In situ implantation of PolyPOSS blocks in Nafion (R) matrix to promote its performance in direct methanol fuel cell

Department of Chemical and Biomolecular Engineering, National University of Singapore, BLK E5 02-02, 4 Engineering Drive 4, Singapore 117576, Singapore
Journal of Membrane Science (Impact Factor: 5.06). 07/2008; 320(1-2):310-318. DOI: 10.1016/j.memsci.2008.04.013


Fabrication of recast Nafion®-117 membrane using the dipolar aprotonic solvent will normally lead to a random matrix. On the contrary, when a designed amount of vinyl-pendant octasiloxane (Q8M8V) cubic molecules was included into the Nafion® matrix during the recasting process and then subjected to polymerization, a nonrandom matrix was obtained. This paper provides an insight into the matrix-formatting role of rigid poly(Q8M8V) blocks, generated in situ in Nafion® matrix, according to thermal analyses (thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA) and Differential Scanning Calorimetry (DSC)) and electron microscopic images of the resulting composite matrix. The P(Q8M8V) played a role in restricting random extensions of proton-conducting channels (PCCs) and promoted ordered assembling of Nafion® molecules. As a result, compared with the recast pristine Nafion® membrane, the composite membranes containing P(Q8M8V) of 5–15 wt.% manifested obvious improvement on both repression of methanol permeability and promotion of power density output of the single direct methanol fuel cell (DMFC).

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    ABSTRACT: Unique starburst nanoparticles are synthesized via grafting polyacrylonitrile short chains to the cubic polyhedral oligomeric silsesquioxane (POSS) by atom transfer radical polymerization (ATRP). Introduction of these branched nanoparticles (sb-POSS) into the sulfonic perfluoro polymer (SPFP, e.g. Nafion®) matrix in appropriate contents gives significant improvements in the performance of SPFP membranes as direct methanol fuel cell (DMFC). This enhancement is associated with the initial clustering of sb-POSS particles in the SPFP matrix when the sb-POSS content reaches to 5 wt.%. It has been found, from the differential scanning calorimetry (DSC) observation, that the SPFP molecules wage dual interactions on the sb-POSS particles, namely the hydrophobic perfluoro polymer chains of SPFP repel sb-POSS particles while the hydrophilic moieties associate with them. The content of sb-POSS strongly affects the assembly of hydrophilic channels in the membrane and, therefore, the membrane performance in a single direct methanol fuel cell (DMFC). The sb-POSS (5 wt.%)-SPFP composite membrane manifests an increase of 122% in power output of DMFC at 80 °C. In brief, this work offers a new insight into how the unique interactions between soft nanoparticles and amphiphilic polymer chains affects performances of proton exchange membranes (PEMs) in DMFC.
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