###### Abstract  
Using a process-enhanced micro-impinging stream reactor (MISR) and a co-precipitation route, NiCo\({}_{2}\)S\({}_{4}\) and NiCo\({}_{2}\)S\({}_{4}\)/rGO electrode materials were successfully prepared, respectively. Owing to its excellent micromixing performance, the MISR-prepared NiCo\({}_{2}\)S\({}_{4}\)/rGO composites had a smaller size and less agglomeration than the same composites prepared in a traditional stirred reactor (STR). The specific capacity of the MISR-prepared composites was as high as 198.0 mAh g\({}^{-1}\) under the current density of 1 A g\({}^{-1}\). The cycling stability of the composites also improved significantly after being modified with reduced graphene oxide (rGO), and they displayed a fine cycling stability, which maintained a retention rate of 83.6% after 1000 cycles of charging and discharging. micro-impinging stream reactor; micromixing; NiCo\({}_{2}\)S\({}_{4}\) composite; hybrid supercapacitor +
Footnote †: journal: Applied Sciences  
single-component sulfides, the electrochemical action of nickel-cobalt bimetallic sulfides can give rise to more complex redox reactions, resulting in higher specific capacities [11]. However, NiCo\({}_{2}\)S\({}_{4}\) is highly dependent on the surface Faraday redox reaction and phase transition process caused by ion intercalation, and the reaction kinetics are unfavorable during the rapid charge and discharge process, leading to poor rate performance and electrochemical stability, which will limit its practical application in hybrid supercapacitor technology [11]. Current studies have found that doping nano-structured electroactive materials on a carbon material substrate may be one of the effective and feasible strategies to solve the above problems [12], which guarantees the efficient utilization of active substances and reaction kinetics. For example, graphene has been reported as an exceptional substrate material for improving the electrochemical activity of ultrafine materials [13; 14]. However, due to poor interface bonding with the graphene surface, nanoparticles generally tend to agglomerate and detach from the graphene surface, resulting in a decrease in energy storage performance. Therefore, the application of metal sulfides such as NiCo\({}_{2}\)S\({}_{4}\) that can bind to the graphene surface stably without agglomerating will be a good solution to improve the performance of its hybrid supercapacitors [15]. NiCo\({}_{2}\)S\({}_{4}\)/FO composites can be synthesized by different routes, such as hydrothermal [16], electrodeposition [17], co-precipitation [18], and self-template methods [19]. Compared with other methods, co-precipitation has the advantages of a simple preparation process, low cost, and easy control of preparation conditions for large-scale production. The co-precipitation method involves using the precipitant and two or more metal salt solutions to obtain a solid product after co-precipitation. It can precipitate several components at the same time, and the distribution of the components is relatively uniform [20]. It is generally believed that the degree of supersaturation has a great nonlinear effect on the nucleation rate and a high level of supersaturation is the thermodynamic driving force for the phase transition during crystallization processes [21; 22]. Since the precipitation process is exceptionally fast, rapid micromixing is essential to create a homogeneous supersaturation, which will in turn ensure the product quality [23]. However, due to the poor micromixing performance and mass transfer efficiency in traditional stirred reactors (STRs), it is difficult to achieve uniform supersaturation, which will have a significant impact on the crystal size distribution and also lead to uneven element distribution in the prepared materials [24]. A proper measure to solve this problem is to develop a reactor with excellent micromixing performance in which a uniform supersaturated environment for nucleation will be provided [25; 26].