Magnesium-ion batteries hold promise as next-generation secondary battery systems owing to its low cost, safety and high volumetric capacity. Magnesium metal silicates exhibit potential electrode ...materials with high specific capacities. However, the strong electrostatic interaction between Mg2+ and host lattice due to its divalency as well as antisite cation exchange, induces slow intercalation kinetics of Mg ions within the crystal lattices. Thus, nanocrystalline particles with shortened Mg ion diffusion distance enable the insertion/extraction of Mg ions and improve specific capacities of the batteries. Herein, we report the low-temperature production of crystalline MgMnSiO4 and MgCoSiO4 nanoparticles by a rapid supercritical fluid processing. The extraction of magnesium ions from the olivine framework has been confirmed by X-ray photoelectron spectroscopy, revealing its ability as active materials for magnesium-ion battery.
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•The low-temperature production of MgMnSiO4 and MgCoSiO4 nanoparticles.•A rapid supercritical fluid processing synthesis.•The extraction of magnesium from the olivine framework in Mg-ion battery.•Samples was studied by X-ray photoelectron spectroscopy.
The spinel MgMn2O4, a cathode material with theoretical capacity of 272 mA h g–1, holds promise for future application in high volumetric magnesium-ion batteries. Atomic-resolution imaging of the ...structure of the spinel and its surface composition would advance our understanding on its electrochemical properties, mass, and charge transport behavior in electrodes. We observe directly, by aberration-corrected scanning transmission electron microscopy (STEM), the atomic structure of cubic spinel MgMn2O4 for the first time. More importantly, we find that a thin stable surface layer of rocksalt MgMnO2 was grown on a bulk cubic spinel phase. The formation of a rocksalt phase was induced by reconstruction of the spinel phase, i.e., the insertion of Mg into the spinel lattice together with Mg/Mn cation exchange and Frenkel-defect-mediated relocation of Mg cations. This new structural analysis provides a critical step toward understanding and tuning the electrochemical performance of spinel oxide in rechargeable Mg-ion batteries.
Molybdenum sulfides are very attractive noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER) from water. The atomic structure and identity of the catalytically active sites ...have been well established for crystalline molybdenum disulfide (c-MoS2) but not for amorphous molybdenum sulfide (a-MoSx), which exhibits significantly higher HER activity compared to its crystalline counterpart. Here we show that HER-active a-MoSx, prepared either as nanoparticles or as films, is a molecular-based coordination polymer consisting of discrete Mo3S13(2-) building blocks. Of the three terminal disulfide (S2(2-)) ligands within these clusters, two are shared to form the polymer chain. The third one remains free and generates molybdenum hydride moieties as the active site under H2 evolution conditions. Such a molecular structure therefore provides a basis for revisiting the mechanism of a-MoSx catalytic activity, as well as explaining some of its special properties such as reductive activation and corrosion. Our findings open up new avenues for the rational optimization of this HER electrocatalyst as an alternative to platinum.
•A facile manufacturing process of new Rb2CO3-decorated In2O3 sensor.•The Rb2CO3/In2O3 composite sensor detecting 100 ppb level NO2 gas at room temperature under visible light illumination.•Propose ...the mechanism for the high sensing performance realized by high rate of electron supply to the receptor.•Good sensing performance of high selectivity, stability, repeatability, linearity, with discussion of the humidity effect.
The Rb2CO3-decorated In2O3 sensor is prepared for detection of NO2 at room temperature under light irradiation. Physical and chemical properties of the materials and structures are thoroughly investigated by various analytical tools of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy, thereby confirming the formation of the Rb2CO3/In2O3 p-n junction at the interface. The Rb2CO3-decoration effect on In2O3 sensor is examined under light irradiation of different wavelengths and intensities. Rb2CO3-decoration exhibits much higher sensing performance than pure In2O3 sensor, and furthermore, the visible light irradiation improves in the response level and sensing kinetics. The sensor detects less than 100 ppb NO2. In addition, the Rb2CO3-decorated In2O3 sensor shows high selectivity, stability, repeatability, and linearity. The ultimate performance of the nanostructured sensor is elucidated by the depletion model of the conduction type gas sensors. The effect of humidity on the sensing performance is also investigated.
Structural studies of high voltage cathode materials are necessary to understand their chemistry to improve the electrochemical performance for applications in lithium ion batteries. LiNiPO4 nanorods ...and nanoplates are synthesized via a one pot synthesis using supercritical fluid process at 450 °C for 10 min. The X-ray diffraction (XRD) analysis confirmed that LiNiPO4 phase is well crystallized, phase purity supported by energy dispersive spectroscopy (EDS) and elemental mapping by scanning electron transmission electron microscopy (STEM). For the first time, we have carried out direct visualization of atom-by-atom structural observation of LiNiPO4 nanomaterials using high-angle annular dark-field (HAADF) and annular bright-field (ABF) scanning transmission electron microscopy (STEM) analysis. The Rietveld refinement analysis was performed to find out the percentage of antisite defects presents in LiNiPO4 nanoplates and about 11% of antisite defects were found. Here, we provide the direct evidence for the presence of Ni atoms in Li sites and Li in Ni sites as an antisite defects are provided for understanding of electrochemical behavior of high voltage Li ion battery cathode materials.
