Alessandra Carbone

Optical and sensing features of TPPS4 J-aggregates embedded in Nafion® membranes: influence of casting solvents

The tetraanionic water soluble meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS4) can be easily embedded into Nafion®, obtaining membranes which exhibit interesting optical properties strongly dependent both on the aggregation extent and on the organic solvent used for the re-cast procedure.

Conductivity and dielectric relaxation in crosslinked PVA by oxalic and citric acids

In this work we investigated polyvinyl alcohol films which we crosslinked at various crosslinking degrees by oxalic and citric acids for the fuel cell applications. We studied the effects of the crosslinking on structure, thermal properties, electric conductivity and dielectric relaxations. The glass transition temperature is increased indicating the lowering of the local mobility of the polymer chains. X-ray diffraction showed the presence of non-dissociated acid phases in dried samples. The Dc conductivity increases by increasing both the relative humidity and the temperature obeying to an Arrhenius law with activation energy compatible with proton conductivity type. The Ac conductivity studied between 10−1 Hz and 1 MHz showed a power law response in the high frequency range. This behavior characterizes the charge transport in disordered materials. At low frequencies the Ac conductivity is governed by the electrode/sample interface polarization. The use of the dielectric permittivity indicates the presence of a relaxation process attributed to electrode/sample interface polarization and another relaxation process attributed to alpha relaxation of the polyvinyl alcohol chains.

Comparative Investigation on Nano-Sized SiO2 as a Filler for Proton Exchange Membranes (PEM) Fuel Cells

A commercial hygroscope SiO2 was used as an inorganic filler in a Nafion ® polymeric matrix. The influence on chemical-physical properties and electrochemical behaviour in Polymer Electrolyte Fuel Cells (PEFCs) was investigated in terms of amount and particle size of the introduced inorganic compound. Such SiO2 has got a good water retention capacity that improves the water uptake and contributes to improve the stiffness of the developed membranes, probably making more efficacy in the medium temperature operation. Current density values of about 720mW/cm 2 and 640W/cm 2 at 80°C and 110°C (0.6V and 100%RH), respectively were reached from the NSiO2 membrane containing a 5%wt/wt of oxide with a particle size of 7 nm. Such result compared to a home-made bare Nafion membrane showed an important improvement, high lightening the benefit of the inorganic filler when PEFC operates at medium temperature.

Double filler reinforced ionomers: a new approach to the design of composite membranes for fuel cell applications

A novel approach to mechanically reinforce polymer electrolyte membranes for fuel cells was developed by using hydrophilic zirconium phosphate (ZP) and hydrophobic fluoroalkyl zirconium phosphate (ZF) as a two-component mixed filler of a short-side-chain perfluorosulfonic acid (PFSA) membrane. Composite membranes filled with 10 wt% ZF and 5 wt% ZP have a strongly enhanced elastic modulus (E) and yield stress (σY) with respect to the unmodified PFSA (ΔE/E ∼ 300%, ΔσY/σY ∼ 95% at 70 °C and 80% relative humidity (RH)) and to the single filler membranes with optimized ZP or ZF loadings. In the RH range 50–95%, the in-plane conductivity of the mixed filler membrane is comparable with that of the unmodified PFSA, both at 80 and 110 °C, in spite of a lower water content. At 50% RH, the mixed filler membrane shows better fuel cell performance in H2/air than the neat PFSA in terms of higher OCV, lower H2 crossover and greater power density, with peaks of 0.82 W cm−2 at 80 °C, and 0.70 W cm−2 at 110 °C.