Designing of WS₂@NiCoS@ZnS Nanocomposite Electrode Material for High-Performance Energy Storage Applications

Abstract

Researchers are developing innovative electrode materials with high energy and power densities worldwide for effectual energy storage systems. Transition metal dichalcogenides (TMDs) are arranged in two dimensions (2D) and have shown great promise as materials for photoelectrochemical activity and supercapacitor batteries. This study reports on the fabrication of WS₂@NiCoS and WS₂@NiCoS@ZnS hybrid nano-architectures through a simple hydrothermal approach. Because of the strong interfacial contact between the two materials, the resultant hierarchical hybrids have tunable porosity nanopetal decorated morphologies, rich exposed active edge sites, and high intrinsic activity. The specific capacities of the hybrid supercapacitors built using WS₂@NiCoS and WS₂@NiCoS@ZnS electrodes are 784.38 C g⁻¹ and 1211.58 C g⁻¹ or 2019.3 F g⁻¹, respectively, when performed at 2 A g⁻¹ using a three-electrode setup. Furthermore, an asymmetric device (WS₂@NiCoS@ZnS//AC) shows a high specific capacity of 190.5 C g⁻¹, an energy density of 49.47 Wh kg^−1, and a power density of 1212.30 W kg⁻¹. Regarding the photoelectrochemical activity, the WS₂@NiCoS@ZnS catalyst exhibits noteworthy characteristics. Our findings pave the way for further in-depth research into the use of composite materials doped with WS₂ as systematic energy-generating devices of the future.

1. Introduction

The energy issue and the need for electricity have gained prominence due to social improvements. Thus, developing novel electrode materials has received a lot of interest in energy-efficient transformation and storage [1,2]. Electrochemical capacitors (ECs) are experiencing a growing demand, particularly for cutting-edge, flexible, electrochemical energy storage technologies that are portable and wearable [3,4]. ECs possess numerous mandatory features compared to lithium/sodium ion or solid-state batteries. These include durable cycle stability, high specific capacitance, quick charge/discharge capability, remarkable power density, and safe operation at a reasonable cost. Due to their low energy density, extensive efforts have been dedicated to enhancing their intrinsic properties. This involves modifying electrode designs, expanding the surface area, creating electrodes with excellent electrical and ionic conductivity, and creating mechanically and chemically robust interfaces [5,6].

