Electrochemical oxidation of H2, CO, and CO/H2 mixtures on patterned Ni anodes on YSZ electrolytes

Single-cell solid oxide fuel cell experiments using thin-film, sputter-deposited Ni pattern anodes microfabricated on single-crystal yttria-stabilized zirconia (YSZ) electrolyte disks have been performed to examine the electrochemical oxidation of H-2, CO, and CO/H-2 mixtures. Porous lanthanum strontium manganate (LSM)/YSZ cathodes have been used and characterized in separate symmetric cell experiments such that Ni anode overpotentials and impedances can be isolated. Post-test scanning electron microscopy imaging revealed that at the high temperatures (735-850 degrees C), the 100-nm thin Ni patterns broke up into interconnected regions resulting in three-phase boundary lengths that roughly correlated with the original coverage area of the pretested dense Ni patterns. Electrochemical characterization for H-2, CO, and CO/H-2 oxidation under dry and wet (similar to 4% H2O) feeds showed that the interconnected anode overpotentials and polarization resistances correlated with the original Ni pattern area for the various pattern geometries. Higher activation overpotentials and polarization resistances observed for CO in comparison to H-2 were not observed for CO/H-2 mixtures down to 25% H-2. Results indicated detrimental effects of H2O on CO oxidation power densities due to drops in open-circuit voltages without reduction in polarization resistance, and enhancement due to water-gas shift reactions was not seen. Our results provide the basis for insights into H-2 and CO electro-oxidation on Ni/YSZ anodes.