Facile fabrication of Co₂CuS₄ nanoparticle anchored N-doped graphene for high-performance asymmetric supercapacitors

A novel strategy for the synthesis of high-quality ternary cobalt copper sulfide nanoparticles (NPs) anchored on nitrogen doped graphene nanosheets (Co₂CuS₄/NG) was developed via a one-pot solvothermal method. FE-SEM and TEM images showed that the Co₂CuS₄ NPs with an average size of ∼21 nm were anchored to NG nanosheets. The NG nanosheets provide a large surface area to reduce self-aggregation and confine the shape of the Co₂CuS₄ NPs for a highly conductive network to boost the charge transport properties of energy storage devices. Impressively, the synergetic Co₂CuS₄/NG composite showed a high specific capacitance of ∼1005 F g^-1 at 1 A g^-1, excellent rate capability (770 F g^-1 at 50 A g^-1), and outstanding stability (96.3% capacitance retention after 5000 cycles). The electrochemical performance of the Co₂CuS₄/NG composite was superior to that of monometallic CoS/NG, Cu₂S/NG composite, pure Co₂CuS₄, and NG. An asymmetric supercapacitor device fabricated using the Co₂CuS₄/NG composite as the positive electrode material and NG as the negative electrode material illustrates the outstanding performance for practical energy storage devices. The asymmetric supercapacitor device delivers superb energy density (53.3 W h kg^-1), high power density (∼10936 W kg^-1 at 38.4 W h kg^-1), and a long-cycle life (∼4000 times).