Intellectual Merit

1. 10 μm 10 μm The Effect of Hydrogen and Water Vapor on the Oxidation of Chromia-Forming Alloys,Jeffrey W. Fergus, Auburn University, DMR 0551896 Intellectual Merit Crofer22APU SS 430 The objective of this project is to understand the degradation mechanisms of chromium-containing alloys used as the interconnect materials in solid oxide fuel cells (SOFCs). The interconnect material connects the two electrodes and is thus exposed to both oxidizing (air) and reducing (fuel) environments. After target operational lifetimes on the order of 40,000 hours, scale growth and chromium poisoning can lead to degradation in performance. Both of these are controlled by the composition and transport properties of the oxidation scale. Although the scale formed on interconnect alloys is primarily chromia, other elements from the alloy, such as Fe and Mn, can be incorporated in the scale and affect both the growth rate and chromium vaporization. The micrographs to the right show the oxidized surfaces of two alloys being considered for use as SOFC interconnects: SS 430 and Crofer22APU. In both cases, after oxidation the outer layer contains significant amounts of Mn and Fe and the composition of the large crystals is close to that of the spinel, MnCr2O4, which is confirmed by x-ray diffraction. This outer spinel layer is beneficial to alloy performance, because it has a relatively high conductivity (and thus reduced ohmic resistance) and reduces the amount of chromium vaporization (and thus decreases chromium poisoning). MnCr2O4 Spinel Crofer22APU SS 430 Spinel Formation on Interconnect Alloys after 400 Hours at 800°C in Air.

2. The Effect of Hydrogen and Water Vapor on the Oxidation of Chromia-Forming Alloys,Jeffrey W. Fergus, Auburn University, DMR 0551896 Broader Impacts SOFCs in FutureGen Zero-Emission Fossil Fuel Power Plant The primary advantages and disadvantages of SOFCs result from their high operating temperature. While the high temperature can lead to degradation of components, which is the focus of this project, it also accelerates the reactions in the fuel, so SOFCs can be used with a variety of fuels, which expands the potential applications of SOFCs. One example is in clean coal power plants, such as those being developed in the U.S. Department of Energy’s FutureGen project. Because of their tolerance to CO, SOFCs can use the gas produced by coal gasification, so that they can be integrated into a clean and efficient energy conversion system. In addition to the fuel tolerance, the heat generated by the SOFC can be used in the CO2 sequestration process. Another promising application for SOFCs is in the use of reformed diesel or biofuels. The higher tolerance to fuel impurities reduces the reformation requirements and expands the types of fuels that can be used with on-board reformation. For example, distributed or mobile SOFC power plants can reduce the cost of transporting raw materials and thus improve the economic viability of renewable fuels derived from agricultural products. Coal H2O Air Air separation O2 Marketable ash /slag by product Gasification Marketable sulfur by product Gas cleaning CO2 separation CO2 sequestration CO, H2 Air CO, H2, CO2 SOFC anode SOFC cathode Air