Low and intermediate temperature metal supported solid oxide fuel cell operating with practical fuels

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Solid oxide fuel cells (SOFC) are high temperature fuel cells that can achieve high electrical efficiency and be used in combined heat and power. Because of the high operating temperatures, the electro-catalyst is usually nickel, which is also an active reforming catalyst. SOFCs are, therefore, fuel-flexible and can run with natural gas, alcohol, LPG, syngas (i.e. products from gasification or reforming, usually composed primarily of CO and H2), etc. State-of-the-art SOFCs operate in the range 800-1000C. Because of such high temperatures, materials are limited to ceramic ones, thus making SOFC expensive and brittle. In order to reduce cost and improve durability and ruggedness, efforts are being made to reduce the operating temperature below 750C so that metals could be used as support; such design is called metal-supported cell (MSC). If fuel reforming is desired, the cell temperature should not be too low; for MSC, temperatures around 625-700C (Intermediate Temperature) would be ideal. If reforming is not an issue (e.g. with H2 or eventually syngas), then the cell temperature could drop in the 500-600C range (Low Temperature). **An important obstacle against the direct use of hydrocarbons in SOFC is the propensity for carbon to deposit on the Ni electro-catalyst (also referred to as coking). In addition, most of the practical fuels contain sulphur, which is also a problem in conventional SOFC anodes. MSC actually offers the possibility to tackle both the coking and sulphur issues. Design of carbon and sulphur resistant MSC is the primary objective of the proposed research.**The first point is that in MSC, the anode is usually comprised of Ni and some ceria-based materials, such as samaria-doped ceria (SDC). Ceria is known to increase both coking and sulphur resistance. Ceria is also active toward oxidation reactions. The second point is that in MSC, the anode can be designed so that part of the metal support becomes the primary electronic conductor of the anode; this function is usually that of Ni in non-metal supported SOFC cells. The implication is that the Ni content can be then considerably reduced. In the proposed work we are aiming at making MSC anodes with highly dispersed and non-coarsening Ni nanoparticles. We will fabricate MSC button cells following two MSC fabrication methods: 1) Ni-SDC infiltrated in YSZ backbone with YSZ electrolyte and 2) Ni-SDC co-firing with SDC electrolyte. The MSC button cells will then be tested under various conditions of temperatures and feed compositions in an electrochemical test station to assess their performance, stability, and resistance to coking and sulphur. **In addition to the experimental work, we will also develop elementary-based reaction single cell simulations to serve as a design tool to optimize the anode. These simulations will be developed in Comsol Multiphysics and will be able, among others, to predict carbon deposition. The kinetics of charge transfer reactions on Ni-SDC is very important in this model, but they are currently not known. An in-depth kinetic study using pattern anode, for which we have developed some expertise, will also be carried out. Additional kinetic studies will also be pursued for chemical reactions on Ni-SDC, such as water-gas shift and CO disproportionation. The simulation will be validated using the MSC electrochemical tests over a wide range of operating conditions. The validated model will then be used to study the effect of operating and structural parameters, such as anode thickness and porosity, temperature or feed composition, in order to evaluate conditions that lead to stable operation using methane and syngas fuels. Whenever possible, those conditions will be checked experimentally.