In situ implantation of PolyPOSS blocks in Nafion® matrix to promote its performance in direct methanol fuel cell
ABSTRACT 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).
- [Show abstract] [Hide abstract]
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.Journal of Membrane Science. 01/2009;
- [Show abstract] [Hide abstract]
ABSTRACT: In this work, polysiloxane-modified perfluorosulfonic acid (PFSA) membranes were prepared by a directed sol–gel synthesis method with (3-mercaptopropyl) methyldimethoxysilane (MPMDMS) as the precursor of silicon alkoxide in the supercritical carbon dioxide (Sc-CO2) system. Contents of polysiloxane in the modified PFSA membranes were varied according to the added amount of precursor MPMDMS. The chemical and physical properties of these modified PFSA membranes were characterized by using attenuated total reflection-infrared spectra, X-ray diffraction, thermogravimetric analysis, universal testing machine, scanning electron microscopy and transmission electron microscope. The measurement results indicated that the polysiloxane particles were not restricted in the ion clusters and well dispersed in the PFSA membrane with ordered size of about 80–100 nm. In the meanwhile, the polysiloxanes have been incorporated into the hydrophobic fluorocarbon backbone regions and interacted with C–F backbones of PFSA polymers. Dimensional stability of the modified PFSA membrane was improved after the impregnation by using Sc-CO2. The modified membranes almost can remain the same high tensile strength as the pristine membrane. Performance of these modified membranes was evaluated in terms of proton conductivity and methanol permeability. The highest selectivity value (ratio of proton conductivity to methanol permeability) of the modified membrane was about 75.6% higher than that of pristine PFSA membrane because of its higher proton conductivity and lower methanol permeability. All the results indicated that this novel synthesis method in Sc-CO2 system is a promising method to improve the properties of PFSA membrane for direct methanol fuel cell application.International Journal of Hydrogen Energy. 01/2009;