Fluorinated poly(p-triphenylene isatin) anion exchange membranes based on hydrophilic hydroxyl side chain modulation for fuel cells

Abstract

The development of alkaline fuel cells is moving forward at an accelerated pace, and the application of ether-free bonded polymers to anion exchange membranes (AEMs) has been widely investigated. However, the question of the “trade-off” between AEM ionic conductivity and dimensional stability remains difficult. The strategy of inducing microphase separation to improve the performance of AEM has attracted much attention recently, but the design of optimal molecular structures is still being explored. Here, this work introduced different ratios of 3-bromo-1,1,1-trifluoroacetone (x = 40, 50, and 60) into the main chain of poly(p-terphenylene isatin). Because fluorinated groups have excellent hydrophobicity, hydrophilic hydroxyl-containing side chains are introduced to jointly adjust the formation of phase separation structure. The results show that PTI-PTF₅₀-NOH AEM with the appropriate fluorinated group ratio has the best ionic conductivity and alkali stability under the combined effect of both. It has an ionic conductivity of 133.83 mS cm⁻¹ at 80 °C. In addition, the OH⁻ conductivity remains at 89% of the initial value at 80 °C and 3 M KOH for 1056 h of immersion. The cell polarization curve based on PTI-PTF₅₀-NOH shows a power density of 734.76 mW cm⁻² at a current density of 1807.7 mA cm⁻².