Remarkable chemical adsorption of manganese-doped titanate for direct carbon dioxide electrolysis

Abstract

Chemical adsorption of CO₂ in composite cathodes at high temperatures plays a significant role in the electrochemical conversion of CO₂ into fuels in efficient solid oxide electrolysers. In this work, the active Mn with multi-oxidation states is introduced into the B-site lattice of the redox-stable (La, Sr)TiO_3+δ to create oxygen vacancies both in the bulk and on the surface. The ionic conductivities of the Mn-doped titanate are remarkably enhanced by 1–2 orders of magnitude at intermediate temperatures in reducing or oxidizing atmospheres. The chemical adsorption of CO₂ is accordingly enhanced by approximately 1 order of magnitude for the Mn-doped titanate and the onset temperature of strong chemical desorption is consequently extended to as high as approximately 800 °C of the common operation temperature of solid oxide carbon dioxide electrolysers. First principles calculations reveal that oxygen vacancy defect sites created by Mn dopants substantially contribute to the chemical adsorption of CO₂ and the strong bonding of the oxide ions in CO₂ to the nearest cations on the (La,Sr)O- or (Ti,Mn)O₂-terminated facets not only activates CO₂ molecules but also considerably increases the desorption temperature. The highest current efficiencies of approximately 100% are obtained with the Mn-doped titanate cathodes for the direct electrolysis of CO₂ in oxide ion-conducting solid oxide electrolysers.