Promotion of oxygen reduction and evolution by applying a nanoengineered hybrid catalyst on cobalt free electrodes for solid oxide cells

Abstract

A key requirement for the widespread commercialization of solid oxide cell (SOC) technology is to develop cost-effective oxygen electrodes with sufficiently high electro-catalytic activity and durability at intermediate temperatures (600–750 °C). Here we report a remarkable enhancement of electro-catalytic activity of cobalt-free (La_0.6Sr_0.4)_0.98FeO_3−δ (LSF) electrodes by applying a nanoengineered hybrid catalyst coating composed of nanoparticles of Ce_0.85Gd_0.15O_2−δ (CGO) and Pr₆O₁₁via co-infiltration. Different from the conventional infiltration with a precursor of metal nitrate, here a mixture solution of colloidal CGO nanocrystals and Pr(NO₃)₃ is used for infiltration to enable the desired nanoengineered architecture. The resulting hybrid-catalyst-coated LSF electrode exhibits a very low polarization resistance of 0.017 Ω cm² at 750 °C, about one order of magnitude lower than that of bare LSF (0.197 Ω cm²). Furthermore, the Ni/yttria-stabilized zirconia (YSZ) fuel-electrode-supported cell with this hybrid-catalyst-coated LSF electrode displays excellent performance in both fuel-cell and electrolysis operations, while it also offers good durability tracked over 1000 h of fuel-cell operation. The unique catalytic activity of the hybrid-catalyst-coated LSF electrode is attributed to the combined effects of accelerating oxygen surface exchange kinetics by Pr₆O₁₁ and enhancing the available surface area by the nanoporous architecture of the catalyst coating. Moreover, combined with the modification of the Ni/YSZ electrode, stable electrolysis operation at 650 °C under −0.5 A cm⁻² with a voltage close to 1.3 V is achieved on a cell prepared without cobalt. This work not only opens the opportunity for applying cobalt-free oxygen electrodes in SOCs but also proposes a co-infiltration strategy to develop a highly active and robust catalyst coating by combined tuning of composition and morphology, which may also be applicable to other devices such as metal–air batteries and membrane reactors.