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In situ formation of oxygen vacancy in perovskite Sr 0.95 Ti 0.8 Nb 0.1 M 0.1 O 3 (M = Mn, Cr) toward efficient carbon dioxide electrolysis

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ABSTRACT

In this work, redox-active Mn or Cr is introduced to the B site of redox stable perovskite Sr0.95Ti0.9Nb0.1O3.00 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 Sr0.95Ti0.9Nb0.1O3.00 to reduced Sr0.95Ti0.9Nb0.1O2.90 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 Sr0.95Ti0.8Nb0.1M0.1O3.00 (M = Mn, Cr) to Sr0.95Ti0.8Nb0.1M0.1O2.85. 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.

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TGA of reduced samples in Ar atmosphere: (a) STNO and (c) STNMO. Desorption of CO2 for reduced samples in CO2 atmosphere: (b) STNO and (d) STNMO.
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f9: TGA of reduced samples in Ar atmosphere: (a) STNO and (c) STNMO. Desorption of CO2 for reduced samples in CO2 atmosphere: (b) STNO and (d) STNMO.

Mentions: The adsorption of CO2 was investigated for the STNO and STNMO samples using TGA tests in Ar and 100% CO2 from room temperature to 1000°C at a rate of 10°C min−1. In Figs. 9 (a) and (c), the weights of the reduced STNO and STNMO samples are unchanged in an Ar atmosphere in the temperature range of 200 to 1000°C, which are employed as references. By contrast, the weight loss of the reduced STNO sample after CO2 adsorption above 400°C reaches approximately 0.15%. The chemical desorption is observed at approximately 600°C (Fig. S5 (a)), which implies the presence of chemical adsorption of CO2 on the reduced STNO sample. However, the weight loss of the reduced STNMO sample after CO2 adsorption is substantially increased to 1%, and the strong chemical desorption has been extended to approximately 800°C, as shown in Fig. S5 (b). In addition, the specific surface area of the STNO and STNMO powders are similar to each other (2.5 m2·g−1). The desorption of CO2 was calculated, and the results are presented in Figs. 9 (b) and (d) for STNO and STNMO, respectively. The desorption volume of CO2 is significantly enhanced to approximately 1.0 ml·m−2 catalyst for the Mn-doped STNMO sample, and the onset of the desorption temperature is as high as 800°C, which is near the decomposition temperature of common carbonates. The significant enhancement in the CO2 adsorption on the reduced STNMO sample is due to the accommodation of CO2 molecules on the oxygen-vacancy-related defect sites in the form of strong bonding between CO2 molecules and substrates2334. It should be noted that the acidity of Nb/Ti is stronger than that of Mn, which restricts the chemical adsorption of CO2, even though oxygen deficiency is also observed in the reduced STNO sample. The strong chemical adsorption and activation of CO2 are expected to significantly enhance the electrode performance and the CO2 splitting under electrolysis conditions.


In situ formation of oxygen vacancy in perovskite Sr 0.95 Ti 0.8 Nb 0.1 M 0.1 O 3 (M = Mn, Cr) toward efficient carbon dioxide electrolysis
TGA of reduced samples in Ar atmosphere: (a) STNO and (c) STNMO. Desorption of CO2 for reduced samples in CO2 atmosphere: (b) STNO and (d) STNMO.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC5382710&req=5

f9: TGA of reduced samples in Ar atmosphere: (a) STNO and (c) STNMO. Desorption of CO2 for reduced samples in CO2 atmosphere: (b) STNO and (d) STNMO.
Mentions: The adsorption of CO2 was investigated for the STNO and STNMO samples using TGA tests in Ar and 100% CO2 from room temperature to 1000°C at a rate of 10°C min−1. In Figs. 9 (a) and (c), the weights of the reduced STNO and STNMO samples are unchanged in an Ar atmosphere in the temperature range of 200 to 1000°C, which are employed as references. By contrast, the weight loss of the reduced STNO sample after CO2 adsorption above 400°C reaches approximately 0.15%. The chemical desorption is observed at approximately 600°C (Fig. S5 (a)), which implies the presence of chemical adsorption of CO2 on the reduced STNO sample. However, the weight loss of the reduced STNMO sample after CO2 adsorption is substantially increased to 1%, and the strong chemical desorption has been extended to approximately 800°C, as shown in Fig. S5 (b). In addition, the specific surface area of the STNO and STNMO powders are similar to each other (2.5 m2·g−1). The desorption of CO2 was calculated, and the results are presented in Figs. 9 (b) and (d) for STNO and STNMO, respectively. The desorption volume of CO2 is significantly enhanced to approximately 1.0 ml·m−2 catalyst for the Mn-doped STNMO sample, and the onset of the desorption temperature is as high as 800°C, which is near the decomposition temperature of common carbonates. The significant enhancement in the CO2 adsorption on the reduced STNMO sample is due to the accommodation of CO2 molecules on the oxygen-vacancy-related defect sites in the form of strong bonding between CO2 molecules and substrates2334. It should be noted that the acidity of Nb/Ti is stronger than that of Mn, which restricts the chemical adsorption of CO2, even though oxygen deficiency is also observed in the reduced STNO sample. The strong chemical adsorption and activation of CO2 are expected to significantly enhance the electrode performance and the CO2 splitting under electrolysis conditions.

View Article: PubMed Central - PubMed

ABSTRACT

In this work, redox-active Mn or Cr is introduced to the B site of redox stable perovskite Sr0.95Ti0.9Nb0.1O3.00 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 Sr0.95Ti0.9Nb0.1O3.00 to reduced Sr0.95Ti0.9Nb0.1O2.90 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 Sr0.95Ti0.8Nb0.1M0.1O3.00 (M = Mn, Cr) to Sr0.95Ti0.8Nb0.1M0.1O2.85. 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.

No MeSH data available.