An efficient and robust lanthanum strontium cobalt ferrite catalyst as a bifunctional oxygen electrode for reversible solid oxide cells

Abstract

Reversible solid oxide cells (SOCs) are unique devices that perform interconversion between chemical energy (particularly hydrogen) and electricity, providing efficient energy storage for site-specific and weather-dependent solar and wind resources. One of the key requirements for achieving high-performance reversible SOCs is the development of highly active bifunctional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, we investigate a La_0.2Sr_0.8Co_0.8Fe_0.2O_3−δ (LSCF2882) material as a novel oxygen electrode for reversible SOCs at intermediate temperatures. Unlike most widely used La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF6428) with a rhombohedrally distorted perovskite structure, LSCF2882 possesses a simple cubic perovskite structure with a symmetric BO₆ octahedral network. Furthermore, the 3D bond valence sum calculation of the LSCF2882 structure suggests a reduction in oxygen ion conduction barrier energy. Oxygen surface exchange (k_chem) and diffusion (D_chem) coefficients of LSCF2882 determined by electrical conductivity relaxation are consistently remarkably higher by >2 and 20 times compared to those of LSCF6428 at 700 °C, respectively. This result is further supported by a 43% reduction in the oxygen vacancy formation energy of LSCF2882 determined from density functional theory calculations. The reversible SOCs with LSCF2882 oxygen electrodes greatly outperform LSCF6428 cells in both fuel cell (2.55 W cm⁻²) and electrolysis mode (2.09 A cm⁻² at 1.3 V) at 800 °C, with excellent reversible cycling stability. Our findings strongly suggest that LSCF2882 is a promising candidate as a bifunctional oxygen electrode for high performance reversible SOCs at reduced temperatures.