Microporous Adamantane-Grafted Poly(terphenyl piperidinium) Anion Exchange Membranes for Improved Alkaline Fuel Cells and Water Electrolysis

Microporous anion exchange membranes (AEMs) featuring rapid and selective ion-water transport have been extensively employed in various electrochemical devices, including AEM water electrolysis (AEMWE), AEM fuel cells (AEMFC), and aqueous flow batteries. Traditionally, the synthesis of microporous polymers has predominantly been dependent on the integration of bulky and twisted structural units within the polymer backbone. In this work, we introduce an efficient approach for fabricating microporous poly(terphenyl piperidinium) AEMs by the grafting of bulky adamantane side chains. Two series of adamantane-grafted AEMs, derived from poly(<i>p</i>-terphenyl piperidinium) (PTP) and poly(<i>m</i>-/<i>p</i>-terphenyl piperidinium) (<i>m</i>PTP) polymers, were synthesized, exhibiting an enhanced fraction of free volume and subsequently high λ-normalized hydroxide conductivity. The incorporation of adamantane markedly enhanced the membranes' resistance to degradation under alkaline and oxidative conditions, and the <i>m</i>PTP-ada-15 membrane demonstrated a 15% reduction in conductivity and an 18% decrease in dry weight after 1360 and 240 h of immersion in 1 M NaOH at 80 °C and in Fenton's reagent, respectively. Furthermore, the microporous AEMs functionalized with adamantane side chains exhibited superior performance in AEMFCs and AEMWEs relative to their ungrafted analogues, achieving a peak power density of 1230 mW cm^-2 and a current density of 4.47 A cm^-2 at 2.0 V for the <i>m</i>PTP-ada-15 membrane.