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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.

No MeSH data available.


The electrical conductivity of STNO, STNMO and STNCO (a) as a function of temperature in 5%H2/Ar from 400 to 800°C and as a function of oxygen partial pressure (from 10−20 to 10−2 atm) at 800°C for (b) STNO, (c) STNMO and (d) STNCO.
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f7: The electrical conductivity of STNO, STNMO and STNCO (a) as a function of temperature in 5%H2/Ar from 400 to 800°C and as a function of oxygen partial pressure (from 10−20 to 10−2 atm) at 800°C for (b) STNO, (c) STNMO and (d) STNCO.

Mentions: The dependence of conductivities on the temperature and oxygen partial pressure (pO2) is studied to investigate the electrical properties of the STNO, STNMO and STNCO samples. As observed in Fig. 7 (a), the conductivity of the reduced STNO, STNMO and STNCO samples display typical metallic behaviors with negative temperature coefficients in 5%H2/Ar, which indicates a typical n-type conducting mechanism in reducing atmospheres. The reduced STNCO, STNMO and STNO samples exhibit similar conductivity values in 5%H2/Ar of approximately 36.3, 54.5 and 60.2 S·cm−1 at 800°C, respectively. The conductivity of the reduced STNO sample is higher than that of the reduced STNMO and STNCO, which is most likely due to Mn or Cr doping at the B-sites of STNO. Therefore, the electron is consumed by the hole generated by the combination of the oxygen vacancy and atmospheric oxygen. The conductivities of the reduced STNO, STNMO and STNCO samples are strongly dependent on the pO2, as observed in Figs. 6 (b), (c) and (d). The n-type conductivity rapidly decreases as the pO2 increases from 10−16 to 10−15 atm, which is due to the conversion of Ti3+ to Ti4+ in the gradually decreasing reducing atmosphere at 800°C. However, the conductivity does not change over a wide range of pO2, which is most likely due to the rapid change in the pO2 in this range, and the sample is not in an equilibrium state, which causes an inconsistent change in the conductivity. In addition, a significant decrease in the conductivity is observed for pO2 above 10−4 atm due to the sufficient oxidation of Ti3+ to Ti4+ in the samples, and the sample finally transforms into a p-type conductor with a low conductivity at 800°C in air. As observed in Fig. S3, the conductivities of oxidized STNO and STNMO gradually improve with temperature, which indicates a typical p-type semiconducting behavior. The conductivity only reaches approximately ~10−3 S·cm−1 for oxidized STNO and ~10−2 S·cm−1 for STNMO at 800°C in air due to an increase in the charge carriers generated by the combination of the oxygen vacancy created by the Mn dopant and the atmospheric oxygen. The material is redox stable; however, the conductivity is not stable in a wide range of pO2 because the oxidation of the material leads to the loss of electronic conductivity. This material adapts well to a reducing condition but loses conductivity in an oxidizing atmosphere.


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
The electrical conductivity of STNO, STNMO and STNCO (a) as a function of temperature in 5%H2/Ar from 400 to 800°C and as a function of oxygen partial pressure (from 10−20 to 10−2 atm) at 800°C for (b) STNO, (c) STNMO and (d) STNCO.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f7: The electrical conductivity of STNO, STNMO and STNCO (a) as a function of temperature in 5%H2/Ar from 400 to 800°C and as a function of oxygen partial pressure (from 10−20 to 10−2 atm) at 800°C for (b) STNO, (c) STNMO and (d) STNCO.
Mentions: The dependence of conductivities on the temperature and oxygen partial pressure (pO2) is studied to investigate the electrical properties of the STNO, STNMO and STNCO samples. As observed in Fig. 7 (a), the conductivity of the reduced STNO, STNMO and STNCO samples display typical metallic behaviors with negative temperature coefficients in 5%H2/Ar, which indicates a typical n-type conducting mechanism in reducing atmospheres. The reduced STNCO, STNMO and STNO samples exhibit similar conductivity values in 5%H2/Ar of approximately 36.3, 54.5 and 60.2 S·cm−1 at 800°C, respectively. The conductivity of the reduced STNO sample is higher than that of the reduced STNMO and STNCO, which is most likely due to Mn or Cr doping at the B-sites of STNO. Therefore, the electron is consumed by the hole generated by the combination of the oxygen vacancy and atmospheric oxygen. The conductivities of the reduced STNO, STNMO and STNCO samples are strongly dependent on the pO2, as observed in Figs. 6 (b), (c) and (d). The n-type conductivity rapidly decreases as the pO2 increases from 10−16 to 10−15 atm, which is due to the conversion of Ti3+ to Ti4+ in the gradually decreasing reducing atmosphere at 800°C. However, the conductivity does not change over a wide range of pO2, which is most likely due to the rapid change in the pO2 in this range, and the sample is not in an equilibrium state, which causes an inconsistent change in the conductivity. In addition, a significant decrease in the conductivity is observed for pO2 above 10−4 atm due to the sufficient oxidation of Ti3+ to Ti4+ in the samples, and the sample finally transforms into a p-type conductor with a low conductivity at 800°C in air. As observed in Fig. S3, the conductivities of oxidized STNO and STNMO gradually improve with temperature, which indicates a typical p-type semiconducting behavior. The conductivity only reaches approximately ~10−3 S·cm−1 for oxidized STNO and ~10−2 S·cm−1 for STNMO at 800°C in air due to an increase in the charge carriers generated by the combination of the oxygen vacancy created by the Mn dopant and the atmospheric oxygen. The material is redox stable; however, the conductivity is not stable in a wide range of pO2 because the oxidation of the material leads to the loss of electronic conductivity. This material adapts well to a reducing condition but loses conductivity in an oxidizing atmosphere.

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.