Highly uniform and monodispersed CuCo 2 S 4 ball-in-ball hollow nanospheres (HNSs) are successfully synthesized from CuCo-glycerate nanospheres (NSs) precursors via a facile two-step solvothermal process. The most influential parameter in anion exchange reaction between glycerate and sulfur ion is the solvothermal time, which plays a significant role in enhancing the structural and electrochemical properties. Impressively, CuCo 2 S 4 ball-in-ball HNSs obtained through a sulfurization reaction time of 18 h show high capacitance (442 F g À1 at current density of 0.5 A g À1 ) and superior electrochemical stability (84.5% at 5 A g À1 after 5000 cycles), which can realize highperformance materials for supercapacitors.

Nickel sulfides have drawn much attention with the benefits of a high redox activity, high electrical conductivity, low cost, and fabrication ease; however, these metal sulfides are susceptible to mechanical degradation regarding their cycling performance. Conversely, hollow carbon shells exhibit a substantial electrochemical steadiness in energy storage applications. Here, the design and development of a novel millerite core-nitrogen-doped carbon hollow shell (NiS-NC HS) structure for electrochemical energy storage is presented. The nitrogen-doped carbon hollow shell (NC HS) protects against the degradation and the millerite-core aggregation, giving rise to an excellent rate capability and stability during the electrochemical charging-discharging processes, in addition to improving the NiS-NC HS conductivity. The NiS-NC HS/18h supercapacitor electrode displays an outstanding specific capacitance of 1170.72 F g (at 0.5 A g ) and maintains 90.71% (at 6 A g ) of its initial capacitance after 4000 charge-discharge cycles, owing to the unique core-shell structure. An asymmetric-supercapacitor device using NiS-NC HS and activated-carbon electrodes exhibits a high power and energy density with a remarkable cycling stability, maintaining 89.2% of its initial capacitance after 5000 cycles.

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Metal‐organic frameworks (MOFs) have emerged as one of the most outstanding innovated and functional materials for electrochemical application. Here, the structure of novel MOFs‐derived hierarchically porous Nickel@Carbon nanospheres (HP‐Ni@C‐N) synthesized via pyrolysis after the solvothermal reaction is discussed. The method includes the decomposition of the trimesic acid as an organic molecule at a specific temperature of transformation into a carbon matrix wrapping of nickel nanoparticles (Ni NPs). Furthermore, HP‐Ni@C‐N supported on nickel foam as an electrochemical energy storage supercapacitor application and obtained 912 F g−1 at 10 mV s−1 is reported. Interestingly, the covalent bridge between the Ni core and carbon shell facilitates the faster ions transportation. Therefore, it is presumed that this work can be informative and elucidative for the construction of MOFs‐derived transition metals hybrid nanostructures.

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