Rapid and large-scale synthesis of polydopamine based N-doped carbon spheres@CoxNi1-x(OH)2 core-shell nanocomposites for high performance supercapacitors

Abstract

The properties of electrode materials are greatly determined by their structures including surface area, pore size distribution and conductivity. Aiming for the advanced structure, we successfully design and develop a core-shell nanocomposite of polydopamine based N-doped carbon spheres (NCSs) and CoxNi1-x(OH)2 by a fast and simple two-step method. Firstly, regular NCSs are directly derived from carbonization of polydopamine, which offer conductive cores for fast electronic transport. Then, flower-like shells consisting of interlinked CoxNi1-x(OH)2 ultrathin nanosheets are vertically and evenly grafted on the surface of NCSs substrate by a chemical bath deposition method, which is faster and more suitable for large-scale production than hydrothermal synthesis. To get the homogeneous bimetal hydroxides CoxNi1-x(OH)2 through this rapid precipitation process, the influences of Co doping content on the morphologies, structure and capacitance properties of hybrids are further analyzed. Results show that the obtained NCSs@CoxNi1-x(OH)2 nanocomposite with small amount of Co doping exhibits impressively enhanced specific capacitance (2065 F g−1 at 1 A g−1) and rate capability (1429 F g−1 even at 45 A g−1) than NCSs@Ni(OH)2. The outstanding capacitive performance of this kind of nanocomposite is due to its large surface area, optimum porous size distribution and retained flower-like morphology, especially the high electrical conductivity originating from conductive skeleton of NCSs and Co ion doping. Furthermore, using the optimized NCSs@CoxNi1-x(OH)2 and activated carbon as a positive and negative electrode, the as-prepared energy storage device achieves higher energy (16–37 Wh kg−1) and power density (8−0.4 kW kg−1), along with satisfactory cycling stability.