Calcium- and Cobalt-Doped Yttrium Chromites as an Interconnect Material for Solid Oxide Fuel Cells

Abstract

The structural, thermal, and electrical characteristics of calcium- and cobalt-doped yttrium chromites were studied for potential use as interconnect material in high temperature solid oxide fuel cells as well as other high temperature electrochemical and thermoelectric devices. The compositions formed single-phase orthorhombic perovskite structures in a wide range of oxygen pressures. Sintering behavior was remarkably enhanced as a result of cobalt substitution for chromium, and densities 95 and 97% of theoretical density were obtained after sintering at in air, when was 0.2 and 0.3, respectively. The electrical conductivity in both oxidizing and reducing atmospheres was significantly improved with cobalt additions, and was 49 and 10 S/cm at and 55 and 14 S/cm at in air and forming gas, respectively, for . The conductivity increase upon cobalt substitution for chromium was attributed to the charge carrier density increase as confirmed by Seebeck measurements. The thermal expansion coefficient was increased with cobalt content and closely matched to that of an 8 mol % yttria-stabilized zirconia (YSZ) electrolyte for . For , and YSZ were found to be chemically compatible for firing temperatures to at least .