Stabilization of Orthorhombic CoSe₂ by 2D-rGO/MWCNT Heterostructures for Efficient Hydrogen Evolution Reaction and Flexible Energy Storage Device Applications

Abstract

In view of recent environmental concerns, development of sustainable as well as renewable energy sources, such as the production of hydrogen through electro-reduction of water and energy storage devices in particular high power density as well as eco-friendly supercapacitors have become exigency for energy security. Herein, cobalt selenides (CoSe 2 ) and their carbon allotropic heterostructures have been synthesized and explored for bifunctional applications. The designed CoSe 2 /rGO/MWCNT heterostructure with an effective interface construction possessed enhanced HER (η 20 :131 mV, Tafel slope: 52 mV/ dec, stable up to ∼8.5 h) in alkaline pH. Owing to its storage performance, the asymmetric CoSe 2 /rGO/MWCNT//F-MWCNT device also proved to have excellent high capacitance (23.73 F/g at mass normalized current density of 30 A/g), high energy density (44.64 Wh/kg at a power density of 22.32 W/kg @ 6 A/g), and good cycling stability (91.03% capacitance retention after 3000 cycles). The experimental data are also supported by the results from density functional theory simulations in terms of the computed overpotential for HER activity and the quantum capacitance for charge storage performance. The interactions between CoSe 2 and carbon allotropes CNT/rGO are due to charge transfer from the Co 3d orbital of CoSe 2 to the C 2p orbital. Because of this interaction, the density of states shows enhancement near the Fermi level for hybrid structures, which indicates an increase in the conductivity of the material. The theoretical computed overpotential for HER activity follows the trend CoSe 2 > CoSe 2 /MWCNT > CoSe 2 /rGO > CoSe 2 /rGO/ MWCNT, supporting the experimental data. Also, the quantum capacitance is highest for the ternary heterostructure CoSe 2 /rGO/ MWCNT, justifying its superior charge storage performance as obtained from the experimental data. This work provides technological insights into the design of an efficient and cost-effective catalyst for sustainable hydrogen production and flexible energy storage applications.

1T-VS2/MXene Hybrid as a Superior Electrode Material for Asymmetric Supercapacitors: Experimental and Theoretical Investigations

“…However, the emergence of a broad peak around 27 deg. in all the VS 2 -MXene composites may be due to the increase in the interlayer spacing of pristine VS 2 . , Furthermore, it is worthy to note that there is a formation of TiO 2 (Burkite phase) confirming from the weak intense peaks around 53–54 and 62–64° due to partial oxidation of fluorinated Ti 2+ , which does not show any direct effect on the morphology of MXenes Figure b shows the comparison FT-IR spectrum of pure VS 2 , MXene, and hybrids.…”

MoWS2 nanosheets incorporated nanocarbons for high-energy-density pseudocapacitive negatrode material and hydrogen evolution reaction

“…For practical use, we fabricated the asymmetric device in a similar way, except the aqueous electrolyte was replaced with a K 2 SO 4 –PVA solid gel electrolyte and the entire set-up was pouched inside 4 × 4 cm 2 squares of Kapton tape. 27…”

“…For practical use, we fabricated the asymmetric device in a similar way, except the aqueous electrolyte was replaced with a K 2 SO 4 -PVA solid gel electrolyte and the entire set-up was pouched inside 4 Â 4 cm 2 squares of Kapton tape. 27 For HER measurements, linear sweep voltammetry (LSV) was employed. The active-material-coated GCE, platinum (Pt) wire, and Ag/AgCl were considered to be the active, counter and reference electrodes, respectively.…”

“…where h stands for the overpotential, J signies the current density, a is the Tafel constant, and b represents the Tafel slope. 27…”

“…CSCR was previously prepared and showed excellent charge storage performance, as described elsewhere. 27 In a three-electrode set up, both the positive and negative electrodes were inspected and the respective optimised potential windows were analysed (Fig. S4 †).…”