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The thermal, mechanical, and electric properties of hybrid membranes based on Nafion that contain a [(ZrO2)·(Ta2O5)0.119] "core–shell" nanofiller are elucidated. DSC investigations reveal the presence of four endothermic transitions between 50 and 300 °C. The DMA results indicate improved mechanical stability of the hybrid materials. The DSC and DMA results are consistent with our previous suggestion of dynamic R-SO3H…[ZrTa] cross-links in the material. These increase the thermal stability of the -SO3H groups and the temperature of thermal relaxation events occurring in hydrophobic domains of Nafion. The broadband electrical spectroscopic analysis reveals two electric relaxations associated with the material's interfacial (σIP) and bulk proton conductivities (σEP). The wet [Nafion/(ZrTa)1.042] membrane has a conductivity of 7.0 × 10-2 S cm-1 at 115 °C, while Nafion has a conductivity of 3.3 × 10-2 S cm-1 at the same temperature and humidification conditions. σEP shows VTF behavior, suggesting that the long-range conductivity is closely related to the segmental motion of the Nafion host matrix. Long-range conduction (σEP) occurs when the dynamics of the fluorocarbon matrix induces contact between different delocalization bodies (DB), which results in proton exchange processes between these DBs. [ABSTRACT FROM AUTHOR]

Conformational changes in polymer films exposed to high-pressure CO2have been investigated with Fourier transform infrared (FT-IR) spectroscopy. The experimental setup, based on a custom-made stainless steel optical cell with CaF2windows, allows measurements in a CO2environment for pressures up to 6 MPa, in a temperature range from 293 to 353 K and in the mid-infrared (1000–4000 cm–1). Poly(methyl methacrylate) (PMMA), a polymer with a side group (C-type), was studied to monitor the spectral changes as a function of CO2pressure and was compared to poly(d,l-lactic-co-glycolic acid) (PLGA), a polymer without a side group (B-type). By monitoring the characteristic carbonyl bands, conformational changes that occur due to molecular interactions between the high-pressure CO2and the polymers were explored at a constant pressurization rate (0.02 MPa/min) and temperature. Spectral changes are observed only for PMMA, where the vibrational band at 1680 cm–1disappears with increasing pressure. The spectra of PLGA do not show any significant change in the presence of high pressure CO2in the investigated range. The behavior of the absorbance peak as a function of pressure and temperature highlights the presence of dynamic cross-links (DCs) between the side groups of PMMA films obtained by solvent casting below the glass transition temperature of the polymer. The spectral features are correlated using a model that accounts for CO2diffusion and the relaxation kinetics of the polymer chains in the thin film. The disappearance of the vibrational band attributed to the DCs for PMMA is related to the glass transition temperature, and a retrograde vitrification phenomenon is observed. This approach can be considered a useful alternative to magnetic suspended balance for the study of polymer–gas systems. [ABSTRACT FROM AUTHOR]

We report on the development of two new Pt-free electrocatalysts (ECs) for the oxygen reduction reaction (ORR) process based on graphene nanoplatelets (GNPs). We designed the ECs with a core-shell morphology, where a GNP core support is covered by a carbon nitride (CN) shell. The proposed ECs present ORR active sites that are not associated with nanoparticles of metal/alloy/oxide but are instead based on Fe and Sn subnanometric clusters bound in coordination nests formed by carbon and nitrogen ligands of the CN shell. The performance and reaction mechanism of the ECs in the ORR are evaluated in an alkaline medium by cyclic voltammetry with the thin-film rotating ring-disk approach and confirmed by measurements on gas-diffusion electrodes. The proposed GNP-supported ECs present an ORR overpotential of only ca. 70 mV higher with respect to a conventional Pt/C reference EC including a XC-72R carbon black support. These results make the reported ECs very promising for application in anion-exchange membrane fuel cells. Moreover, our methodology provides an example of a general synthesis protocol for the development of new Pt-free ECs for the ORR having ample room for further performance improvement beyond the state of the art. [ABSTRACT FROM AUTHOR]

Polybenzimidazole (PBI) has becomea popular polymer of choicefor the preparation of membranes for potential use in high-temperatureproton exchange membrane polymer fuel cells. Phosphoric acid-dopedcomposite membranes of poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole](PBI4N) impregnated with hafnium oxide nanofiller with varying contentlevels (0–18 wt %) have been prepared. The structure–propertyrelationships of both the undoped and acid-doped composite membranesare studied using thermogravimetric analysis, modulated differentialscanning calorimetry, dynamic mechanical analysis, wide-angle X-rayscattering, infrared spectroscopy, and broadband electrical spectroscopy.Results indicate that the presence of nanofiller improves the thermaland mechanical properties of the undoped membranes and facilitatesa greater level of acid uptake. The degree of acid dissociation withinthe acid-doped membranes is found to increase with increasing nanofillercontent. This results in a conductivity, at 215 °C and a nanofillerlevel x≥ 0.04, of 9.0 × 10–2S cm–1for [PBI4N(HfO2)x](H3PO4)y. This renders nanocomposite membranes of this type as goodcandidates for use in high temperature proton exchange membrane fuelcells (HT-PEMFCs). [ABSTRACT FROM AUTHOR]

The development of polymer electrolyteswith high ionic conductivity,high lithium transference number, and high electrochemical stabilityis one of the main aims in the field of lithium battery research.In this work, we describe the synthesis and the characterization ofnew electrolyte systems, composed of three-dimensional hybrid inorganic–organicnetworks doped with LiClO4. The preparation route comprisesonly three steps, namely a sol–gel reaction, salt dissolution,and an epoxide polymerization reaction. The lithium concentration,and thus the lithium transference number, was modulated by addinglithium hydroxide in the sol–gel step. In this way, seven electrolyteswith varying salt concentrations were prepared. The hybrid electrolytesare characterized by good ionic conductivities (up to 8·10–5S/cm at room temperature) and high thermo-mechanicaland electrochemical stabilities. Stability tests versus lithium metalvia galvanostatic polarization showed that this material is superiorwith respect to reference poly(ethylene oxide) based electrolytes. [ABSTRACT FROM AUTHOR]

This study focuses on changes in the structure of ionomer membranes, provided by the 3M Fuel Cells Component Group, as a function of the equivalent weight (EW) and the relationship between the structure and the properties of the membrane. Wide-angle X-ray diffraction results showed evidence of both non-crystalline and crystalline ordered hydrophobic regions in all the EW membranes except the 700 EW membrane. The spectral changes evident in the vibrational spectra of the 3M membranes can be associated with two major phenomena: (1) dissociation of the proton from the sulfonic acid groups even in the presence of small amounts of water; and (2) changes in the conformation or the degree of crystallinity of the poly(tetrafluoroethylene) hydrophobic domains both as a function of EW and membrane water content. All the membranes, regardless of EW, are thermally stable up to 360 °C. The wet membranes have conductivities between 7 and 20 mS/cm at 125 °C. In this condition, the conductivity values follow VTF behavior, which suggests that the proton migration occurs via proton exchange processes between delocalization bodies (DBs) that are facilitated by the dynamics of the host polymer. The conductivity along the interface between the hydrophobic and hydrophilic domains makes a larger contribution in the smaller EW membranes likely due to the existence of a greater number of interfaces in the membrane. The larger crystalline domains present in the higher EW membranes provide percolation pathways for charge migration between DBs, which reduces the probability of charge transfer along the interface. Therefore, at higher EWs although there is charge migration along the interface within the hydrophobic-hydrophilic domains, the exchange of protons between different DBs is likely the rate-limiting step of the overall conduction process. [ABSTRACT FROM AUTHOR]