Various additives to Ni-Fe systems are studied as cermet cathodes for CO2 electrolysis (973-1173 K) using a La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) electrolyte, which is one of the most promising oxide-ion conductors for intermediate-temperature solid-oxide electrolysis cells in terms of ionic-transport number and conductivity. It is found that Ni-Fe-La0.6Sr0.4Fe0.8Mn0.2O3 (Ni-Fe-LSFM) exhibits a remarkable performance with a current density of 2.32 A cm-2 at 1.6 V and 1073 K. The cathodic overpotential is significantly decreased by mixing the LSFM powder with Ni-Fe, which is related to the increase in the number of reaction sites for CO2 reduction. For Ni-Fe-LSFM, much smaller particles (<200 nm) are sustained under CO2 electrolysis conditions at high temperatures than for Ni-Fe. X-ray diffraction analysis suggests that the main phases of Ni-Fe-LSFM are Ni and LaFeO3; thus, the oxide phase of LaFeO3 is also maintained during CO2 electrolysis. Analysis of the gaseous products indicates that only CO is formed, and the rate of CO formation agrees well with that of a four-electron reduction process, suggesting that the reduction of CO2 to CO proceeds selectively. It is also confirmed that almost no coke is deposited on the Ni-Fe-LSFM cathode after CO2 electrolysis.
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