Simple Additive-Free Method to Manganese Monoxide Mesocrystals and Their Template Application for the Synthesis of Carbon and Graphitic Hollow Octahedrons

Mesocrystals are of great importance owing to their novel hierarchical microstructures and potential applications. In the present work, a simple additive-free method has been developed for the controllable synthesis of manganese monoxide (MnO) mesocrystals, in which cheap manganese acetate (Mn­(Ac)₂) and ethanol were used as raw materials without involving any other expensive additives such as surfactants, polyelectrolyte, or polymers. The particle size of the resulting MnO mesocrystals is tunable in the range 400–1500 nm by simply altering the concentration of Mn­(Ac)₂ in ethanol. The percentage yield of the octahedral MnO mesocrystals is about 38 wt % with respect to the starting Mn­(Ac)₂. The selective adsorption of oligomers, which was resulted from the polymerization of ethanol, acted as an important role for the mesocrystal formation. A mechanism involving the oriented aggregation of MnO nanoparticle subunits and the subsequent ripening process was proposed. Moreover, for the first time, the as-synthesized MnO mesocrystals were employed as a novel template to fabricate functional materials with an octahedral morphology including MnO@C core/shells, carbon, and graphitic hollow octahedrons. This method shows the importance of mesocrystals not only for the field of material research but also for the application in functional materials synthesis

Engineering Thin MoS₂ Nanosheets on TiN Nanorods: Advanced Electrochemical Capacitor Electrode and Hydrogen Evolution Electrocatalyst

The poor intrinsic conductivity of MoS₂ presents a huge barrier for the exploitation of its versatile properties, especially as an electrochemical capacitor (EC) electrode and hydrogen evolution reaction (HER) catalyst. Toward this challenge, TiN nanorods coated by randomly oriented MoS₂ nanosheets (TMSs) are engineered as state-of-the-art electrodes for ECs and HER. In light of the synergistic effects, TMS electrodes show favorable performance as both a binder-free EC electrode and HER catalyst. Importantly, the optimal TMS achieves an areal capacitance of 662.2 mF cm^–2 at 1 mA cm^–2 with superior rate capability and ultralong cycling stability. As the catalyst for HER in 0.5 M H₂SO₄, it shows an overpotential of 146 mV at 10 mA cm^–2, a favorable Tafel slope, and good electrocatalytic stability. All of the results highlight the favorable integration of TiN and MoS₂ and provide clear insight correlating the hybrid structure and the corresponding electrochemical performance