The CoNi@C/Mo_1.33C <i>i</i>‐MXene Derived from Novel (Mo_2/3<i>R</i>_1/3)₂GaC (<i>R</i> = Dy, Ho, Er, Tm, and Lu) Nanolaminations for Electrochemical Application in Electrocatalytic Hydrogen Evolution and Sup

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.