In situ formation of oxygen vacancy in perovskite Sr0.95Ti0.8Nb0.1M0.1O3 (M = Mn, Cr) toward efficient carbon dioxide electrolysis

Abstract

In this work, redox-active Mn or Cr is introduced to the B site of redox stable perovskite Sr_0.95Ti_0.9Nb_0.1O_3.00 to create oxygen vacancies in situ after reduction for high-temperature CO₂ electrolysis. Combined analysis using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and thermogravimetric analysis confirms the change of the chemical formula from oxidized Sr_0.95Ti_0.9Nb_0.1O_3.00 to reduced Sr_0.95Ti_0.9Nb_0.1O_2.90 for the bare sample. By contrast, a significant concentration of oxygen vacancy is additionally formed in situ for Mn- or Cr-doped samples by reducing the oxidized Sr_0.95Ti_0.8Nb_0.1M_0.1O_3.00 (M = Mn, Cr) to Sr_0.95Ti_0.8Nb_0.1M_0.1O_2.85. The ionic conductivities of the Mn- and Cr-doped titanate improve by approximately 2 times higher than bare titanate in an oxidizing atmosphere and 3–6 times higher in a reducing atmosphere at intermediate temperatures. A remarkable chemical accommodation of CO₂ molecules is achieved on the surface of the reduced and doped titanate, and the chemical desorption temperature reaches a common carbonate decomposition temperature. The electrical properties of the cathode materials are investigated and correlated with the electrochemical performance of the composite electrodes. Direct CO₂ electrolysis at composite cathodes is investigated in solid-oxide electrolyzers. The electrode polarizations and current efficiencies are observed to be significantly improved with the Mn- or Cr-doped titanate cathodes.