Nonlinear Harmonic Techniques for Studies of Solid Oxide Fuel Cell Electrodes

University Of Washington, Seattle WA

Investigators

Abstract

CBET-0829171 Adler Advances in ceramic manufacturing have revitalized interest in the solid oxide fuel cell (SOFC) as an efficient means to recover electricity from fossil and renewable hydrocarbons, including biomass. Developers have successfully lowered operating temperatures of SOFCs below 600°C, leading to improved reliability and reduced capital cost. One factor leading to these successes has been the use of alternate electrode materials based on mixed-conducting ceramics (materials which carry both oxygen ions and electrons), often called mixed conductors. Although promising, the reason mixed-conductors improve performance remains unclear, and they also suffer from poorly-understood degradation problems. In order to develop a better understanding of how mixed-conductors work as electrodes, Adler and his coworkers at the University of Washington have been developing a new electrochemical measurement technique called "nonlinear electrochemical impedance spectroscopy" (NLEIS). This technique relies on small (almost immeasurable) harmonic signals generated when an oscillating current is passed through the electrode. A relevant analogy is music. The reason you can tell the difference between different instruments playing the same note is that each instrument also generates harmonic and anharmonic tones in conjunction with the primary tone being played. These small extra signals are detected by your ear, and act like a fingerprint for the physical process generating them (vibrating string of a guitar, resonating wooden cavity of a violin, etc). In the same way NLEIS helps the Adler group figure of what physical of chemical process is limiting or degrading electrode performance. In this renewal, Adler's group will use NLEIS to study an array of materials (SOFC cathodes and anodes) having well-defined microstructure made by pulsed-laser deposition and nanofabrication. They will also further develop the technique, including methods for improved acquisition and interpretation of NLEIS data. Intellectual Merit of the Proposed Activity - The proposed work forms part of a broader effort to better understand high-temperature solid-state electrode reactions, of critical importance to several technologies including solid oxide fuel cells, oxide sensors, and oxygen separation devices. This project involves original and transformative concepts in both experimental techniques and theory/modeling, and will complement more applied projects involving fuel cell electrode development (DOE/SECA), and understanding the electrocatalytic role of 3-D microstructure using FIB-SEM (NSF collaborative research grant with Northwestern University). The principal investigator has 19 years of academic and industrial experience in this field, while the proposing institution is a world leader in electrochemical engineering and electrocatalysis. The proposed work would also advance a burgeoning international collaboration between the University of Washington and Tohoku University, one of the world's leading institutes for high-temperature electrochemical materials. Broader Impacts of the Proposed Work - In addition to gaining knowledge of direct interest to SOFC's, this work will develop transformative techniques of general interest in other areas of electrochemical engineering, including membrane fuel cells (of all types), solid-state and thin-film batteries, electrochemical materials processing, electrochemical sensors, coatings and thin films, and other solid-state interfacial devices. This work will support the education of individual scientists and engineers (including at least one women), and involve opportunities for students to participate in both national and international collaborative research. Results and knowledge will be disseminated widely through the literature, while strong ties of the PI to industry and more applied programs will aid direct impact on commercial development. This research program will also directly enhance the PI's educational program, which includes internet-based UW courses on fuel cells, and an Electrochemical Society short course.