Limits...
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

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.


XRD Rietveld refinement patterns of (a) oxidized STNO, (b) reduced STNO, (c) oxidized STNMO, (d) reduced STNMO, (e) oxidized STNCO and (f) reduced STNCO.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: XRD Rietveld refinement patterns of (a) oxidized STNO, (b) reduced STNO, (c) oxidized STNMO, (d) reduced STNMO, (e) oxidized STNCO and (f) reduced STNCO.

Mentions: Figs. 1 (a) and (b) present the XRD Rietveld refinement patterns of the oxidized and reduced STNO powders, respectively. The refinement of the oxidized and reduced samples yields χ2, wRp and Rp values of 1.46, 6.27% and 4.95% and 1.47, 6.52% and 5%, respectively, indicating close agreements with the experimental data. Based on the experimental and calculated results, the phase structure of both the oxidized and reduced samples is consistent with the perovskite structure with a space group of Pm-3m32. The crystal cell parameter of the oxidized STNO is 3.9146(8) Å, which is slightly smaller than that of the reduced STNO (i.e., 3.9191(8) Å). The chemical oxidation states of Ti and Nb are +4 and +5 with ionic radii of 0.605 and 0.69 Å, respectively, in the oxidized STNO. By contrast, a portion of the Ti and Nb has been transformed into Ti3+ (0.67 Å) and Nb4+ (0.74 Å) in the reduced STNO sample, which may cause the cell parameter expansion, even though oxygen loss is observed after the high-temperature reduction. Nevertheless, no phase transition is observed in the STNO even after the high-temperature treatment in a reducing atmosphere, which confirms the superior redox stability of the niobate-titanate ceramics. As demonstrated in Figs. 1 (c) and (d), the XRD Rietveld refinement patterns of single-phase STNMO show the successful partial replacement of Ti with Mn at the B-site. The refinement of the oxidized and reduced samples yields χ2, wRp and Rp values of 1.196, 5.64% and 4.47% and 1.365, 5.90% and 4.53%, respectively. The cell parameter is 3.9139(4) Å for the oxidized STNMO, which is smaller than that of the oxidized STNO sample due to the smaller ionic radii of Mn4+ (0.53 Å) in contrast to Ti4+ and Nb5+. However, the cell parameter of the reduced STNMO increases to 3.9187(6) Å due to the partial transformation of Mn4+, Nb5+ and Ti4+ to Mn3+ (0.645 Å), Nb4+ (0.74 Å) and Ti3+ (0.67 Å), respectively, leading to expansion of the cell parameters in the reduced samples. A similar change is also observed for Cr-doped STNO in Figs. 1 (e) and (f). The refinement results of the oxidized and reduced STNCO yield χ2, wRp and Rp values of 1.329, 6.22% and 4.09% and 1.024, 6.40% and 4.37%, respectively. For the oxidized STNCO, the cell parameter is 3.91304(4) Å, which is slightly smaller than that of the oxidized STNO because a small amount of Cr6+ (0.44 Å) is present in STNCO. However, the cell parameters of the reduced STNCO increase to 3.91461(27) Å because of the transformation of Cr6+, Nb5+ and Ti4+ to Cr3+ (0.615 Å), Nb4+ (0.74 Å) and Ti3+ (0.67 Å), respectively, leading to the expansion of the cell parameters of the reduced STNCO. Fig. S1 presents the XRD patterns of the Sr0.95Ti0.9−xNb0.1CrxO3 (x = 0.1, 0.2 and 0.3) powders after calcining in air at 1300°C for 10 h; however, a single-phase material is only achieved with x = 0.1 (Sr0.95Ti0.8Nb0.1Cr0.1O3, STNCO). High-resolution transmission electron microscopy (HRTEM) analysis of the oxidized and reduced STNO sample indicates a lattice spacing of 0.280 and 0.284 nm for (110), respectively, as shown in Figs. 2 (a) and (b). The corresponding lattice spacing of the oxidized sample increases from 0.276 nm (110) to 0.279 nm (110) for the reduced STNMO sample (Figs. 2 (c) and (d)), which further confirms the lattice expansion of the reduced sample. In addition, the corresponding lattice spacing of the oxidized STNCO increased from 0.276 nm (110) to 0.277 nm (110) for the reduced STNCO in Figs. 2 (e) and (f), further confirming the lattice expansion of the reduced sample.


