Characterization and Application of Metal Composite Nano-Catalysts for Improved Solid Oxide Fuel Cell Performance and Stability with Hydrocarbon Containing Fuels

Implementation of nano-catalyst materials into solid oxide fuel cell (SOFC) electrodes to improve performance and stability has been widely studied. Addition of the nano-catalysts into an electrode structure serves to enhance the electrochemical performance of the SOFC by increasing the Triple Phase Boundary (TPB) area, improving redox stabilization, and modifying reaction kinetics of hydrocarbon gases that cause anode degradation due to carbon deposition. Typical Ni-based cermet anodes suffer from anode deactivation due to carbon build up under hydrocarbon flows. Carbon builds up and covers the TPB area which results in poor electrochemical performance. Larger carbon deposits can block pores within the anode microstructure which leads to gas diffusion issues. Carbon buildup also causes mechanical stresses to the electrode due to volumetric changes which can lead to fracture and complete failure of the cell. This work studied nano-catalyst decoration of the Ni-based cermet anodes with catalysts that promote internal reforming to protect against coking. The addition of active metal components and ceramic reforming promoters were investigated. Multi-component systems with several catalysts were also examined. Uniform incorporation of nano-catalyst into the anode microstructure was achieved through a patented liquid phase surfactant assisted process (using various catechol surfactants). Deposition loading densities and distribution of nanoparticles was controlled by altering the surfactant and catalyst solution concentrations. This work defined initial morphology and studied the coarsening/annealing kinetics of nano-catalysts used for enhanced solid oxide fuel cell (SOFC) operation. Nano-catalyst depositions were performed on flat single crystal surfaces using a bio-inspired surface modification technique. 3D profiles of the nanoparticles at various coarsening stages were obtained using atomic force microscopy (AFM). X-ray photoelectron spectroscopy (XPS) was used to track the changes in composition. Figure 1 shows AFM imaging of single component cerium oxide and cobalt oxide depositions on flat single crystal yttrium stabilized zirconia (YSZ) before and after 24 h of annealing in reducing conditions. Impregnated SOFCs were tested for 200+ h in constant load while operating under high methane fuel streams. Fuel compositions were selected to have high hydrocarbon content to accelerate degradation. Deposition techniques were optimized for multi-component internal reforming catalysts to obtain sustained performance enhancement. Current-voltage-power (I-V-P) measurements and electrochemical impedance spectroscopy (EIS) results were used for evaluation. Post-mortem microstructure and chemistry characterizations were used in analysis. Impregnated SOFCs demonstrated greater than 50% sustained improvement in harsh environments in long-term tests where the anode was subjected to 40% CH 4 for 200+ h. Acknowledgements: Work supported by a subcontract under the GE Aerospace’s US DOE- ARPA-E project (DE-AR0001344) entitled “FueL CelL Embedded ENgine (FLyCLEEN)”. Material characterization and imaging work was made possible with the support of the West Virginia University Shared Research Facilities. Figure 1