This report describes a study of the effect of SiO2 nanopowders on the mechanism of ionic motion and interactions taking place in hybrid inorganic-organic membranes based on Nafion. Five nanocomposite membranes of the formula [Nafion/(SiO2)x] with SiO2 ranging from 0 to 15 wt % were prepared by a solvent casting procedure. TG measurements demonstrated that the membranes are thermally stable up to 170 degrees C but with the loss water it changes the cluster environments and changes the conductivity properties. MDSC investigations in the 90-300 degrees C temperature range revealed the presence of three intense overlapping endothermal peaks indicated as I, II, and III. Peak I measures the order-disorder molecular rearrangement in hydrophilic polar clusters, II corresponds to the endothermic decomposition of -SO3 groups, and III describes the melting process in microcrystalline regions of hydrophobic fluorocarbon domains of the Nafion moiety. ESEM with EDAX measurements revealed that the membranes are homogeneous materials with smooth surfaces. DMA studies allowed us to measure two relaxation modes. The mechanical relaxation detected at ca. 100 degrees C is attributed to the motion of cluster aggregates of side chains and is diagnostic for R-SO3H...SiO2 nanocluster interactions. DMA disclosed that at SiO2/-SO3H (psi) molar ratios lower than 1.9, the oxoclusters act to restrict chain mobility of hydrophobic domains of Nafion and the dynamics inside polar cages of [Nafion/(SiO2)x] systems; at psi higher than 1.9, the oxoclusters reduce the cohesiveness of hydrophilic polar domains owing to a reduction in the density of cross-links. FT-IR and FT-Raman studies of the [Nafion/(SiO2)x] membranes indicated that the fluorocarbon chains of Nafion hydrophobic domains assume the typical helical conformation structure with a D(14pi/15) symmetry. These analyses revealed four different species of water domains embedded inside polar cages and their interconnecting channels: (a) bulk water [(H2O)n]; (b) water solvating the oxonium ions directly interacting with sulfonic acid groups [H3O+...SO3(-)-].(H2O)n; (c) water aggregates associated with H3O+ ions [H3O+.(H2O)n]; and (d) low associated water species in dimer form [(H2O)2]. The conductivity mechanism and relaxation events were investigated by broadband dielectric spectroscopy (BDS). [Nafion/(SiO2)x] nanocomposite membranes were found to possess two different molecular relaxation phenomena which are associated with the alpha-relaxation mode of PTFE-like fluorocarbon domains and the beta-relaxation mode of acid side groups of the Nafion component. Owing to their strong coupling, both these relaxation modes are diagnostic for the interactions between the polar groups of the Nafion host polymer and the (SiO2)x oxoclusters and play a determining role in the conductivity mechanism of the membranes. The studies support the proposal that long-range proton charge transfer in [Nafion/(SiO2)x] composites takes place due to a mechanism involving exchange of the proton between the four water ...

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This report describes the preparation of a new nano‐electrocatalyst for applications in polymer electrolyte fuel cells operating with H2 and methanol. The nano‐electrocatalyst, having the composition K0.12[Pt1Fe1.6C55N0.12], consists of a distribution of Pt and Fe bimetallic clusters supported on carbon nitride nanoparticles. This material was synthesized by thermal treatment of a zeolitic inorganic–organic polymer electrolyte‐like (Z‐IOPE) precursor, prepared by reacting H2PtCl6 and K3Fe(CN)6 in the presence of sucrose, as organic binder, in a water solution. This reaction allows the desired material to be prepared by means of a sol→gel process followed by a gel→plastic transition. The morphology and surface properties of K0.12[Pt1Fe1.6C55N0.12] were studied via scanning and high‐resolution transmission electron microscopies and X‐ray photoelectron spectroscopy. Far‐infrared, mid‐infrared, and micro‐Raman‐laser spectroscopies, as well as X‐ray diffraction studies, together with detailed compositional data reveal the structural information and describe the interactions characterizing the mass activity of the K0.12[Pt1Fe1.6C55N0.12] system. This material has structural and morphological features that are very different to those usually found in commercially available electrocatalysts for application in H2 polymer electrolyte membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs). K0.12[Pt1Fe1.6C55N0.12] consists of active bimetallic catalytic sites supported on a mixture of α and graphitic carbon nitride‐like nanoparticles. The studies performed by cyclic voltammetry with the thin‐film rotating‐disk electrode indicate that the performance of K0.12[Pt1Fe1.6C55N0.12] and of the EC‐20 reference material is a) equal to –255 and –216 A g–1 Pt, respectively, in the oxygen‐reduction reaction at 0.75 V; and b) equal to 967 and 533 A g–1 Pt, respectively, in the hydrogen‐oxidation reaction at potentials lower than 0.2 V. The activation potential of K0.12[Pt1Fe1.6C55N0.12] is about 15 mV higher than that of the EC‐20 reference. In conclusion, the proposed synthesis route is general and promising for the development of new, improved nano‐electrocatalysts for low‐temperature fuel cells such as PEMFCs and DMFCs.

Phenylethanethiolate monolayer-protected Au38 and Au140 nanoclusters were modified by ligand place exchange with a series of thiolated peptides. The peptides were homooligomers based on the alpha-aminoisobutyiric acid unit. The effects of changing the peptide concentration and the peptide length in the capping monolayer were studied by differential pulse voltammetry. The results showed that the redox behavior of the nanoparticles can be affected very significantly by such modifications. For example, the first oxidation peak of Au38, a cluster displaying molecule-like behavior, could be shifted positively by as much as 0.7-0.8 V. Detectable redox shifts were noted even when one single oriented peptide was in the Au140 monolayer. These effects were attributed to the molecular dipole moments of the peptide ligands.