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The fuel cell is the best alternative to compensate for today's energy demand, but the high cost of fabrication of membranes ( e.g. , Nafion) hampers the widespread commercialization. Plant-derived nanocellulose is renewable, most abundant, and biocompatible with high strength and tunable surface chemistry. Here we have demonstrated the jute derived-nitro-oxidized carboxycellulose nanofibers (NOCNFs) as a viable and sustainable substitute for synthetic ionomer membranes used in proton exchange fuel cells (PEFCs). NOCNFs were obtained in two functionalities: carboxylate and carboxylic acid which were then transformed into nanopaper I and II, respectively. This is the first report where NOCNFs with two different functionalities were tested in PEFCs. The results indicated that nanopaper II performed better than nanopaper I with a high proton conductivity of 14.2 mS cm −1 and power density of 19.1 mW cm −2 at high temperature (80 °C) operation in PEFCs, along with excellent durability even for 24 h of operation. 

Liquid flow batteries have potential to achieve high energy efficiency as a large-scale energy storage system. However, the ion exchange membranes (IEMs) currently used in flow batteries do not have high ion selectivity and conductance at the same time, owing to the trade-off between ionic membrane resistance and ion selectivity. Here, we report a rationally designed sulfonated aromatic polymer membrane which can greatly mitigate the trade-off limitation and achieve high performance vanadium RFB. Small-angle X-ray scattering studies and density functional theory calculations indicated that the narrowly distributed aqueous ionic domain of just the right width (<7 Å) and the strong hydrogen bond interaction of vanadium species with a unique polymer side chain structure play a key role in improving the ion selectivity. Our systematic studies of the polymer structures, morphologies, and transport properties provide valuable insight that can aid in elucidating the structure–property relationship of IEMs and in establishing design criteria for the development of high-performance membranes.