Electronegativity principles in metal oxides based supercapacitors

Low-dimensional high entropy oxide (FeCoCrMnNi)3O4 for supercapacitor applications

Previous studies have found that high entropy oxides can be used as electrode materials for supercapacitors. However, there is still the problem of their low energy density. We tried to increase the energy density while increasing the specific capacitance of high entropy oxides from the potential window. Transition metal elements Fe, Co, Cr, Mn and Ni were selected for their electrochemical activity, and high entropy oxides were prepared by a sol-gel method under different calcination temperatures. The calcination temperature affects the structural morphology and crystallinity of the high entropy oxides and thus also affects the electrochemical performance. The spinel-phase (FeCoCrMnNi)₃O₄ with a high specific surface area of 63.1 m² g^-1 was prepared at a low calcination temperature of 450 °C. The specific capacitance is 332.2 F g^-1 at a current density of 0.3 A g^-1 in 1 M KOH electrolyte with a wide potential window of (-1, 0.6). An improved energy density of 103.8 W h kg^-1 is reached via the designed microstructure of the high entropy oxide electrode.

Can Empirical Biplots Predict High Entropy Oxide Phases?

High entropy oxides are entropy-stabilised oxides that adopt specific disordered structures due to entropy stabilisation. They are a new class of materials that utilises the high-entropy concept first discovered in metallic alloys. They can have interesting properties due to the interactions at the electronic level and can be combined with other materials to make composite structures. The design of new meta-materials that utilise this concept to solve real-world problems may be a possibility but further understanding of how their phase stabilisation is required. In this work, biplots of the composition’s mean electronegativity are plotted against the electron-per-atom ratio of the compounds. The test dataset accuracy in the resulting biplots improves from 78% to 100% when using atomic-number-per-atom Z/a ratios as a biplot parameter. Phase stability maps were constructed using a Voronoi tessellation. This can be of use in determining stability at composite material interfaces.

One-pot synthesis of manganese oxide/graphene composites via a plasma-enhanced electrochemical exfoliation process for supercapacitors

In this work, a feasible one-pot approach to synthesize manganese oxide/graphene composites, the so-called plasma-enhanced electrochemical exfoliation process (PE³P), has been developed. Herein, a composite of graphene decorated with manganese oxide nanoparticles was prepared via PE³P from a KMnO₄ solution and graphite electrode under a voltage of 70 V in an ambient environment. By controlling the initial KMnO₄ concentration, we obtained distinct MnO₂/graphene samples. The prepared samples were characterized by scanning electron microscopy, transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and Raman spectroscopy. The electrochemical measurements of the MnO₂/graphene composites revealed that the specific capacitance of the samples is approximately 320 F g^-1 at a scan rate of 10 mV s^-1, which is comparably very high for manganese oxide/carbon-based supercapacitor electrode materials. Considering the simple, low-cost, one-step and environmentally friendly preparation, our approach has the potential to be used for the fabrication of MnO₂/graphene composites as the electrode materials of supercapacitors.

Evaluation of Electronegativity Scales

Scales of electronegativity values are used by chemists to describe numerous chemical features such as chemical mechanisms, bond polarity, band gap, atomic hardness, etc. While the many scales provide similar trends, all differ in their predictive quality. Confirmation of the quality of a new scale often uses a previous scale for comparison but does not use independent means to demonstrate the merits of the scale. Utilizing a table of binary compounds of known ionic, covalent, and metallic bonding characters, a means to evaluate electronegativity scales is developed here. By plotting the electronegativity values of the two bonded atoms in binary compounds of a known bonding character, a tripartite separation results that generally divides the three bond types. Using the results of graphs of this sort, the success of bonding separations of 14 different scales of electronegativity has been evaluated on the basis of three quantitative parameters that can provide a measure of the quality of the scales. Three scales, those of Allen, Martynov and Batsanov, and Nagle, have been shown to be superior in their ability to predict the expected separation of bond types. Since this scheme successfully demonstrates the ability to evaluate the quality of electronegativity scales, it can be applied to other scales to establish their effectiveness in predicting bond types in binary compounds and thus the quality of the scales. This scheme is applied to a recently published electronegativity scale to evaluate the ability to determine its quality.