Synthesis of Graphene Oxide Coating on ZnCo2S4 Using Hydrothermal Method for Electrochemical Capacitors Applications
S. Deepalakshmi | M.S. Revathy* | J. Richards Joshua | L. Saravanan | S. Thanikaikarasan* | R. Jansi | M.A. Majeed Khan | O. Savadogo
© 2023 IIETA. This article is published by IIETA and is licensed under the CC BY 4.0 license (http://creativecommons.org/licenses/by/4.0/).
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Due to the manufacturing and utilization of innovative electric devices which need energy storage systems using edge-cutting technologies as electrochemical capacitors in many areas including mobility, there is an increased demand for research and development on new materials for energy storage devices. In this research, a bimetallic sulfide as ZnCo2S4 with graphene oxide was identified and developed as electrode material for an electrochemical capacitor. Synthesis of ZnCo2S4 and ZnCo2S4@GO(1%) was elaborated by hydrothermal method. Characterization of materials was achieved using X-ray diffraction, Field Emission Scanning Electron Microscopy, Cyclic Voltammetry, and galvanostatic charge-discharge analysis. From the result, it is observed that the specific capacitance of ZnCo2S4@GO(1%) is 1060 Fg-1 at the current density of 1 Ag-1 was greater compared with ZnCo2S4. ZnCo2S4@GO(1%) has a power density of 8500 W Kg-1 with an energy density of 43 Wh Kg-1. Due to the addition of GO the electrochemical performance was improved on ZnCo2S4. From the excellent result, it is observed that ZnCo2S4@GO(1%) is the right choice for the fabrication of energy storage devices.
graphene oxide, hydrothermal method, supercapacitor, X-Ray diffraction & zinc cobalt sulfide
In this world, most people use a lot of devices with energy storage devices which increases the flexibility of the product usage. Resource utilization, compatibility, flexibility, and being environmentally friendly are the main purpose of a lot of manufacturing companies. Manycompanies introduce innovative devices with long time storage forhome appliances and medical purposes. So they require long time usage with large energy storage. In recent decades, energy storage is the challenging because of demand in various applications such as smartphones, wearable devices, medical appliances, home appliances, etc. [1]. The usage of these products grows day to day by consumers around the world. While concentrating on the next version of devices, the enhancement of energy storage device performance will be concentrated. A recent study of many articles highlighted the enhancement of the capacity of energy storage in materials. As already know, batteries have large storage capacity and long life compared with other energy storage devices as shown in Table 1. However, supercapacitors have a short duration of life for energy storage but have high performance for small device applications. Energy storage devices such as supercapacitors, capacitors, batteries, etc. should be improved by choosing novel materials for the fabrication of devices shown in Table 1 [2]. Metal oxides and metal sulfides [3] are good choices for energy storage devices. Nowadays researchers have their choice of graphene oxide for enhancing the electrochemical performance of the metal oxides or metal sulfides [4]. By adding graphene oxide with metal oxide/metal sulfides, the morphology nature of the material does not change instead it enhances the performance of the material. Choosing the right dopant is also challenging for the perfect material. Metal oxides are utilized by many researchers. The same performance can be achieved while referring to many articles in the journal. From the reference, the following experimental preparation has been done for analyzing the electrochemical performance of the sample material [2, 5, 6].
Table 1. Comparision of various energy storage devices
|
Parameter |
Capacitors |
Supercapacitors |
Batteries |
|
Energy Storage |
Watt –Sec |
Watt –Sec |
Watt-Hour |
|
Energy Density |
0.01-0.05 WhKg-1 |
1-5 WhKg-1 |
8-600 WhKg-1 |
|
Power Density |
High, >5000 WKg-1 |
High, >4000WKg-1 |
Low, 100-3000WKg-1 |
|
Lifetime |
>100K cycles |
>100K cycles |
150-1500 Cycles |
|
Power Delivered |
Rapid Discharge Linear/Exponential Voltage Decay |
Rapid Discharge Linear/Exponential Voltage Decay |
Constant Voltage over long time period |
|
Charge/Discharge Time |
Pico Seconds to Milli Seconds |
Milli Seconds to Seconds |
1-10 Hours |
|
Charge Method |
Voltage across Terminals |
Voltage across Terminals |
Current & Voltage |
|
Form Factor |
Small to Large |
Small |
Large |
|
Weight |
1 Grams-10 Kilograms |
1-2 Grams |
1 Grams to >10 Kilograms |
|
Operating Voltalge |
6V-800V |
2.3V-2.7V/Cell |
1.2V-4.2V/Cell |
|
Operating Temparature |
-20 to +100℃ |
-40 to +85℃ |
-20 to +65℃ |
2.1 Hydrothermal method for preparation of ZnCo2S4
The chemical has been bought from inside Tamilnadu without purity. During synthesis, a solution with a transparent pink color was obtained by stirringa well of 99% Sigma Aldrich 10 mL of glycerol (Merk, 99%), 50 mL of isopropanol, 0.08 g of Zn(NO3)2·6H2O and 0.15 g of Co(NO3)2·6H2O. After the added Thioures as a sulfide source was liquified well with the above solution and maintained at a temperature of 160℃ for a period of 18 hours in the Teflon- lined autoclave. The resultant solid substance was purified with ethanol and water until reached room temperature and then evaporated to 80℃ in a vacuum oven. Finally, ZCS (ZnCo2S4) was obtained.
