In-situ construction of amorphous-crystalline heterojunction in Co-MOF@Ti₃C₂T_x enables dramatically enhanced energy storage performance of supercapacitor

Two-dimensional (2D) transition-metal carbides and nitrides known as MXenes are gaining recognition in energy storage devices due to their unique physicochemical properties. However, MXene-based energy storage devices pose challenges due to their susceptibility to oxidative degradation and restacking of nanosheets at ambient conditions. In this work, Co-MOF nanopolyhedrons were embedded in 2D Ti₃C₂T_x nanosheets to form a composite material and applied as supercapacitor (SC) electrode. The Co-MOF@Ti₃C₂T_x electrode shows excellent performance in three- and two-electrode systems in the aqueous basic electrolyte. The specific capacitances of 582, 366, and 165 F g⁻¹ at 1 A g⁻¹ for the Co-MOF@Ti₃C₂T_x, Co-MOF, and Ti₃C₂T_x electrodes are measured in three-electrode systems, respectively. The charge storage analysis indicated that the Co-MOF@Ti₃C₂T_x electrode exhibits a hybrid nature, achieving a capacitive storage of 69.89 % at a scan rate of 4 mV s⁻¹. The charge storage mechanism was investigated by ex-situ XRD, XPS, and HRTEM analysis, which showed the intercalation/de-intercalation of K⁺ in the Co-MOF@Ti₃C₂T_x electrode. Furthermore, a full device was fabricated (Co-MOF@Ti₃C₂T_x//AC-ASC), which shows high energy and power densities (54.1 Wh kg⁻¹ at 1055.5 W kg⁻¹). The Co-MOF@Ti₃C₂T_x//AC-ASC also shows good rate performance and cycling stability of 91.2 % after 10000 cycles. The high surface area of Co-MOF, combined with the excellent conductivity of Ti₃C₂T_x, improved the availability of active sites and facilitated rapid ion transport. This study offers a novel approach to advance the 2D Ti₃C₂T_x-based materials for high-performance SCs.