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
XRD Rietveld refinement patterns of (a) oxidized STNO, (b) reduced STNO, (c) oxidized STNMO, (d) reduced STNMO, (e) oxidized STNCO and (f) reduced STNCO.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: XRD Rietveld refinement patterns of (a) oxidized STNO, (b) reduced STNO, (c) oxidized STNMO, (d) reduced STNMO, (e) oxidized STNCO and (f) reduced STNCO.
Mentions: Figs. 1 (a) and (b) present the XRD Rietveld refinement patterns of the oxidized and reduced STNO powders, respectively. The refinement of the oxidized and reduced samples yields χ2, wRp and Rp values of 1.46, 6.27% and 4.95% and 1.47, 6.52% and 5%, respectively, indicating close agreements with the experimental data. Based on the experimental and calculated results, the phase structure of both the oxidized and reduced samples is consistent with the perovskite structure with a space group of Pm-3m32. The crystal cell parameter of the oxidized STNO is 3.9146(8) Å, which is slightly smaller than that of the reduced STNO (i.e., 3.9191(8) Å). The chemical oxidation states of Ti and Nb are +4 and +5 with ionic radii of 0.605 and 0.69 Å, respectively, in the oxidized STNO. By contrast, a portion of the Ti and Nb has been transformed into Ti3+ (0.67 Å) and Nb4+ (0.74 Å) in the reduced STNO sample, which may cause the cell parameter expansion, even though oxygen loss is observed after the high-temperature reduction. Nevertheless, no phase transition is observed in the STNO even after the high-temperature treatment in a reducing atmosphere, which confirms the superior redox stability of the niobate-titanate ceramics. As demonstrated in Figs. 1 (c) and (d), the XRD Rietveld refinement patterns of single-phase STNMO show the successful partial replacement of Ti with Mn at the B-site. The refinement of the oxidized and reduced samples yields χ2, wRp and Rp values of 1.196, 5.64% and 4.47% and 1.365, 5.90% and 4.53%, respectively. The cell parameter is 3.9139(4) Å for the oxidized STNMO, which is smaller than that of the oxidized STNO sample due to the smaller ionic radii of Mn4+ (0.53 Å) in contrast to Ti4+ and Nb5+. However, the cell parameter of the reduced STNMO increases to 3.9187(6) Å due to the partial transformation of Mn4+, Nb5+ and Ti4+ to Mn3+ (0.645 Å), Nb4+ (0.74 Å) and Ti3+ (0.67 Å), respectively, leading to expansion of the cell parameters in the reduced samples. A similar change is also observed for Cr-doped STNO in Figs. 1 (e) and (f). The refinement results of the oxidized and reduced STNCO yield χ2, wRp and Rp values of 1.329, 6.22% and 4.09% and 1.024, 6.40% and 4.37%, respectively. For the oxidized STNCO, the cell parameter is 3.91304(4) Å, which is slightly smaller than that of the oxidized STNO because a small amount of Cr6+ (0.44 Å) is present in STNCO. However, the cell parameters of the reduced STNCO increase to 3.91461(27) Å because of the transformation of Cr6+, Nb5+ and Ti4+ to Cr3+ (0.615 Å), Nb4+ (0.74 Å) and Ti3+ (0.67 Å), respectively, leading to the expansion of the cell parameters of the reduced STNCO. Fig. S1 presents the XRD patterns of the Sr0.95Ti0.9−xNb0.1CrxO3 (x = 0.1, 0.2 and 0.3) powders after calcining in air at 1300°C for 10 h; however, a single-phase material is only achieved with x = 0.1 (Sr0.95Ti0.8Nb0.1Cr0.1O3, STNCO). High-resolution transmission electron microscopy (HRTEM) analysis of the oxidized and reduced STNO sample indicates a lattice spacing of 0.280 and 0.284 nm for (110), respectively, as shown in Figs. 2 (a) and (b). The corresponding lattice spacing of the oxidized sample increases from 0.276 nm (110) to 0.279 nm (110) for the reduced STNMO sample (Figs. 2 (c) and (d)), which further confirms the lattice expansion of the reduced sample. In addition, the corresponding lattice spacing of the oxidized STNCO increased from 0.276 nm (110) to 0.277 nm (110) for the reduced STNCO in Figs. 2 (e) and (f), further confirming the lattice expansion of the reduced sample.

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.