Lithium superoxide

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Lithium superoxide
Identifiers
3D model (JSmol)
  • InChI=1S/Li.O2/c;1-2/q+1;-1
    Key: GMZGUKXTXROVJB-UHFFFAOYSA-N
  • [Li+].O=[O-]
Properties
LiO2
Molar mass 38.94 g·mol−1
Density g/cm3, solid[ clarification needed ]
Melting point <25 °C (decomposes)
Related compounds
Other cations
Related Lithium oxides
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Lithium superoxide is an unstable inorganic salt with formula Li O 2. A radical compound, it can be produced at low temperature in matrix isolation experiments, or in certain nonpolar, non-protic solvents. Lithium superoxide is also a transient species during the reduction of oxygen in a lithium–air galvanic cell, and serves as a main constraint on possible solvents for such a battery. For this reason, it has been investigated thoroughly using a variety of methods, both theoretical and spectroscopic.

Contents

Structure

The LiO2 molecule is a misnomer: the bonds between lithium and oxygen are highly ionic, with almost complete electron-transfer. [1] The force constant between the two oxygen atoms matches the constants measured for the superoxide anion (O2) in other contexts. The bond length for the O-O bond was determined to be 1.34 Å. Using a simple crystal structure optimization, the Li-O bond was calculated to be approximately 2.10 Å. [2]

There have been quite a few studies regarding the clusters formed by LiO2 molecules. The most common dimer has been found to be the cage isomer. Second to it is the singlet bypyramidal structure. Studies have also been done on the chair complex and the planar ring, but these two are less favorable, though not necessarily impossible. [3]

Production and reactions

Lithium superoxide is extremely reactive because of the odd number of electrons present in the π* molecular orbital of the superoxide anion. [4] Matrix isolation techniques can produce pure samples of the compound, but they are only stable at 15-40 K. [3]

At higher (but still cryogenic) temperatures, lithium superoxide can be produced by ozonating lithium peroxide (Li2O2) in freon 12:

Li2O2(f12) + 2 O3(g) → 2 LiO2(f12) + 2 O2(g)

The resulting product is only stable up to −35 °C. [5]

Alternatively, lithium electride dissolved in anhydrous ammonia will reduce oxygen gas to yield the same product:

[Li+][e](am) + O2(g) → [Li+][O2](am)

Lithium superoxide is, however, only metastable in ammonia, gradually oxidizing the solvent to water and nitrogen gas:

2 O2 + 2 NH3 → N2 + 2 H2O + 2 OH

Unlike other known decompositions of LiO2, this reaction bypasses lithium peroxide. [6]

Occurrence

Like other superoxides, lithium superoxide is the product of a one-electron reduction of an oxygen molecule. It thus appears whenever oxygen is mixed with single-electron redox catalysts, such as p-benzoquinone. [7]

In batteries

Lithium superoxide also appears at the cathode of a lithium-air galvanic cell during discharge, as in the following reaction: [8]

Li+ + e + O2 → LiO2

This product typically then reacts and proceed to form lithium peroxide, Li2O2

2 LiO2 → Li2O2 + O2

The mechanism for this last reaction has not been confirmed and developing a complete theory of the oxygen reduction process remains a theoretical challenge as of 2022. [9] Indeed, recent work suggests that LiO2 can be stabilized via a suitable cathode made of graphene with iridium nanoparticles. [10]

A significant challenge when investigating these batteries is finding an ideal solvent in which to perform these reactions; current candidates are ether- and amide-based, but these compounds readily react with the superoxide and decompose. [9] Nevertheless, lithium-air cells remain the focus of intense research, because of their large energy density—comparable to the internal combustion engine. [8]

In the atmosphere

Lithium superoxide can also form for extended periods of time in low-density, high-energy environments, such as the upper atmosphere. The mesosphere contains a persistent layer of alkali metal cations ablated from meteors. For sodium and potassium, many of the ions bond to form particles of the corresponding superoxide. It is currently unclear whether lithium should react analogously. [11]

See also

Related Research Articles

<span class="mw-page-title-main">Alkali metal</span> Group of highly reactive chemical elements

The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). Together with hydrogen they constitute group 1, which lies in the s-block of the periodic table. All alkali metals have their outermost electron in an s-orbital: this shared electron configuration results in their having very similar characteristic properties. Indeed, the alkali metals provide the best example of group trends in properties in the periodic table, with elements exhibiting well-characterised homologous behaviour. This family of elements is also known as the lithium family after its leading element.

In chemistry, a superoxide is a compound that contains the superoxide ion, which has the chemical formula O−2. The systematic name of the anion is dioxide(1−). The reactive oxygen ion superoxide is particularly important as the product of the one-electron reduction of dioxygen O2, which occurs widely in nature. Molecular oxygen (dioxygen) is a diradical containing two unpaired electrons, and superoxide results from the addition of an electron which fills one of the two degenerate molecular orbitals, leaving a charged ionic species with a single unpaired electron and a net negative charge of −1. Both dioxygen and the superoxide anion are free radicals that exhibit paramagnetism. Superoxide was historically also known as "hyperoxide".

