Hydrothermal synthesis of Ni@C core–shell composites with high capacitance

Abstract

Ni@C core–shell composites with different crystal structures were synthesized by chemical reduction of nickel (II) acetate tetrahydrate using ethylene glycol as reducing agent and sodium citrate as a carbon source, followed by annealing at different temperatures in the nitrogen atmosphere. X-ray diffraction analysis indicates that the crystal structure of Ni is dependent on the annealing temperatures. At 250°C, both face-centered cubic and hexagonal closed-packed (hcp) phases of Ni coexist in the Ni@C composites, whereas there is only hcp phase Ni observed as being annealed at 300°C. The synthesized Ni@C composites were applied as electrode materials for supercapacitors and exhibited superior electrochemical performances. Especially, the electrode annealed at 250°C displays the highest specific capacitance of 530Fg−1 in 2MKOH solution at a current density of 1Ag−1. In addition, the synthesized Ni@C composite electrodes also show excellent rate capability and cycle stability, presenting the promising potential as electrode material for supercapacitors.