Facile Synthesis of Yolk-Shelled CuCo₂Se₄ Microspheres as a Novel Electrode Material for Supercapacitor Application

Recently, metal selenides have attracted much attention in the energy storage applications. This attention is due to the outstanding properties of metal selenides (lower cost, lower electronegativity, and environmental friendliness) compared to metal sulfides and oxides. In this work, novel yolk-shelled CuCo₂Se₄ (YS-CCS) microspheres are synthesized by a facile two-step hydrothermal method and used as an electrode material for high-performance supercapacitors (SCs) in alkaline media. The proposed YS-CCS electrode shows remarkable electrochemical performance, including fast kinetics, high reversibility, low internal resistance (0.45 Ω), excellent specific capacitance (512 F g^-1 at a current density of 1A g^-1), high rate capability (70.8% after increasing the current density six times), and good cycling stability (about 83.7% of the initial retention after 6000 successive charge-discharge cycles). Furthermore, an asymmetric supercapacitor (ASC) is assembled by using the YS-CCS (as a cathode electrode material) and active carbon (as an anode electrode material). The assembled device delivers a maximum energy density of 9.45 W h kg^-1 and a power density up to 850 W kg^-1 in a wide potential window of 1.70 V. Meanwhile, the ASC device exhibits superb rate capability (∼84.67%) after increasing the current density five times and very good capacitance retention (∼88%) after 6000 cycles.