Proton, Hydroxide Ion, and Oxide Ion Affinities of Closed-Shell Oxides: Importance for the Hydration Reaction and Correlation to Electronic Structure

Bjørheim, Tor S.; Hoedl, Maximilian F.; Merkle, Rotraut; Kotomin, E. A.; Maier, Joachim

doi:10.1021/acs.jpcc.9b07570

Cited by 27 publications

(29 citation statements)

References 39 publications

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“…The ionization potential (IP) can be obtained from the difference between the vacuum potential ( V va c ) and the energy of the highest occupied Kohn‐Sham orbital defined, as simulations suggest, as the valence band maximum

()(, I P = V_{vac} ‐ E_{VBM})

32 . From the point of view of charge equilibrium, proton addition and electron removal from the structure are equivalent processes, and it is known from other studies, that the IP values may correlate with proton affinity 33 . For example, in multiple oxygen‐containing molecules, a linear relation between these two parameters was found 34 .…”

Section: Resultsmentioning

confidence: 99%

“…32 From the point of view of charge equilibrium, proton addition and electron removal from the structure are equivalent processes, and it is known from other studies, that the IP values may correlate with proton affinity. 33 For example, in multiple oxygen-containing molecules, a linear relation between these two parameters was found. 34 A constant E VBM value maybe surprising, considering the higher protonation of samples with higher dopant content reported previously.…”

Section: X-ray Photoelectron Spectroscopy (Xps)mentioning

confidence: 99%

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Antimony substituted lanthanum orthoniobate proton conductor – Structure and electronic properties

et al. 2020

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X‐ray and neutron diffraction have been utilized to analyze the crystalline and electronic structure of lanthanum orthoniobate substituted by antimony. Using X‐ray absorption spectroscopy and photoelectron spectroscopy, changes in the electronic structure of the material upon substitution have been analyzed. The structural transition temperature between fergusonite and scheelite phases for 30 mol% antimony substitution was found to be 15°C. Based on the neutron data, the oxygen nonstoichiometry was found to be relatively low. Moreover no influence on the position of the valence band maximum was observed. The influence of the protonation on the electronic structure of constituent oxides has been studied. Absorption data show that the incorporation of protonic defects into the lanthanum orthoniobate structure leads to changes in lanthanum electronic structure and a decrease in the density of unoccupied electronic states.

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()(, I P = V_{vac} ‐ E_{VBM})

Section: Resultsmentioning

confidence: 99%

Section: X-ray Photoelectron Spectroscopy (Xps)mentioning

confidence: 99%

Antimony substituted lanthanum orthoniobate proton conductor – Structure and electronic properties

et al. 2020

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“…The stability of protons appears to be enhanced with the increasing Ce content, in line with previous reports of more favorable hydration thermodynamics of Equation (1) for BaZrO 3 and BaCeO 3 due to the more basic nature of the latter. [ 51,53 ] However, the more favorable hydration thermodynamics is accompanied by reduced proton mobility with increasing Ce content. A number of DFT calculations have shown that the migration energy of protons in Y doped BaCeO 3 (0.45 eV) [ 54 ] is higher than that of Y doped BaZrO 3 (0.31 eV).…”

Section: Discussionmentioning

confidence: 99%

Yttrium‐Doped Barium Zirconate‐Cerate Solid Solution as Proton Conducting Electrolyte: Why Higher Cerium Concentration Leads to Better Performance for Fuel Cells and Electrolysis Cells

Han

Liu

Bjørheim

et al. 2021

Advanced Energy Materials

102

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Proton conducting Y‐doped BaZrO3, BaCeO3 and their solid solutions are receiving increasing attention due to their promising application as electrolytes in ceramic fuel cells and electrolysis cells. However, the literature indicates a clear tendency that the performance of the cells increases with increasing Ce content in the electrolyte. In this work, to elucidate this phenomenon, a systematic work is performed on investigating the phase, hydration, and transport behaviors of BaZr0.8−xCexY0.2O3−δ (BZCY20). The results reveal that in the temperature range between 500 and 700 °C, with increasing Ce content, the dehydration temperature elevates and the proton concentration increases, showing that the Ce component favors the stabilization of protons. Furthermore, the transport number of hole conduction decreases, whereas the transport number of ionic conduction increases with the increasing Ce content. By further separating the contribution of oxide ions and protons, it is found that the oxide ion conductivity increases with the increasing Ce content at higher temperatures of 600 and 700 °C. Such decreased hole conductivity and increased oxide ion conductivity result in the enhancement of the ionic conduction of BZCY20 with increasing Ce content, and therefore improve the performance of fuel cells and electrolysis cells.

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“…Formation of protonic defects is a result of either hydration or hydrogenation, and is expected to scale with the concentration of oxygen vacancies or electron holes, respectively [35][36][37]. Both depend on the average Co oxidation state, while no correlation between the water uptake and Co-oxidation state is seen.…”

Section: Oxygen Non-stoichiometrymentioning

confidence: 99%

Structure and water uptake in BaLnCo2O6−δ (Ln =La, Pr, Nd, Sm, Gd, Tb and Dy)

et al. 2020

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The structure of BaLnCo2O6-δ (Ln =La, Pr, Nd, Sm, Gd, Tb and Dy) is was studied by the means of synchrotron radiation powder X-ray diffraction, neutron powder diffraction and Transmission Electron Microscopy (TEM), while water uptake properties were analysed with the use of thermogravimetry (TG) and water adsorption isotherms. The structure refinement revealed that the dominant phase in all compositions was orthorhombic with an ordering of the A-site cations along the c-axis and ordering of oxygen vacancies along the b-axis, which was also directly evidenced by TEM. It was shown that both unit cell volume and average Co-oxidation state at room temperature decrease linearly with decreasing Ln radius. TG water uptake experiments in humidified N2-O2 gas mixture at 300°C revealed that among all compositions, only BaLaCo2O6-δ and BaGdCo2O6-δ exhibit significant water uptake. Surface water adsorption studies showed that the α, a normalised parameter reflecting the surface hydrophilicity, mostly independently of Ln radius was close to 0.5, which means that the surface is neither hydrophobic nor hydrophilic. The results indicated that water uptake observed at 300 °C is a bulk process, which cannot be described by standard hydration/hydrogenation reaction and it is related to the layered structure of the perovskite lattice and characteristic to La or Gd being present in the lattice.

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Proton, Hydroxide Ion, and Oxide Ion Affinities of Closed-Shell Oxides: Importance for the Hydration Reaction and Correlation to Electronic Structure

Cited by 27 publications

References 39 publications

Antimony substituted lanthanum orthoniobate proton conductor – Structure and electronic properties

Antimony substituted lanthanum orthoniobate proton conductor – Structure and electronic properties

Yttrium‐Doped Barium Zirconate‐Cerate Solid Solution as Proton Conducting Electrolyte: Why Higher Cerium Concentration Leads to Better Performance for Fuel Cells and Electrolysis Cells

Structure and water uptake in BaLnCo2O6−δ (Ln =La, Pr, Nd, Sm, Gd, Tb and Dy)

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