Exploring Ca?Ce?M?O (M = 3d Transition Metal) Oxide Perovskites for Solar Thermochemical Applications [electronic resource]

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Tác giả:

Ngôn ngữ: eng

Ký hiệu phân loại: 621.3 Electrical, magnetic, optical, communications, computer engineering; electronics, lighting

Thông tin xuất bản: Washington, D.C. : Oak Ridge, Tenn. : United States. Dept. of Energy. Office of Energy Efficiency and Renewable Energy ; Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2020

Mô tả vật lý: Size: p. 9964-9982 : , digital, PDF file.

Bộ sưu tập: Metadata

ID: 255578

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Chủ đề

Solar thermochemical (STC) processes hold promise as efficient ways to generate renewable fuels, fuel precursors, or chemical feedstocks using concentrated sunlight. Specifically, one actively researched approach is the two-step STC cycle, which uses a redox-active, off-stoichiometric, transition-metal oxide material to split water and/or CO
2
, generating H
2
and/or CO, respectively, or syngas (a combination of H
2
and CO). Identifying novel metal oxides that yield larger reduction extents (practically achievable off-stoichiometries) than the state-of-the-art CeO
2
is critical. Here, we explore the chemical space of Ca?Ce?M?O (M = 3d transition metal, except Cu and Zn) metal oxide perovskites, with Ca and/or Ce occupying the A site and M occupying the B site within an ABO
3
framework, as potential STC candidates. We use density functional theory (DFT)-based calculations and systematically evaluate the oxygen vacancy (VaO) formation energy (? enthalpy of reduction in an STC cycle), electronic properties, thermodynamic stability of CaMO
3
, CeMO
3
, and Ca
0.5
Ce
0.5
MO
3
perovskites, and the VaO formation energy within Ca
0.5
Ce
0.5
Ti
0.5
Mg
0.5
O
3
perovskite. We consider only Ca and/or Ce on the A site because of their similar size and the potential redox activity of Ce
4+
. If both Ce and M exhibit simultaneous reduction with Va
O
formation, the resulting perovskite could exhibit a larger entropy of reduction than a single cation reduction. The increased entropy produces increased reduction for fixed temperature, partial pressure of oxygen, and reduction enthalpy, and therefore increased STC efficiency. Importantly, we identify Ca
0.5
Ce
0.5
MnO
3
, Ca
0.5
Ce
0.5
FeO
3
, and Ca
0.5
Ce
0.5
VO
3
to be promising candidates based on their Va
O
formation energy and thermodynamic (meta)stability. Moreover, based on our calculated on-site magnetic moments, electron density of states, and electron density differences between pristine and defective structures, we find Ca
0.5
Ce
0.5
MnO
3
to exhibit simultaneous reduction of both Ce
4+
(A-site) and Mn
3+
(B-site), highlighting a particularly promising candidate for STC applications with a predicted higher entropy of reduction than CeO
2
. Lastly, we extract metrics that govern the trends in Va
O
formation energies, such as standard reduction potentials, and provide pointers for further experimental and theoretical studies, which will enable the design of improved materials for the STC cycle.

1. 14 solar energy
2. 30 direct energy conversion
3. 36 materials science
4. Chemical structure
5. Density functional theory
6. Et al
7. Oxygen
8. Perovskites
9. Redox reactions
10. Solar thermochemical
11. Water splitting

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