H-2 and CO oxidation process at the three-phase boundary of Cu-ceria cermet anode for solid oxide fuel cell

摘要

Cu-ceria cermets have been widely investigated as the anode materials for solid oxide fuel cells (SOFCs) that operated with hydrocarbon fuels. However, the anode reaction processes are not clear yet, especially those at the ceria-Cu-gas three phase boundary (3 PB). This work investigates samaria-doped ceria (SDC)-Cu-gas 3 PB reaction kinetics for the oxidation of H-2 and CO, the products from hydrocarbons via external and internal reforming. Electrochemical conductivity relaxation measurement demonstrates that Cu is a synergistic catalyst that can significantly increase the reaction rate. The reaction at 3 PB contributes 813/66.8% of H-2/CO oxidation when 5.4% SDC surface is covered with Cu particles. Combining with AC impedance analysis, elementary steps are proposed for the reaction at 3 PB. Water vapor combining to oxygen vacancy and carbon monoxide transforming to carbonate are the rate determining steps for the oxidation of H-2 and CO, respectively. Cu-SDC has shown much higher catalytic activity, i.e. about fivefold reaction rate, for the oxidation of CO than H-2. In addition, Cu-SDC electrodes exhibit lower interfacial polarization resistance and lower activation energy for the electrochemical oxidation of CO than H-2. Consequently, CO is easier to be oxidized than H-2 when the Cuceria anode is fueled with syngas, the reforming product from hydrocarbons. (C) 2017 Elsevier B.V. All rights reserved.