Low Temperature Cathode Supported Electrolytes

Abstract

This project has three main goals: Thin Films Studies, Preparation of Graded Porous Substrates and Basic Electrical Characterization and testing of Planar Single Cells.This period has continued to address the problem of making dense ½ to 5µm thick dense layers on porous substrates (the cathode LSM).Our current status is that we are making structures of 2-5cm 2 in area, which consist of either dense YSZ or CGO infiltrated into a 2-5µm thick 50% porous layer made of either nanoncrystalline CGO or YSZ powder. This composite structure coats a macroporous cathode or anode; which serves as the structural element of the bi-layer structure. These structures are being tested as SOFC elements.A number of structures have been evaluated both as symmetrical and as button cell configuration.Results of this testing indicates that the cathodes contribute the most to cell losses for temperatures below 750°C.In this investigation different cathode materials were studied using impedance spectroscopy of symmetric cells and IV characteristics of anode supported fuel cells. (SSCF). A new technique for filtering the Fourier transform of impedance data was used to increase the sensitivity of impedance analysis.By creating a filter specifically for impedance spectroscopy the resolution was increased. The filter was tailored to look for specific circuit elements like R//C, Warburg, or constant phase elements. As many as four peaks can be resolved using the filtering technique on symmetric cells. It may be possible to relate the different peaks to material parameters, like the oxygen exchange coefficient. The cathode grouped in order from lowest to highest ASR is LSCF < PSCF < SSCF < YSCF < LSM. The button cell results agree with this ordering indicating that this is an important tool for use in developing our understanding of electrode behavior in fuel cells. 2 LOW TEMPERATURE CATHODE SUPPORTED ELECTROLYTESReport for Period October 1, 2001 to March 31, 2002 Fuel cell design by itself is a complicated problem. Many particular directions need to be analyzed and solved to get the final result, but there is no doubt that the combination of the materials involved in this design is a key issue. During the past few years there has been an effort promoted by the US Department of Energy (SECA Program) to lower the operating temperature of solid oxide fuel cells. As a result, the solid oxide fuel cell activities at the Electronic Materials Applied Research Center (EMARC) of the University of Missouri-Rolla (UMR) have been focused on the fabrication of thin (0.5 to 5µm thick), dense electrolyte layers of either zirconia or ceria. The route that has been taken is to deposit a polymer precursor solution, which contain the cations of the chosen electrolyte onto a substrate and subsequently convert the resulting polymeric films into dense layers by thermal treatment.The efficiency of oxygen ion permeation through the SOFC structure is obviously a main issue [1]. Different components influence this ion permeation [2]. First of all, for the electrolyte...