Ru-doped lanthanum ferrite as a stable and versatile electrode for reversible symmetric solid oxide cells (r-SSOCs)

Abstract

In the current scenario of innovative energy systems, reversible solid oxide cells (r-SOCs) are widely recognized as promising devices, thanks to their high conversion efficiency in both power-to-fuel and fuel-to-power modes. A crucial aspect for their scale-up is the development of multi-functional compounds that can work as either air or fuel electrodes. The most reliable alternative to conventional materials for r-SOCs are perovskite oxides. Sr-substituted lanthanum ferrites (LSF) show large mixed ionic and electronic conductivity (MIEC) and versatile catalytic activity upon B-site doping. Nevertheless, their poor stability in highly reducing environments precludes their widespread application. In this work, 5 mol% Ru-doped lanthanum ferrite La0.6Sr0.4Fe0.95Ru0.05O3-δ (LSFR05) is investigated as a multi-functional electrode for reversible and symmetric solid oxide cells (r-SSOCs). Ru-doping promotes LSF stability, retaining a higher lattice oxygen content. Upon reduction, LSFR05 exhibits exsolution of uniformly dispersed catalytically active Fe–Ru nanoparticles. All-perovskite symmetric cells showed remarkably high power density as H2–SOFC at 850 °C (602 mW cm−2), while in CO2-SOEC mode a current density output of 1.39 A cm−2 at 1.5 V was obtained. With a standard 70:30 CO2:CO gas composition, the cell showed a polarization resistance as low as 165 mΩ cm2. The complete SOFC-SOEC reversibility was successfully assessed for over 200 h.