Transition metal dichalcogenides (TMDs) have advanced significantly because of their superb catalytic activity in electrochemical applications, affordability, and terrestrial abundance [7,8,9,10]. TMD has a triple-layer packing arrangement with a thickness ranging from 6 to 7 Å that is weakly connected to neighboring layers by van der Waals forces [11,12]. Molybdenum sulfides (MoS₂) and tungsten sulfides (WS₂) are two examples of metal sulfide TMD structures with a hexagonally packed structure resembling graphite. In this configuration, covalent bonding is used to introduce metal layers between two sulfur layers. Because MoS₂ and WS₂ have a huge specific surface area, many sulfur-active facets, and multivalent oxidation states of transition metal ions, they may transfer and accumulate charges efficiently [13,14]. Pure WS₂-based electrochemical devices cannot be further improved due to the limited exposure of active sites and their inherent semiconducting nature [15,16]. Recently, numerous studies have focused on enhancing the number of active facets in WS₂ through doping with heteroatoms, creating defects/vacancies, designing various crystal phases and morphologies, and tuning the active area [17,18,19]. Hence, developing electrode materials exhibiting high active facets oriented toward edges/defects represents a promising approach for hydrogen production and energy storage [20,21]. Apart from the mechanism for storing charges, the presentation of the device is also influenced by the electrode material. The fundamental qualities of an ideal positive electrode material for supercapattery include porous structure, excellent conductivity, and electroactivity [22,23]. Transition metal phosphides, oxides, and sulfides are appropriate materials for positive electrodes [24,25,26]. Transition metal sulfides’ robust electroactivity and chemical stability make them highly suitable electrode materials [25,27]. For example, Rauf et al. documented the electrochemical analysis of ZnS nanowires deposited on nickel foil. The ZnS electrode demonstrated a specific capacity (Qs) of 81 F g⁻¹ at 0.5 A g⁻¹ [28]. The ZnS electrode confirmed an energy density (E_d) of 51 Wh kg⁻¹ at a power density (P_d) of 200 W kg⁻¹, sustaining cyclic stability of 87% after 10,000 charge–discharge cycles. Wan and collaborators hydrothermally synthesized cobalt sulfide (CoS) nanotubes, revealing a Qs of 285 F g⁻¹ at 0.5 A g⁻¹ with 99% cyclic stability. The collaborative impact of both ZnS and CoS enhanced the electrode performance, as evidenced by the ZnS/CoS binary composite developed by Chameh et al., which displayed an exceptional Qs of 1646 F g⁻¹ at 1 A g⁻¹ [29]. The combination of ZnS and CoS in the composite resulted in an E_d of 39.41 Wh kg⁻¹ paired with a P_d of 7080 W kg⁻¹ while maintaining 89.0% capacitance retention in an asymmetry device. Furthermore, Wang et al. reported synthesizing a ternary metal sulfide electrode in which three transition metals combined to form NiCoMnS₄ produced an extraordinary Qs of 2470.40 F g⁻¹ at 1 A g⁻¹ [30]. The synthesis method is crucial, as it significantly influences the electrochemical capabilities and performance of nanomaterials. For example, CoS synthesized through a hydrothermal approach [27] exhibited a Cs value of 506.70 F g⁻¹ at 1.5 A g⁻¹. In contrast, CoS synthesized using sonochemical methods, as reported by Iqbal et al., showed a Cs value of approximately 340 F g⁻¹ [31]. The 2D TMDs are a new class of positive electrode materials for supercapattery that may be used to attain higher specific energy. These TMDs are composed of two chalcogen atoms (X) and a transition metal atom (M) bound together by covalent bonds to create the structure known as X–M–X. Their inherent layered configuration facilitates the insertion of ions between these layers, facilitating swift ionic diffusion and thereby enhancing their electrochemical performance [32]. TiS₂, MoS₂, WS₂, MoSe₂, and WSe₂ are only a few of the TMDs that have remarkable electrochemical performance [33]. The presence of various oxidation states (approximately +2.0 to + 6.0) and a substantial surface area enable 2D materials to undergo electrochemical and electrostatic charge storage processes. This, in turn, results in elevated specific capacitance (Cs) and energy density (Ed) values for the electrode [34,35]. Gupta and colleagues employed hydrothermal synthesis to produce layered MoS₂, which was subsequently subjected to electrochemical testing [36]. The graphene-like configuration resulted in a capacitance (Cs) value of 255 F g⁻¹ at 0.25 A g⁻¹, along with an energy density (Ed) of 35.50 Wh k g⁻¹ under the same current density. Moreover, the MoS₂ electrode showed remarkable stability across many cycles, exhibiting only a 30% reduction in its original capacitance. WS₂, another transition metal dichalcogenide (TMD) with a graphene-like structure, features a layer-to-layer distance of approximately 0.170 nm, facilitating easy intercalation of metal ions and contributing to its outstanding electroactive properties [37]. While TMDs exhibit impressive capacitive characteristics, they often suffer from reduced cyclic stability and conductivity. To address these limitations, researchers enhance these materials by creating hybrid structures of transition metal sulfides, which have proven particularly effective for such combinations. The cyclic stability of WS₂ and CoS was found to be 89.83% and 92.50%, respectively, in research conducted by Krishna et al. This stability was significantly improved to 97.10% when WS₂ was combined with CoS [38]. The electrical resistance values for WS₂ nanorods and Co₃S₄ microspheres were 3.02 Ω and 3.81 Ω, respectively, according to an independent study by Shrivastav et al. Upon combining these materials, the hybrid electrode exhibited a reduced resistance, measuring 2.73 Ω [39].

