Prospects on utilization of biopolymer materials for ion exchange membranes in fuel cells

Cellulose and its derivatives, and chitosan are biopolymers that are touted as promising green alternatives for fuel cell ion exchange membrane (IEM) components due to their ubiquitous nature leading to low costs, environmental compatibility, and flexibility for modification. This review analyzes the various ways bacterial cellulose, nanocrystalline cellulose, cellulose nanofibers, cellulose acetate, and chitosan have been utilized in IEM synthesis. Key points realized from the rigorous literature evaluation are: (1) cellulosic and chitosan-based components were effectively used as both substrate and reinforcement, providing enhanced mechanical properties and additional sites for ion transport functionalization, (2) membrane fabrication involving grafting and crosslinking exhibited better mechanical and chemical stability compared to doping and impregnating techniques, (3) clever use of structures such as interpenetrating and semi-interpenetrating networks, like nanofiber skeletons, provided significant reduction in membrane swelling which is important in biopolymer-containing membranes due to its inherent hydrophilicity, and (4) the use of cellulosic materials had consistently resulted to improved methanol barrier characteristics for direct methanol fuel cell applications. However, a large portion of biopolymer-based IEM literature predominantly focused on proton exchange membrane research, and it is recommended that more attention should be shifted towards exploring biopolymer-based anion exchange membranes taking into consideration effective strategies that address the balance between swelling and performance.