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.
NiMo-calcium-doped ceria catalysts for inert-substrate-supported tubular solid oxide fuel cells running on isooctane
Abstract A calcium-doped ceria (Ce1-xCaxO2−δ, 0 ≤ x ≤ 0.3) has been applied as a ceramic support in NiMo-based catalysts for an internal reforming tubular solid oxide fuel cell running on isooctane. Introducing calcium into the CeO2-based ceramic was found to improve conductivity of Ce1-xCaxO2−δ. The Ce0.9Ca0.1O2−δ (x = 0.10) sample exhibited an optimum conductivity of 0.045 S cm−1 at 750 °C. The transport of oxygen ions in Ce1-xCaxO2−δ promoted the catalytic partial oxidation of isooctane in the NiMo–Ce1-xCaxO2−δ catalyst, which increased the fuel conversion as well as H2 and CO yields. As a result, the NiMo–Ce0.9Ca0.1O2−δ (x = 0.10) catalyst exhibited a high isooctane conversion of 98%, and the H2 and CO yields achieved 74% and 83%, respectively, for reforming of isooctane and air at the O/C ratio of 1.0 at 750 °C. Furthermore, the NiMo–Ce0.9Ca0.1O2−δ catalyst has been applied as an internal reforming layer for an inert-substrate-supported tubular solid oxide fuel cell running on isooctane/air. Due to its high reforming activity, the single cell presented an initial maximum power density of 355 mW cm−2 in isooctane/air at 750 °C and displayed stable electrochemical performance during ~30 h operation. These results demonstrated the application feasibility of the NiMo–Ce0.9Ca0.1O2−δ catalyst for direct internal reforming solid oxide fuel cells running on isooctane/air.
Effect of superficial gas velocity on the particle temperature distribution in a fluidized bed with heat production
The heat transfer behavior of particles and gas in an olefin polymerization fluidized bed was numerically analyzed using an in-house developed 3-D computational fluid dynamics discrete element model (CFD-DEM). First the implementation of the model was verified by comparing simulation results with analytical results. A constant volumetric heat production rate was implemented in the particle energy equation to mimic the heat production due to the polymerization reaction. It was found that the probability density function (PDF) of the particle temperature becomes more homogeneous with increasing superficial gas velocity. Furthermore, instantaneous snapshots of the thermal driving force (the difference between the single particle temperature and bed-average gas temperature, Tp− ) for different heat production rates provide detailed insight in the particle temperature distribution inside the fluidized bed. The time- and bed-averaged particle convective heat transfer coefficient, which was calculated by Gunn׳s correlation, was found to be independent of the superficial gas velocity. This is explained by the fact that the relative velocity of gas and particles in the emulsion phase, where most of the particles and gas interact, is hardly influenced when increasing the gas superficial velocity. From the spatial distribution of Nusselt number, it becomes apparent that the high heat transfer regions are found in the wake of rising bubbles, whereas low heat transfer rates are found in the clouds of the bubbles.