Blend Membranes Consisting of Sulfonated Poly(ether ether ketone) and Polysulfone Bearing 4-Nitrobenzimidazole for Direct Methanol Fuel Cells

Abstract

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Acid–base blend membranes consisting of sulfonated poly(ether ether ketone) and 5-amino-benzotriazole tethered polysulfone for DMFC

“…Since the longer side chain and the more number of nitrogen sites (four) in amino-benzotriazole may make the proton hopping much easier in the blend membranes consisting of SPEEK and PSf-BTraz compared to that in membranes consisting of other N-heterocycles, the SPEEK/PSf-BTraz membrane shows the highest proton conductivity among the blend membranes investigated. Additionally, as we reported before [22], the pK a values of the heterocycles could also influence the proton conductivity of this type of blend membranes. For example, the SPEEK/PSf-NBIm blend membrane shows higher proton conductivity compared to that of SPEEK/PSf-BIm as the pK a value of NBIm is lower than that of BIm due to the electron-withdrawing effect of the nitro functional group attached to BIm.…”

“…As mentioned earlier, we previously reported tethering different N-heterocycles (BIm, ABIm, NBIm, and PImd) to PSf and investigated the properties of blend membranes consisting of SPEEK and PSf tethered with the heterocycles [20][21][22][23]. To have a better understanding of the effects of the size, pK a , and the number of nitrogen atoms of the heterocycles tethered to PSf on the properties of the blend membranes based on acid-base interactions, blend membranes consisting of the SPEEK and different basic polymers (shown in Fig.…”

“…In this study, SPEEK with an IEC of 1.42 meq/g was used. The polysulfones tethered with different heterocycles (BIm, ABIm, NBIm, PImd) were synthesized using CPSf-158 as a precursor and following the procedure reported before [20][21][22][23].…”

“…Since there is a greater number of sulfonic acid groups compared to the number of heterocycle groups in the blend membranes, the vehicle-type proton conduction mechanism is predominant, while the Grotthuss-type mechanism involving the nitrogen atoms on the heterocycles may provide an enhancement in the proton conduction by providing additional proton transfer "bridges". Moreover, the insertion of the heterocycles into the ionic clusters formed by the sulfonic acid groups could broaden the proton transfer channels [22,23], resulting in an enhancement in the vehicle mechanism. The longer side chains of PSf-BTraz and the higher number of nitrogen sites (four) in the 5-amino-benzotriazole groups may facilitate easier proton hopping in the SPEEK/PSf-BTraz blend membranes compared to that in the SPEEK/PSf-BIm; in fact, the latter exhibits lower proton conductivity compared to the former with the same [-SO 3 H]/[heterocycle] ratio as shown in Table 3.…”

“…Because of this reason, more attention is being directed towards the development of ionomer networks containing ionically cross-linked blend systems such as SPPO (poly(2,6-dimethyl-1,4-phenylene oxide))/PBI (polybenzimidazole respectively), SPEEK/PBI, and SPSf/aminated PSf, which are more flexible [16][17][18][19]. Our group reported recently [20][21][22][23] that blend membranes based on acid-base interactions between the sulfonic acid groups of SPEEK and the N-heterocycle groups (benzimidazole (BIm), amino-benzimidazole (ABIm), nitrobenzimidazole (NBIm), and 1H-perimidine (PImd)) tethered to PSf show improved DMFC performance compared to plain SPEEK membranes due to both suppressed methanol crossover and enhanced proton conductivity. This blend membrane concept is based on industrially available, inexpensive polymer precursors like PEEK and PSf, which are compatible with each other due to their similar aromatic backbones.…”