Synthesis and Substitution Chemistry of Redox-Active Manganese/Cobalt Oxide Nanosheets

Abstract

We report the synthesis and electrochemical properties of Co-substituted manganese oxide nanosheets (Mn 1− x Co x O 2 ). Polycrystalline samples of layered Na 0.6 Mn 1−x Co x O 2 (x = 0.2−0.5) were synthesized as starting materials. A linear decrease in the lattice constant a with increasing Co content supported the successful substitution of Co 3+ ions for Mn 3+ ions in the host layers. Acid-exchange treatment of the Na 0.6 Mn 1−x Co x O 2 powders resulted in the formation of H−Mn 1−x Co x O 2 while preserving the Mn/Co ratio and layered structure. Exfoliation of H−Mn 1−x Co x O 2 was achieved by reaction with tetra−n−butylammonium ions, yielding unilamellar Mn 1−x Co x O 2 (x = 0.2−0.5) nanosheets with a thickness of 0.8 nm. The optical absorption peak of the obtained Mn 1−x Co x O 2 nanosheets was continuously blueshifted as the Co content increased. The Mn 1−x Co x O 2 nanosheets exhibited well-defined redox peaks, which were shifted to a negative potential with increasing Co content. These results suggest that the 3d orbitals of Mn and Co are mixed owing to their statistical distribution in the nanosheets. The Mn 1−x Co x O 2 nanosheet electrodes showed a capacitance of 700−1000 F g −1 and improved cycle performance compared to MnO 2 nanosheets.

Two-Dimensional Molecular Sheets of Transition Metal Oxides toward Wearable Energy Storage

“…27 Similarly, composition-tailored Co-and Ru-doped manganese oxide nanosheets with improved cycle performance for energy storage systems have been prepared. 28 Many physical and chemical properties, such as band structure and out-of-plane mass transport behavior, are heavily dependent on accurate control over the sheet thickness or the layer number of sheet stacks. To demonstrate this aspect, layered perovskite oxides, a homologous series of Dion−Jacobson phases represented by the general chemical formula of KCa 2 Na n−3 Nb n O 3n+1 (n = 3−7), are a good system, exhibiting high flexibility of crystal structure and chemical composition.…”

“…Upon doping with transition metals such as Co and Fe, titania sheets with unique ferromagnetic properties can be obtained by delaminating the corresponding doped layered precursors . Similarly, composition-tailored Co- and Ru-doped manganese oxide nanosheets with improved cycle performance for energy storage systems have been prepared …”

2D Superlattices for Efficient Energy Storage and Conversion

“…)‐intercalated form, which is then swollen and delaminated into unilamellar nanosheets in formamide (Figure c) . Moreover, the composition, thickness, and lateral size of the obtained unilamellar nanosheets can be rationally designed and precisely controlled.…”

Nickel-Doped Sodium Cobaltite 2D Nanomaterials: Synthesis and Electrocatalytic Properties

“…The usual delamination strategy for such intercalated compounds is based on consecutive intercalations with progressively larger species in order to decrease electrostatic interactions, until the structure is split apart forming a colloidal suspension. The procedure is the only one reported so far to exfoliate sodium cobaltites produced as bulk solids, − and very recently manganese-substituted sodium cobaltites, but it resulted in a strong reduction of Co species and the formation of CoO nanosheets, thus leading to a loss of the electrocatalytically relevant Co 4+ /Co 3+ couple. A direct synthesis where the individual particles obtained would be as thin as possible, close to single layers, would overcome time-consuming iterative method and, more important, maintain the high mean oxidation state of cobalt.…”