Preparation,Characterization And Application Of Side-chain-type Aromatic Ion Exchange Membranes For Fuel Cells

Fuel cells, especially proton-exchange membrane fuel cells (PEMFC) and alkaline anion-exchange membrane fuel cell (AAEMFC) are attracting extensive attention. Cation-exchange membrane (CEM) and anion-exchange membrane (AEM) as the key component of PEMFC and AAEMFC respectively, however, are facing such a state-of-the-art i.e., despite the high price, perfluorosulfonic acid membranes such as Nafion is still the only commercial CEM for PEMFC while no commercially available AEM for AAEMFC. Therefore, the development of CEM and AEM with high performance but low price is vital to the further development and commercialization of PEMFC and AAEMFC.Side-chain-type sulfonated aromatic polymers (SCT-SAPs) with similar chemical structure to Nafion but much lower price are very promising materials to replace Nafion. On the other hand, considering the similar conducting mechanism of OH-to H+, Side-chain-type quarternized aromatic polymers (SCT-QAPs) are expected to be promising AEM materials, but reports on SCT-QAPs are in lack. In this context, novel SCT-SAPs and SCT-QAPs with distinct side-chains and main-chains and novel approaches to their preparation are addressed herein, and summarized as follows:(1) To obtain side-chain-type sulfonated poly(phenylene oxide), bromomethylated poly(phenylene oxide)(BPPO) was modified via etherification reaction to introduce pendant naphthalene sulfonic acid groups. As-prepared PEM exhibited not only outstanding dimensional stability in water (i.e., no more than32%water uptake and no more than11%linear expansion ratio in water at80℃), but also high proton conductivity comparable to that of Nafion115.(2) Side-chain-type sulfonated aromatic diarene monomer2,2-di(3-sulfopropyloxy) biphenyl disodium (DSOBP) was first synthesized via one step. Then side-chain-type sulfonated aromatic poly(ether ketone)(SCT-SPEK-x) were synthesized via direct polyacylation between DSOBP and an aromatic diacidic acid monomer in Eaton’s reagent, where the contents of sulfonic acid groups in SCT-SPEK-x were precisely tuned by the adding ratio of DSOBP. The proton conductivity of membrane SCT-SPEK-1.0at room temperature was higher than that of Nafion115and the output power density of a single cell using membrane SCT-SPEK-1.0was also higher than that of a single cell using Nafion115under the same test condition;(3) Dibenzo18-crown-6was used as an un-sulfonated diarene monomer to copolymerize with DSOBP monomer in Eaton’s reagent to obtain side-chain-type sulfonated aromatic poly(ether ketone) containing crown-ether moieties in the main-chain (SCT-SPEKC-x), where the contents of sulfonic acid groups in S SCT-SPEKC-x were precisely tuned by the adding ratio of DSOBP. H3+O dissociated by pendant sulfonic acid groups could form complex with crown-ether via hydrogen bonding. The proton conductivity of membrane SCT-SPEKC-2.5at room temperature was1.7-fold that of Nafion115and the output power density of a single cell using membrane SCT-SPEKC-2.0was also higher than that of a single cell using Nafion115under the same test condition;(4) Side-chain-type quarternized aromatic diarene monomer2,2-di(4-N, N’, N"-trimethyl ammonium butyloxy) biphenyl dibromide (QBP) was first synthesized via one step. Then side-chain-type quarternized aromatic poly(ether ketone)(SCT-QPEK-x) were synthesized via direct polyacylation between DSOBP and an aromatic diacidic acid monomer in trifluoromethane sulfonic acid, where the contents of quarternary ammonium groups in SCT-QPEK-x were precisely tuned by the adding ratio of QBP. Distinct side-chain-type quarternary ammonium groups endowed membrane SCT-QPEK-1.0with super alkaline hydrothermal resistance and high alkaline anion conductivity. The peak power density of a single cell using membrane SCT-QPEK-1.0could reach120mW/cm-2;(5) Dibenzo18-crown-6was used as an un-quarternized diarene monomer to copolymerize with QBP monomer in trifluoromethane sulfonic acid to obtain side-chain-type quarternized aromatic poly(ether ketone) containing crown-ether moieties in the main-chain (SCT-QPEKC-x), where the contents of quarternary ammonium groups in SCT-QPEKC-x were precisely tuned by the adding ratio of QBP. SCT-QPEKC-x exhibited high alkaline anion conductivity, but the complex between crown-ether and K+seemed to lower the conductivity.