Sorption and transport properties of 2-acrylamido-2-methyl-1-propanesulfonic acid-grafted bacterial cellulose membranes for fuel cell application

Abstract

This study investigated the sorption and transport properties of proton-conducting membranes based on a bacterial cellulose (BC) biopolymer with 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) grafted using ultraviolet (UV)-induced polymerization. The transport properties of the membranes were characterized according to their self-diffusion coefficients and methanol permeabilities. Using pulsed field-gradient nuclear magnetic resonance (PFG-NMR) technology, the water and methanol self-diffusion coefficients through the AMPS-g-BC membrane were identified as 1.48 × 10−5 cm2 s−1 and 5.30 × 10−6 cm2 s−1, respectively. The methanol permeability of the AMPS-g-BC membrane was 5.64 × 10−7 cm2 s−1, which was approximately 42% of that of Nafion 115. The differences in the transport behaviors of the Nafion 115 and AMPS-g-BC membranes correlated with the sorption characteristics of solvent uptake and lambda (λ) values (number of solvent molecules absorbed per sulfonic acid). The ratio of the water and methanol λ values (i.e., λCH3OH/λH2O) for the AMPS-g-BC membrane was 0.07, which indicated its sorption preference for water compared to methanol. Overall, results indicate that the AMPS-g-BC membrane is an effective methanol barrier and a potential solid electrolyte candidate for direct methanol fuel cells.