Preparation And Characterization Of Ionic Conducting Composite Membranes Based On Poly(Phenylene Oxide)

Fuel cell is a new type of energy device which can convert the chemical energy directly into electrical energy through electrochemical reaction.Among the various fuel cells,both the proton exchange membrane fuel cells and anion exchange membrane fuel cells use solid polymer membranes as the electrolyte.As a key component of the fuel cell,the performance of the ionic conducting membranes determines the efficiency of the fuel cells.Currently,one of the key problems is that the membrane has high conductivity and normally accompanying with serious swelling and resulting in mechanical degradation,which has been the challenge for the further development of polymer electrolyte materials.To enhance dimensional stability and mechanical strength of ionic conducting membranes,the inorganic compounds have been empolyed as additives to prepare the hybrid membranes with superior properties.Brominated polyphenylene oxide(BPPO)with different degrees of bromination was used as membrane matrix,which had good physical and chemical properties.Graphene oxide and silica were selected as fillers,respectively,to prepare a series of organic-inorganic composite membranes.The percentage of inorganic fillers and the percentage of acid doping level of the membranes were all mass percent.The effects of inorganic materials on the properties of the composite membranes were systematically investigated.Trimethylammonium chloride was ued to modify silica(MSiO2)to improve the compatibility between silica and PPO.Composite anion exchange membranes and hybrid proton exchange membranes were prepared,respectively.The properties of ionic conducting membranes including conductivity,swelling ratio and mechanical properties were evaluated.The results indicated that the mechanical strength of the composite anion exchange membranes increased with the increase of the MSiO2 content.The tensile strength of QAPPO/2%MSiO2 was up to 13.8 MPa,which was twice as that of the pristine QAPPO membrane.The composite anion exchange membrane exhibited a hydroxide conductivity of 39 mS cm-1 at 80?.The introduced inorganic materials reduced the swelling and increased the dimensional stability of the composite proton exchange membranes.The QAPPO/1%MSiO2/PA membrane with the PA doping level of 111%exhibited the mechanical strength as high as 11.6 MPa at room temperature.The proton conductivity of QAPPO/0.25%MSiO2/PA membrane was 46 mS cm-1 at 180? without humidifying.Modification of GO(mGO)was performed via the ring-open reaction between the epoxy group on the GO and the amine group of 1-(3-Aminopropyl)imidazole.The imidazole ring on mGO reacted with benzyl bromide of BPPO to form ionic bonds.The strong interaction between mGO and the BPPO made it easy to fabricate the homogeneous membranes.The experiment results showed that the proton conductivities of hybrid membranes were obviously improved since the imidazolium groups and the functional groups on the surface of mGO had affinity PA for a high acid doping level.QAPPO/3%mGO/PA membrane exhibited high proton conductivity of 0.121 mS cm-1,whereas QAPPO/PA membrane had a conductivity of 65 mS cm-1 at 180 ?.The tensile strength were 2.43 MPa for QAPPO/3%mGO/PA membrane and 6.67 MPa for QAPPO/PA membrane at room temperature,respectively.Grafting of 3-dimethylaminopropylamine onto the surface of graphene oxide was made and the composite proton exchange membranes of QAPPO/x%pGO were prepared with the solution-casting method.The effects of pGO on proton conductivity,thermal stability and mechanical properties were systematically investigated.The results showed that the conductivity of hybrid membranes increased with the increase of the pGO content,while a highest mechanical was reached with the pGO additive range of 0.25-4.0%.The proton conductivities for the QAPPO/4%pGO/PA membrane and QAPPO/PA membrane were 88 and 45 mS cm-1 at 180?,respectively.The tensile strength of QAPPO/1%pGO/PA composite membrane was 7.9 MPa at room temperature,which was 1.5 times that of the QAPPO/PA membrane.