Self-assembly of multiwall carbon nanotubes on sulfonated poly (arylene ether ketone) as a proton exchange membrane

Membranes of sulfonated poly (arylene ether ketone) containing carboxyl groups (SPAEK-C) are modified by alternating deposition of oppositely charged polyelectrolytes [carboxyl-functionalized multiwalled carbon nanotubes (C-MWCNTs) and chitosan (CS)] in order to reduce methanol crossover and maintain high proton conductivity in a direct methanol fuel cell (DMFC). Fourier transform infrared spectroscopy confirms that C-MWCNTs and CS are assembled in the multilayers. The morphology of membranes is studied by scanning electron microscopy. The results confirm the presence of thin C-MWCNTs/CS multilayers coated on the SPAEK-C membrane. The SPAEK-C-(C-MWCNTs/CS)_n membranes maintain high proton conductivity values up to 0.058 Scm⁻¹ at 25 °C and 0.24 Scm⁻¹ at 80 °C, which are superior to previous layer-by-layer assembled polyelectrolyte systems. Meanwhile, the methanol permeability of these modified membranes is effectively reduced. The selectivity of SPAEK-C-(C-MWCNTs/CS)_n is two orders of magnitude greater than that of Nafion® 117, making these modified membranes a good alternative to be used in DMFCs. The thermal stability, water uptake, swelling ratio and proton conductivity of SPAEK-C and SPAEK-C-(C-MWCNTs/CS)_n membranes are also investigated.