Current-Collector-Optional Measurements to Quantify Precious Metal and Polarization Impacts on Oxygen Surface Exchange Coefficients

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Catalytic electrochemical devices are of increasing importance in alternative energy, environmental protection, and life-support technologies. The project focuses on a class of high-temperature devices including fuel cells, electrolyzers, oxygen generators, solar energy concentrators, and catalytic converters, that are often limited in performance by the slow exchange of oxygen with the surrounding atmosphere. Oxygen exchange is promoted by Mixed Ionic Electronic Conducting (MIEC) oxygen exchange catalysts. However, the identification of materials with improved oxygen exchange is presently limited by experimental artifacts associated with measuring the catalyst’s oxygen exchange rate (as typically characterized by a rate coefficient known as k(chem)). The project will quantify the sources of errors and lack of lab-to-lab reproducibility in traditional electrochemical k(chem) measurements, while demonstrating the effectiveness of a novel non-electrochemical thin-film method for accurately measuring oxygen exchange rates. Beyond the technical aspects, the project involves educational and outreach activities ranging from introducing 4-8th grade girls to engineering to teaching a course at the Michigan State Grandparent University Summer Camp. Recent experiments by the investigator’s group, and others, have demonstrated that precious metal current collectors, even unpolarized ones, can alter high-temperature MIEC k(chem) values. However, the full extent to which precious metal surface additions and/or electric polarization influence high-temperature MIEC k(chem) values, and the mechanisms by which this occurs, have yet to be fully explored. Hence, the objective of the project is to: 1) quantify the impact intentionally-added Pt surface additions and/or electric polarization have on the 400-600°C k(chem) of Pulsed Laser Deposited (PLD) praseodymium cerium oxide (PCO) thin films, 2) determine the mechanisms by which these fabrication and testing modifications alter the PCO k(chem), and 3) identify possible sources of previously-unrecognized, inadvertent precious metal contamination. This will be achieved by comparing the k(chem) values obtained from an in situ, non-contact, current-collector-optional wafer curvature measurement technique developed in the investigator’s group with those obtained via simultaneous Electrical Conductivity Relaxation and Electrochemical Impedance Spectroscopy. In addition, surface and bulk thin film composition and structural characterization techniques (such as X-Ray Diffractometry, Scanning Electron Microscopy, X-Ray Photoelectron Spectroscopy, and Secondary Ion Mass Spectrometry) will be used to identify relationships between k(chem) and materials properties.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.