Preparation And Conduction Properties Study Of High-Temperature Proton Exchange Membrane Prepared By Hybridization Method

High-temperature proton exchange membrane fuel cell(HT-PEMFC) has attracted considerable attentions due to fast electrode reaction kinetics, high eliminated CO poisoning of platinum electrocatalyst, high efficiency of residual heat recovery and simplified heat and water management and Proton exchange membranes(PEM) is another core component in HT-PEMFC besides catalyst. However, most developed PEM, including commercial Nafion, suffers from a significant decline of proton conductivity and fuel cell perforamce due to the lose of water content above 100 oC,which are mianly caused by the absence of continuous and efficient proton transfer highway. Now, it is a crucial issue to develop PEM with high performace working under high temperature and anhydrous conditions for technology development of HT-PEMFC.To explore the methods and theories on intensification of the proton transfer properties of membrane operated under anhydrous condition, this paper concentrates on two key issues, including the fabrication of anhydrous proton transfer pathway and the optimizing of chemical environment among transfer pathway. Accoding to hybridization method, silicon dioxide particles(SiO2) or graphene oxide(GO)modified by polymer layer or acid-base block copolymer brushes was embedded in polymer matrix to prepare composite membrane. And the low-energy-barrier anhydrous proton conduction channels were fabricated at organic-inorganic interface,in hope of improving the proton conductivity of PEM. The relevant means and theories on intensification of proton conduction in PEM are proposed tentatively by investigating the influence of organic-inorganic interfacial microstructure on the ability and efficiency of proton conduction. The main details were summarized as follows:(1) The preparation of acid-base composite membrane by employing dopamine modified SiO2. Inspired by the bioadhesion principle, dopamine was hired to ornament SiO2(DSiO2) in the purpose of the introduction of polydopamine layer withamino and imino groups. Afterwards, DSiO2 was incorporated into sulfonated poly(ether ether ketone)(SPEEK) matrix to prepare composite membranes, which yields acid-base pairs at organic-inorganic interface. It is observed that DSiO2 is uniformly dispersed while SiO2 aggragate to the surface images of membrane. Based on the measurement of proton conductivity and activation energy of membrane, it is expected to explore the transfer way and regulatory methods. In particular, the composite membrane with 15 wt% DSiO2 achieves the highest conductivities of 4.52 mS cm-1 at 120 oC under anhydrous condition, 5 times higher than the commercial Nafion membrane.(2) The preparation of acid-base composite membrane by utilizing phosphorylated graphene oxide(PGO). PGO was designed and prepared through distillation–precipitation polymerization, which confered high phosphonic acid loading amount on PGO surface(26.0 wt%). PGO was utilized as conductivity promoters for chositan(CS) by uniformly dispersing into the membrane matrix to obtain the composite membrane. Through investigating systematically the microstructure and proton transport ability of composite membrane, it is found that PGO construct continuous and long-range proton transfer pathways within membrane with the aid of GO’s large surface area and high aspect ratio. Meanwhile, the acid-base pairs generate driven the strong electrostatic interactions between PGO(–PO3H) and CS(–NH2) and then architects low-energy-barrier anhydrous condution pathway. In this way, the conductivity of composite membrane is enhanced. For instance, the composite membrane with 2.5 wt% PGO acquires a 22.2-time increase in conductivity from 0.25 mS cm-1 to 5.79 mS cm-1(160 °C, 0% RH). With this benefit, the hydrogen fuel cell using PGO-filled membranes displays much higher cell performance than those using CS control and GO-filled membranes.(3) The preparation of acid-base composite membrane by acid-base block copolymer brushes grafted graphene oxide(PGO). Herein, four kinds of functionalized graphene oxide nanosheets(FGO) bearing polymer brushes(phosphoric acid brushes, imidazole brushes, acid-base or base-acid block copolymer brushes) were designed exquisitely(P-@SiGO, I-@SiGO, P-I-@Si GO and I-P@SiGO), and then embedded into two typical polymer matrixes(acidic SPEEK)and basic CS) to prepare composite membranes by physically blending. It is noted that the strong electrostatic attractions induce the brushes insert into polymer matrix and form interconnected networks. Especially, the attractions from outer segment could drag the whole brushes to deeply insert into polymer matrix and yield wide and long-range interfacial networks. When employing as proton conductors, these networks can transport protons quickly between FGO and polymer matrix using the functional groups(especially acid-base pairs). For example, 5 wt% FGO afford composite membrane a 6.7 times’ increment of proton conductivity. The similar function of FGOs on proton conduction of acidic SPEEK and basic CS suggest the universality of aforementioned phenomena.