Facile In Situ Synthesis of Co(OH)2–Ni3S2 Nanowires on Ni Foam for Use in High-Energy-Density Supercapacitors

Ni3S2 nanowires were synthesized in situ using a one-pot hydrothermal reaction on Ni foam (NF) for use in supercapacitors as a positive electrode, and various contents (0.3−0.6 mmol) of Co(OH)2 shells were coated onto the surfaces of the Ni3S2 nanowire cores to improve the electrochemical properties. The Ni3S2 nanowires were uniformly formed on the smooth NF surface, and the Co(OH)2 shell was formed on the Ni3S2 nanowire surface. By direct NF participation as a reactant without adding any other Ni source, Ni3S2 was formed more closely to the NF surface, and the Co(OH)2 shell suppressed the loss of active material during charging–discharging, yielding excellent electrochemical properties. The Co(OH)2–Ni3S2/Ni electrode produced using 0.5 mmol Co(OH)2 (Co0.5–Ni3S2/Ni) exhibited a high specific capacitance of 1837 F g−1 (16.07 F cm−2) at a current density of 5 mA cm−2, and maintained a capacitance of 583 F g−1 (16.07 F cm−2) at a much higher current density of 50 mA cm−2. An asymmetric supercapacitor (ASC) with Co(OH)2–Ni3S2 and active carbon displayed a high-power density of 1036 kW kg−1 at an energy density of 43 W h kg−1 with good cycling stability, indicating its suitability for use in energy storage applications. Thus, the newly developed core–shell structure, Co(OH)2–Ni3S2, was shown to be efficient at improving the electrochemical performance.