Fabrication of nickel cobalt bimetallic sulfide doped graphite carbon nanohybrids as electrode materials for supercapacitors

A series of nickel cobalt bimetallic sulfide doped graphite carbon (NCBS/C) nanohybrids were fabricated by cross linking reaction, vacuum freeze-drying, heat treatment and hydrothermal method using sodium alginate (SA) as carbon source, nickel nitrate hexahydrate (Ni(NO3)2·6H2O) and cobalt nitrate hexahydrate (Co(NO3)2·6H2O) as transition metal ions source, thiourea as sulfur source. The electrochemical properties of the NCBS/C nanohybrids as electrode materials could be tuned by adjusting the composition. The results show that the NCBS/C nanohybrid fabricated at the molar ratio of Ni(NO3)2·6H2O to Co(NO3)2·6H2O of 1:1, and the thiourea amount of 0.1 g had the optimal electrochemical properties, the specific capacity was 742.9C g−1 at 1 A g−1, when the current density increased from 0.5 A g−1 to 5 A g−1, the specific capacity could remain 98.2%. The asymmetric supercapacitor assembled by the NCBS/C nanohybrid as the positive electrode, activated carbon as the negative electrode delivered energy density of 53.00 Wh kg−1 at power density of 850 W kg−1, and still maintained 43.57 Wh kg−1 at 4.24 kW kg−1. Moreover, the device had 83.78% capacitance retention after 5000 charge-discharge cycles at 5 A g−1. The nanohybrids with high electrochemical properties could be attributed that the transition metal ions as cross-linking agents were well dispersed in the SA hydrogels as carbon source, resulting in that the in-situ formed nickel cobalt bimetallic sulfide nanoparticles were uniformly doped in graphite carbon materials. The strategy could be applied to fabricate other transition metals compounds doped carbon materials for the development of other high-performance electrode materials.