Highly conductive and cost-effective quaternary (Yb₂O₃)_x(Sc₂O₃)_0.10‒x(CeO₂)_0.01(ZrO₂)_0.89 (x = 0.04–0.10) electrolytes for efficient and durable solid oxide fuel cells

Abstract

(Sc₂O₃)_0.1(CeO₂)_0.01(ZrO₂)_0.89 possesses excellent ionic conductivity among various stabilized ZrO₂ electrolyte materials for solid oxide fuel cells. However, its practical application is limited by susceptibility to phase transition and the high cost of Sc₂O₃ raw material. Herein, we address these challenges by partially replacing Sc₂O₃ in (Sc₂O₃)_0.1(CeO₂)_0.01(ZrO₂)_0.89 with low-cost Yb₂O₃. Quaternary (Yb₂O₃)_x(Sc₂O₃)_0.10‒x(CeO₂)_0.01(ZrO₂)_0.89 (x = 0.04−0.10) electrolyte discs are fabricated by coupling tape casting and in situ solid-state reaction. All Yb₂O₃ doped electrolytes exhibit a single cubic phase structure. With increasing in Yb₂O₃ amount, the grain boundary resistance decreases, leading to improved conductivity at low temperatures. (Yb₂O₃)_0.06(Sc₂O₃)_0.04(CeO₂)_0.01(ZrO₂)_0.89 exhibits the ionic conductivity of 0.088 and 0.0020 S∙cm^‒1 at 800 and 500 °C, respectively. In addition, both the thermal expansion coefficient and three-point bending strength of the electrolytes increase with higher Yb₂O₃ amount, satisfying the criteria for advanced electrolyte materials in solid oxide fuel cells. A single cell configuration comprising a Ni-Gd_0.2Ce_0.8O_1.9 anode|200 μm thick (Yb₂O₃)_0.06(Sc₂O₃)_0.04(CeO₂)_0.01(ZrO₂)_0.89|La_0.6Sr_0.4Co_0.2Fe_0.8O₃ cathode achieves a peak power density of 0.65 W∙cm^‒2 at 800 °C and operates stably for 100 h without noticeable degradation. The present findings provide a new approach for the development of cost-effective and highly conductive ZrO₂-based electrolyte for efficient and durable solid oxide fuel cells.

Graphical abstract

Keywords

solid oxide fuel cells / 10Sc1CeSZ electrolyte / ytterbium doping / phase transition

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