Gradual internal reforming is based on local coupling between steam reforming of the fuel which occurs on a catalyst and hydrogen electrochemical oxidation which occurs at the electrode triple-phase perimeter. In order to demonstrate the feasibility of this strategy, the catalytic and electrochemical properties of lanthanum chromite, pure and impregnated with ruthenium, were investigated. Ruthenium supported on lanthanum chromite exhibits very good catalytic activity for the steam reforming of methane. Full conversion of steam is obtained for ratios H20/CH4 even lower than 1 at 700°C. No carbon deposition could be detected after 100 h of operation. Electrochemical measurements, carried out by impedance spectroscopy on cone-shaped microelectrodes of lanthanum chromite, show that the overpotential resistance under H2/H20 is lower than under CO/CO2 and much lower than under CH4/H20. In the presence of ruthenium, impedance diagrams under hydrogen and methane are fairly similar and gas analysis shows that some methane is reformed. This observation demonstrates that gradual internal reforming can be implemented. A detailed analysis of the electrode impedance diagrams shows that the so-called high-frequency semicircle is virtually independent of the nature of the atmosphere. This indicates that it is not directly related to any chemical or electrochemical step of the electrode reaction.
International audienceThis paper deals with the performance of anhydrous proton-conducting polymers obtained by blending modified Nafion® membranes with proton conducting ionic liquids (PILs). It has been shown that the conductivities depend more on the PIL uptake than on its intrinsic conductivity. Conductivities at 130°C approaching those of current Nafion membranes at 80°C and 98% relative humidity were obtained with the best blends. These data allow considering MEA operating at 120-130°C based on membrane and electrodes incorporating these blends. This is clearly a positive feature for an implementation in hybrid vehicles powered by proton exchange membrane fuel cells (PEMFCs) operating above 100°C. Lastly, preliminary results for a PIL based on a half-neutralized diamine show an improvement in oxidation and, provided that the neutralization is optimized, a neat reinforcement of the Nafion membrane can be expected
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 clearest example is silver, which exhibits excellent electrocatalytical properties for the oxygen electrode reaction and very poor properties for hydrogen oxidation.
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