Thermodynamic and electrical characteristics of NdBaCo2O5+δ at various oxidation and reduction states

Abstract

A solid oxide fuel cell is a device that converts the chemical energy in fuel to the electrical energy directly, efficiently and eco-friendly. The cation ordered perovskite-related oxide, NdBaCo₂O_5+δ (NBCO), is known as one of the best cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) because of their superior electrochemical properties. The aim of this work is to identify the crucial characteristics of NdBaCo₂O_5+δ/YSZ composites, such as the redox properties, the structures, and the electrical conductivities for a new cathode material for IT-SOFCs. Thermodynamic redox properties including oxidation enthalpies and entropies were investigated by coulometric titration. The isotherms were obtained at 923, 973 and 1023 K over a wide range of p(O₂). Oxygen non-stoichiometries have shown that higher temperatures lead the composites to a deeper reduction state rapidly near the p(O₂) of 10⁻⁵ atm and at 1023 K, which can be the sign of the decomposition. Therefore, the NBCO-YSZ composites may not be suitable for the cathodes of SOFCs above operating temperatures of 1023 K due to the decomposition. The oxidation enthalpies and entropies were determined from the isotherms and the electrical conductivities measured by the 4-probe method were high enough for IT-SOFC cathode applications.