This study explores a new approach for creating novel hierarchical lamellar WS₂@NiCoS@ZnS hybrid structures using a hydrothermal method. These structures are formed through a solid interfacial interaction between NiCoS@ZnS and WS₂ nanosheets, making them promising alternatives for current requirements. The hybridization process, which results in the WS₂@NiCoS@ZnS hybrid structure, leads to increased interlayer space amid the duos, enhancing intercalation/extraction ion kinetics and stability. The highly conductive WS₂ nanostructures in the hybrid configuration maximize electrical conductance, facilitating rapid electron-transfer kinetics and improving electrical performance at the interfaces between electrodes and active edges. Utilizing WS₂@NiCoS and WS₂@NiCoS@ZnS hybrid structures in assembled devices demonstrates remarkable capabilities in supercapacitors and photoelectrochemical activities. Specifically, supercapattery incorporating WS₂@NiCoS and WS₂@NiCoS@ZnS electrodes exhibit specific capacity of 784.38 C g⁻¹ and 1211.58 C g⁻¹ or 2019.3 F g⁻¹, respectively, at 2 A g⁻¹ in three-electrode measurements. In supercapattery WS₂@NiCoS//AC and WS₂@NiCoS@ZnS//AC devices, specific capacities of 145.93 and 190.5 C g⁻¹ are achieved, respectively, at 1.5 A g⁻¹, providing an energy density of 49.47 Wh kg⁻¹ at a power density of 1212.30 W kg⁻¹. This supercapattery device (WS₂@NiCoS@ZnS//AC) shows high cyclic stability, columbic efficiency of 93.23%, and capacity retention of 85.19% after 5000 GCD cycles. These results show that the suggested material composition is suitable for applications using supercapattery energy storage devices.

2. Experimental Section

Nanomaterials for supercapattery technology are produced utilizing nickel nitrate hexahydrate (Ni(No₃)₂.6H₂O), cobalt (II) nitrate hexahydrate (Co(NO₃)₂.6H₂O), sodium sulfide, hydrate (Na₂S.nH₂O), tungsten sulfide (WS₂), zinc sulfide (ZnS), lithium nitrate (LiNO₃), potassium hydroxide (KOH), and N-methyl 2-pyrrolidone (NMP) obtained from Sigma-Aldrich. N-polyvinylidene-fluoride (PVDF) and carbon black are obtained from MERCK. The WS₂ powder is needed for the manufacture of WS₂ nanosheets. WS₂ nanosheets are synthesized using the tip-sonication technique, which uses an ultrasonic probe. A surgical HUT 80-1 centrifuge machine is used for material collection and cleaning. To produce WS₂ nanosheets with controlled thickness and size distribution, which are advantageous for applications such as electronics, catalysis, and energy storage, the tip-sonication method is scalable and efficient [40,41].

2.1. Synthesis of NiCoS@ZnS

The NiCoS nanocomposite was synthesized using a hydrothermal technique. Considering this, we have created three solutions: Ni(NO₃)₂.6H₂O (0.3 M) (purity 98%), Co(NO₃)₂.6H₂O (0.3 M) (purity 99.8%), and Na₂S.nH₂O (0.4 M) (purity 99.9%) were mixed individually in 50 mL deionized (DI) water. The obtained mixture was heated at 170 °C for 12 h. NiCoS precipitous was collected and centrifuged at 3000 rpm. The recovered samples were extensively cleaned with DI water and ethanol to remove leftover pollutants. Figure 1 shows a schematic of the synthesis process of WS₂ nanosheets, deposition, and electrode testing steps of the electrode. We prepared NiCoS@ZnS by physical blending of 80/20 wt.%

2.2. Synthesis of WS₂@NiCoS@ZnS Nanocomposite

In a 50 mL mixture of NMP solvent, 6 g of pure WS₂ powder is mixed. A probe sonicator is used to sonicate the mixture for 3 h. Centrifuging the sonicated WS₂/NMP combination at 1500 rpm for 3.5 h yields the dispersed WS₂ nanosheet solution. Using a mortar and pestle, a 5 wt% mixture of WS₂ nanosheet powder and NiCoS@ZnS is prepared. Figure 1 is a simplified flow diagram showing the steps involved in creating WS₂ nanosheets, WS₂@NiCoS@ZnS, and characterizing the final product. The electrode slurry is made up of active material (80%), carbon black (10%), and PVDF binder (10%). After stirring the ingredients in a slurry tube all night, the resulting homogeneous slurry was pipetted over the nickel foam. Properly cleansing and washing the nickel foam (NF) with HCL, ethanol, and DI water is preceded for deposition. The electrolyte slurry is deposited on a 1 × 1 cm² area of nickel foam, with 5 mg of the deposited material. An electrochemical test using a 1.0 M KOH electrolyte is performed on the dried WS₂@NiCoS@ZnS electrode.

