Liquid phase reduction synthesis of cobalt boride-activated carbon composite with improved specific capacitance and retention rate as a new positive electrode material for supercapacitors
Transition metal compounds have a high theoretical capacity, thus they are also promising candidates for application as supercapacitors. In this work, a cobalt boride–activated carbon composite had been synthesized and applied to an electrode material of supercapacitor the first time. A cobalt boride-carbon composite was prepared using activated carbon(AC) as an additive and cobalt dichloride/sodium borohydride as starting materials. The addition of a small amount of activated carbon greatly improved the electrochemical performance of cobalt boride. By compositing cobalt boride with AC, the challenge of low electrical conductivity of CoB can be addressed. In a 6 M KOH alkaline aqueous electrolytes, the CoB-AC was used as the positive electrode material for asymmetric supercapacitor(ASC) in order to carry out the electrochemical test. At 0.5 A g−1, compared with bare cobalt boride, introducing activated carbon could raise the specific capacitance by 49.5%, up to 193.64 C g-1. Furthermore, an asymmetric supercapacitor was prepared, utilizing positive CoB-AC and negative activated carbon, respectively. The electrochemical behaviors of the prepared asymmetrical supercapacitor were evaluated by cyclic voltammetry, alternating current impedance, and galvanostatic charge-discharge techniques. It showed a wide potential window of 1.6 V and after 10 000 charge/discharge cycles, an outstanding cycle stability retention rate was maintained 80% at 2 A g-1. The as-fabricated ASC device could achieve a maximum energy density of 19.14 Wh kg-1 at a power density of 200.59 W kg-1. We hope that our present work will provide a new solution for designing highly high specific capacity supercapacitors.