The CoNi@C/Mo_1.33C i‐MXene Derived from Novel (Mo_2/3R_1/3)₂GaC (R = Dy, Ho, Er, Tm, and Lu) Nanolaminations for Electrochemical Application in Electrocatalytic Hydrogen Evolution and Supercapacitance

Abstract 2D Mo_1.33C i‐MXene is highly promising for electrochemical applications. Here, a synthetic strategy is reported, enabling the uniform distribution of carbon‐coated CoNi (CoNi@C) nanoparticles on the vacancy‐ordered Mo_1.33C i‐MXene nanosheets, thereby fully exposing the active sites of CoNi@C. First, five novel Ga‐containing (Mo_2/3R_1/3)₂GaC (R = Dy, Ho, Er, Tm, and Lu) i‐MAX phases are synthesized as the precursor and found to be crystallized into Cmcm structure, followed by hydrothermal etching and delamination. Subsequently, CoNi– MOF is in situ grown on derived Mo_1.33C i‐MXene nanosheets. By modifying the loading mass and annealing condition, CoNi–MOF is transformed into the CoNi@C and the CoNi@C/Mo_1.33C displayed outstanding hydrogen evolution reaction activity with low overpotential (73 mV at 10 mA cm⁻²) and small Tafel slope (84 mV dec⁻¹). Moreover, the gravimetric capacitance is also increased from 68 F g⁻¹ in CoNi@C to 575.1 F g⁻¹ in CoNi@C/Mo_1.33C‐50 at 0.5 A g⁻¹. After ≈5000 cycles, activation is complete, and the specific capacitance reaches its maximum value. Additionally, the specific capacitance remains stable at 95% after additional 10 000 cycles. This work improves the catalytic and supercapacitor performance of composite nanomaterials by optimizing the distribution of active sites on Mo_1.33C i‐MXene, and also extends the application of Mo_1.33C i‐MXene.