Electrolysis of H2O and CO2 in an oxygen-ion conducting solid oxide electrolyzer with a La0.2Sr0.8TiO3+δ composite cathode

Abstract

Solid oxide electrolyzers have attracted a great deal of interest in recent years because they can convert electrical energy into chemical energy with high efficiency. Ni/YSZ cathodes are generally utilized for high temperature electrolysis of H2O and CO2 in oxygen-ion conducting solid oxide electrolyzers; however, such electrodes can only operate under reducing conditions. In an atmosphere without a flow of reducing gas, cathodes based on La0.2Sr0.8TiO3+δ (LST) are a promising alternative. Solid Oxide Electrolyzers with LST cathodes without pre-reduction were used at 700 °C for the electrolysis of 3%H2O/97%N2 and 100%CO2, and promising polarization impedance data were obtained in both atmospheres. The electrochemical results indicated that the electrochemical reduction of the La0.2Sr0.8TiO3+δ cathode was the main process at low electrical voltages, while the electrolysis was the main process at high voltages because ion transportation in the electrolyte limited the overall efficiency. The electrolysis of H2O was determined to be more efficient than the electrolysis of CO2 under the same conditions. The Faraday efficiencies of H2O and CO2 were 85.0% and 24.7%, respectively, at 700 °C and a 2 V applied potential.