Catalytic Synthesis Of Addition-type Norbornene Copolymer And Its Quaternary Ammonium Functional Modification For Preparation Of Direct Methanol Fuel Cell Alkaline Anion-exchange Membranes

Direct methanol fuel cells are efficient energy conversion devices that canconvert chemical energy to electricity, directly, and have been attracting attention as aclean energy technology. It can be divided into proton exchange membrane directmethanol fuel cells (PEM-DMFCs) and anion exchange membrane direct methanolfuel cells (AEM-DMFCs). The novel AEM-DMFCs have received significant interestin recent years relative to PEM-DMFCs, because of advantages when operating underalkaline conditions. AEM-DMFCs use non-noble metals or inexpensive metal oxidesas catalysts to greatly reduce the cost of the device. And the electrode reactionkinetics can be enhanced in the high PH. The key way to acquire higher OH-conductivity of AEM is designing a novel copolymer with high ion exchange capacity(IEC).Addition-type polynorbornene (PNB) with the dual-ring structure limits itscommercialization, as results of its poor flexibility, bad solubility and brittleness.PNB is predicted to a commercial level, if a suitable functional PNB is discovered.The situation inspired us to design and synthesis a novel norbornene copolymercontaining flexible group or polar functional groups. AEM based on addition-typenorbornene copolymer by its quaternary ammonium functional modification,possesses high thermal stability, good mechanical properties, excellent dielectricproperties, high methanol permeability, as well as good chemical stability.Firstly,2-butoxymethylene-5-norbornene (BN) and2-(4-phenyl-butoxymethy-lene)-5-norbornene (PhBN) were prepared successfully. Addition-type norbornenecopolymer P(BN/PhBN) were synthesized via the vinyl addition copolymerization ofBN and PhBN by using bis-(β-ketonaphthylamino) nickel(II)/B(C6F5)3catalyticsystem. The catalytic system exhibited high activity (about104gpolymer/(molNih)) andthe obtained copolymers have high molecular weight (1.33-2.72×105). All themonomers and copolymers were determined by IR,1H NMR and GPC. Thecopolymers’ structure can be controlled by insertion rate of PhBN (22%,40%,77%).Meanwhile, the aimed copolymers have good film forming, better solubility, andbetter processibility. Furthermore, the obtained copolymers can be functionallymodified by sulfonation or quaternization on phenyl group and applied to the ionic exchange membrane.Then, the chloromethylated copolymers CP(BN/PhBN) with different degree ofchloromethylation (87%,71%,64%) were achieved easily by functional modified onnorbornene copolymer. Furthermore, alkaline Anion-exchange Membranes wereobtained by quaternary ammonium functional modification, forming with copolymersolution (8%) and alkalization. A series of quaternized P(BN/PhBN) with comb-shaped structures which induced hydrophilic-hydrophobic separation weresynthesized and determined by TEM or SEM. The application performance of AEMwas studied by controlling the content of PhBN or adding different long alkyl sidechains pendant to the nitrogen-centered cation. The results showed that AEM hasexcellent dimensional stability, with swelling degree in plane between0.9-3.3%, aswell as high ion exchange capacity, up to1.83mmol/g. On the other hand, weevaluated the chemical stabilities of the AEM under6mol/L NaOH solution andfound that its ion conductivity hardly decayed after a week and retained theirexcellent flexibility at room temperature over a month. We measured the conductivityof the alkalized QC6P(BN/PhBN)-22membrane in NaOH (aq.) at differentconcentration and demonstrated its increased conductivity with the concentration.Meanwhile, we conducted the temperature-dependent conductivity measurement from30oC to80oC, and observed the increased conductivity with the operationtemperature or IEC, up to4.14×10-3S/cm at80oC. Moreover, we demonstrated thatthe methanol permeability of these membranes were in the range of1.97-20.4×10-7cm2/s, which is lower than that of Nafion.A series of anion-conductive and durable polymer electrolyte with long alkylside chains or the content of PhBN (22-77%) and their corresponding AEM wereachieved, successfully. The membranes having excellent dimensional stability, goodchemical stabilities, better alcohol resistance, and high IEC can improve theperformance of DMFCs. Unfortunately, the AEM showed low ionic conductivity,related to their low water uptake. The hydroxide conductivity can be enhanced byadding the hydrophilic group on the copolymer chain or doping the functionalinorganic nanoparticles in the following studies.