Nickel–cobalt layered double hydroxide/NiCo2S4/g-C3N4 nanohybrid for high performance asymmetric supercapacitor

Graphitic carbon nitride (g-C3N4) with semiconducting nature can be considered for energy storage system by modifying its electrical conductivity and structural properties through formation of hybrid with materials such as bimetallic metal sulfide and nickel-cobalt layered double hydroxide (LDH). g-C3N4 as a N-rich compound with basic surface sites can change the surface properties of nanohybrid and impress the charge transfer. In this study, a nanohybrid based on nickel-cobalt LDH and sulfide and graphitic carbon nitride (NiCo LDH/NiCo2S4/g-C3N4) was synthesized through a three-step method. At first, Ni doped ZIF-67 was formed at the surface of g-C3N4 nanosheets and then the product was calcined in a furnace to form NiCo2O4/g-C3N4. At next step, the sample was hydrothermally converted to NiCo2S4/g-C3N4 using thioacetamide and finally modified with NiCo LDH nanoplates to form porous structure with high surface area. The NiCo LDH/NiCo2S4/g-C3N4 nanohybrid showed high specific capacitance of 1610 F g−1 at current density of 1 A g−1 and also excellent stability of 108.8% after 5000 cycles at potential scan rate of 50 mV s−1, which makes it promising candidate for energy storage. An asymmetric system was prepared using nickel foams modified with NiCo LDH/NiCo2S4/g-C3N4 and g-C3N4 as positive and negative electrodes, respectively. The specific capacitance of 246.0 F g−1 was obtained at 1 A g−1 in 6 M KOH solution and system maintained 90.8% cyclic stability after 5000 cycles at potential scan rate of 50 mV s−1. The maximum energy density and power density of the system were calculated as 82.0 Wh kg−1 and 12,000 W kg−1, respectively, which demonstrate its capability for energy storage.