<span class="mw-page-title-main">Magnesium peroxide</span> Chemical compound

Magnesium peroxide (MgO2) is an odorless fine powder peroxide with a white to off-white color. It is similar to calcium peroxide because magnesium peroxide also releases oxygen by breaking down at a controlled rate with water. Commercially, magnesium peroxide often exists as a compound of magnesium peroxide and magnesium hydroxide.

<span class="mw-page-title-main">Potassium superoxide</span> Chemical compound

Potassium superoxide is an inorganic compound with the formula KO2. It is a yellow paramagnetic solid that decomposes in moist air. It is a rare example of a stable salt of the superoxide anion. It is used as a CO2 scrubber, H2O dehumidifier, and O2 generator in rebreathers, spacecraft, submarines, and spacesuits.

<span class="mw-page-title-main">Singlet oxygen</span> Oxygen with all of its electrons spin paired

Singlet oxygen, systematically named dioxygen(singlet) and dioxidene, is a gaseous inorganic chemical with the formula O=O (also written as 1
[O
2
]
or 1
O
2
), which is in a quantum state where all electrons are spin paired. It is kinetically unstable at ambient temperature, but the rate of decay is slow.

<span class="mw-page-title-main">Hexamethylphosphoramide</span> Chemical compound

Hexamethylphosphoramide, often abbreviated HMPA, is a phosphoramide (an amide of phosphoric acid) with the formula [(CH3)2N]3PO. This colorless liquid is a useful reagent in organic synthesis.

A solvated electron is a free electron in a solution, in which it behaves like an anion. An electron's being solvated in a solution means it is bound by the solution. The notation for a solvated electron in formulas of chemical reactions is "e". Often, discussions of solvated electrons focus on their solutions in ammonia, which are stable for days, but solvated electrons also occur in water and many other solvents – in fact, in any solvent that mediates outer-sphere electron transfer. The solvated electron is responsible for a great deal of radiation chemistry.

<span class="mw-page-title-main">Lithium peroxide</span> Chemical compound

Lithium peroxide is the inorganic compound with the formula Li2O2. It is a white, nonhygroscopic solid. Because of its high oxygen:mass and oxygen:volume ratios, the solid has been used to remove CO2 from the atmosphere in spacecraft.

The Haber–Weiss reaction generates •OH (hydroxyl radicals) from H2O2 (hydrogen peroxide) and superoxide (•O2) catalyzed by iron ions. It was first proposed by Fritz Haber and his student Joseph Joshua Weiss in 1932.

<span class="mw-page-title-main">Lithium cobalt oxide</span> Chemical compound

Lithium cobalt oxide, sometimes called lithium cobaltate or lithium cobaltite, is a chemical compound with formula LiCoO
2
. The cobalt atoms are formally in the +3 oxidation state, hence the IUPAC name lithium cobalt(III) oxide.

Dioxygen complexes are coordination compounds that contain O2 as a ligand. The study of these compounds is inspired by oxygen-carrying proteins such as myoglobin, hemoglobin, hemerythrin, and hemocyanin. Several transition metals form complexes with O2, and many of these complexes form reversibly. The binding of O2 is the first step in many important phenomena, such as cellular respiration, corrosion, and industrial chemistry. The first synthetic oxygen complex was demonstrated in 1938 with cobalt(II) complex reversibly bound O2.

The lithium–air battery (Li–air) is a metal–air electrochemical cell or battery chemistry that uses oxidation of lithium at the anode and reduction of oxygen at the cathode to induce a current flow.

A metal–air electrochemical cell is an electrochemical cell that uses an anode made from pure metal and an external cathode of ambient air, typically with an aqueous or aprotic electrolyte.

A potassium-ion battery or K-ion battery is a type of battery and analogue to lithium-ion batteries, using potassium ions for charge transfer instead of lithium ions. It was invented by the Iranian/American chemist Ali Eftekhari in 2004.

Yang Shao-Horn is a Chinese American scholar, Professor of Mechanical Engineering and Materials Science and Engineering and a member of Research Laboratory of Electronics at the Massachusetts Institute of Technology. She is known for research on understanding and controlling of processes for storing electrons in chemical bonds towards zero-carbon energy and chemicals.

In chemistry, the oxygen reduction reaction refers to the reduction half reaction whereby O2 is reduced to water or hydrogen peroxide. In fuel cells, the reduction to water is preferred because the current is higher. The oxygen reduction reaction is well demonstrated and highly efficient in nature.

Rubidium superoxide or rubidium hyperoxide is a chemical compound with the chemical formula RbO2. In terms of oxidation states, the negatively charged superoxide and positively charged rubidium give it a structural formula of (Rb+)(O−2).

<span class="mw-page-title-main">Caesium peroxide</span> Chemical compound

Caesium peroxide or cesium peroxide is an inorganic compound of caesium and oxygen with the chemical formula Cs2O2. It can be formed from caesium metal by adding a stoichiometric amount in ammonia solution, or oxidizing the solid metal directly.