3. Results and Discussion

Characterization Techniques

Crystalline quality and phase purity of WS₂@NiCoS@ZnS were investigated using XRD. The perceived sharp peaks assert the presence of crystalline WS₂, ZnS, NiCoS@ZnS, NiCoS, WS₂@NiCoS, and WS₂@NiCoS@ZnS, as depicted in Figure 2a. In the case of NiCoS, the XRD peaks at 2θ values of 16.09°, 27.7°, 31.9°, 39.32°, 45.03°, 50.14°, and 55.08°, corresponding to the planes (100), (002), (400), (311), (004), (511), and (440), respectively (JCPDS card No. 23-382) [42,43,44]. The deflection peaks of hexagonal phase WS₂ in the pattern at 2θ 14.5°, 33.5°, 42.06°, and 61° correspond to (002), (004), (006), and (008) (JCPDS No: 37-1492) [45]. In ZnS, the peak becomes visible at 28.6°, 48.03°, and 65.6°, consistent with the (111), (220), and (311) plane, which serves as evidence for the presence of ZnS [46].

When choosing the nanomaterial for use in supercapattery, its structure is essential. Electrode material and electrolyte interact well due to the material’s surface topography. According to the claim, the shape of the material affects its capacitive and conductive characteristics [39].

The XRD for NiCoS, NiCoS@ WS_2, and NiCoS@WS₂@ZnS is shown in Figure 2a, whereas big particles result from the aggregation of smaller particles and nanosheet stacking. The Figure clearly shows WS₂ nanosheets interspersed throughout the NiCoS@ZnS aggregates. By increasing the material’s conductive and capacitive properties, nanosheets make the charging and discharging process easier. In addition to facilitating charge transfer, these nanosheets make additional active sites available for the infusion of metal ions.

The WS₂@NiCoS@ZnS nanocomposite materials’ SEM picture is shown in Figure 2b. NiCoS@ZnS nanocomposites that have established excellent contact with WS₂ nanosheets are suggested by the fragments’ transparency and few-layer thickness, which are signs of the presence of dopants in the WS₂ hybrid materials [47]. The WS₂ enhanced the pores’ area and surface energy and NiCoS@ZnS nanoflakes, which is necessary to store plenty of charge carriers and maintain their transparency [48,49].

Moreover, a thermogravimetric analysis (TGA) test is used to evaluate the material’s stability and purity. The skeletons of the treated materials must be visible, which requires TGA analysis. The TGA is performed for the WS₂@ZnS, WS₂@NiCoS, and WS₂@NiCoS@ZnS between 0 and 750 °C to determine the relationship between temperature and weight loss. Figure 2c shows a slight weight loss between 30 to 180 °C. The mass of the pure WS₂@ZnS sample drops dramatically between 200 and 450 °C. It has been observed that the WS₂@NiCoS exhibited a gradual decrease in weight when subjected to temperatures ranging from 200 to 450 °C. This is mainly attributable to the pyrolysis of oxygenated and hydrogenated units [50]. Notably, the WS₂@NiCoS@ZnS composite has a minor weight defeat of 17.22 wt%, considerably smaller than WS₂@ZnS (40%) and WS₂@NiCoS (30%).

The BET estimates the surface area, pore volume, and pore size, which may be controlled to improve the electrode’s performance. Additionally, to find out the exact surface areas of the samples, it is used to calculate the adsorption and desorption of nitrogen. The average pore size, surface area, and pore volume of WS₂@ZnS are 33.7 nm, 34.4 m² g^−1, and ~17.51 cm³ g^−1, respectively (Figure S1a). In the case of WS₂@NiCoS, the pore size, surface area, and pore volume are 27.5 nm, 44.8 m² g^−1, and ~67 cm³ g⁻¹, respectively (Figure S1b). Figure 2d shows that WS₂@NiCoS@ZnS has the pore size, surface area, and pore volume of 27.5 nm, 44.8 m² g^−1, and ~67 cm³ g^−1, respectively. WS₂@NiCoS@ZnS composite has a high surface area-to-volume ratio, which means it can have more adsorption and reactive sites available, which means it can keep its photocatalytic activity [51,52,53,54]. According to the findings of the BET study, WS₂@NiCoS@ZnS has a higher surface area, which permits a more substantial anticipation of charges on the electrode surface [55]. High-charge storage capacity and quick ion diffusion are made possible by the composite’s enormous surface area and pore volume [56].

