A study of direct-conversion SOFC with n-butane at higher fuel utilization

The performance of solid-oxide fuel cells (SOFCs) with Cu-ceria yttria-stabilized zirconia anodes in n-butane at 973 K has been studied as a function of fuel conversion. In order to simulate the local anode environment at high fuel utilization, n-butane was oxidized with O-2 in a separate reactor before sending the fuel to a small 0.45 cm(2) cell. When n-butane oxidation was carried out over a ceria catalyst at 973 K, the main oxidation products were CO2 and H2O. By comparing the performance of the cell in the partially oxidized fuel to the performance of the cell in n-butane diluted in He, it was demonstrated that CO2 and H2O have only minimal effect on cell performance other than to dilute the fuel. This dilution of the fuel results in a significant decrease in performance at higher fuel conversions. When n-butane oxidation was carried out over a Pd-ceria catalyst, significant amounts of H-2 were generated by steam reforming of hydrocarbons with the steam generated by hydrocarbon oxidation. As a result, the maximum power density generated by the cell increased with fuel conversions up to 30% and remained very high at fuel conversions up to at least 70%. Based on these results, it is suggested that the inclusion of a steam-reforming catalyst within the anode compartment of direct-conversion SOFC should improve their performance at high fuel utilization. (C) 2003 The Electrochemical Society.