO and PA into SPEEK did not only improve the physicochemical performance of the membranes in terms of thermal stability,water uptake,dimensional stability,proton conductivity and methanol permeation resistance,but also relieved PA leaching from the membranes though acid-base interactions.The resulting composite membranes exhibited enhanced proton conductivities in extended humidity ranges thanks to the hygroscopic character of PA and the increased water uptake.Moreover,the unique self-ionization,self-dehydration and non-volatile properties of PA improved the high-temperature proton conductivities(?)of PA-doped membranes.The PA-doped SPEEK/ABPBI-GO-3.0 delivered a ? of 7.5 mS cm-1 at 140 ?/0%RH.This value was four-folds higher than that of pristine SPEEK membranes.The PA-doped SPEEK/ABPBI-GO-3.0 based fuel cell membranes delivered power densities of 831.06 mW cm-2 and 72.25 mW Cm-2 at 80 ?/95%RH and 120 ?/0%RH,respectively.By contrast,the PA-doped SPEEK membrane generated only 655.63 mW cm-2 and 44.58mW cm-2 under the same testing conditions.