Facile One-Step Template-Free Synthesis of Uniform Hollow Microstructures of Cryptomelane-Type Manganese Oxide K-OMS-2

Abstract

Hollow microstructures of cryptomelane-type manganese oxide were produced in a template-free one-step process based on the fine-tuning of the oxidation rate of manganese species during the synthesis. The tuning of the reaction rate brought about by a mixture of the oxidants oxone and potassium nitrate becomes apparent from the gradual physical changes taking place in the reaction medium at early times of the synthesis. The successful synthesis of the hollow uniform structures could be performed in the ranges 120-160 degrees C and 8.2-10.7 for temperature and mass ratio oxone/potassium nitrate, respectively. Independent of the conditions of the synthesis, all of the complex microstructures showed the same pattern for the array of very long nanofibers in which some of these elongated around the surface confining the cavity and the other fibers grew normal to the surface created by the previous arrangement. A mechanism based on the heterogeneous nucleation of the cryptomelane phase on the surface of an amorphous precursor and the growth of the nanoscale fibers by processes such as dissolution-crystallization and lateral attachment of primary nanocrystalline fibers is proposed to explain the formation of the hollow structures.

Potassium‐Based α‐Manganese Dioxide Nanofiber Binder‐Free Self‐Supporting Electrodes: A Design Strategy for High Energy Density Batteries

“…The weight‐loss profiles of the OMS‐2 materials can be separated into three segments . One, in the room temperature to 250 °C range, weight loss is attributed to physisorbed water . The weight loss of the BFSS cathodes and Pwdr‐OMS‐2 is approximately 1.8–2.0 %.…”

“…For comparison, the TGA profile of MWNTs was also determined (Figure S3). The weight‐loss profiles of the OMS‐2 materials can be separated into three segments . One, in the room temperature to 250 °C range, weight loss is attributed to physisorbed water .…”

“…The weight loss of the BFSS cathodes and Pwdr‐OMS‐2 is approximately 1.8–2.0 %. Two, in the 250–450 °C range, the weight loss is assigned to the loss of structural (tunnel) water . The weight loss of Pwdr‐OMS‐2 and BFSSC‐0 is the same (≈1 %) and corresponds to approximately 0.031 units of water per molecular formula, K 0.11 MnO 2 ⋅ 0.031 H 2 O.…”

“…[28,[35][36][37][38] One,i nt he room temperature to 250 8Cr ange,w eight loss is attributed to physisorbed water. [35,36,38] Thew eight loss of the BFSS cathodes and Pwdr-OMS-2 is approximately 1.8-2.0 %. Tw o, in the 250-450 8Cr ange,t he weight loss is assigned to the loss of structural (tunnel) water.…”

K0.25Mn2O4nanofiber microclusters as high power cathode materials for rechargeable lithium batteries

“…[32][33][34][35][36] Single-crystalline K 0.25 Mn 2 O 4 could be suitable as a cathode material for lithium ion batteries because its potassium ions can not only maintain the structure, but also increase the ion diffusion rate. [26][27][28][29][30] Solution B was prepared by dissolving 1.5 g of oxone in 10 mL of double de-ionized water.…”