Ni2CoS4@(NiCo)Se2 bimetallic selenides with core–shell heterostructure in-situ generated on Ni2CoS4 nanorods arrays for high performance supercapacitors

In this paper, Ni2CoS4@(NiCo)Se2/NF core–shell structural nanocomposites are successfully prepared on nickel foam (NF) substrates through a convenient hydrothermal method and tube furnace calcination. Firstly, NiCo2O4/NF is acquired by a one-step simple hydrothermal method and one-step tube furnace calcination, then it is sulfidated via a one-step hydrothermal method, and finally selenized by stirring to obtain Ni2CoS4@(NiCo)Se2/NF. The results show that in the three-electrode test, the specific capacitance of the Ni2CoS4@(NiCo)Se2 electrode is able to reach 6054 mF·cm−2 at a current density of 10 mA·cm−2. The excellent performance of Ni2CoS4@(NiCo)Se2/NF nanocomposites is supposed to give rise to the bimetallic synergistic effect, as well as the unique core–shell structure of its surface-loaded nanosheets. In addition, all-solid-state asymmetric supercapacitors (ASCs) are composed of activated carbon (AC) as the anode and Ni2CoS4@(NiCo)Se2/NF as the cathode. The prepared Ni2CoS4@(NiCo)Se2/NF//AC ASC devices reach an energy density of 53 Wh kg−1 at a power density of 480 W kg−1. Simultaneously, Ni2CoS4@(NiCo)Se2/NF//AC ASC device has an excellent specific capacitance of 149.06F g−1 at a current density of 0.6 A/g and a capacitance retention rate of 84.0 % after 10,000 electrochemical cycles, which proves its good cycling stability. Impressively, two Ni2CoS4@(NiCo)Se2/NF//AC ASC devices connected in series can light up a 2.5 V LED lamp and continue to illuminate it for 11 min. Our results show that Ni2CoS4@(NiCo)Se2/NF nanocomposites with core–shell structures have great application potential in energy storage devices.