Mixed-Conductor Sr₂Fe_1.5Mo_0.5O_6−δ as Robust Fuel Electrode for Pure CO₂ Reduction in Solid Oxide Electrolysis Cell

Abstract

Electrolysis of carbon dioxide to carbon monoxide, through which the greenhouse gas could be effectively utilized, using solid oxide electrolysis cells is now attracting much interest. Here, we show for the first time that the redox-stable Sr2Fe1.5Mo0.5O6−δ (SFM) ceramic electronic-ionic conductor can be used as the electrocatalyst to electrolyze and convert 100% CO2 to CO without using any safe gases like H2 and CO. SFM maintained its cubic structure and had an electrical conductivity of 21.39 S cm–1 at 800 °C in 1:1 CO–CO2 atmosphere. Its surface reaction coefficient for CO2 reduction is 7.15 × 10–5 cm s–1 at 800 °C. Compared with those reported for the typical oxide ceramic electrodes, high electrochemical performance has been demonstrated for single phase SFM cathode using 100% CO2 as the feeding gas. For example, a current density of 0.71 A·cm–2 was obtained using a fuel cell supported on LSGM (La0.9Sr0.1Ga0.8Mg0.2O3−δ) electrolyte operated at 800 °C and an applied voltage of 1.5 V. The electrolysis performance was further improved by using SFM–Sm0.2Ce0.8O2−δ composite cathode, and the current density increased to 1.09 A·cm–2 under the same operation conditions. Durability test at 800 °C for 100 h demonstrated a relatively stable performance for CO2 electrolysis under harsh conditions of 100% CO2 without safe gas and above 1 A cm–2 current density, which is seldom achieved in the literature but highly desirable for the commercial application, indicating that SFM is a highly promising ceramic fuel electrode for CO2 electrolysis.