Highly Active 2D Layered MoS 2 -rGO Hybrids for Energy Conversion and Storage Applications

Abstract

The development of efficient materials for the generation and storage of renewable energy is now an urgent task for future energy demand. In this report, molybdenum disulphide hollow sphere (MoS₂-HS) and its reduced graphene oxide hybrid (rGO/MoS₂-S) have been synthesized and explored for energy generation and storage applications. The surface morphology, crystallinity and elemental composition of the as-synthesized materials have been thoroughly analysed. Inspired by the fascinating morphology of the MoS₂-HS and rGO/MoS₂-S materials, the electrochemical performance towards hydrogen evolution and supercapacitor has been demonstrated. The rGO/MoS₂-S shows enhanced gravimetric capacitance values (318 ± 14 Fg^-1) with higher specific energy/power outputs (44.1 ± 2.1 Whkg^-1 and 159.16 ± 7.0 Wkg^-1) and better cyclic performances (82 ± 0.95% even after 5000 cycles). Further, a prototype of the supercapacitor in a coin cell configuration has been fabricated and demonstrated towards powering a LED. The unique balance of exposed edge site and electrical conductivity of rGO/MoS₂-S shows remarkably superior HER performances with lower onset over potential (0.16 ± 0.05 V), lower Tafel slope (75 ± 4 mVdec^-1), higher exchange current density (0.072 ± 0.023 mAcm^-2) and higher TOF (1.47 ± 0.085 s^-1) values. The dual performance of the rGO/MoS₂-S substantiates the promising application for hydrogen generation and supercapacitor application of interest.

Figure 1

The schematic presentation for the synthesis of MoS₂-HS and rGO/MoS₂-S hybrids.

Figure 2

SEM image of MoS₂-HS.

Figure 3

HRTEM image of MoS₂-HS.

Figure 4

SEM (a,b) and HRTEM (c–g) image of the rGO/MoS₂-S.

Figure 5

The Raman Spectra of MoS₂-HS and rGO/MoS₂-S hybrid.

Figure 6

(a) CV of rGO/MoS₂-S hybrid at different scan rate (1 to 200 mV/s), (b) CV of MoS₂-HS, rGO and rGO/MoS₂-S hybrid at 10 mV/s, (c) GCD data of rGO/MoS₂-S hybrid at different current density and (d) GCD of MoS₂-HS, rGO and rGO/MoS₂-S hybrid at a current density of 1 A/g.

Figure 7

(a) Plot of specific capacitance vs. scan rates, (b) Ragone plot (energy density vs power density) (c) Plot of capacitance retention at different cycles of MoS₂-HS, rGO and rGO/MoS₂-S hybrid and (d) Photograph demonstrating the powering of a red LED with a stack of two coin cell type supercapacitor device fabricated from rGO/MoS₂-S hybrid.

Figure 8

(a) Linear sweep voltammograms (LSV) of bare GC, Pt/C, MoS₂-HS, rGO and rGO/MoS₂-S hybrid modified electrodes towards HER in 1 M H₂SO₄ at a sweep rate of 5 mV/s, (b) Corresponding Tafel plots, (c) Nyquist plots of MoS₂-HS, rGO and rGO/MoS₂-S hybrid modified electrodes. (d) The long-term stability of rGO/MoS₂-S hybrid at 10 mA/cm² and the inset in (d) shows the photograph of the rGO/MoS₂-S hybrid modified electrode before and during the time of the stability test.