Effects of dilution on methane entering an SOFC anode

Methane and other hydrocarbons such as propane and butane are ideal fuels for SOFCs operating in portable devices for domestic or leisure use [J. Power Sources 71 (1998) 268]. This paper addresses the fuel entry conditions necessary for such devices. A gas manifold system was connected to a micro-tubular zirconia cell 2 mm diameter with lanthanum strontium manganite cathode and nickel/zirconia/ceria anode. Wire current collectors were used to obtain electrochemical performance data via a potentiostat system. The reaction products from the anode were analysed by mass spectroscopy to elucidate the reaction mechanism, and temperature programmed oxidation allowed the carbon deposition to be evaluated [Proceedings of the 4th European Solid Oxide Fuel Cell Forum, Luzern, July 2001, p.151]. Carbon deposition was substantial near open circuit voltage, when little oxygen was flowing to the anode. Dilution with inert gas or with CO2 caused a significant change in the reaction mechanism. The conclusion was that diluted methane could be fed directly into the SOFC, and that particular compositions (e.g. biogas at 30% methane and 70% carbon dioxide) gave optimum performance with little carbon fouling.