One-step electrochemical controllable preparation of nickel cobalt sulfide nanosheets and its application in supercapacitors

•CoNi sulfides nanosheets with 3D porous structure were controllably prepared.•Mischcrystal growth can be controlled by unipolar pulse electrodeposition.•Defects on the grain boundary can provide fast diffusion channels for ions.•Asymmetric supercapacitor shows longterm cycle stability and high energy density. The bimetallic sulfides hold great promise for achieving high-performance supercapacitors. A facile unipolar pulse electrodeposition (UPED) method is developed to prepare nickel cobalt sulfides/polypyrrole (PPy) nanocomposites on carbon paper as electrode for supercapacitors, in which the crystalline structure, morphology and electrochemical performance of Co-Ni sulfides can be readily manipulated by simply changing the Co/Ni molar ratio in the electrodeposition electrolyte. It is demonstrated that the optimal CNS-3 electrode delivers the highest specific capacitance (2004 F g−1 at 1 A g−1), excellent rate capability and superior cycling stability. The outstanding electrochemical capacitive behavior can be ascribed to the synergistic effect of the Co-Ni sulfides, the 3D integrated porous structure of the electrode, as well as the conductivity and adhesion of PPy. Furthermore, an asymmetric supercapacitor (ASC) fabricated by the CNS-3 as positive electrode and activated carbon as negative electrode also displays remarkable electrochemical performance with ultralong cycle life and high energy density. These results manifest the great potential of CNS-3 in the development of high-performance supercapacitor electrode materials. Theoretically, the green and efficient UPED technology could also allow preparing other bimetallic or polymetallic sulfides with controllable composition, crystal structure and morphology. [Display omitted]