Successive cation and anion exchange strategy towards hierarchical Ni-Co sulfide arrays for high-performance hybrid supercapacitors

Abstract

The specific energy of hybrid supercapacitors (HSCs) is mainly limited by the low specific capacity and poor rate performance of the battery electrode. Herein, a series of Ni-Co sulfides with hierarchical architectures on the Ni foam were constructed by successive cation and anion exchange reactions, and were investigated as battery electrodes for HSCs. This special hierarchical structure allows the active materials effective exposed and participate in the redox reaction, and enables the rapid transport of electrons and ions. In addition, the synergistic effect between Ni and Co can effectivley improve the electrochemical activity and reversible specific capacity of HSCs. Benefiting from these advantages in combination, the Ni-Co sulfides with optimum cation reaction time exhibits a high specific capacity of 929 C g -1 at 2 A g -1 , which is batter than the Co sulfides and other NiCo sulfide samples. The Ni-Co sulfide electrode has been used as the positive electrode for HSCs, which demonstrates a specific energy of 51.9 W h kg -1 at a specific power of 838.7 W kg -1 with a value 14.1 Wh kg -1 can be retained at11.6 kW kg -1 . Our work developed a robust method for transforming momometal sulfides to their bimetal counterparts while maintaining the hierarchical structures, which is very promising for multifunctional material designing and their performance optimization.