Anchoring nickel-cobalt sulfide nanoparticles on carbon aerogel derived from waste watermelon rind for high-performance asymmetric supercapacitors

In this work, NixCo3-xSy nanoparticles supported by carbon aerogel (CA) were prepared through an innovative hydrothermal and calcining process with the waste watermelon rind as a carbon source, and then the as-prepared NixCo3-xSy/CA composites were performed as an excellent electrode of supercapacitors. The addition of CA substrate can provide abundant reactive sites. For contrast, the electrochemical properties of NixCo3-xSy/CA with different ratios of Ni:Co have been tested. Expectedly, the NiCo2S4/CA hybrid showed the best electrochemical performance. Therefore, a combination of asymmetric supercapacitorcomposed of NiCo2S4/CA as the positive electrode and activated CA (alpha-CA) as the negative electrode was successfully assembled, wherein alpha-CA was prepared by using K2FeO4 as the poreforming agent. The alpha-CA possessed a three-dimensional (3D) hierarchical porous structure and large specific surface area, thus exhibited an improvement on cycling stability and conductivity. The asymmetric supercapacitor demonstrates a maximum energy density of 33.8 Wh kg(-1) at a power density of 800 W kg(-1) with a long cycle life of 87.4% capacitance retention after 10,000 cycles at 10 A g(-1). This facile, environmentally-friendly, and cost-effective strategy provides more possibilities for the rational fabrication of high-performance supercapacitors. (C) 2020 Elsevier B.V. All rights reserved.