Classification criteria for solid oxide fuel cell electrode materials

In an attempt to establish comparison criteria for the electrocatalytical properties of electrode materials, systematic measurements were carried out on microelectrodes of simple shapes. The overpotential resistances were normalized with respect to the electrode triple-phase boundary length and the electrode capacitances to the electrode interface area. Results obtained on metals such as Ag, Pt, Au, and Ni, and on some oxides, under either cathodic or anodic atmospheres, show marked differences which allow us to classify them. The positions of several materials in the cathode and anode material lists can be significantly different, indicating different electrocatalytical requirements under solid oxide fuel cell cathode and anode atmospheres. The dearest example is silver, which exhibits excellent electrocatalytical properties for the oxygen electrode reaction and very poor properties for hydrogen oxidation.</p

Solvation of sulphonic acid groups in Nafion® membranes from accurate conductivity measurements

The wide degree of scatter of experimental data shows unambiguously that Nafion®117 conductivity is very sensitive to climatic conditions, temperature and relative humidity. In order to allow equilibrium with the surrounding atmosphere to be reached rapidly, a conductivity cell, adapted to a small size membrane samples, has been designed. Conductivity measurements have been carried out by electrochemical impedance spectroscopy (EIS) between 10 °C and 95 °C in a broad domain of relative humidity, i.e., 10–98%. The measurement set up provides reproducible data with a total uncertainty of 30% in a large range of conductivity values. These accurate data enable a power relationship to be proposed at constant temperature between conductivity and relative humidity. This suggests that the solvation process of a sulphonic acid group involves four water molecules. Based on the assumption that a proton mobility depends weakly on temperature, a solvation enthalpy of a sulphonic acid group by water of −135 kJ mol−1 is deduced from conductivity variations with the temperature. Keywords: Proton conductivity, Nafion®117, Measurement device, Solvation, Enthalp

Synthesis, Testing, and Characterization of a Novel Nafion Membrane with Superior Performance in Photoassisted Immobilized Fenton Catalysis

International audienceA new type of Nafion/Fe structured membrane ensuring faster kinetics, higher efficiency, and mechanical properties has been prepared and will be compared in its performance with the Fe-exchanged commercial Dupont 117 Nafion/Fe membrane during the abatement of model organic compounds. During the casting of the laboratory Nafion sample, the iron ions were introduced directly into the Nafion oligomer solution. This novel laboratory Nafion/Fe was tested as an immobilized catalyst in the degradation of several toxic pollutants showing a faster photoassisted degradation kinetics and a wider effective photocatalytic pH range compared to the Fe-exchanged commercial Dupont 117 Nafion/Fe membrane. When carrying out Ar ion sputtering of the 50 topmost catalyst layers, evidence is presented by X-ray photoelectron spectroscopy that Fe ions are found in the inner Nafion layers and seem to be responsible for the immobilized photoassisted Fenton processes leading to the degradation of 4-chorophenol (4-CP) taken as a model organic pollutant for the degradation process reported in this study. In the laboratory sample, the iron oxy/hydroxy Nafion moiety undergoes a transition to a more stable Nafion/Fe species during 4-CP degradation as determined by X-ray diffraction. This more stable form shows a higher iron dispersion and crystallinity compared to the fresh sample and is stabilized by the Nafion matrix avoiding the formation of separate iron phases. By infrared absorption (Fourier transform infrared), evidence is presented for the band of akaganeite-like species at 870 cm-1 on the laboratory Nafion/Fe sample. This band disappears after 4-CP degradation because of the formation of the more highly dispersed iron species. Sputtering experiments show a decrease of F-containing groups in the laboratory Nafion/Fe samples closer to the catalyst upper layer while the amounts of Fe, C, and in particular O species increase in the topmost layer(s). In particular, the oxygenated species develop in the Nafion/Fe up to 50 Å below the catalyst surface. These species remain stable during the long-term Nafion/Fe degradation of 4-CP. Dynamo-mechanical analysis performed on laboratory Nafion/Fe membrane samples revealed that these membranes possessed a greater mechanical modulus and resistance than the commercial Dupont 117 Nafion membrane

Chemically controlled protective film based on biphenyl derivatives for high potential lithium battery

International audienceHigh potential cathodes are of strong interest to improve lithium-ion battery performances, nevertheless, no compatible electrolyte above 4.5–4.8 V vs Li+/Li was found yet. The main strategies involved the use of protective film inhibiting and/or delaying electrolyte degradation. In this context, we focused on the use of adapted modified biphenyls to form a protective film at the positive electrode. Particularly phosphate biphenyl derivatives oxidation permits to produce a protective film which significantly decreases the self-discharge without compromising the lithium intercalation kinetic