(535a) Reforming Kinetics of Methane, Ethane and Ethanol within a Ni-Ysz Anode

Solid Oxide Fuel Cells (SOFCs) have the ability to produce electrical energy at high efficiencies and also have an advantage over some other fuel cell technologies in that they can run on both fossil and renewable fuels. However, at their high operating temperatures, typically 600-800 C, one expects gas-phase reactions to occur, thereby changing the composition of the fuel stream. These species can then react catalytically within the porous anode. Typically this reaction will be steam reforming to form a mixture of CO and H2 (the steam is produced by electrochemical oxidation of the H2 at the three phase boundary). CO further reacts with the steam via the water-gas-shift reaction to form additional H2. Thus, the ultimate rate of H2 production, which governs the fuel cell performance, is contingent upon both the gas-phase and catalytic reactions. We discuss an approach to quantitatively characterize the reforming reactions and present results for the reforming kinetics of methane, ethane and ethanol. In an operating SOFC the interface between the porous anode structure and the dense electrolyte membrane is completely obscured from direct observation, thus making it difficult to characterize the catalytic reactions occurring within the anode. Our experiment is designed (cf. Fig. 1) to create an envi-ronment that is much more amenable than the fuel cell itself for the investigation of the catalytic kinet-ics. This assembly is placed within a furnace. The reactants and products are monitored by mass spec-troscopy. The experimental results are interpreted using a model that incorporates channel gas flow, po-rous-media transport, and elementary heterogeneous chemical kinetics. We have done mercury po-rosimetry experiments and TEM measurements to determine the transport parameters of the anode. To verify that the model is consistent with respect to these transport properties, experiments with non-reactive gases were performed. These data are consistent with the transport model predictions, with the only assigned parameter being the tortuosity. The original microkinetic reforming model was modified to incorporate the results of DFT plane wave calculations to determine the energetics of the specific sur-face reactions that are involved in the reforming and water gas shift reactions. For CH4, the model pre-dictions based on these DFT results agree quite well with the data for both steam and dry reforming at 700 and 800¨¬C. Currently we are extending the mechanism to C2H6 and C2H5OH. This combination of modeling and experiment is providing valuable insight into the details of on-anode reforming. In particular, it allows us the opportunity to explore in a quantitative manner the ef-fects of changing properties of the anode (e.g., porosity, nature of the metal used, the metal loading). This in turn will directly affect the rate of heat release within the anode. The understanding that emerges from this analysis can play an important role in developing the optimal design of anode structures for solid-oxide fuel cells.