Toward tailored anion exchange membranes for high-performance electrocatalytic oxidation of HMF to FDCA

Membrane separator that is highly ionic conductive and alkaline stable is essential for the efficient, scalable electrocatalytic oxidation of HMF to FDCA, a key process for sustainable development. Drawing inspiration from the microstructural design of Nafion, we developed a series of side-chain imidazolium-functionalized anion exchange membranes (AEMs), employing the chemically stable polyethersulfone (PES) as the base polymer. Functionalization of PES side chains with chloromethyl groups, followed by C2-substituted imidazolium modification, enabled precise tuning of the membrane's physicochemical properties and structural characteristics. This tailored approach yielded an optimized DIM-PES-1.0 AEM exhibiting complete HMF conversion, with 94.0 % selectivity for FDCA and 94.1 % Faradaic efficiency, outperforming the commercial Fumasep FAA-3-PK-130 AEM, which achieved only 85.5 % FDCA selectivity under similar conditions. Notably, the DIM-PES-1.0 AEM demonstrated high alkaline stability, substantially retaining its electrocatalytic activity across 15 cycles, in contrast to the rapid degradation observed in FAA-3-PK-130 AEM after only three cycles. Our findings showcase a scalable, efficient strategy for producing high-performance AEMs under mild conditions, highlighting their potential for advancing sustainable electrocatalytic processes.