Flowery nickel-cobalt hydroxide a solid-liquid sulphur ion grafting route and its application in hybrid supercapacitive storage.

In our research, a two-step solid-liquid route was employed to fabricate flowery nickel-cobalt hydroxide with sulphur ion grafting (Ni1Co2-S). The utilization of NaOH/agar and NaS/agar could efficiently retard the release rates of OH or S ions at the solid-liquid interface due to strong bonding between agar hydrogel and these anions. Ni1Co2-S generally displays ultrathin flowery micro-frame, ultrathin internal nanosheets and expanded pore size. Besides, the introduction of suitable sulphide species into nickel-cobalt hydroxide could improve its conductivity due to the lower band gap of Ni-Co sulphide. The supercapacitive electrode Ni1Co2-S presented capacitance of 1317.8 F g (at 1 A g) and suitable rate performance (77.9% at 10 A g and 59.3% at 20 A g). Furthermore, a hybrid supercapacitor (HSC) was developed utilizing positive Ni1Co2-S and negative activated carbon electrodes. As expected, the HSC device exhibited excellent specific capacitance (117.1 F g at 1 A g), considerable energy densities (46.7 W h kg at 0.845 kW kg and 27.5 W h kg even at 9 kW kg) and suitable cycling performance, which further illuminated the high energy storage capacity of Ni1Co2-S.