Study of the Direct Oxidation of Methane in Solid Oxide Fuel Cells

Abstract

Solid oxide fuel cells (SOFCs) are electrochemical devices that have received great interest recently because of their promise for clean and efficient power generation. Since SOFCs generate electricity directly through electrochemical processes that do not involve combustion, fuel cells are not limited by the Carnot cycle and thus, very high efficiency can be achieved. For instance, current state-of-the-art fuel cells can reach 50% efficiency while that of conventional power generation devices are generally below 30%. The high efficiency is a key mean that will enable the use of fossil fuels at reduced carbon emissions. The ideal fuel for fuel cells is hydrogen. However, hydrogen is not available directly in nature but must be made using another fossil fuel and/or energy sources. For the immediate future, except for a few niche markets, fuel cells will have to use hydrocarbons as fuel. The ideal hydrocarbon fuel would be natural gas since a natural gas infrastructure readily exists. Natural gas has indeed been used to run various fuel cells. However, natural gas cannot be used directly as a fuel for fuel cells because of its low reactivity. Natural gas must be converted to more reactive components, typically to carbon monoxide and hydrogen via the steam reforming or partial oxidation processes, before being injected in the fuel cell. The extra conversion step consumes extra energy and requires an additional reactor, thus making the overall system complex and reducing the overall efficiency. The situation is even worst if Polymer Electrolyte Membrane Fuel Cells (PEMFCs) are used since these fuel cells cannot tolerate any presence of CO and additional reactors are thus needed to convert CO to H{sub 2} and to remove residual CO from the gas stream. High temperature fuel cells, especially solid oxide fuel cells (SOFCs), due to their high operating temperatures, have the potential to operate directly on natural gas. The direct operation on natural gas represents a significant simplification of the system, resulting in lower cost and higher system efficiency. To date, despite several recently published works, there is not a clear demonstration of the possibility to operate SOFCs directly on natural gas. The actual reactions that happen at the fuel cell anode are still not well understood. In this one-year project, we explored the possibility of direct methane oxidation in SOFCs.