Metal organic frameworks derived Ni-doped hierarchical NiXCo1-XS@C bundled-like nanostructures for enhanced supercapacitors

Abstract

Metal-organic frameworks (MOFs) and their derivatives in the area of energy store have received extensive attention. Here, 3D hierarchical bundle-like micro/nanostructure Ni-Co-MOFs were designed via a co-precipitation and external metal-atom doping strategy. Based on the distinctive precursor, a carbon coated Ni-Co-S nanoparticles were prepared through a two-step thermal annealing. The Ni doping into CoS can both regulates electronic structure and stabilizes Co species as electrode material for supercapacitor. By optimizing the content of Ni-doping, the fabricated NiXCo1-XS/C-3 with 25% Ni-doping shows remarkable specific capacitance (709 C/g at 1 A/g), superior rate capability and excellent cycling stability. An asymmetric supercapacitor with an energy density of 45.3 Wh/kg was acquired successfully in two-electrode system. NiXCo1-XS possess a high OH− adsorption energy compared to single NiS and CoS was proved by density functional theory calculations. Strong OH− adsorption ability is conducive to capture electrolyte ions, which leads to rapid redox reaction kinetics. In addition, this work provides new ideas for how to design metal sulfide-based supercapacitor positive electrode materials.