X-ray photoelectron spectroscopy (XPS) analysis determines the WS₂@NiCoS@ZnS nanocomposite. As shown in Figure S2a, two XPS spectra of Ni 2P_3/2 and Ni 2P_1/2 were seen with binding energies of 856.7 and 871.5 eV, respectively [57]. This demonstrates that NiCoS has both Ni²⁺ and Ni³⁺ peaks [35]. As seen in Figure S2b, the spectrum investigation of Co2P presented two unique peaks at 778.4 and 793.7 eV, which corresponded to Co2P_3/2 and Co 2P_1/2, respectively. Here, we may see the existence of Co²⁺ and Co³⁺. The presence of Zn²⁺ is indicated by two peaks in the Zn 2P spectra, as shown in Figure S2c: one at 1046.5 eV for Zn 2P_1/2, and another one at 1023 eV for Zn 2P_3/2. The orbit splitting for the latter peak is 23.5 eV. As shown in Figure S2d, the presence of sulfur in the composite is confirmed by the S 2P_3/2 peak at 161.0 eV and the S 2P_1/2 peak at 163.6 eV. Figure S2e from the literature shows that the XPS spectra of WS₂ also include peaks of W4f_7/2, W4f_5/2, and W 5P_3/2, with binding energies of 32.98 eV, 35.89 eV, and 37.78 eV, respectively, all corresponding to the W in 4⁺ form in WS₂ nanosheets [58].

4. Electrochemical Analyses

Electrochemical characterization of the electrode materials begins by recording CV at a constant potential window (PW) of 0 to 0.6 V and different scan rates from 5 mV s⁻¹ to 60 mV s⁻¹. The CV comparison of all electrodes (WS₂, ZnS, NiCoS, WS₂@ZnS, WS₂@NiCoS, NiCoS@ZnS, and WS₂@NiCoS@ZnS measured at 5 mV s⁻¹ in 1M KOH electrolyte is shown in Figure 3a. The CV profiles with their faradaic peaks in Figure 3b–d represent the battery-grade quality of WS₂@ZnS, WS₂@NiCoS, and WS₂@NiCoS@ZnS, respectively. The redox-active properties of WS₂@NiCoS@ZnS contribute to the higher peak current determined from the CV, as seen in Figure 3d. When we increase the scan rate, there is a noticeable change in the peak currents of both pristine and doped material. This shift might be caused by the high ion mobility rate, which is faster than the faradaic processes and raises the peak currents.

We also used GCD tests to see how much energy the electrode materials could store at room temperature, with a constant voltage ranging from 0 to 0.6 V and different current densities of 2.0 A g⁻¹ to 3.0 A g⁻¹. Figure 4a displays the GCD plots of WS₂, ZnS, NiCoS, WS₂@ZnS, WS₂@NiCoS, and WS₂@NiCoS@ZnS using 1 M KOH electrolyte at 2 A g⁻¹. Figure 4b–d shows the CV curves of WS₂@ZnS, WS₂@NiCoS, and WS₂@NiCoS@ZnS, respectively. The greater area under the curve, which indicates improved charge storage capacity, is seen in the comparative study of a CV of WS₂@NiCoS@ZnS material. The WS₂@NiCoS@ZnS shows highly preferable GCD results over other reference samples, as shown in Figure 4d. The improved performance of WS₂@NiCoS@ZnS in a 1.0 M KOH electrolyte solution is due to the increased ionic mobility and conductivity and the small hydrated ionic radii of KOH ions.

