Developing Cost-Effective Dense Continuous SDC Barrier Layers for SOFCs

Abstract

Solid oxide fuel cells (SOFCs) with lanthanum strontium cobalt ferrite (LSCF) cathodes often employ a samaria-doped or gadolinia-doped ceria (SDC or GDC, respectively) barrier layer between the cathode and the yttria-stabilized zirconia (YSZ) electrolyte to inhibit Sr from migrating to the YSZ surface where it reacts to form electrically-resistive strontium zirconate during cathode sintering. Because the SDC must be sintered at limited temperatures (generally ≤1200°C) to avoid forming a CeO2-ZrO2 solid solution that has significantly lower ionic conductivity, screen printed barrier layers are often porous after firing. Electrochemical tests of cells with dense, continuous pulsed laser deposited (PLD) SDC found that these cells exhibited significantly higher performance than those with the conventional screen-printed porous SDC layers. Thus, PNNL began investigating the fabrication of dense, continuous SDC barrier layers using cost-effective deposition by screen printing which is amenable to industrial production of SOFCs. Many approaches to improve the SDC density have been explored including the use of powder with reduced particle sizes, inks with increased solids loading, and doping with sintering aids. While some of these tests were successful in enhancing the density of the SDC, the stresses induced by constrained sintering on the surface of previously-fired YSZ caused cracks and discontinuities in the SDC barrier layer. These results together with steps that have been taken to address the constrained sintering issue will be presented.