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

Abstract

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 H2O2 (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 H2/O2 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.