Sustainable PVA/Cellulose Nanocrystal-Based Proton Exchange Membranes for Potential Application in Glucose Biofuel Cells

Agricultural waste valorization offers a sustainable route for developing advanced materials for renewable energy applications. In this study, cellulose nanocrystals (CNCs) were extracted from melon agricultural residues through hydrochloric, sulfuric, and phosphoric acid hydrolysis and incorporated into a poly(vinyl alcohol) (PVA) matrix to fabricate proton exchange membranes for potential applications in glucose biofuel cells. The influence of CNC surface chemistry on membrane morphology, crystallinity, thermal stability, mechanical properties, proton conductivity, and glucose permeability was systematically investigated. CNC incorporation improved membrane compactness, crystallinity, and physicochemical stability compared with neat PVA. Among the developed membranes, PVA/CNC-S exhibited the best overall performance, showing the highest proton conductivity (1.032 × 10−2 mS·cm−1 at 50 °C) and the lowest glucose permeability (3.25 × 10−9± 0.15 cm2·s−1). Furthermore, the composite membranes exhibited enhanced thermal and oxidative stability due to strong intermolecular interactions between PVA and functionalized CNCs. The results reveal that CNC surface chemistry plays a crucial role in regulating membrane transport properties and structural organization. In particular, sulfate-functionalized CNCs improved proton transport while minimizing glucose crossover. These findings highlight the potential of agricultural waste-derived PVA/CNC membranes as sustainable, low-cost, and efficient proton exchange membranes for potential applications in glucose biofuel cells and related bioelectrochemical energy systems.