Low-Temperature Hydrothermal Synthesis of Mn₃O₄ and MnOOH Single Crystals: Determinant Influence of Oxidants

Abstract

The determinant influences of oxidants on the single-crystalline nature of manganese oxides (i.e., Mn 3 O 4 and MnOOH single crystals) through a low-temperature hydrothermal synthesis route from a simple aqueous solution containing 20 mM Mn(CH 3 COO) 2 • 4H 2 O at 120 °C are demonstrated in this work. The absence of oxygen molecules in the precursor solution limits formation of Mn 3+ , while saturation of oxygen in the precursor solution causes partial oxidation of Mn 2+ , favoring direct synthesis of Mn 3 O 4 single crystals (hausmannite). Addition of K 2 S 2 O 8 causes complete oxidation of Mn 2+ to Mn 3+ , favoring formation of MnOOH single crystals. The shape of as-prepared Mn 3 O 4 examined by HR-TEM is polyhedral, i.e., cubic and rhombohedral, while MnOOH prefers to form nanowires. X-ray diffraction, HRTEM, electron diffraction, and Raman spectroscopic analyses confirm the single-crystalline nature of the as-synthesized Mn 3 O 4 and MnOOH. With potentiodynamic (CV) activation for 200 cycles between 0 and 1.0 V in 1 M Na 2 SO 4 at 25 mV s -1 , the activated Mn 3 O 4 shows relatively high capacitance (∼170 F g -1 obtained at 500 mV s -1 ), high-power nature, and excellent stability for the supercapacitor application. The ideal capacitive responses of activated Mn 3 O 4 are definitely different from those of the potentiodynamically activated MnOOH.

Manipulating coupling state and magnetism of Mn-doped ZnO nanocrystals by changing the coordination environment of Mn via hydrogen annealing

“…In the literature, this mode is reported in the Raman spectra of Mn 2 O 3 [31] and MnOOH. [32] As with our samples, the coordination environments of Mn in ZnMn 2 O 4 , ZnMnO 3 , Mn 2 O 3 , and MnOOH are also in the form of a MnO 6 octahedron. As a result, we attribute AM2 to a mode arising from MnO 6 octahedral coordination.…”

Sulfidation of NiMn‐Layered Double Hydroxides/Graphene Oxide Composites toward Supercapacitor Electrodes with Enhanced Performance

“…The Raman spectrum of LDHS and LDHGOS can be seen from Figure S4a (Supporting Information). The peaks located at wavenumber of 286.6 and 339.4 cm −1 can be ascribed to Mn 3 O 4 , [ 31 ] while the peaks at 540.3 and 1057.6 cm −1 are caused by NiS. [ 32 ] From the Raman spectrum, it is deduced that sulfi dation can effectively increase the conductivity of GO, simultaneously remove the defects, and also dope S into the graphitic structure, which will be elucidated later.…”

Sponge-Like Porous Manganese(II,III) Oxide as a Highly Efficient Cathode Material for Rechargeable Magnesium Ion Batteries

“…28 In an effort to search for potential cathode materials for MIB, manganese-containing compounds have been investigated as attractive materials because of their low cost, environmental friendliness and high natural abundance. [29][30][31] Among them, MnO2 is perhaps the most extensively studied electrode material in many kinds of batteries. [32][33][34] Several polymorphs of MnO2 have also been investigated as possible MIB cathodes, [35][36][37][38][39] especially α-MnO2.…”