Enhanced supercapacitor performance of bimetallic metal selenides via controllable synergistic engineering of composition

Bimetallic metal selenides have gained increasing attention as potential electrode materials for energy storage systems owing to good electrical conductivity and superior electrochemical activity. Herein, the Ni_xCo_ySe₂ (x+y=1) electrodes are prepared by a facile and rapid electrodeposition process. The electrochemical performance is optimized via adjusting the ratio of Co and Ni. It is turned out that equivalent Co and Ni in the composite (Ni_1/2Co_1/2Se₂) shows the best supercapacitor performance, including high specific capacity (166.1 mAh g⁻¹) and long-term stability. Moreover, Density Functional Theory (DFT) calculation confirms the covalent interaction between nickel and cobalt, implying the existence of synergistic effect. To assess the practical value of the rationally designed Ni_1/2Co_1/2Se₂ electrode material, an asymmetric supercapacitor device is fabricated (Ni_1/2Co_1/2Se₂//AC), which delivers a high energy density of 46.0 Wh kg⁻¹ at 1141 W kg⁻¹, coupled with 9.8% capacity loss after 10000 cycles. Notably, the low-voltage setups (LED and electric fan) can be easily activated by two devices in series, further demonstrating the great potential for practical application of Ni_1/2Co_1/2Se₂ electrode.