Hybridization of dissimilar materials is a promising solution to improve desired properties in various applications. Herein, we chemically grew a conductive polymer (polypyrrole, PPy) on ...graphene-supported manganese ferrite microspheres (MG, ∼344 nm in size) to form PPy/MG hybrids at various PPy contents (20, 33.3, and 42.9 wt%). PPy, MG binary, and PPy/MG ternary hybrids were comprehensively characterized to correlate their structure, morphology, and properties. Electrochemical measurements revealed a significantly enhancement of capacitive performances of PPy/MG as comparison to those of each component. Consequently, the combination of PPy and MG resulted in maximum specific capacitance of 147.2 F/g at scan rate of 10 mV/s or 66.1 F/g at current density of 0.5 A/g. These synergistic and cooperative effects are attributed to reduced diffusion resistance in the PPy/MG hybrids. This work thus suggests an efficient strategy to develop high-performance material for supercapacitor electrode.
An electrode made of Au nanoparticles, ca. 13 nm in diameter, displays outstanding catalytic activity for the hydrogen evolution reaction in water. At an overpotential of 200 mV it operates with a ...catalytic rate TOF of 0.3 s-1, which is among the best performances ever achieved for a Pt-free H2-evolving catalyst.
Magnesium metal complex oxides are potential electrode materials for magnesium ion batteries with high specific capacities. However, the strong electrostatic interaction between Mg2+ and the host ...lattice due to its divalency induces slow intercalation kinetics of Mg ions within the crystal lattices. Thus, nanocrystalline particles with shortened Mg ion diffusion distance enable the insertion/extraction of Mg ions and improve the specific capacities of the batteries. Herein, we report the facile rapid production of crystalline MgCo2O4 and Mg2/3Ni4/3O2 nanocrystals by rapid supercritical fluid processing. The phase transition from spinel to rocksalt during the Mg2+ ion intercalation has been confirmed by high-resolution transmission electron microscopy. The nanosheets of Mg2/3Ni4/3O2 rocksalt nanocrystals were controllably synthesized for the first time, which are active materials for magnesium-ion batteries.
Amorphous molybdenum selenide nanopowder, obtained by refluxing Mo(CO)6 and Se precursors in dichlorobenzene, shows several structural and electrochemical similarities to the amorphous molybdenum ...sulfide analogue. The molybdenum selenide displays attractive catalytic properties for the hydrogen evolution reaction in water over a wide range of pH. In a pH 0 solution, it operates with a small onset overpotential of 125 mV and requires an overpotential of 270 mV for generating a catalytic current of 10 mA/cm2. Compared with molybdenum sulfide, the selenide analogue is more robust in a basic electrolyte. Therefore, molybdenum selenide is a potential candidate for incorporating within an electrolyzer or a photoelectrochemical cell for water electrolysis in acidic, neutral, or alkaline medium.
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•Porous ε-MnO2 microcubes prepared by glucose-urea-assisted hydrothermal synthesis.•Urea and glucose as the morphology-directing and soft-template agents, respectively.•Obtained ...materials exhibit great porosity, reducibility, lattice oxygen reactivity and Mn4+ fraction.•Mutual effects of porosity, reducibility, lattice oxygen reactivity and Mn4+ fraction on catalytic performance.•Long-term stability of ε-MnO2 at 245 °C for 10 h at GHSV = 60,000 h−1.
3D architectures porous epsilon-type manganese dioxide (ε-MnO2) microcubes (PEMD) are successfully prepared by a glucose-urea-assisted hydrothermal synthesis of MnCO3-carbon composites followed by annealing. It turns out that urea essentially assists in building the cubic shape while glucose plays a crucial role to form carbon inside the microcrystals, which are latterly removed by annealing to generate the porous structure. As a result, ε-MnO2 materials possessing extraordinary features including the high porosity, reducibility, lattice oxygen reactivity and Mn4+ fraction, are feasible tailored. These unique properties, all together, significantly improve the catalytic performances of complete oxidation of toluene. Thus, it is found that the optimal catalyst (manganese-glucose-urea ratio of 6-2-6) synthesized at 180 °C exhibits an excellent activity for the complete oxidation of toluene (T90 = 243 °C, lower 10 °C than that of pristine ε-MnO2) and stability up to 10 h.
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