Enhanced performances of NiCoSe2 electrode coated with Ag nanoparticles by magnetron sputtering for the applications of asymmetric supercapacitors

In this work, a binder -free energy -storage electrode material of Ag nanoparticles coated nickel cobalt selenide (NiCoSe2) on Ni foam (NF) was first proposed. Wherein, NiCoSe2 was synthesized by one-step hydrothermal method using ascorbic acid as reductant, and the coating of Ag nanoparticles on NiCoSe2 were performed by magnetron sputtering method. The specific surface area was greatly increased due to the deposited Ag nanoparticles, and in this way the impedance of the electrode decreased, and the electrochemical properties were enhanced. When the magnetron sputtering time is 10 s, Ag/NiCoSe2 electrode exhibits the most excellent performances. However, further increase of sputtering time may result in the over cover on NiCoSe2, with great deterioration in electrochemical behavior. Single NiCoSe2 electrode possesses an area capacitance of 1600.7 mF cm -2 at a current density of 2 mA cm -2, while Ag/NiCoSe2 electrode could reach up to 2280 mF cm -2. The asymmetric supercapacitor (ASC) assembled by Ag/NiCoSe2 and activated carbon (AC) electrodes shows a high energy density of 0.171 mWh cm -2 as well as a power density of 17.340 mW cm -2, and the cyclic stability remains at 90.1% after 4000 cycles, which is superior to 83.7% of the NiCoSe2 single electrode.