Highly Active Layered Cobaltite Air-Electrode Materials for Reversible Solid Oxide Cells

Abstract

The use of fossil fuels, which have increased rapidly since the Industrial Revolution, is causing serious climate change. To overcome this, interest in clean and sustainable energy sources to replace fossil fuels is increasing worldwide. Among alternative energies, the electricity generation from solar and wind resources is difficult to achieve sustainable energy production regardless of the weather and season. Hence, hydrogen is considered as the most promising energy source to replace fossil fuels because of its clean, storable, sustainable, and transportable characteristics.Recently, reversible fuel cells that can both produce hydrogen with surplus power and generate electricity using the stored hydrogen have attracting attentions as an electrochemical device to promote reliable and economical hydrogen society [1]. Among them, reversible solid oxide cells show high efficiency in a fuel cell mode due to their high operating temperature (700-1000 ℃). However, reversible solid oxide cells exhibit relatively low performance in water-electrolysis cell mode [2]. The main reason of low performance in the solid oxide electrolysis cell mode is the sluggish kinetics of oxygen evolution reactions in air-electrode. Therefore, the electrolysis performance of reversible solid oxide cells can be greatly improved if the air-electrode with high catalytic activity for oxygen evolution reactions is developed.Among many candidate materials for air-electrodes, cobalt-based layered materials are known to have good electrocatalytic properties in oxygen reduction and oxygen evolution reactions with high electronic conductivity (σ = 100–240 S·cm-1 at 450–650 °C) [3, 4]. Herein, we introduce a novel layered structure material, Ba2Co9O14 (BCO), as air-electrode materials for highly efficient and durable reversible solid oxide cells. In order to further enhance the catalytic property of BCO, Nd and Ca are doped into Ba-site. The Nd0.1Ca0.1Ba1.8Co9O14-cell shows a maximum power density of 2.6 W·cm-2 in fuel cell mode, current density of –4.36 A/cm2 under applied voltage of 1.6 V in electrolysis cell mode, at 800 ℃, surpassing previous reported results of air-electrode catalysts for reversible solid oxide cells.