Enhanced energy storage performance and theoretical studies of 3D cuboidal manganese diselenides embedded with multiwalled carbon nanotubes.

The burst of energy produced from the sustainable energy sources need to be harnessed by energy storage systems. Development of novel and advanced energy storage devices such as supercapacitors discover an enormous future ahead. Recently, hybrid supercapacitors (electric double layer capacitor (EDLC) and pseudocapacitors) trend to be used as energy storage interfaces for their improved efficacy in energy density without altering the power density. In the ongoing workplan, transition metal selenides MnSe2 and its hybrid with multiwalled carbon nanotubes (MWCNTs) are synthesized by a simplistic hydrothermal protocol. Certainly, cubic phases of MnSe2-MWCNT(MS/CNT) manifested superior electrochemical performance in both symmetric and asymmetric full cell configurations in contrast to prestine MnSe2(MS). The asymmetric MS/CNT cell achieved an excellent charge storage capability with an high energy density of 39.45 Wh kg-1 at a power density of 2.25 kW kg-1 maintaining an energy density of 14.5 Wh kg-1 at a high power density of 4.5 kWh kg-1 and also revealed long term stability over 5000 consecutive charge/discharge cycles (capacitance retention of 95.2%). Furthermore, the preferable growth along (200) direction in the presence of MWCNTs favoured in enriching the supercapacitive property of MS. The quantum capacitance of MnSe2surfaces and MS/CNT heterostructure has been estimated using density functional theory simulation to confirm the experimental outcomes. Theoretical investigation simultaneously exposed the contribution of (200) plane of MnSe2 and MWCNTs cultured in enhanced DOS (density of states) near the Fermi level that remarkably promoted the energy storage efficiency of MS/CNT.

Comparative electrochemical energy storage performance of cobalt sulfide and cobalt oxide nanosheets: experimental and theoretical insights from density functional theory simulations.

In this study, we have carried out studies on supercapacitor performance comparing cobalt oxide (Co3O4) with cobalt sulfide (Co3S4) nanosheets grown using a facile electrodeposition approach. We have investigated the origin of enhanced energy storage performance of Co3S4 as compared to Co3O4 both by supported experiments and density functional theory investigations. Cobalt oxide exhibits a specific capacitance of 200 F g-1 at a current density of 2 A g-1, whereas a high specific capacitance of 558 F g-1 was achieved in the case of the Co3S4 nanosheets. The enhanced supercapacitor performance of Co3S4 is due to the high surface area, better wettability and high conductivity of the nanosheets. The asymmetric device exhibited a maximum energy density of 47.3 W h kg-1 with a power density of 2388.4 W kg-1 for Co3S4//MWCNT. The electrochemical impedance spectroscopic analysis revealed that Co3O4 has a substantially bigger semicircle as compared to Co3S4, confirming inferior charge-transfer characteristics in Co3O4. Density functional theory (DFT) simulations revealed that bulk structures of both Co3S4 and Co3O4 have an anti-ferromagnetic (AFM) configuration with Co atoms at the tetrahedral site having an opposite spin (∼2.55 µB each) and those at the octahedral sites being non-magnetic. Co3S4 nanosheets are found to be more conducting due to the presence of higher density of states near the Fermi level and a smaller bandgap compared to Co3O4 which support the observed experimental data on enhanced energy storage performance of Co3S4.

Synthesis of CuSbS2 Nanoplates and CuSbS2-Cu3SbS4 Nanocomposite: Effect of Sulfur Source on Different Phase Formation.

Layered CuSbS2 and related ternary metal chalcogenides have attracted huge research interest due to their potential applications in sustainable energy storage, photovoltaics, and related area. Here, we report facile synthesis of CuSbS2 nanoplates and CuSbS2-Cu3SbS4 nanocomposite using hot injection method with varying sulfur precursors. Elemental sulfur (S8) as sulfur precursor results in nanoplates of pure CuSbS2, while thioacetamide (TA) as sulfur source gives nanocomposite with Cu3SbS4 nanoparticle decorated on the surface of CuSbS2 nanoplates. The ease of reduction of TA as compared to sulfur at high temperature, in the presence of oleylamine, promotes the oxidation of antimony from (III) to (V) state and the formation of Cu3SbS4 phase containing Sb(V). Raman scattering study confirms the presence of Cu3SbS4 phase in CuSbS2-Cu3SbS4 nanocomposite. X-ray photoemission spectroscopy study on CuSbS2 nanoplates and CuSbS2-Cu3SbS4 nanocomposite confirms the desired valence state of the constituent elements. Electrochemical properties measurement shows better specific capacitance for CuSbS2-Cu3SbS4 nanocomposite (151 F/g) as compared to CuSbS2 nanoplates along with long-term cyclic stability with 68.2% capacitance retention.