Gradual Internal Methane Reforming in Intermediate‐Temperature Solid‐Oxide Fuel Cells

Abstract

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.

SOFC Long Term Operation in Pure Methane by Gradual Internal Reforming

“…Below 1/3, the system will not release enough steam to ensure itself complete conversion, and methane will diffuse into the cermet yielding fast coking. More details concerning this concept will be found in our previous work (7)(8)(9)(10)(11)(12). This simplified principle mechanism was applied here study and the faradaïc efficiency was first optimized in H 2 above 1/3 by adjusting the experimental parameters (fuel concentration and flow rates).…”

Thin Film Microelectrodes in SOFC Electrode Research

“…A reference electrode is thus not required to separate the properties of the counter and working electrode. The same property also applies to microelectrodes realized by pressing sharpened electrode crystals or wires onto the electrolyte surface [27][28][29][30][31][32][33][34][35][36][37][38][39][40]. In these cases, however, the advantage of having morphologically and chemically well-defined interfaces is lost.…”

Nanocomposite Catalysts for Steam Reforming of Methane and Biofuels: Design and Performance

“…2. Replacing doped zirconia by perovskites (mainly, doped La chromites) promoted by metals active in SR (Ni or precious metals, mainly, Ru) (Peña-Martínez et al, 2006;Sfeir et al, 2001;Sauvet & Irvine, 2004;Vernoux et al, 1998;Wan & Goodenough, 2005). In this case, insufficient conductivity of perovskites in reducing conditions could be a problem (Plint et al, 2006).…”