Engineering raspberry-like CuCo2S4@ZnS hollow particles encapsulated with reduced graphene oxide for hybrid supercapacitors

Transition-metal sulfides (TMSs) stand out as promising materials for supercapacitors due to their plentiful electroactive sites and relatively high conductivity compared with their oxide counterparts. Among them, copper-cobalt sulfides are regarded as effective active materials, but their specific capacity and cycling durability cannot meet expectations. To mitigate these issues, elaborate synthesis and design of hollow nanostructures with high complexity have been considered an effective approach. Also, hybridizing reduced graphene oxide (rGO) with complex hollow nanostructures to improve capacity behaviors, enhance electrical conductivity, and enlarge the surface area is highly desired. Considering this, in this work, we demonstrate the construction of raspberry-like CuCo2S4@ZnS hollow particles (RCCS-ZSH), in which the CuCo2S4 hollow nanospheres (CCS-HSs) are well confined in the porous ZnS shells. By controlling the sulfidation reaction time during the sulfidation reactions, an optimized sample (RCCS-ZSH8) was achieved with superior electrochemical performance. Then, the as-prepared RCCS-ZSH8 nanostructures were encapsulated in the rGO network (RCCS-ZSH8-rGO) to form a unique nanoarchitecture. In such a structure, the RCCS-ZSH8 nanostructures are characterized by abundant electroactive sites and easy ion diffusion. More importantly, the encapsulating of the rGO network around RCCS-ZSH8 particles not only endows the composites with better electrical conductivity but also inhibits the aggregation of particles and maintains structural durability throughout the longevity test. Therefore, the RCCS-ZSH8-rGO-based electrode presents tremendous supercapacitive properties with its attractive capacity of 1346 C g(-1) and excellent longevity (95.4%) after 10 000 cycles. Eventually, a hybrid supercapacitor apparatus (RCCS-ZSH8-rGO//AC) based on the RCCS-ZSH8-rGO cathode and activated carbon (AC) anode exhibits a reasonable energy/power density of 64.2 W h kg(-1)/802.5 W kg(-1) and remarkable durability (92.8% of initial capacity for 10 000 cycles at 8 A g(-1)). This research thus presents a useful protocol for the rational engineering of rGO-encapsulated complex hollow nanostructures for various applications.