Hydrothermal Synthesis of Bimetallic Spinel MCo2O4/MXene (M = Ni, Zn) Composites as Efficient Supercapacitor Electrodes

MXene is an ideal choice for electrode material in supercapacitors due to its outstanding metallic conductivity, hydrophilic nature, and surface redox activity as well as superior chemical stability. The two-dimensional (2D) metal carbide NbC₂Tₓ-MXene exhibits significant potential as a pseudocapacitive electrode material for energy storage applications. Restacking of MXene's layers makes, however, difficult access of ions, which lowers volumetric performance and also reduces ion and electron transport. To overcome this challenge, different metal-based oxides with MXene composites, namely, MCo₂O₄/composite (where M = Ni and Zn), were synthesized using a simple cost-effective hydrothermal method through a self-assembly process. These heterostructure composites reduced the specific capacitance loss brought on by volumetric variations by preventing MXene layers from restacking and at the same time improving the exposure of electrochemically active sites in MCo₂O₄/composite. Structural, morphological, and electrochemical analysis revealed that both composites have efficient and remarkable electrochemical properties with unique morphology. Detailed electrochemical analysis revealed that NiCo₂O₄/MXene have pseudocapacitive behavior with greater specific capacitance as compared with ZnCo₂O₄/MXene. NiCo₂O₄/MXene exhibited specific capacitance of 1575 F g⁻¹ at 1 A g⁻¹ with 89% cyclic stability over 10,000 cycles. Moreover, asymmetric supercapacitors constructed using NiCo₂O₄@Nb₂C as cathode and commercial activated carbon (AC) as anode demonstrated a high energy density of 31.2 Wh kg⁻¹ at a power density of 800 W kg⁻¹ Additionally, they exhibited excellent long-term cycling stability, retaining 81.2% of their initial capacitance after 5000 cycles.