A Study of 8YSZ/GDC Bi-Layered Electrolyte: The Effect of 2 Mol% Fe2O3 Dopant on Sintering and Conductivity

The primary requirements for an electrolyte material in a Solid Oxide Cell (SOC) is the ability to provide a sufficiently high level of oxide ion conduction while preventing both the mixing of reactant gas species and leakage of current through the electrolyte. Commonly, 8 mol% Yttria-stabilised Zirconia (8YSZ) or Gd_0.1Ce_0.9O_1.95 (GDC) are used in high performance cells. Whilst GDC has higher oxide ion conductivity than YSZ, it suffers from electronic conduction due to the partial reduction of Ce⁴⁺ to Ce³⁺ during operation which is detrimental to cell performance. In this work we present the use of a bi-layer 8YSZ/GDC electrolyte as an effective solution to avoid ceria reduction in a fuel (reducing) environment, thereby preventing current leakage across the electrolyte, while maintaining high oxide ion conduction.  Electrolytes were produced via tape-casting, a low-cost, mass-production technique.  A transition metal oxide sintering aid of 2 mol% Fe₂O₃ was used to reduce the sintering temperature while also mitigating the formation of a low conductivity interlayer. This study aims to determine the role of Fe₂O₃ during the sintering process and its subsequent influence on microstructure and the total conductivity of the bi-layer electrolyte.