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Dendrimer-encapsulated Pt nanoparticles (G4OHPt) were prepared by chemical reduction at room temperature. The G4OHPt, with average diameters of ca. 2.7 nm, were characterized by X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. Electrocatalytic behavior for oxygen reduction reaction was investigated using a rotating disk electrode configuration in an acidic medium, with and without the presence of methanol (0.01, 0.1, and 1 M). Kinetic studies showed that electrodes based on Pt nanoparticles encapsulated inside the dendrimer display a higher selectivity for ORR in the presence of methanol than electrodes based on commercial Pt black catalysts. Also, the dendritic polymer confers a protective effect on the Pt in the presence of methanol, which allows its use as a cathode in a direct methanol fuel cell operating at different temperatures. Good performance was obtained at 90 °C and 2 bar of pressure with a low platinum loading on the electrode surface. [ABSTRACT FROM AUTHOR]

Pt and Pt-Fe catalysts supported on multiwalled carbon nanotubes (MWCNTs) were prepared by impregnation and reduction at intermediate temperature (400°C). The MWCNTs with diameters ranging from 20 to 100 nm were synthesized by a spray pyrolysis technique. Pt/MWCNTs and Pt-Fe/MWCNT catalysts were characterized by X-ray diffraction, X-ray fluorescence, scanning electron microscope-energy dispersive X-ray analysis, and transmission electron microscopy techniques. The electro-catalytic behavior for the oxygen reduction reaction was investigated in rotating disk electrode configuration in an acidic medium, also in the presence of various methanol concentrations (0.01, 0.1, and 1 M). An anodic shift of the peak potential for methanol oxidation of ~150 mV was observed in the presence of 1 M methanol concentration for the Pt-Fe catalyst compared to the Pt catalyst. Both materials were used as cathodes in a direct methanol fuel cell at 30 and 60°C. A better performance was obtained for the cell based on Pt-Fe/MCWNTs as cathode catalyst. Although slight iron dissolution was observed after two weeks of discontinuous operation, the performance of the Pt-Fe catalyst was larger than the Pt catalyst. [ABSTRACT FROM AUTHOR]

Abstract: A new generation of highly efficient and non-polluting energy conversion and storage systems is vital to meeting the challenges of global warming and the finite reality of fossil fuels. In this work, nanosized Pt/IrO2 electrocatalysts are synthesized and investigated for the oxygen evolution and reduction reactions in unitized regenerative fuel cells (URFCs). The catalysts are prepared by decorating Pt nanoparticles (2–10 nm) onto the surface of a nanophase IrO2 (7 nm) support using an ultrasonic polyol method. The synthesis procedure allows deposition of metallic Pt nanoparticles on Ir-oxide without causing any occurrence of metallic Ir. The latter is significantly less active for oxygen evolution than the corresponding oxide. This process represents an important progress with respect to the state of the art in this field being the oxygen electrocatalyst generally obtained by mechanical mixing of Pt and IrO2. The nanosized Pt/IrO2 (50:50 wt.%) is sprayed onto a Nafion 115 membrane and used as dual function oxygen electrode, whereas 30 wt.% Pt/C is used as dual function hydrogen electrode in the URFC. Electrochemical activity of the membrane-electrode assembly (MEA) is investigated in a single cell at room temperature and atmospheric pressure both under electrolysis and fuel cell mode to assess the perspectives of the URFC to operate as energy storage device in conjunction with renewable power sources. [Copyright &y& Elsevier]

IrO2/Pt catalysts (at different concentrations) were synthesized by incipient wetness technique and characterized by XRD, XRF, and SEM. Water electrolysis/fuel cell performances were evaluated in a 5 cm2 single cell under Unitized Regenerative Fuel Cell (URFC) configuration. The IrO2/Pt composition of 14/86 showed the highest performance for water electrolysis and the lowest one as fuel cell. It is derived that for fuel cell operation an excess of Pt favours the oxygen reduction process whereas IrO2 promotes oxygen evolution. From the present results, it appears that the diffusion characteristics and the reaction rate in fuel cell mode are significantly lower than in the electrolyser mode. This requires the enhancement of the gas diffusion properties of the electrodes and the catalytic properties for cathode operation in fuel cells. [ABSTRACT FROM AUTHOR]

Abstract: A nanocomposite re-cast Nafion hybrid membrane containing titanium oxide calcined at T =400°C as an inorganic filler was developed in order to work at medium temperature in polymer electrolyte fuel cells (PEFCs) maintaining a suitable membrane hydration under fuel cell operative critical conditions. Nanometre TiO2 powder was synthesized via a sol–gel procedure by a rapid hydrolysis of Ti(OiPr)4. The membrane was prepared by mixing a Nafion–dimethylacetammide (DMAc) dispersion with a 3wt% of TiO2 powder and casting the mixture by Doctor Blade technique. The resulting film was characterised in terms of water uptake and ion exchange capacity (IEC). The membrane was tested in a single cell from 80 to 130°C in humidified H2/air. The obtained results were compared with the commercial Nafion115 and a home-made recast Nafion membrane. Power density values of 0.514 and 0.256Wcm−2 at 0.56V were obtained at 110 and 130°C, respectively, for the composite Nafion–Titania membrane. Preliminary tests carried out using steam reforming (SR) synthetic fuel at about 110°C have highlighted the benefit of the inorganic filler introduction when PEFC operates at medium temperature and with processed hydrogen. [Copyright &y& Elsevier]