Component-controllable bimetallic nickel cobalt selenides (Ni x Co1-x )0.85Se for high performance supercapacitors

Highlights: • (Ni_xCo_1-x)_0.85Se with different Ni to Co ratios were easily synthesized by hydrothermal method. • Bimetallic nickel cobalt selenides exhibit more excellent electrochemical performance than Ni_0.85Se and Co_0.85Se. • The synergistic effect between Ni ions and Co ions contributes to improved capacity. In this study, bimetallic nickel cobalt selenides (Ni_xCo_1-x)_0.85Se with different Ni to Co ratios were synthesized via one-pot hydrothermal treatment, and their electrochemical performance, as electrode materials for supercapacitors, were systematically studied for the first time. The bimetallic nickel cobalt selenides (Ni_xCo_1-x)_0.85Se show more excellent electrochemical performance than that of the monometallic selenides Ni_0.85Se and Co_0.85Se. Meanwhile, through varying the Ni to Co ratio, the (Ni_0.5Co_0.5)_0.85Se delivers the highest specific capacity, excellent rate capability, and good cycling stability. Upon analysis, the superior electrochemical performance of bimetallic nickel cobalt selenides (Ni_xCo_1-x)_0.85Se, especially (Ni_0.5Co_0.5)_0.85Se, ascribe to the synergistic effect between the more electrochemical active composition (Ni ions) and the faster transfer of electron (Co ions).