Determination of Changes in Surface Chemistry of SOFC Seal Materials
EMSL Project ID
26391
Abstract
Solid oxide fuel cells (SOFC) have emerged as a clean and efficient technology for the direct conversion of hydrocarbons and coal-derived fuels to electrical energy. The key feature of the SOFC is its high chemical to electrical energy conversion efficiency, tolerance to gas phase poisons, and availability of high quality heat. SOFC operating conditions, however, place severe demands on cell and stack designs and the materials of construction involved in their fabrication due to high operating temperatures, presence of temperature gradients and the complex exposure environments (oxidizing and reducing). One of the key challenges to be overcome in SOFC stack technology is related to the need for effective, reliable seals between the interconnects and cells in order to prevent mixing of the oxidant and fuel gases. Many SOFC sealing approaches rely on a glass which will soften and "glue together" the adjacent stack components during stack fabrication (at a temperature above the operating temperature), but then become rigid and immobile, due to devitrification, when cooled to the operating temperature. Glass-based seals represent a relatively easy means of sealing an SOFC stack (at least initially), but they face challenges in meeting the stringent SOFC operating requirements. One key challenge for glass-based sealants involves the need to understand and control their reactivity with the gaseous constituents of the highly oxidizing and reducing environments present within the SOFC stack. Interactions with SOFC gases can compromise the seal itself, through reduced strength and/or hermeticity due to volatilization of seal material, and also could cause deterioration in cell performance if the volatilized constituents interact unfavorably with the cell electrode and/or electrolyte materials. PNNL is developing glass seal materials for SOFC stacks for the DOE Office of Fossil Energy. These new materials show great promise for their intended application, however it has been determined through weight loss measurements that some volatilization of seal material does occur during prolonged exposure to the SOFC operating environment. The objective of this proposal is to perform surface and near surface analyses to develop an understanding of the changes in surface and near surface chemistry of candidate glass seal materials after exposure to the SOFC operating environment. Appropriate EMSL surface analysis techniques (such as XPS) will be used to quantitatively determine the elements which volatilize from the material. This information will allow us to assess whether the observed volatility is likely to represent a problem during SOFC stack operation due to potential interaction of the volatilized species with other components of the stack, especially the cell electrodes and electrolytes.
Project Details
Project type
Limited Scope
Start Date
2007-07-06
End Date
2007-09-05
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members