Electrodeposited MnCO3as a High Performance Electrode Material for Supercapacitor

Tuning the Magnetization of Manganese (II) Carbonate by Intracrystalline Amino Acids

Incorporation of organic molecules into the lattice of inorganic crystalline hosts is a common phenomenon in biomineralization and is shown to alter various properties of the crystalline host. Taking this phenomenon as a source of inspiration, it is shown herein that incorporation of specific single amino acids into the lattice of manganese (II) carbonate strongly alters its inherent magnetic properties. At room temperature, the magnetic susceptibility of the amino-acid-incorporating paramagnetic MnCO₃ decreases, following a simple rule of mixtures. When cooled below the Néel temperature, however, the opposite trend is observed, namely an increase in magnetic susceptibility measured in a high magnetic field. Such an increase, accompanied by a drastic change in the Néel phase transformation temperature, results from a decrease in MnCO₃ orbital overlapping and the weakening of superexchange interactions. It may be that this is the first time that the magnetic properties of a host crystal are tuned via the incorporation of amino acids.

Two-Dimensional NH4V3O8 Nanoflakes as Efficient Energy Conversion and Storage Materials for the Hydrogen Evolution Reaction and Supercapacitors

Herein, for the first time, we present two-dimensional (2D) NH₄V₃O₈ nanoflakes as an excellent material for both energy conversion of the hydrogen evolution reaction and storage of supercapacitors by a simple and fast two-step synthesis, which exhibit a completely sheet-like morphology, high crystallinity, good specific surface area, and also stability, as determined by thermogravimetric analysis. The 2D-NH₄V₃O₈ flakes show an acceptable hydrogen evolution performance in 0.5 M H₂SO₄ on a glassy carbon electrode (GCE) coated with 2D-NH₄V₃O₈, which results in a low overpotential of 314 mV at -10 mA cm^-2 with an excellent Tafel slope as low as 90 mV dec^-1. So far, with the main focus on energy storage, 2D-NH₄V₃O₈ nanoflakes were found to be ideal for supercapacitor electrodes. The NH₄V₃O₈ working electrode in 1 M Na₂SO₄ shows an excellent electrochemical capability of 274 F g^-1 at 0.5 A g^-1 for a maximum energy density of 38 W h kg^-1 at a power density as high as 250 W kg^-1. Moreover, the crystal structure of 2D-NH₄V₃O₈ is demonstrated by density functional theory (DFT) computational simulation using three functionals, GGA, GGA + U, and HSE06. The simple preparation, low cost, and abundance of the NH₄V₃O₈ material provide a promising candidate for not only energy conversion but also energy-storage applications.

MnCO3 on Graphene Porous Framework via Diffusion-Driven Layer-by-Layer Assembly for High-Performance Pseudocapacitor

Diffusion-driven layer-by-layer (dd-LbL) assembly is a simple yet versatile process that can be used to construct graphene oxide (GO) into a three-dimensional (3D) porous framework with good mechanical stability. In particular, the oxygen functional groups on the GO surface are well retained, providing nucleation sites for further chemical reactions to be performed upon. Therefore, such a scaffold should serve as a promising starting material for creating a wide range of 3D graphene-based composites while maintaining a high accessible surface area. Herein, we demonstrate the use of the porous GO macrostructure derived from dd-LbL assembly for the preparation of graphene-MnCO₃ hybrid structures. MnCO₃ is a newly reported pseudocapacitive material for supercapacitors; however, its electrochemical performance is hampered by its low electrical conductivity and poor chemical stability. Through reaction between KMnO₄ and GO during a hydrothermal process, the surface of the porous scaffold was rendered with uniform MnCO₃ nanoparticles. With the reduced graphene oxide (rGO) sheets serving as the conductive backbone, the resultant MnCO₃ nanoparticles exhibited a capacitance of 698 F g^-1 at a charge/discharge current of 0.5 mA (320 F g^-1 for the combined rGO and MnCO₃ composite). Furthermore, the electrode maintained 77% of its initial capacity even after 5000 cycles of charge/discharge tests at 20 mA.

Temperature-controlled hydrothermal synthesis of γ-MnOOH, Mn3O4 and MnCO3 on a carbon cloth for supercapacitor applications

In this study, a reaction temperature-controlled synthesis of γ-MnOOH, Mn₃O₄ and MnCO₃ (and also their mixture) on carbon cloth via a hydrothermal method is investigated, and the formation mechanism is discussed.

A Co3O4/MnCO3 heterojunction on three-dimensional nickel foam for an enhanced oxygen evolution reaction

A Co₃O₄/MnCO₃ heterojunction on NF with a unique architecture exhibits prominent OER activity and stability that is superior to most Co₃O₄-based catalysts.

Few-layered mesoporous graphitic carbon nitride: a graphene analogue with high capacitance properties

Exfoliation of multi-layered MGCN into few-layered MGCN results in 50% enhancement in the specific capacitance value.