Pure CO2 electrolysis over an Ni/YSZ cathode in a solid oxide electrolysis cell

Abstract

Traditional nickel/yttria stabilized zirconia (Ni/YSZ) electrodes have been widely used as the cathode in a solid oxide electrolysis cell due to its high performance. However, Ni/YSZ cathodes are usually considered to be easily oxidized during pure CO₂ electrolysis at high temperature, so a reductive gas such as H₂ or CO is mixed with pure CO₂ to protect the Ni/YSZ cathode from being oxidized. The real necessity of a reductive gas has not been systematically confirmed yet. Herein, stable pure CO₂ electrolysis over the Ni/YSZ cathode is achieved at 1.5 V and 700 °C for 60 hours without any reductive gas. In situ electroreduction of the nickel oxide/yttria stabilized zirconia electrode and theoretical calculations suggest that the electrolysis voltage provides continuous electrons across the Ni/YSZ cathode and diminishes Ni oxidation in pure CO₂ electrolysis. In addition, the electrochemical performance of CO₂ electrolysis over the Ni/YSZ cathode without a reductive gas is verified to be higher than that with a reductive gas. Therefore, pure CO₂ electrolysis over the Ni/YSZ cathode not only operates stably, but also possesses high electrochemical performance.