The ability of the electrodes to store charge is indicated by their specific capacitance (Cs) and specific capacity (Qs), which are determined using the relationships provided below:

$${\mathrm{Q}}_{\mathrm{s}}={\displaystyle \frac{1}{\mathrm{m}\mathrm{v}}}{\int }_{V_i}^{V_f}\left(\mathrm{I}\times \mathrm{V}\right) \mathrm{d}\mathrm{V}$$

(1)

$${\mathrm{C}}_{\mathrm{s}}={\displaystyle \frac{1}{\mathrm{m}\mathrm{v}∆\mathrm{V}}}{\int }_{V_i}^{V_f}\left(\mathrm{I}\times \mathrm{V}\right) \mathrm{d}\mathrm{V}$$

(2)

Herein, ‘m’ stands for loading mass, ‘v’ for scan rate, ‘∆V’ for voltage, and the integral section implies the region encircled by the CV profile. These correlations show that Qs and Cs directly impact the area of a CV. When the scan rate increases, the peak currents increase due to the acceleration of faradaic reactions, and the Qs decrease because the reaction time is reduced. The electrode materials WS₂, ZnS, NiCoS, WS₂@ZnS, WS₂@NiCoS, and WS₂@NiCoS@ZnS are further studied electrochemically with 1 M KOH. The base reference materials WS₂, NiCoS, WS₂@ZnS, WS₂@NiCoS, and WS₂@NiCoS@ZnS delivered the maximum Q_s of 560.97 C g⁻¹, 695.61 C g⁻¹, 799.66 C g⁻¹, 942.81 C g⁻¹, and 1189.30 C g⁻¹ at 5 mV s⁻¹, correspondingly, as shown in Figure 5a. The electrode with composite material WS₂@NiCoS performed better than the base materials as it provided a Q_s value of 942.81 C g⁻¹ due to the complementary effects of NiCoS and WS₂. Finally, cyclic voltammetry measurements are performed on the NiCoS@ZnS doped with WS₂ nanosheets. The sample with the highest Qs value, 1189.30 C g⁻¹, was the electrode with WS₂ doped material. Due to the abundance of active sites made accessible for faradaic reactions by WS₂ nanosheets, the higher Qs are the outcome. The improved electroconductivity of the electrode resulted from the increased adhesion of NiCoS@ZnS to WS₂ nanosheets, which opened up more pathways for electron transport. Results for specific capacitance (Cs), as determined by Equation (2). The Cs of WS₂, NiCoS, WS₂@ZnS, WS₂@NiCoS, and WS₂@NiCoS@ZnS are claimed to be 934.95 C g⁻¹, 1159.35 C g⁻¹, 1332.76 C g⁻¹, 1571.35, and 1982.16 C g⁻¹ at 5 mV s⁻¹ is represented in Supplementary Information Figure S4a.

The nonlinearity of the GCD profiles with a little hump and their uniformity reveals that the material is of battery-grade quality, which is shown by the reversibility of the faradaic reactions and subsequent CV results. As we increase the current density value, the discharge time reduces, reducing the time available for the faradaic processes. This reduction in discharge duration diminishes the electrode’s capacity to store charge. The Qs and Cs, which are calculated using the supplied relations below, determine the capacity to store charge:

$${\mathrm{Q}}_{\mathrm{s}} = {\displaystyle \frac{\mathrm{I}\times ∆\mathrm{t}}{\mathrm{m}}}$$

(3)

$${\mathrm{C}}_{\mathrm{s}} = {\displaystyle \frac{\mathrm{I}\times ∆\mathrm{t}}{\mathrm{m}\times ∆\mathrm{V}}}$$

(4)

where ‘m’ stands for loaded mass on Ni foam, ‘∆t’ for discharging time (Sec), and ‘∆V’ for the operating voltage. The Q_s values of WS₂, NiCoS, WS₂@ZnS, WS₂@NiCoS, and WS₂@NiCoS@ZnS delivered the maximum Q_s are 502.24 C g⁻¹, 576.82 C g⁻¹, 666.38 C g⁻¹, 784.38 C g⁻¹, and 1211.58 C g⁻¹ at 2 A g⁻¹, respectively, as shown in Figure 5b. When WS₂ nanosheets were added to the NiCoS@ZnS electrode material, the electrode demonstrated superior electrochemical performance during testing. At 2 A g⁻¹, the WS₂-doped NiCoS@ZnS had an exceptional Qs value of 1211.58 C g⁻¹. The GCD-related Cs values trend of WS₂, NiCoS, WS₂@ZnS, WS₂@NiCoS and WS₂@NiCoS@ZnS are claimed to be 934.95 F g⁻¹, 1159.35 F g⁻¹, 1332.76 F g⁻¹, 1571.35 F g⁻¹ and 1982.16 F g⁻¹ at 5 mV s⁻¹ is represented in Supplementary data as a bar graph showing Figure S4b. Anodic peak current and cathodic peak current refer to the electrochemical behavior of a material in CV experimentation. WS₂@NiCoS@ZnS is a composite material composed of tungsten disulfide (WS₂) coated with nickel cobalt sulfide (NiCoS) and further coated with zinc sulfide (ZnS). The anodic peak current typically corresponds to the oxidation process (loss of electrons), while the cathodic current corresponds to the reduction process (gain of electrons). We can see here that when the scan rate (SR) increases, the anodic current also increases. The maximum calculated current values of the Anodic and cathodic peaks are 55 mA and −42 mA, as shown in Figure 5c.

