Ca-Fe co-doped La0.75Sr0.25Cr0.5Mn0.5O3 cathodes with high electrocatalytic activity for direct CO2 electrolysis in solid oxide electrolysis cells

Abstract

Solid oxide electrolysis cell (SOEC) is a promising electrochemical device for effectively and sustainably converting CO2 into CO, and the development of SOEC depends on the exploitation of appropriate cathodes with good catalytic activity and stability. La0.75Sr0.25Cr0.5Mn0.5O3 (LSCM)-based cathodes have been widely studied due to the excellent redox stability and good compatibility with other components of SOEC. La0.75Sr0.2Ca0.05Cr0.5Mn0.5O3 (LSCCM) fabricated in our previous work shows a relatively satisfying electrocatalytic performance and is expected to be further optimized. Herein, Fe-doped LSCCM, La0.75Sr0.2Ca0.05Cr0.5Mn0.5−xFexO3 (LSCCMFex, x = 0, 0.05, 0.1, 0.15, denoted as LSCCM, LSCCMFe5, LSCCMFe10, and LSCCMFe15, respectively) materials, are investigated as the cathodes for direct CO2 electrolysis in SOEC. Specifically, LSCCMFe5 material shows a good chemical compatibility with Gd0.1Ce0.9O2-δ (GDC) electrolyte and excellent chemical stability in 30% CO/CO2 atmosphere. Compared with the LSCCM electrode, the LSCCMFe5 cathode presents 30.5% decrease in polarization resistance for a half cell under pure CO2 atmosphere at 800 ℃ and 42.3% increase in current density (0.60 A cm−2) for the direct CO2 electrolysis of a single cell with an applied voltage of 1.6 V at 800 ℃. LSCCMFe5 exhibits a high electrocatalytic activity among various LSCM-based cathodes. The improvement in electrocatalytic performance could be due to the enhanced chemical adsorption of CO2 and increased highly active O-/O22- species related to the newly generated oxygen vacancy via Fe-doping, leading to favorable surface reaction kinetics. Moreover, no degradation could be observed for the single cell after the direct CO2 electrolysis test up to 100 h, suggesting an attractive competitiveness for the application of Fe-doped LSCCM cathodes to SOECs.