Synergistically Active NiCo2S4 Nanoparticles Coupled with Holey Defect Graphene Hydrogel for High‐Performance Solid‐State Supercapacitors

Nickel cobalt sulfide nanoparticles embedded in holey defect graphene hydrogel (HGH) that exhibit highly porous structures and uniform nickel cobalt sulfide nanoparticle sizes are successfully prepared by a facile solvothermal–hydrothermal method. As an electrode material for supercapacitors, the as‐prepared NiCo2S4@HGH shows ultra‐high specific capacitances of 1000 F g−1 and 800 F g−1 at 0.5 and 6 A g−1, respectively, owing to the outstanding electrical conductivity of HGH and high specific capacitance of NiCo2S4. After 2100 charge/discharge cycles at a current density of 6 A g−1, 96.6 % of the specific capacitance was retained, signifying the superb durability of NiCo2S4@HGH. Moreover, remarkable specific capacitance (312.6 F g−1) and capacity retention (87 % after 5000 cycles) at 6 A g−1 were displayed by the symmetric solid‐state supercapacitor fabricated by using NiCo2S4@HGH electrodes. These auspicious supercapacitor performances demonstrate that the as‐developed solvothermal–hydrothermal approach can be widely used to prepare graphene‐coupled binary metal sulfides for high‐performance supercapacitor applications. Holey defect, Batman! A facile solvothermal method encompassing an ion exchange process was used to imbed NiCo2S4 on holey defect graphene hydrogel. The resulting material showed remarkable electrochemical performance when used as a supercapacitor electrode free of binding and conducting agents.