High-temperature conversion of methane on a composite gadolinia-doped ceria-gold electrode

Direct electrochemical oxidation of methane was attempted on a gadolinia-doped ceria Ce(0.6)Gd(0.4)O(1.8) (CG4) electrode in a solid oxide fuel cell using a porous gold-CG4 mixture as current collector Gold is relatively inert to methane in contrast to other popular SOFC anode materials such as nickel and platinum. CG4 was found to exhibit a low electrocatalytic activity for methane oxidation as well as no significant reforming activity implying that the addition of an electrocatalyst or cracking catalyst to the CG4 anode is required for SOFC operating on methane. The methane conversion observed at the open-circuit potential and low anodic overpotentials seems to be due to thermal methane cracking in the gas phase and on the alumina surfaces in the cell housing. At high anodic overpotentials, at electrode potentials where oxygen evolution was expected to take place, the formation of CO(2) increased sharply. No carbon deposition was observed on the CG4 electrode after operating at 1000 degrees C during 350 h of total testing time with partial pressures of methane and steam in the range of 0.5-33 and 3-26 kPa, respectively. (C) 1999 Elsevier Science B.V, All rights reserved.