Ternary composite proton exchange membranes based on sulfonated poly(vinyl alcohol)/chitosan/cellulose nanocrystals for direct methanol fuel cells

The utilization of biobased materials has received much attention in greener energy applications because of their abundance, low cost, biodegradability, and environmental sustainability. Herein, ternary composite proton exchange membranes (CPEMs) have been prepared using sulfonated poly (vinyl alcohol) (SPVA) and chitosan (CH) as a polymer blend matrix and cellulose nanocrystal (CNC) as a reinforcing nanofiller, via solution casting method. The improved interactions between the sulfonic acid groups of SPVA and the amine groups of CH, along with the extensive hydrogen bonding through the hydroxyl groups, facilitated the proton transfer in the SPVA/CH blend membranes. The ternary CPEMs using the optimized blend ratio (SPVA/CH = 90/10) filled with different loading of CNCs exhibited further enhanced proton conductivity, higher mechanical properties and thermal stability, and lower methanol permeability compared to the SPVA/CH blend membranes. The SPVA/CH-CNC CPEMs with 3 wt.% CNC loading (SPVA/CH-CNC/90/10-3) showed an enhanced proton conductivity of 75 +/- 1 mS/cm at 25 degrees C and 50% RH and a lower methanol permeability of 1.69 x 10-7 cm2/s at 25 degrees C as compared to SPVA and SPVA/CH blend membranes. The SPVA/CH-CNC/90/10-3 composite membranes displayed almost a 30.5% reduction in methanol permeability with respect to SPVA/CH/90/10 and exhibited a selectivity of 4.43 x 108 mS.s/cm3 which is higher than that for the SPVA (1.65 x 108 mS.s/cm3) and SPVA/CH-90/10 membranes (2.42 x 108 mS.s/cm). Therefore, the SPVA/CH-CNC/90/10-3 composite membrane shows its potential to be used as a PEM in direct methanol fuel cell applications.