Eco-friendly polyelectrolyte nanocomposite membranes based on chitosan and sulfonated chitin nanowhiskers for fuel cell applications

Novel sulfonic acid-functionalized chitin nanowhiskers (sChW) with enhanced proton conductivity were prepared for fabricating green and environmentally friendly chitosan (CS)-based nanocomposite polymer electrolyte membranes (PEMs). The performance of sChW in the development of direct methanol fuel cell (DMFC) nanocomposite membranes was also assessed. The manufactured nanocomposite membranes were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), CHNS elemental analysis, X-ray diffractometry (XRD), ion-exchange capacity (IEC), water uptake, as well as proton conductivity and methanol permeability. The results showed that modification of chitin nanowhiskers (ChW) with sulfonic acid groups, as the proton-conducting sites, could enhance proton conductivity of the manufactured membranes, leading to a fall in methanol permeability, as a result of attractive interactions between the negatively charged sulfonic acid groups on the surface of sChW and the positively charged amine groups in the chitosan chains. Thus, the selectivity parameter (the ratio of the proton conductivity to methanol permeability) of the chitosan-based nanocomposite membranes significantly increased from 3900 for pristine chitosan PEM to 26,888 S.s.cm−3 (ca. 6.8 times) for a membrane with 5% (wt) sChW. The functionalization strategy used herein can pave the way for the development of efficient polyelectrolyte membranes for applications in direct methanol fuel cells.