## 3 Results and Discussion
### Electrochemical Properties and Characterization of NiCo\({}_{2}\)S\({}_{4}\)/rGO Composites
ensure fast charge-discharge ability, due to the special 3D conductive network of the hybrid material for rapid transmission of ions; therefore, it suggests that the rGO sheets are ideal substrates for the uniform nucleation and growth of NiCo\({}_{2}\)S\({}_{4}\) particles. Figure 9c reveals the fitting Nyquist plots for the NiCo\({}_{2}\)S\({}_{4}\) and NiCo\({}_{2}\)S\({}_{4}\)/rGO composites. The semicircle diameter of NiCo\({}_{2}\)S\({}_{4}\) modified with rGO became smaller, suggesting that the \(R\)ct was decreased and the electrical conductivity of NiCo\({}_{2}\)S\({}_{4}\) was enhanced due to the doping of rGO and the even loading process in MISR. The cycling performance of NiCo\({}_{2}\)S\({}_{4}\)/rGO and NiCo\({}_{2}\)S\({}_{4}\) composites at a current density of 1 A g\({}^{-1}\) was recorded as illustrated in Figure 9d. It shows that the initial specific capacities of the two composite materials prepared at the same optimal conditions were 198.0 and 191.8 mAh g\({}^{-1}\), respectively. After 1000 charge-discharge cycles, their specific capacity retention rates were 83.6% and 74.4%, respectively. Therefore, the NiCo\({}_{2}\)S\({}_{4}\) composites modified by rGO had not only higher initial specific capacity, but also more superior cycling performance, because the unique structure of NiCo\({}_{2}\)S\({}_{4}\)/rGO can offer more electroactive sites for rapid diffusion of ions. Figure 9e,f show the SEM images of NCO\({}_{2}\)S\({}_{4}\)/rGO before and after the 1000 cycle test. The particles on the electrode sheet consisted of the active material, acetylene black, and the PVDF binder. Their shape and size both remained nearly the same, suggesting that the electrode had good stability during consecutive charge and discharge processes. Table 1 compares the electrochemical performance of the NiCo\({}_{2}\)S\({}_{4}\)/rGO composites prepared in this study with other similar nickel-cobalt-based sulfide materials by different synthesis methods, all of which have been converted into capacity with the same unit [48]. The electrode materials in this work and the references had the same charge-discharge mechanism with a 3-electron process, implying the same theoretical capacity of 263.8 mAh g\({}^{-1}\). This shows that our NiCo\({}_{2}\)S\({}_{4}\)/rGO composite had the highest initial specific capacity, but its cycling stability was not very satisfactory. However, compared with other methods, MISR technology has several significant advantages. Firstly, the MISR equipment is convenient to construct and easy to operate. Then, it can operate continuously to reduce the reaction time dramatically and to assure the stability of product quality. Moreover, the numbering-up technology of MISR can readily increase its production capacity. Hence, the MISR method might be a prospective technology for preparing high-performance composites by co-precipitation. In addition, to further explore the electrochemical performance of NiCo\({}_{2}\)S\({}_{4}\)/rGO in specific devices, a simple hybrid supercapacitor (HSC) was constructed as shown in Figure 10a. Figure 10b shows the CV curve of activated carbon as a negative electrode with a voltage window of -1 to 0 V, which maintained the characteristic rectangle of an electric double-layer capacitor. Therefore, the cyclic voltammetry (CV) voltage window of the HSC device shown in Figure 10b should be set to 1.5 V. CV curves of the ASC device at various scan rates (10 to 100 mV s\({}^{-1}\)) are presented in Figure 10c. The broad redox peak indicates that the HSC device composed of NiCo\({}_{2}\)S\({}_{4}\)/rGO had the battery-type capacity. The charging and discharging platform of the HSC device is not obvious in Figure 10d, but  
Figure 8: (**a**) TEM; (**b**) low-magnification and (**c**) high-magnification SEM images of the NiCo\({}_{2}\)S\({}_{4}\)/rGO composites. it shows an almost axisymmetric curve, suggesting an excellent capacitive characteristic.