Gradual internal methane reforming in intermediate-temperature solid-oxide fuel cells

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 H2O/CH4 even lower than 1 at 700 degrees C. No carbon deposition could be detected after 100 h of operation. Electrochemical measurements, carried out by impedance spec troscopy on cone-shaped microelectrodes of lanthanum chromite, show that the overpotential resistance under H-2/H2O is lower than under CO/CO2 and much lower than under CH4/H2O. 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.