Highly active and robust A-site deficient La0.77Sr0.2Co0.2Fe0.8O3-δ fiber base electrode for intermediate temperature solid oxide cells

Abstract

The combination of solid oxide electrolysis cells (SOECs) and solid oxide fuel cells (SOFCs) is expected to solve the problems of energy conversion and storage. However, the insufficient catalytic capacity and poor durability of the oxygen electrodes in solid oxide cells (SOCs) at intermediate temperatures pose a huge challenge for SOCs applications. In this work, A-site deficient La_0.77Sr_0.2Co_0.2Fe_0.8O_3-δ nanorod materials coated with Ce_0.8Gd_0.2O_1.9 (GDC) are prepared to suppress cation surface segregation and enhance charge transfer kinetics by reducing internal elastic force of perovskite and meanwhile applying external compressive stress with an oxygen-ion conductor. As a result, the composite cathode with a GDC to La_0.77Sr_0.2Co_0.2Fe_0.8O_3-δ weight ratio of 0.59 (La_0.77Sr_0.2Co_0.2Fe_0.8O_3-δ@GDC0.59) exhibits excellent electrochemical performance and long-term stability when operating in both SOFCs and SOECs modes. XPS results show that the La_0.77Sr_0.2Co_0.2Fe_0.8O_3-δ@GDC0.59 oxygen electrode exhibits no significant Sr/Fe surface segregation after operating in SOFCs and SOECs modes for 200 h. Density functional theory calculation and physiochemical characterization confirm that Sr segregation phenomenon is well inhibited through the novel A-site deficient structural design of perovskite materials, which eliminates the major residual internal elastic force of La_0.8Sr_0.2Co_0.2Fe_0.8O_3-δ crystal, and GDC coating further relieves the lattice transformation of La_0.77Sr_0.2Co_0.2Fe_0.8O_3-δ upon the additional introduction of A-site deficiency and oxygen vacancy. This well-orchestrated composite cathode design provides a new perspective in stabilizing perovskite crystalline structure toward high-performance SOCs with extended operating life.