2.2 Hydrothermal method for preparation of ZnCo2S4@GO
The above procedure was followed for GO coating on ZnCo2S4 by adding 0.2g of ZnCo2S4 and GO 1% in 50 ml of the liquified solution for the time of 2 hrs. A temperature of 140℃ for 12 hrs was maintained at the Teflon-lined autoclave. The previous procedure was followed for evaporating the solution. The resultant sample was ZCS@GO(1%). The experimental procedure is shown in Figure 1.
Figure 1. Experimental procedure for preparation of ZnCO2S4 and ZnCO2S4@GO 1% using hydrothermal method
2.3 Chararterisation of the samples using XRD, FESEM, CV, and GCD methods
2.3.1 XRD (X-ray Diffraction) characterisation method
The XRD patterns of the samples were obtained using Rigaku powder diffractometer. The wavelength of the Cu K radiation utilised in the experiment was 0.154 nm, and the range of the angle 2 theta was 10 degrees to 80 degrees, in 0.2 degree increments.
2.3.2 FESEM (Field emission scanning electron microscopy) charaterisation method
The morphology information of the sample was analyzed using SEM-EDS (ZEISS-EVO/18, Germany) to get FE-SEM and EDX pictures.
2.3.3 CV (Cyclic Voltammetry), and GCD (Galvanostatic charge/discharge) charaterisation methods
The electrochemical analysis was performed using Bio-logic 350 (France). The CV analysis was performed at the voltage range of about 0 – 0.6 V. The galvanostat charge/discharge analysis was performed at the voltage range 0 – 0.5V at different current densities (1 – 20 Ag-1).
3.1 X-ray diffraction
XRD was investigated to analyze the crystallographic structure of the sample. Figure 2 shows the XRD investigation of the prepared material. The peaks of ZnCo2S4 and ZnCo2S4@GO(1%) are same aslocated at 15.9°, 26.22°, 30.83°, 37.86°, 46.19°, 49.12°, 53.87°, 63.86°, 67.34°, 69.69°, 73.56, 75.92° that corresponds to the miller indices (040), (044), (111), (131), (151), (202), (246), (422), (444), (533), (701), (731) planes. From XRD patterns were taken and referred with JCPDS (47-1656) data which confirms that there are purity peaks were observed and proves that the nature of the sample was pure crystalline. The outer surface of ZnCo2S4 contains the coating of graphene oxide which proves that the sample has good electrochemical performance with enhancement of electron transport.
Figure 2. X-Ray diffraction analysis of ZCS and ZCS@GO(1%)
3.2 FESEM analysis
The Microstructure Analysis of ZnCo2S4 and Graphene Oxide with coated ZnCo2S4 was shown in the Figure 3(a), (b), (c) and (d). Figure 3(a) and (b) show the FESEM results of ZnCo2S4 . It shows that there are flakes-like petals randomly appearing all over the sample. The Petal diameter is about 50-60 nm. Figure 3(c) and (d) describe the FESEM results of ZnCo2S4@GO(1%). Due to the addition of 1% of Graphene Oxide, flower-like flakes appeared and Graphene oxide distributes as a thin layer on the outer surface of ZnCo2S4. While comparing with ZnCo2S4 and ZnCo2S4@GO(1%), the diameter and morphological structure were changed from flakes-like petals to flower-like flakes because of the increasing ratio of GO coating. The thickness of ZnCo2S4@GO(1%) is 2-4 nm.
Figure 3. FESEM analysis, (a) & (b) ZnCo2S4 (c) & (d) ZnCo2S4@GO(1%)
3.3 Cyclic voltammetry
The electrochemical efficiency analysis was studied by using a three-electrode setup. The prepared electrode materials were ZnCo2S4 and ZnCo2S4 GO(1%). A 3.0M KOH was used as electrolyte for the CV analyses. The CV curves of both ZnCo2S4 and ZnCo2S4@GO(1%) were taken with a scan rate of 1 mV sec-1 and are given in Figure 4(a) and (b).
Figure 4. Cyclic voltammetry curves (a) ZnCo2S4(ZCS) (b) ZnCo2S4@GO(1%)(ZCS@GO(1%))
The rising and falling appearance of outstanding redox current peaks in the identical location. The properties of faradic reaction sharpening and pseudo-capacitance may be deducted from the appearance of the curves that are analyzed using prepared electrode materials. The electrochemical performance analysis shows that the curve of ZnCo2S4@GO(1%) was a higher region than that of the curve of ZnCo2S4. It was observed that the electrochemical performance of ZnCo2S4@GO(1%) was higher than ZnCo2S4.
