Solid Oxide Fuels Cells (SOFCs) have tremendous potential as efficient and clean energy conversion devices. They are the most desirable fuel cells for stationary power generation and as auxiliary power sources in transport applications. The fuel flexibility and higher efficiency of the SOFC make it a favorable choice over conventional combustion systems. However, there are some major roadblocks to the effective commercialization of SOFC technology. High operating temperatures are required due to low activity of the cathode catalysts, thus dictating the use of more expensive materials for the SOFC components as well as balance of plant. Moreover, the state-of-the-art Nickel –Yttria Stabilized Zirconia (Ni-YSZ) cermet anode catalysts are extremely susceptible to poisoning by sulfur in the fuel, as well as coking on operation with carbonaceous fuels. Ni also tends to sinter at elevated temperatures. Since these fuel cells are envisioned to be used with Coal and Natural Gas as fuels, stable and active anode catalysts are required.
There is a need for significant work in developing and testing new catalyst formulations for both electrodes. The cathode reaction is the reduction of gas phase oxygen to form oxide ions that are then transported through the electrolyte to the anode. At the cathode, the drive is to develop perovskite oxide materials which are capable of conducting and activating oxygen at lower temperatures and are more active than the state of the art Lanthanum Manganite based catalysts. The current research focused on developing new formulations based on doping of Lanthanum Ferrites and exploring their properties and their activity and performance as SOFC cathodes. The effect of varying the dopant levels on the physiochemical properties as well oxygen mobility and oxygen content in the samples is explored. The effect of substitution of the La ions with Sr on the A-site is studied in detail and the oxygen activation and transport properties are explored as a function of Sr content. Methane oxidation is used as a model reaction to study oxygen activation energies over the materials. X-ray Photoelectron Spectroscopy and Mössbauer Spectroscopy are used to study the surface and bulk properties. Additional doping with aliovalent metals such as Zn, Cu and Ni on the B-site is studied and the surface and bulk properties are examined using X-ray Diffraction (XRD), Thermogravimetric analysis (TGA), X-Ray Absorption Fine Structure (XAFS) techniques and using methanol as a probe molecule. Further in-sight into oxygen activation properties is obtained by CO2 Temperature-Programmed Oxidation (TPO) and methane oxidation reactions.
On the anode side, the emphasis is in exploring the nature and mechanism of deactivation of the state of the art Nickel-Yttria stabilized Zirconia (Ni-YSZ) catalysts. The effect of water in sulfur poisoning on the catalyst is examined through steady-state reaction testing as well as bulk and surface characterization using XAFS studies and temperature programmed desorption (TPD) experiments. Based on these results, new formulations are explored and tested for their activity for the various anode reactions as well as the tolerance to sulfur poisoning and coking. The new catalyst development is carried out in a two pronged approach. Transition metal based bi-metallic catalysts are explored. Simultaneously, perovskite oxide materials are also tested for their catalytic activity and performance as SOFC anodes. Coking and sulfur tolerance studies are performed and characterization is performed using XPS and TPD studies.