Pulse Reactor Studies to Assess the Potential of La_0.75Sr_0.25Cr_0.5Mn_0.4X_0.1O_3-δ (X = Co, Fe, Mn, Ni, V) as Direct Hydrocarbon Solid Oxide Fuel Cell Anodes

Abstract

A pulse reactor technique was utilized to measure CH4 oxidation rates under solid oxide fuel cell (SOFC) anode conditions. La0.75Sr0.25Cr0.5Mn0.4X0.1O3−δ powders (LSCMX, X = Co, Fe, Mn and Ni) were synthesized and were found to be phase-pure perovskites, space group R3̅C. All compositions were determined by XRD to be stable up to 800 °C in dry 20% CH4/N2, at which point small amounts of a Ruddlesden-Poepper (RP) phase A2BO4-δ were detected. At higher temperatures, MnO and metallic Fe were observed, but no Ni and Co phases could be detected. Measurements of the CH4 reaction rates on LSCMX samples provided indirect evidence for the instability of Ni and Co containing perovskites at temperatures higher than 650 and 750 °C, respectively. At 600 and 650 °C, CH4 oxidation rates for LSCMCo and LSCMNi were similar to the rates on LSCM. At higher temperatures, CO2 and CO production on LSCMCo and LSCMNi samples was enhanced, which was ascribed to the exsolution of Co and Ni from the perovskite lattice. CO2 production rates on LSCM and LSCMFe continuously decreased with oxygen stoichiometry whereas LSCMCo and LSCMNi produced CO2 in two separate regions of oxygen stoichiometry. The second region was attributed to the reduction of Co and Ni, respectively, present either as a metal oxide or in an RP phase. For all temperatures, LSCMFe had the lowest CH4 reaction rate of the materials tested.