Nickel-Based Anodes for Single-Chamber Solid Oxide Fuel Cells: A Catalytic Study
Single-chamber solid oxide fuel cells (SOFCs) are an alternative concept to traditional SOFCs. Conventional anodes, which consist of a cermet of metallic Ni and an ionic conductor, have to work under a mixture of hydrocarbon and oxygen. This paper presents a catalytic study of C 3 H 8 oxidation by Ce 0.9 Gd 0.1 O 1.95 and nickel. The influences of temperature and oxygen to propane ratio on the nickel oxidation state are clarified, thanks to catalytic tests and electrical conductivity measurements. The results show that the temperature must be higher than a critical value to maintain the nickel particles in the metallic state. Furthermore, at high temperatures, the conversion of the initial mixture leads to the water-gas-shift equilibrium.
Single-Chamber SOFCs with a Ce0.9Gd0.1 O 1.95 Electrolyte Film for Low-Temperature Operation
Single-chamber solid oxide fuel cells (SOFCs) with an anode-supported Ce 0 . 9 Gd 0 . 1 O 1 . 9 5 electrolyte were operated in a mixture of butane and air at furnace temperatures of 200-300°C. The electromotive force (emf) of the cell and the voltage drop were strongly influenced by the catalytic activity of the anode for the partial oxidation of butane. The promotion of hydrogen formation by the addition of Ru to the anode caused an increase in the emf and a reduction in the voltage drop. As a result, stable power densities of 44 and 176 mW cm - 2 were obtained at 200 and 300°C, respectively.
Effect of varying titania surface coverage on the chemisorptive behavior of nickel
Abstract Temperature-programmed desorption (TPD) of CO and H2 from nickel surfaces containing varying amounts of titania showed that the effects of titania adspecies are predominantly short-ranged. Titania surface species block CO adsorption at strongly bound sites (believed to be sites atop individual Ni atoms) corresponding to heats of adsorption in the range 134–139 kJ · mol−1; in addition, titania enhances adsorption into more weakly bound sites (believed to be bridging and hollow sites between Ni atoms) with heats of adsorption from 91 to 107 kJ · mol−1. For hydrogen adsorption, overall adsorption strength was increased with increasing concentration of surface titania. In addition, a new, activated adsorption state was created and is believed to be associated with hydrogen at sites on titania. The variations of the initial sticking coefficients of CO and H2 as a function of titania precoverages show that at low titania coverage each Tiox moiety influences approximately 4–10 Ni surface atoms. The long-range electronic influence of titania at a concentration of 0.1 monolayer was estimated to be responsible for only a 6-kJ · mol-1 decrease in the CO heat of adsorption. Qualitatively, similar results were found for an alumina-containing Ni surface, although alumina appears to be more poorly dispersed than titania on Ni. This suggests that the effects of metal oxide species on metal surfaces may be generalized to include irreducible support materials.