Caesium sesquioxide is a chemical compound with the formula Cs2O3 or more accurately Cs4O6. It is an oxide of caesium containing oxygen in different oxidation states. It consists of caesium cations Cs+, superoxide anions O−2 and peroxide anions O2−2. Caesium in this compound has an oxidation state of +1, while oxygen in superoxide has an oxidation state of −1/2 and oxygen in peroxide has an oxidation state of −1. This compound has a structural formula of (Cs+)4(O−2)2(O2−2). Compared to the other caesium oxides, this phase is less well studied, but has been long present in the literature. It can be created by thermal decomposition of caesium superoxide at 290 °C.

Iridium compounds are compounds containing the element iridium (Ir). Iridium forms compounds in oxidation states between −3 and +9, but the most common oxidation states are +1, +2, +3, and +4. Well-characterized compounds containing iridium in the +6 oxidation state include IrF6 and the oxides Sr2MgIrO6 and Sr2CaIrO6. iridium(VIII) oxide was generated under matrix isolation conditions at 6 K in argon. The highest oxidation state (+9), which is also the highest recorded for any element, is found in gaseous [IrO4]+.

References

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  2. Lau, Kah Chun; Curtiss, Larry A.; Greeley, Jeffrey (2011-11-09). "Density Functional Investigation of the Thermodynamic Stability of Lithium Oxide Bulk Crystalline Structures as a Function of Oxygen Pressure". The Journal of Physical Chemistry C. American Chemical Society (ACS). 115 (47): 23625–23633. doi:10.1021/jp206796h. ISSN   1932-7447.
  3. 1 2 Bryantsev, Vyacheslav S.; Blanco, Mario; Faglioni, Francesco (2010-07-16). "Stability of Lithium Superoxide LiO2 in the Gas Phase: Computational Study of Dimerization and Disproportionation Reactions". The Journal of Physical Chemistry A. American Chemical Society (ACS). 114 (31): 8165–8169. Bibcode:2010JPCA..114.8165B. doi:10.1021/jp1047584. ISSN   1089-5639. PMID   20684589.
  4. Lindsay, D. M.; Garland, D. A. (1987). "ESR spectra of matrix-isolated lithium superoxide". The Journal of Physical Chemistry. American Chemical Society (ACS). 91 (24): 6158–6161. doi:10.1021/j100308a020. ISSN   0022-3654.
  5. Vol'nov, I. I.; Tokareva, S. A.; Belevskii, V. N.; Klimanov, V. I. (1967-07-01). "Investigation of the nature of the interaction of lithium peroxide with ozone". Bulletin of the Academy of Sciences of the USSR, Division of Chemical Science. 16 (7): 1369–1371. doi:10.1007/BF00905329. ISSN   1573-9171.
  6. Zhang, Xinmin; Guo, Limin; Gan, Linfeng; Zhang, Yantao; Wang, Jin; Johnson, Lee R.; Bruce, Peter G.; Peng, Zhangquan (2017-05-18). "LiO 2 : Cryosynthesis and Chemical/Electrochemical Reactivities". The Journal of Physical Chemistry Letters. 8 (10): 2334–2338. doi: 10.1021/acs.jpclett.7b00680 . ISSN   1948-7185. PMID   28481552. S2CID   46818521.
  7. Nava, Matthew; Zhang, Shiyu; Pastore, Katharine S.; Feng, Xiaowen; Lancaster, Kyle M.; Nocera, Daniel G.; Cummins, Christopher C. (2021-12-13). "Lithium superoxide encapsulated in a benzoquinone anion matrix". Proceedings of the National Academy of Sciences. 118 (51). Bibcode:2021PNAS..11819392N. doi: 10.1073/pnas.2019392118 . ISSN   0027-8424. PMC   8713792 . PMID   34903644.
  8. 1 2 Das, Ujjal; Lau, Kah Chun; Redfern, Paul C.; Curtiss, Larry A. (2014-02-13). "Structure and Stability of Lithium Superoxide Clusters and Relevance to Li–O2 Batteries". The Journal of Physical Chemistry Letters. American Chemical Society (ACS). 5 (5): 813–819. doi:10.1021/jz500084e. ISSN   1948-7185. PMID   26274072.
  9. 1 2 Bryantsev, Vyacheslav S.; Faglioni, Francesco (2012-06-21). "Predicting Autoxidation Stability of Ether- and Amide-Based Electrolyte Solvents for Li–Air Batteries". The Journal of Physical Chemistry A. American Chemical Society (ACS). 116 (26): 7128–7138. Bibcode:2012JPCA..116.7128B. doi:10.1021/jp301537w. ISSN   1089-5639. PMID   22681046.
  10. Lu, Jun (2016). "A lithium - oxygen battery based on lithium superoxide". Nature. 529 (7586): 377–381. Bibcode:2016Natur.529..377L. doi:10.1038/nature16484. PMID   26751057. S2CID   4452883.
  11. For arguments claiming (or assuming) similarity, see: For an argument that the different photoionization rate of lithium should produce a dissimilar equilibrium, see: