Anisotropic swelling cellulose-based semi-interpenetrating network anion exchange membranes via hydrogel method

While high ionic conductivity, robust mechanical properties, and alkaline stability are prerequisites for anion exchange membranes (AEMs), enhanced interfacial mass transfer between AEMs and electrodes is equally critical. Poor interfacial contact impedes ion transport, degrading device performance. Here, we fabricate a semi-interpenetrating (SIPN) AEM (SIPN-cCelx/PDDAy) via a hydrogel strategy using crosslinked cellulose and poly(diallyldimethylammonium) (PDDA), featuring swelling anisotropy and high hydration. Lateral cellulose aggregation induces decoupled swelling: low in-plane swelling (9.0–15.3 % at 80 °C) maintains mechanical integrity, while high through-plane swelling achieves dual functions. It enables adaptive filling of micro-gaps at membrane-catalyst interfaces in membrane electrode assemblies, reducing interfacial resistance, while simultaneously boosting water uptake (277.1–427.4 % at 80 °C) to synergistically enhance ionic conductivity (101.1–143.7 mS cm−1 at 80 °C) via hydrogen-bonding-assisted ion transport. Abundant cellulose hydroxyls further improve mechanical resilience under hydration-dehydration cycles. Besides, the cationic-free cellulose framework combined with stable PDDA ensures good alkaline stability at 60 °C (86.8–92.3 % mass retention and 88.6–94.6 % conductivity retention after 15 days in 1 M KOH). The SIPN-cCel100/PDDA60 delivers a current density of 3.0 A cm−2 at 2.0 V in an AEM water electrolyzer (80 °C).