Two-Dimensional,\nPorous Nickel–Cobalt Sulfide\nfor High-Performance Asymmetric Supercapacitors

Abstract

High specific surface area, high\nelectrical conductivity, and abundant\nchannels have been recognized to favor pseudocapacitors, but their\nrealization at the same time is still a great challenge. Here, we\nreport on nickel–cobalt sulfide nanosheets (NSs) with both\nultrathin thickness and nanoscale pores for supercapacitors. The porous\nNi–Co sulfide NSs were facilely synthesized through micelle-confined\ngrowth and subsequent sulfuration. The NSs are as thin as several\nnanometers and have a large number of pores with a mean size of ∼7\nnm, resulting in ultrahigh atom ratio at surface with unique chemical\nand electronic structure. Therefore, fast diffusion of ions, facile\ntransportation of electrons and high activity make great synergistic\ncontributions to the surface-dependent reversible redox reactions.\nIn the resulted supercapacitors, a specific capacitance of 1304 F\ng^–1 is achieved at a current density of 2 A g^–1 with excellent rate capability that 85.6% of the\noriginal capacitance is remained at 20 A g^–1. The\neffects of crystallinity and self-doping are optimized so that 93.5%\nof the original capacitance is obtained after 6000 cycles at a high\ncurrent density of 8 A g^–1. Finally, asymmetric\nsupercapacitors with a high energy density of 41.4 Wh/kg are achieved\nat a power density of 414 W/kg.