Synthesis of different manganese tungstate nanostructures for enhanced charge-storage applications: theoretical support for experimental findings.

Manganese tungstate (MnWO4) has been widely studied over the past few years due to its outstanding magnetic, catalytic, and sensing features. However, the electrochemical properties of the morphology tuned MnWO4 nanoform is less explored in the literature. Herein, we report the synthesis of MnWO4 nanostructures of different aspect ratios by subtle tuning of the reaction temperature and reaction time. An immediate utility of the size-controlled nanostructures is their use as the electrode material for supercapacitors. The impact of various reaction parameters, namely the growth time and processing temperature, over the MnWO4 nanorods size was studied by different characterization techniques, such as X-ray diffraction, field emission scanning electron microscopy, and Raman spectroscopy. It was shown that all the samples showed considerably good charge-storage properties with the highest values of specific capacitance being 455.07 and 239.07 F g-1 at 2 mV s-1 and 1 A g-1, respectively. The corresponding sample further showed an appreciable capacitance retention of ∼94% even after 10 000 long charge-discharge cycles, indicating a high electrochemical stability of the electrode. Theoretical analysis using density functional theory predicted that the presence of electronic states near Fermi level and the enhanced quantum capacitance were the prime reasons behind the excellent charge-storage performance of the as-synthesized MnWO4.

Graphene-Anchored p-Type CuBO2 Nanocrystals for a Transparent Cold Cathode.

CuBO2 nanostructures were synthesized by employing a low-cost hydrothermal technique to combine into the CuBO2-RGO nanocomposite for the first time using chemically prepared graphene sheets. The nanohybrid samples were characterized for structural information using X-ray diffraction (XRD) that revealed the proper crystalline phase formation of CuBO2 unaltered by composite formation with graphene. Raman spectroscopic studies were employed to confirm the presence of graphene. A morphological study with field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) suggested the proper wrapping of RGO sheets over CuBO2 nanocubes. Moreover, the close proximity of lattice planes of CuBO2 and RGO to each other was observed in high-resolution TEM studies that were correlated with the Raman spectroscopic studies. Finally, the samples were characterized to study the field emission (FE) properties of the same using a laboratory-made high-vacuum field-emission setup. Finite-element-based theoretical simulation studies were carried out to explain and compare the field emission properties with the experimental results. The FE properties of the composite samples were found to be tuned by the nature of wrapping the RGO sheets over the CuBO2 nanocubes, which was typically dependent upon the spiky morphology of the nanocubes.