Catalytic study of SOFC electrode materials in engine exhaust gas atmosphere

A single chamber solid oxide fuel cell (SC-SOFC) is a device able to produce electricity from a mixture of hydrocarbons and oxidant. An innovative application of this system would be to recover energy from exhaust gas of a thermal engine. This paper presents a study of stability and catalytic behaviour of electrode materials composing the cell in a mixture of hydrocarbons (propane, propene), oxygen, carbon monoxide, carbon dioxide, hydrogen and water corresponding to a composition of exhaust gas. A screening of four cathode materials was done, some well-known materials in literature and leading to highest performances such as La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF), Sm_0.5Sr_0.5CoO_3−δ and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ and a last one Pr₂NiO_4+δ (PNO) very promising for conventional SOFCs. Anode material was a cermet composed of nickel and Ce_0.9Gd_0.1O_1.95 which was also selected as the electrolyte material. Chemical stability tests and catalytic activity studies in the gas mixture were performed on the raw materials and have led to a first selection among cathodes. Two hydrocarbons/oxygen ratios (R = HC/O₂) were investigated for materials tests considering the gas mixture stability at high temperature (600 °C): R = 0.21 and 0.44. LSCF and PNO were considered as the most stable cathode materials, besides LSCF demonstrated a lower catalytic activity towards hydrocarbon partial oxidation than PNO especially for the R = 0.44 ratio. As for the anode side, nickel was tested regarding its catalytic activity towards hydrocarbons oxidation. It exhibited catalytic activity towards hydrocarbons partial oxidation, especially for the oxygen-lean ratio (0.44), which gradually decreased while lowering temperature from 620 to 450 °C.