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

A pulse reactor technique was utilized to measure CH 4 oxidation rates under solid oxide fuel cell (SOFC) anode conditions. La 0.75 Sr 0.25 Cr 0.5 Mn 0.4 X 0.1 O 3−δ powders (LSCMX, X = Co, Fe, Mn and Ni) were synthesized and were found to be phase-pure perovskites, space group R 3̅ C . All compositions were determined by XRD to be stable up to 800 °C in dry 20% CH 4 /N 2, at which point small amounts of a Ruddlesden-Poepper (RP) phase A 2 BO 4-δ were detected. At higher temperatures, MnO and metallic Fe were observed, but no Ni and Co phases could be detected. Measurements of the CH 4 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, CH 4 oxidation rates for LSCMCo and LSCMNi were similar to the rates on LSCM. At higher temperatures, CO 2 and CO production on LSCMCo and LSCMNi samples was enhanced, which was ascribed to the exsolution of Co and Ni from the perovskite lattice. CO 2 production rates on LSCM and LSCMFe continuously decreased with oxygen stoichiometry whereas LSCMCo and LSCMNi produced CO 2 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 CH 4 reaction rate of the materials tested.