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KO2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. K is bonded in a distorted q4 geometry to ten equivalent O atoms. There are two shorter (2.71 Å) and eight longer (2.88 Å) K–O bond lengths. O is bonded in a 6-coordinate geometry to five equivalent K and one O atom. The O–O bond length is 1.35 Å.
KO2 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. K is bonded in a distorted hexagonal planar geometry to six equivalent O atoms. There are a spread of K–O bond distances ranging from 2.69–2.79 Å. O is bonded in a 4-coordinate geometry to three equivalent K and one O atom. The O–O bond length is 1.36 Å.
KO2 crystallizes in the cubic Pa-3 space group. The structure is three-dimensional. K is bonded to six equivalent O atoms to form KO6 octahedra that share corners with twelve equivalent KO6 octahedra and corners with six equivalent OK3O tetrahedra. The corner-sharing octahedral tilt angles are 75°. All K–O bond lengths are 2.77 Å. O is bonded to three equivalent K and one O atom to form OK3O tetrahedra that share corners with three equivalent KO6 octahedra and corners with fifteen equivalent OK3O tetrahedra. The corner-sharing octahedral tilt angles are 66°. The O–O bond length is 1.35 Å.
KO2 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. K is bonded in a 9-coordinate geometry to nine O atoms. There are a spread of K–O bond distances ranging from 2.69–2.91 Å. There are two inequivalent O sites. In the first O site, O is bonded in a 5-coordinate geometry to four equivalent K and one O atom. The O–O bond length is 1.36 Å. In the second O site, O is bonded to five equivalent K and one O atom to form a mixture of distorted corner and edge-sharing OK5O octahedra. The corner-sharing octahedra tilt angles range from 18–83°.
KO2 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. K is bonded in a 9-coordinate geometry to nine O atoms. There are a spread of K–O bond distances ranging from 2.68–2.99 Å. There are two inequivalent O sites. In the first O site, O is bonded in a 2-coordinate geometry to four equivalent K and one O atom. The O–O bond length is 1.35 Å. In the second O site, O is bonded to five equivalent K and one O atom to form a mixture of distorted edge and corner-sharing OK5O octahedra. The corner-sharing octahedra tilt angles range from 22–85°.
Abstract As a promising low-cost energy storage device, the development of a rechargeable potassium-ion battery (KIB) is severely hindered by the limited capacity of cathode candidates. Regarded as an attractive capacity-boosting strategy, triggering the O-related anionic redox activity has not been achieved within a sealed KIB system. Herein, in contrast to the typical gaseous open K-O2 battery (O2/KO2 redox), we originally realize the reversible superoxide/peroxide (KO2/K2O2) interconversion on a KO2-based cathode. Controlled within a sealed cell environment, the irreversible O2 evolution and electrolyte decomposition (induced by superoxide anion (O2−) formation) are effectively restrained. Rationally controlling the reversible depth-of-charge at 300 mAh/g (based on the mass of KO2), no obvious cell degradation can be observed during 900 cycles. Moreover, benefitting from electrolyte modification, the KO2-based cathode is coupled with a limited amount of K-metal anode (merely 2.5 times excess), harvesting a K-metal full-cell with high energy efficiency (∼90%) and long-term cycling stability (over 300 cycles).
Flame inhibition by alkali metals has implications for solid fuel combustion, fire safety, and a number of industrial processes. While the mechanism of inhibition is fairly well understood, details related to thermodynamic properties and rate constants are still in question. In the present work, the recombination of Na with OH (R5) and O2 (R7), respectively, was characterized theoretically, and the implications for modeling laminar premixed hydrogen flames doped with sodium species were examined. Third-body collision efficiencies and low-pressure-limit rate constants were obtained using newly fitted ab initio-based potential energy surfaces, classical trajectories, and one-dimensional master equation calculations. The results are consistent with available experimental results and aid in the present modeling study by providing rate information for bath gases and conditions that remain unexplored experimentally. Chemical kinetic modeling of relative Na and absolute H and OH profiles in H2-fueled laminar, premixed flames doped with a sodium salt shows that the most important radical removal cycle is the sequence Na + OH (+M) → NaOH (+M) (R5), NaOH + H → Na + H2O (R12), even under oxidizing conditions. A secondary cycle, Na + O2 (+M) ⇄ NaO2 (+M) (R7), NaO2 + OH → NaOH + O2 (R14), is less important due to the low thermal stability of NaO2. In most flames, reaction R7 is partially equilibrated, and reaction R14 becomes rate-limiting for the second cycle. The flame analysis supports a lower value of k14 than indicated by recent work on KO2 + OH, but more work is required to confirm this.