Spinels for use as Methane Reforming Catalysts in Fuel Flexible Solid Oxide Fuel Cells

Abstract

Several compositions of Ni- and Co- containing aluminate spinels have been synthesized in a reproducible manner, each of which are potential catalyst materials for methane reforming in-situ during SOFC operation. Reduction and reoxidation cycles can be performed at or below typical intermediate temperature SOFC operating temperatures. The defect spinel structure remains intact if a zirconia stabilizer is used. The microstructure of the defect spinel support following reduction varies depending on calcination temperature. The faceted microstructure of the defect spinel support and the metallic particles contributes to the excellent catalytic activity of the material. NiAl2O4 and Ni0.5Co0.5Al2O4 catalysts had nearly 100% CH4 conversion over 16 hours at GHSV=60,000hr-1, with the Co-containing sample losing some activity over the test period. H2 and CO selectivities remained around 80% throughout the test. Less faceted defect spinel catalyst conversion percentages increased with reactor temperature, indicating further reduction of metal from the defect spinel support during testing. Using methane fuel containing 20ppm H2S, conversion and CO selectivity dropped to 0% after 6 and 12 hours in less faceted and more faceted defect spinels, respectively. The spinels can be reduced in methane but acquire a significant amount of carbon buildup with low concentrations of CO. The spinels have been incorporated into a Ni/YSZ cermet anode in 10 and 20 weight percent quantities to study the effect of the spinels on the cell performance and microstructure. Peak power densities in H2 fuel were 0.0153, 0.0076, 0.0025, and 0.0153 W/cm2 for samples containing NiAl2O4, Ni0.5Co0.5Al2O4, CoAl2O4, and no spinel, respectively. In CH4 fuel, peak power densities were 0.0115, 0.0089, 0.0089, and 0.0127 W/cm2 for samples containing NiAl2O4, Ni0.5Co0.5Al2O4, CoAl2O4, and no spinel, respectively. Increasing Co content reduces peak power density values, with the NiAl2O4-containing sample having a similar peak power density to the control Ni/YSZ sample.