Oxidant-assisted direct-sulfidization of nickel foam toward a self-supported hierarchical Ni3S2@Ni electrode for asymmetric all-solid-state supercapacitors

In this work, we demonstrate, for the first time, a low-temperature direct-sulfidization of nickel foam (NF) assisted with oxidant K2S2O8 to fabricate a novel self-supported hierarchical porous Ni3S2@NF electrode for supercapacitors. The resultant Ni3S2@NF electrode exhibits a high specific capacitance of 2519.5 mF cm−2 at a current density of 1.0 mA cm−2, and a rate capability of 68.5% over a current density range of 1–20 mA cm−2. At the same time, the retention of areal specific capacitance amounts to ~100% of its initial capacitance at 20 mA cm−2 after 4000 consecutive charge−discharge cycles. Moreover, an asymmetric all-solid-state supercapacitor device Ni3S2@NF//activated carbon (AC)@NF has been assembled. Remarkably, this device can afford an energy density of 32.0 Wh kg−1 at a power density of 210.8 W kg−1 accompanied with excellent electrochemical cyclic stability. Such outstanding supercapacitive behavior of Ni3S2@NF can be credited to its unique porous interpenetrating architecture and the robust contact of Ni3S2 and NF, which can ensure rapid ion and electron transfers for redox reactions as well as tightly contacts among active component, substrate, and electrolyte. The direct-sulfidization of metals assisted with oxidants can offer a general, scalable, and viable protocol to fabricate high-performance electrochemical materials for energy-storage applications.