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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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Ion conductivity of STNO, STNMO and STNCO as a function of temperature from 400 to 800°C: (a) oxidized samples in air and (b) reduced samples in 5%H2/Ar.
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f8: Ion conductivity of STNO, STNMO and STNCO as a function of temperature from 400 to 800°C: (a) oxidized samples in air and (b) reduced samples in 5%H2/Ar.

Mentions: With the formation of oxygen vacancies in the samples, the ionic conductivities of the Mn- or Cr-doped titanate are expected to remarkably improve. Fig. 8 shows the temperature dependence of the ionic conductivity of the oxidized and reduced samples in air and 5% H2/Ar from 400 to 800°C, respectively. The ionic conductivities of the oxidized and reduced STNO samples improve with temperature and reach approximately 1.8 × 10−4 and 7.3 × 10−4 S·cm−1 in air and 5%H2/Ar, respectively, at 800°C. The reduced sample with a high concentration of oxygen vacancies strongly improves the ionic conductivity, which is approximately 3 times higher. In addition, the impedance spectra for the ionic conductivities of oxidized and reduced STNO at 800°C were also measured, and the results are presented in Figs. S4 (a) and (b), respectively3536. The calculated results show similar values for the ionic conductivities of STNO (i.e., 2.0 × 10−4 for oxidized and 7.1 × 10−4 S·cm−1 for reduced STNO). In Figs. 8 (a) and (b), the ionic conductivities of the oxidized and reduced STNMO as well as the STNCO samples reach 3.8 × 10−4 and 4.4 × 10−3 S·cm−1 and 3.9 × 10−4 and 2.4 × 10−3 in air and 5% H2/Ar at 800°C, respectively. In Fig. S4, the impedance spectra for the ionic conductivities of oxidized and reduced STNMO and STNCO at 800°C are also presented. The results have the same order of magnitudes as those in Fig. 8 (a) and (b). The introduction of redox-active Mn or Cr significantly enhances the ionic conductivity of STNMO or STNCO in contrast to STNO due to the creation of charge carriers and oxygen vacancies in the sample. However, the oxidized STNMO or STNCO sample exhibits low ionic conductivities even though these values are higher than those of the oxidized STNO sample, which are most likely due to insufficient oxygen vacancies; the oxygen vacancies are the charge carriers for oxide ion transport in the sample. However, the oxygen vacancy most likely prefers to exist at the grain boundary and further promote the ionic transport in sintered samples. Upon reduction, the STNMO or STNCO sample with a high concentration of oxygen vacancies exhibits significantly improved oxide-ion conductivity, which is approximately 1 order of magnitude higher in a reducing atmosphere at intermediate temperatures. Therefore, the oxygen vacancy defect site is expected to be able to accommodate the CO2 molecules and enable chemical adsorption2333.


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
Ion conductivity of STNO, STNMO and STNCO as a function of temperature from 400 to 800°C: (a) oxidized samples in air and (b) reduced samples in 5%H2/Ar.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5382710&req=5

f8: Ion conductivity of STNO, STNMO and STNCO as a function of temperature from 400 to 800°C: (a) oxidized samples in air and (b) reduced samples in 5%H2/Ar.
Mentions: With the formation of oxygen vacancies in the samples, the ionic conductivities of the Mn- or Cr-doped titanate are expected to remarkably improve. Fig. 8 shows the temperature dependence of the ionic conductivity of the oxidized and reduced samples in air and 5% H2/Ar from 400 to 800°C, respectively. The ionic conductivities of the oxidized and reduced STNO samples improve with temperature and reach approximately 1.8 × 10−4 and 7.3 × 10−4 S·cm−1 in air and 5%H2/Ar, respectively, at 800°C. The reduced sample with a high concentration of oxygen vacancies strongly improves the ionic conductivity, which is approximately 3 times higher. In addition, the impedance spectra for the ionic conductivities of oxidized and reduced STNO at 800°C were also measured, and the results are presented in Figs. S4 (a) and (b), respectively3536. The calculated results show similar values for the ionic conductivities of STNO (i.e., 2.0 × 10−4 for oxidized and 7.1 × 10−4 S·cm−1 for reduced STNO). In Figs. 8 (a) and (b), the ionic conductivities of the oxidized and reduced STNMO as well as the STNCO samples reach 3.8 × 10−4 and 4.4 × 10−3 S·cm−1 and 3.9 × 10−4 and 2.4 × 10−3 in air and 5% H2/Ar at 800°C, respectively. In Fig. S4, the impedance spectra for the ionic conductivities of oxidized and reduced STNMO and STNCO at 800°C are also presented. The results have the same order of magnitudes as those in Fig. 8 (a) and (b). The introduction of redox-active Mn or Cr significantly enhances the ionic conductivity of STNMO or STNCO in contrast to STNO due to the creation of charge carriers and oxygen vacancies in the sample. However, the oxidized STNMO or STNCO sample exhibits low ionic conductivities even though these values are higher than those of the oxidized STNO sample, which are most likely due to insufficient oxygen vacancies; the oxygen vacancies are the charge carriers for oxide ion transport in the sample. However, the oxygen vacancy most likely prefers to exist at the grain boundary and further promote the ionic transport in sintered samples. Upon reduction, the STNMO or STNCO sample with a high concentration of oxygen vacancies exhibits significantly improved oxide-ion conductivity, which is approximately 1 order of magnitude higher in a reducing atmosphere at intermediate temperatures. Therefore, the oxygen vacancy defect site is expected to be able to accommodate the CO2 molecules and enable chemical adsorption2333.

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.