The conductivity and capacity to store charge of the WS₂, NiCoS, WS₂@ZnS, WS₂@NiCoS@, and WS₂@NiCoS@ZnS electrodes were compared by performing EIS. Where the real and imaginary axes meet at higher frequencies is the electrode materials’ equivalent series resistance (ESR). The ESR governs the conductivity of the electrode material. More resistance indicates a higher ESR value and vice versa. Figure 5d shows the material’s equivalent ESR value determined using EIS. This proves that WS₂@NiCoS@ZnS has the lowest value among the other samples. There is no sample with a lower equivalent series resistance value than WS₂@NiCoS@ZnS. The unique microporous design of the composite allows it to have synergistic effects, leading to decreased charge transfer resistance.

Additionally, the materials are examined for their potential applications by conducting electrochemical tests using a two-electrode setup. To achieve this, we use Whatman filter paper as a dielectric medium to separate the cathode and anode electrodes, and we combine active materials (WS₂@ZnS, WS₂@NiCoS, and WS₂@NiCoS@ZnS) with activated carbon (AC) chips. A schematic representation of the setup device is shown in Figure 6a. The electrochemical data indicate that the combination of the battery and supercapacitor grade electrodes’ faradic and capacitive behaviors results in a higher energy storage capacity for the device. Redox processes allow battery-grade electrodes to store large amounts of energy; in contrast, supercapacitor-grade electrodes store charge by absorbing and desorbing charges.

The electrochemical performance of WS₂@NiCoS@ZnS was assessed using a CV investigation using a three-electrode setup and a scan rate of 5 mV s⁻¹. Figure 6b illustrates the virtually rectangular curves of the capacitive-type electrode and the redox peaks of the battery-type electrode. The high-performance WS₂@NiCoS@ZnS//AC asymmetric device’s cyclic voltammograms were recorded at 5 mV s⁻¹ to 50 mV s⁻¹ across a wide voltage range of 0 to 1.6 V are shown in Figure 6c. Quasi-rectangular curves in the coupled electrodes’ CV show the existence of both kinds of processes. Moreover, increasing the scanning speed does not affect the CV’s form, indicating its high-rate capacity and stability.

Similarly, the supercapattery (WS₂@NiCoS@ZnS//AC) is subjected to GCD cycles at various current densities (1.5 to 2.0 A g⁻¹) and potential window (PW) of 0–1.6 V, as shown in Figure 6d. The Q_s of WS₂@ZnS//AC, WS₂@NiCoS//AC, and WS₂@NiCoS@ZnS//AC at 1.5 to 2.0 A g⁻¹ values are 99.17 C g⁻¹, 145.93 C g⁻¹, and 190.5 C g⁻¹, given in Figure 6e. The decrease in Qs value when the current densities are increased is due to the reduced time for ions to interact with the active material. The homogeneous distribution of NiCoS@ZnS on WS₂, the special porous structure of the composite, which offers more active sites for charge storage, is responsible for the device’s exceptional performance. Supplementary data in Figure S5 show a bar graph to calculate the specific capacitance values for each of the other three devices as WS₂@ZnS//AC, WS₂@NiCoS//AC, and WS₂@NiCoS@ZnS//AC. Here, WS₂@NiCoS@ZnS//AC is operated for 5000 GCD cycles at 2.0 A g⁻¹. The device stability before and after 5000 GCD cycles is shown in Figure 6f.

