Performance of Solid-state Hybrid Energy-storage Device using Reduced Graphene-oxide Anchored Sol-gel Derived Ni/NiO Nanocomposite

Abstract

The influence of (nickel nitrate/citric acid) mole ratio on the formation of sol-gel end products was examined. The formed Ni/NiO nanoparticle was anchored on to reduced graphene-oxide (rGO) by means of probe sonication. It was found that the sample obtained from the (1:1) nickel ion: citric acid (Ni²⁺: CA) mole ratio resulted in a high specific capacity of 158 C/g among all (Ni²⁺: CA) ratios examined. By anchoring Ni/NiO on to the rGO resulted in enhanced specific capacity of as high as 335 C/g along with improved cycling stability, high rate capability and Coulombic efficiency. The high conductivity and increased surface area seemed responsible for enhanced electrochemical performances of the Ni/NiO@rGO nanocomposite. A solid-state hybrid energy-storage device consisting of the Ni/NiO@rGO (NR₂) as a positive electrode and the rGO as negative electrode exhibited enhanced energy and power densities. Lighting of LED was demonstrated by using three proto-type (NR₂⁽⁺⁾|| rGO^(-)) hybrid devices connected in series.

Figure 1

(a) XRD patterns, (b) Raman spectra and (c) FT-IR spectra of the Ni/NiO (1:1), rGO and NR₂ samples.

Figure 2

SEM images of (a) Ni/NiO (1:1), (b) rGO, (c) Composite NR₂ and (d) TEM image of NR₂. Elemental mappings (e–f) and EDAX profile of NR₂.

Figure 3

(a) Cyclic voltammograms at 5 mV/s, (b) Charge-discharge profiles at 1 A g⁻¹, and (c) specific capacity recorded on the samples obtained from each of (Ni²⁺: CA) mole ratios in 1 M KOH.

Figure 4

(a) Cyclic voltammograms at 5 mV/s, (b) Charge-discharge profiles at 1 A/g and (c) Specific capacity recorded for the pristine, NR₁, NR₂ and NR₃ electrodes in 1 M KOH.

Figure 5

(a,b) Cyclic voltammograms at various scan rates, (c,d) Charge-discharge profiles at various current densities and (e,f) dependence of specific capacityon current density recorded of pristine Ni/NiO(1:1) (left) and NR₂ (right) electrodes in 1 M KOH.

Figure 6

Life-cycle data and Coulombic efficiency recorded at 5 A/g in 1 M KOH for (a) pristine Ni/NiO (1:1) and (b) NR₂ electrodes.

Figure 7

(a) Nyquist plots recorded on the rGO, Ni/NiO (1:1) and NR₂ electrode in 1 M KOH and (b) Polarization (I-V) curves ofthe pristine Ni/NiO and NR₂ samples.

Figure 8

(a) Cyclic voltammograms at various scan rates, (b) Charge-discharge profiles at different current densities, (c) Variation of specific capacitance with current density and (d) Life-cycle data as well as Coulombic efficiency recorded for the rGO electrode in 1 M KOH.

Figure 9

(a) CV plotsof the rGO, NR₂ and solid-state hybrid device, (b) CV plots at different potential windows, (c) CV plots in the potential range 0–1.45 V at different scan rates, and (d) Charge-discharge profiles at different current densitiesrecorded for the device in PVA/KOH gel electrolyte.

Figure 10

(a) Ragone plot, (b) stability studies at different current densities, (c) cycle-life data and Coulombic efficiency recorded for the hybrid device consisting of the NR₂ positive electrode and rGO negative electrode in gel-type electrolyte and (d) photograph of the fabricated three hybrid devices lighting an LED.