Poly(vinyl alcohol)/Poly(diallyldimethylammonium chloride) anion-exchange membrane modified with multiwalled carbon nanotubes for alkaline fuel cells

摘要

Hydroxyl anion conducting membrane composed of poly(vinyl alcohol) (PVA), poly(diallyldimethylammonium chloride) (PDDA), and hydroxylated multiwalled carbon nanotubes (MWCNTs-OH) have been synthesized via a facile blending-casting method assisted by a hot-chemical cross-linking process. Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) showed that PDDA and MWCNTs-OH were successfully introduced into the PVA matrix and MWCNTs-OH could effectively improve the network structure of the membrane. With the addition of MWCNTs-OH, many properties of the membranes such as thermal, chemical, mechanical stability and swelling property were improved significantly. Most prominent is the improvement of mechanical property, where the PVA/PDDA/MWCNTs-OH(1:0.5/3?wt.%) membrane showed high tensile strength of 40.3?MPa, tensile elongation of 12.3% and high Young's modulus of 782.8?MPa. Moreover, MWCNTs-OH bound the polymer chains in the membranes more compactly, resulting in decreased water uptake. By tuning the mass fraction of PVA, PDDA, and MWCNTs-OH in the membrane, the maximum OH~(?) conductivity (0.030?S?cm~(?1) at room temperature) was achieved for the composition of 0.5?wt.% MWCNTs-OH doped with the PVA: PDDA (1:0.5 by mass) blend. The membranes showed excellent oxidative stability when treated with both a solution of H_(2)O_(2) (30?wt.%) at room temperature and in a hot KOH solution (8?M) at 80?°C. Based on the full aliphatic structure membrane (PVA/PDDA-OH/1?wt.%MWCNTs-OH), membrane electrode assemblies (MEAs) fabricated with Pt/C cathode catalyst can achieve power densities of 41.3?mW?cm~(?2) and 66.4?mW?cm~(?2) in a H_(2)/O_(2) system at room temperature and 40?°C, respectively. Using CoPc as the Pt-free cathode catalyst, power densities of 9.1?mW?cm~(?2) and 14.0?mW?cm~(?2)?at room temperature and 40?°C were obtained, respectively.