Nanoscale Intertwined Biphase Nanofiber as Active and Durable Air Electrode for Solid Oxide Electrochemical Cells

Abstract

The poor temperature activity and durability due to surface Sr segregation are two main challenges restricting the practicability of state-of-the-art La1–xSrxCo1–yFeyO3 (LSCF) air electrodes for solid oxide electrochemical cells (SOCs). This article reports the recent discovery to unleash the constraints of performance and stability by constructing a novel nanofiber air electrode consisting of a LSCF host and GDC guest in nanoscale intertwined moiety (LSCF/GDC NF). The electrical conductivity relaxation and distribution of relaxation time results collectively disclosed the boosted surface oxygen exchange rate by two orders of magnitude at moderate SOC operation conditions (600 °C), as compared to commercial LSCF (1.01 × 10–3 cm s–1 vs 4.1 × 10–5 cm s–1). As a result, the electrochemical performance was synchronically promoted by over 5-fold (0.12 Ω·cm2 vs 0.64 Ω·cm2). Moreover, the interval stability test over 200 h in switching atmospheres (air/H2O/CO2) buttresses the superb robustness of LSCF/GDC NF with an extremely slow deactivation rate of 1.79 × 10–6 Ω·cm2 h–1 and nondetectable top-surface Sr segregation, collectively affirmed by X-ray photoelectron spectroscopy and low-energy ion scattering spectra. At atomic scale, the operando X-ray diffraction results preliminarily unravel that the formation of intertwined moiety employs the compressive strain on LSCF, which maintains the length of Sr–O against thermoinduced elongation. In addition, systemically, XPS and density functional theory simulation results prove the thermodynamically favored formation of oxygen vacancies at the biphase boundary in LSCF/GDC NF and raised the energy barrier for the formation of an intrinsic vacant Sr site. This study provides a practical and facile strategy to engineer the air electrode with enhanced performance and durability.