Self-assembly of multiwall carbon nanotubes on sulfonated poly (arylene ether ketone) as a proton exchange membrane
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ORIGINAL PAPER
Self-assembly of multiwall carbon nanotubes on sulfonated poly (arylene ether ketone) as a proton exchange membrane Haidan Lin & Wenmo Sun & Chengji Zhao & Hui Na
Received: 16 June 2013 / Accepted: 13 October 2013 / Published online: 31 October 2013 # Springer Science+Business Media Dordrecht 2013
Abstract 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-bylayer assembled polyelectrolyte systems. Meanwhile, the methanol permeability of these modified membranes is effectively reduced. The selectivity of SPAEK-C-(CMWCNTs/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. Keywords Sulfonated poly (arylene ether ketone) . Proton exchange membrane . Carbon nanotubes . Methanol permeability W. Sun : C. Zhao (*) : H. Na Alan G. MacDiarmid Institute, College of Chemistry, Jilin University, Changchun 130012, People’s Republic of China e-mail: [email protected] H. Lin Jilin Electric Power Research Institute, Changchun 130021, Jilin, People’s Republic of China
Introduction Among the fuel cells, a direct methanol fuel cell (DMFC) using a proton exchange membrane (PEM) is becoming attractive as a promising power source for portable electronics, because of the convenient refueling of liquid fuel, high-energy density, green emission, and low operating temperature [1–3]. Currently, the widely used PEM materials are perfluorinated sulfonated membranes, such as Nafion® series developed by Dupont, due to their superior chemical and mechanical stabilities, and high proton conductivity. However, the high methanol permeability rate across the PEM poses one of the critical problems in the realization of a DMFC for practical use. The methanol crossover increases the over-potential of the cathode due to poisoning of the cathode catalyst, thereby significantly reducing the efficiency of fuel cells [4]. Furthermore, high cost and difficulty in synthesizing and processing impeded their commercial development [5]. Considerable efforts to explore new PEM materials, including sulfonated poly (arylene ether ketone)s (SPAEKs), have been carried out [6
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