The cyclic stability of the device is a significant aspect of its functioning. Figure 7a also displays the GCD duration for 5000 cycles. This discovery proves that the WS₂@NiCoS@ZnS//AC synergy can withstand the negative aspects of both materials. The supercapacitor device’s coulombic efficiency and capacity retention, shown in Figure 7b as final values after 5000 GCD cycles, are 93.23% and 85.19%, respectively.

The electrochem supercapattery device may be best understood by analyzing its energy density (E_d) and power density (P_d). Using the provided relations, we can calculate these values for the present assembly [28]:

$${\mathrm{E}}_{\mathrm{d}}\left(\mathrm{W}\mathrm{h} {\mathrm{k}\mathrm{g}}^{-1}\right)={\displaystyle \frac{{\mathrm{Q}}_{\mathrm{s}}\times ∆\mathrm{V}}{7.2}}$$

(5)

$${\mathrm{P}}_{\mathrm{d}}\left(\mathrm{W} {\mathrm{k}\mathrm{g}}^{-1}\right)={\displaystyle \frac{\mathrm{E}\times 3600}{∆\mathrm{t}}}$$

(6)

Here, ‘∆t’ denotes the discharge time, and ‘∆V’ represents the voltage range. With an outstanding P_d value of 1212.30 W kg⁻¹, the most significant E_d value is 49.47 W h kg⁻¹. The t E_d and P_d results are compared with published data in Figure 7c. The WS₂@NiCoS@ZnS//AC is now recognized as a high-performance supercapattery grade material because of these outstanding findings. The peak current values log against the scanning rate log in Figure 7d. The electrode material’s b-value determines whether it is categorized as a supercapacitor battery or supercapattery. The battery-grade composite electrode material’s b-values fall between 0.0 and 0.5; supercapacitor-grade material is found in the b-values between 0.8 and 1, and supercapattery material is found in the b-values between 0.5 and 0.8 [59]. The b-values for the WS₂@NiCoS@ZnS//AC device support our claim that we have successfully manufactured a supercapattery.

Photochemical Activity

The fundamental workings of the photochemical cell are shown in Figure 8a. The Supplementary Materials include information on the experimental setup, including details and parameters [60,61]. The amperometrically resulting photocurrent was identified in a current versus time profile at chopping illumination settings at open circuit potential (OCP) with frequent on/off cycles, as shown in Figure 8b. Excellent photo-switching performance was achieved by WS₂@NiCoS@ZnS photoelectrode because of its quick response, recovery times, and strong photoactivity. Light illumination begins with the presence of a strong point, which allows the charge separation procedure to be successful. Stable photocurrent starts with an exponential drop. WS₂@NiCoS@ZnS may, thus, be used as a successful photoelectrocatalyst with a better knowledge of adhesion properties on the photoelectrode surface.

5. Conclusions

In short, we used the hydrothermal technique to synthesize the NiCoS@ZnS, and we obtained the WS₂ nanosheets by tip-sonicating the WS₂ nanopowder. SEM makes it possible to observe that the NiCoS@ZnS nanoparticles are implanted on WS₂ nanosheets as a consequence of doping. To investigate the morphology, structure, and composition of the doped material, further structural analysis methods such as XRD, BET, and XPS spectroscopy are used. CV, GCD, and EIS provide a thorough electrochemical investigation of the doped and undoped materials using a three-electrode setup. The sample of NiCoS@ZnS doped with WS₂ nanosheets produced a minimal equivalent series resistance of 3.1 Ω and a good Qs of 1211.58 C g⁻¹ or 2019.3 F g⁻¹ at 1.8 Ag⁻¹ when using an electrolyte solution of 1 M KOH. Following that, two electrode assemblies are used to practically analyze the exceptional properties of WS₂@NiCoS@ZnS. An asymmetric device using the WS₂@NiCoS@ZnS//AC electrode has a high specific capacity of 190.5 C g⁻¹ due to the combined influence of both electrode materials. After 5000 consecutive cycles at 2.0 A g⁻¹, this equates to 49.47 Wh kg⁻¹ E_d and 1212.30 W kg⁻¹ P_d. The remarkable electrochemical outcomes suggest that WS₂@NiCoS@ZnS is a promising material for enhancing energy storage apparatuses.