Proton conductive, low methanol crossover cellulose-based membranes

This work describes the development of sulfated cellulose (SC) polymer and explores its potential as an electrolyte-membrane for direct methanol fuel cells (DMFC). The fabrication of our membranes was initiated by the preparation of the novel sulfated cellulose solution via controlled acid hydrolysis of microcrystalline cellulose (MCC). Ion-conductive crosslinked SC membranes were prepared following a chemical crosslinking reaction. SC solution was chemically crosslinked with glutaraldehyde (GA) and cured at 30^◦C to produce the aforementioned membranes. Effects of GA concentration on methanol permeability, proton conductivity, water uptake and thermal stabilities were investigated. The crosslinking reaction is confirmed by FTIR technique where a bond between the primary OH groups of cellulose and the GA aldehyde groups was achieved, leading to the increased hydrophobic backbone domains in the membrane. The results show that the time of crosslinking reaction highly affects the proton conduction and methanol permeability. The proton conductivity and methanol crossover (3M) of our GA crosslinked SC membranes are 3.7 × 10⁻² mS cm⁻¹ and 8.2 × 10⁻⁹ cm² s⁻¹, respectively. Crosslinked sulfated cellulose films have lower ion conductivity than the state-of-the-art Nafion (10.2 mS cm⁻¹); however, the methanol crossover is three orders of magnitude lower than Nafion membranes (1.0 × 10⁻⁵ cm² s⁻¹ at 1 M). Such biofilms with high methanol resistivity address the major hurdle that prevents the widespread applications of direct alcohol fuel cells.