Nickel-Doped Activated Mesoporous Carbon Microspheres with Partially Graphitic Structure for Supercapacitors

A novel high-performance electrode material, nickel-doped activated mesoporous carbon microsphere (Ni-AMCM), is synthesized by an emulsion-assisted hydrothermal method, followed by a KOH activation process and nickel-doping strategy. The morphology, microstructure, and graphitization degree of Ni-AMCMs are characterized by scanning electron microscopy, nitrogen adsorption and desorption, X-ray diffraction, and Raman spectroscopy. The results show that, when the mass ratio of nickel precursor/AMCMs is 0.02, the resultant sample [denoted as Ni(0.02)-AMCMs] retains the structure parameters of AMCMs, such as the specific surface area, total pore volume, and mean pore size. The intensity ratio of Raman D to G band (I-D/I-G) decreases from 0.99 (AMCMs) to 0.75 [Ni(0.02)-AMCMs], indicating the formation of a partial graphite structure in Ni(0.02)-AMCMs. The Ni-AMCMs combine the features of high specific surface area (similar to 1096 m(2) g(-1)), uniform mesopore size (4.0 nm), regular microspherical shape (0.5-1.0 mu m in diameter), and partially graphitic structure, which endows them good electrochemical performance. The internal resistance of Ni(0.02)-AMCMs is 0.24 Omega, 43% lower than that of AMCMs (0.42 Omega). Correspondingly, Ni(0.02)-AMCM as an electrode in 6 M KOH shows a specific capacitance of 361 F g(-1) at 1.0 A g(-1). It still maintains an electrochemical capacitance of 301 F g(-1) under a high current density of 20.0 A g(-1.) This finding is potentially important for supercapacitor applications, where a fast charge/discharge is required.