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

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 x 10(-5) cm(2) s(-1) and 5.30 x 10(-6) cm(2) s(-1), respectively. The methanol permeability of the AMPS-g-BC membrane was 5.64 x 10(-7) cm(2) 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 (lambda) values (number of solvent molecules absorbed per sulfonic acid). The ratio of the water and methanol lambda values (i.e. lambda(CH3OH)/lambda(H2O)) 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. (C) 2013 Elsevier B.V. All rights reserved.