Advanced Cu0.5Co0.5Se2 nanosheets and MXene electrodes for high-performance asymmetric supercapacitors.

• Novel strategy for the design of Cu x Co 1−x Se 2 nanostructures has been established. • The optimal (Cu 0.5 Co 0.5)Se 2 is proposed as SC electrode for the first time. • The charge storage mechanism of Cu x Co 1−x Se 2 electrodes are discussed in detail. • Merits of binder-free/freestanding electrodes for SC applications is demonstrated. • The assembled ASC exhibits an excellent energy density and ultralong cycle life. Transition-metal chalcogenides (TMCs) have attracted numerous interests in the field of energy storage owing to their exceptional electrical conductivity, ultrahigh specific capacity, etc. Herein, with inspiration from the attractive nanostructures of hierarchical frameworks with interconnected networks, we endeavored to design ternary copper cobalt selenide (Cu x Co 1–x Se 2) nanostructures through a facile and cost-effective hydrothermal and followed by selenization process. The effects of Cu2+ is investigated and shows significant enhancement in the electrochemical performances. The optimal Cu 0.5 Co 0.5 Se 2 nanosheets (NSs) possess hierarchical architectures, large specific surface area, unique porous networks, and excellent intrinsic conductivity that result in superior electrochemical properties by their excellent synergistic effects. Taking advantage of the merits of the rational nanostructures, the Cu 0.5 Co 0.5 Se 2 NSs significantly boost the capacitive performances as ultrahigh specific capacitance of ~1695 F g−1 at a current density of 1 A g−1, and long-term cycling stability (~94.9%). An asymmetric supercapacitor (ASC) device is fabricated using the Cu 0.5 Co 0.5 Se 2 NSs as a positive electrode, and multilayered MXene (Ti 3 C 2) as a negative electrode. Remarkably, the ASC operates at a working potential of 1.6 V and delivers a high energy density (~84.17 Wh kg−1 at 0.604 kW kg−1), high power density (~14.95 kW kg−1 at 57.73 Wh kg−1), and exceptional cycling stability (~91.1% after 10,000 charge–discharge cycles). The energy-storage properties are superior to recently reported TMCs-based ASC, proposing that the Cu 0.5 Co 0.5 Se 2 //MXene ASC has massive potential for next-generation energy-storage systems. [ABSTRACT FROM AUTHOR]