Sr2Fe1.4Mn0.1Mo0.5O6−δ perovskite cathode for highly efficient CO2 electrolysis

Abstract

High-temperature solid oxide cells afford chemical storage of renewable electricity. In particular, the electrochemical conversion of the greenhouse gas CO₂ is attracting increasing interest to facilitate a sustainable energy technology. In this work, the effectiveness of perovskite-structured Sr₂Fe_1.4Mn_0.1Mo_0.5O_6−δ (SFMM0.1) for use as cathode material for CO₂ electrolysis has been investigated. Both parent Sr₂Fe_1.5Mo_0.5O_6−δ (SFM) and SFMM0.1 are found to be redox stable in air and 5% H₂/Ar at 850 °C. Electrical conductivity relaxation experiments and first-principle calculations reveal that oxygen transport, CO₂ adsorption and reduction kinetics are enhanced upon doping of SFM with Mn. The faster CO₂ reduction kinetics observed for SFMM0.1 relative to SFM is reflected in a lower polarization resistance when both materials are used as single-phase electrodes in symmetrical cells. The polarization resistance in 50% CO/CO₂ at 800 °C decreases from 1.15 Ω cm² for SFM to 0.60 Ω cm² for SFMM0.1. Under similar conditions, the polarization resistance decreases further to 0.50 Ω cm² for a symmetrical cell with dual-phase SFMM0.1-SDC (samaria-doped ceria) electrodes. Unprecedented performance is demonstrated when SFMM0.1-SDC is integrated as the cathode in a solid oxide cell for electrolysis of pure CO₂, achieving a current density of 1.35 A cm² at 800 °C at 1.5 V.