3.4 Galvanostatic charge-discharge
The Galvanostatic charge-discharge patterns with various current densities are given in Figure 5(a) and (b). The electrode material ZnCo2S4@GO(1%) has taken a short discharge time, showing that the current density is significantly greater than that of ZnCo2S4. From this, it is observed that ZnCo2S4@GO(1%) in the electrode involves less time in the redox reaction. Due to the shorter time for redox reaction the transport of electrons having velocity is significantly faster than the electrochemical reaction rate. 1060 Fg-1 is the specific capacitance of ZnCo2S4@GO(1%) at the current density of 1 Ag-1. As a result, the ZnCo2S4@GO(1%) electrode material has a specific capacitance (Cg) of 1060 Fg-1 at a current density of 1 Ag-1 with a power density of 8500 W Kg-1 at the energy density 43 Wh Kg-1.
A ZnCo2S4-based electrode exhibited specific capacitance 989 Fg-1 at a current density of 1 Ag-1. Since it is lower compared to the specific capacitance of ZnCo2S4@GO(1%), the power density and energy density were calculated only for ZnCo2S4@GO(1%). Due to the low value of the specific capacitance of the ZnCo2S4-based electrode in comparison to that of ZnCo2S4@GO(1%), it is expected that the power density and the energy density of the ZnCo2S4-based electrode are lower than those of the ZnCo2S4@GO(1%) electrode. This is supported by the surface area of the curves voltage vs time at the current density of 1 Ag-1 A of Figure 5(a) and Figure 5(b). For a current density of 1 Ag-1, the surface area of the curve voltage vs time is lower for ZnCo2S4-based electrode(Figure 5(a)) than that of ZnCo2S4@GO(1%), based electrode (Figure 5(b)).
Effectively, the comparison of the graph of Figure 5(a) and Figure 5(b) indicates that performance of the ZnCo2S4@GO(1%) electrode has improved at higher current densities. During the exchange between electrons and ions at the electrode/electrolyte interface, the efficiency of the electron transfer is higher in the case of the ZnCo2S4@GO(1%) electrode than that of the ZnCo2S4electrode. This can be attributed to the presence of more electrochemically active sites on the ZnCo2S4@GO(1%) electrode due to the graphene oxide coating.
Then, as expected, the specific capacitance of the ZnCo2S4(ZCS) electrode is lower than that of the ZnCo2S4@GO(1%) electrodes which has higher specific capacitance compared to that of ZnCo2S4.
Figure 5. Galvanostatic charge-discharge for various current densities: (a) ZnCo2S4(ZCS) (b) ZnCo2S4@GO(1%)(ZCS@GO(1%))
Thus the ZnCo2S4 and ZnCo2S4@GO(1%) materials were synthesized using the hydrothermal method. The materials characterization methods such as XRD, FESEM, CV, and GCD were used to analyze both electrode materials. From the analysis of XRD, the morphological structure does not change while adding GO in ZnCo2S4 and it is matched with JCPDS (47-1656). From the analysis of FESEM, it is observed that flower-like flakes appeared due to the addition of GO in ZnCo2S4. From the analysis of CV, it is observed that pseudo capacitance and faradic reaction were deducted and ZnCo2S4@GO(1%) has a higher region compared to ZnCo2S4.which shows excellent electron transfer and electrochemical performance. From the analysis of GCD, ZnCo2S4@GO(1%) has a current density that is significantly greater than ZnCo2S4. As a result, it is concluded that ZnCo2S4@GO(1%) electrode material has greater specific capacitance (Cg) 1060 Fg-1 at a current density of 1 Ag-1 with a power density of 8500 W Kg-1 at the energy density 43 Wh Kg-1 whereas the ZnCo2S4(ZCS) based electrode exhibited a specific capacitance (Cg) of 989 Ag-1 at a current density of 1 Ag-1 with a power density. And the enrgy density so it is recommended for the fabrication of Asymmetric supercapacitor as energy storage devices.
The authors extend their sincere appreciation to the Researchers Supporting Project number (RSP2023R130), King Saud University, Riyadh, Saudi Arabia for funding this research.
|
Symbols |
|
|
V |
Voltage |
|
J |
Current density, Ag-1 |
|
Cg |
Specific Capacitance, Fg-1 |
|
T |
Time, S |
|
℃ |
Degree Celcius |
|
Nm |
Nano Meter |
|
Ag-1 |
Ampere per Gram |
|
Fg-1 |
Farad per Gram |
|
S |
Second |
|
Abbreviations |
|
|
Zn(NO3)2·6H2O |
Zinc Nitrate |
|
Co(NO3)2·6H2O |
Cobalt Nitrate |
|
ZnCo2S4(ZCS) |
Zinc Cobalt Sulfide |
|
ZnCo2S4@GO(ZCS@GO) |
Zinc Cobalt Sulfide with Graphene Oxide |
|
GO |
Graphene Oxide |
|
XRD |
X-Ray Diffraction |
|
FESEM |
Field Emission Scanning Electron Microscopy |
|
CV |
Cyclic Voltammetry |
|
GCD |
Galvanostatic Charge-Discharge |
|
JCPDS |
Joint Committee on Powder Diffraction Standards |
|
AgCl |
Silver Chloride |
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