Dimensionally stable cellulose acetate-chitosan semi-interpenetrating polymer network as fuel cell anion exchange membrane

The call for cleaner energy sources motivates the development of anion exchange membrane fuel cells (AEMFC), which offer potential for electricity production using carbon-neutral fuels. However, the focus on biopolymer-based ion exchange membranes (IEM) remains relatively low, despite their strong potential for cost reduction and competitive performance. Studies have demonstrated the fabrication of high-performing synthetic AEMs using semi-interpenetrating polymer networks (SIPNs) showcasing improved mechanical stability and electrochemical properties, offering a pathway for cost-effective AEMFC adoption. In this study, a biopolymer SIPN of cellulose acetate (CA) nanofibers and cross-linked chitosan (CS) was fabricated into AEM. FTIR and Raman spectroscopy confirmed CS addition, its cross-linking to form the SIPN, and subsequent functionalization to obtain the AEM. Thermogravimetric analysis of fabricated AEM revealed thermal stability well within AEMFC operating conditions, and the formation of SIPN structure increased tensile strength by 95%. Deacetylation of cellulose diacetate (CDA) nanofibers into cellulose monoacetate (CMA) and cellulose improved the ion exchange capacity (IEC) by up to 12% due to conversion of the acetyl group into hydroxyl groups acting as active sites for functionalization. Ionic conductivities peaked at 60 °C of 21 mS cm⁻¹ for a 150 μm cellulose-chitosan SIPN AEM. No appreciable change in swelling was observed among membranes of the same components with differing IEC, indicating the SIPN’s ability to restrict membrane expansion despite increased presence of hydrophilic groups. Desirable mechanical integrity was observed with reduced swelling in SIPN AEMs compared to CA film AEMs of the same thickness. These properties demonstrate the success of our fabrication method for a dimensionally stable biopolymer AEM with controlled swelling and appreciable ion transport capabilities that are suitable for fuel cell applications.