Tailoring\nCoNi<sub>2</sub>Se<sub>4</sub>@Ti<sub>2</sub>NbC<sub>2</sub>T<sub><i>x</i></sub> MXene as a Bifunctional\nNanocomposite Electrocatalyst for Overall Water Splitting and

In recent advancements, bimetal MXene has emerged as\na promising\nelectrocatalyst as well as a catalytic supportive material due to\nits unique properties, including rich chemistry and potential metal-like\nconductivity. This study introduces a novel bifunctional electrocatalyst\nfor overall water splitting, involving the synthesis of sea urchin-like\nCoNi<sub>2</sub>Se<sub>4</sub> onto Ti<sub>2</sub>NbC<sub>2</sub>T<sub><i>x</i></sub> using a simple two-step solvothermal method.\nThe developed CoNi<sub>2</sub>Se<sub>4</sub>@Ti<sub>2</sub>NbC<sub>2</sub>T<sub><i>x</i></sub> is subjected to physical and\nsurface topographical investigation using X-ray diffraction, field-emission\nscanning electron microscopy, Raman spectroscopy, and X-ray photoelectron\nspectroscopy techniques. The synergistic effect of the prepared bifunctional\nnanocomposite shows extraordinary kinetic metrics for both HER and\nOER processes. It shows a low overpotential of 76 mV at 10 mA cm<sup>–2</sup> and a small Tafel slope of 78.6 mV dec<sup>–1</sup> for the HER and an overpotential of 203 mV at 10 mA cm<sup>–2</sup> with a Tafel slope of 102.2 mV dec<sup>–1</sup> for the OER.\nCoNi<sub>2</sub>Se<sub>4</sub>@Ti<sub>2</sub>NbC<sub>2</sub>T<sub><i>x</i></sub> exhibits a lower exchange current density\nwith an onset potential that highlights its enhanced performance.\nThis CoNi<sub>2</sub>Se<sub>4</sub>@Ti<sub>2</sub>NbC<sub>2</sub>T<sub><i>x</i></sub> electrocatalyst has achieved a current density\nof 10 mA cm<sup>–2</sup> at 1.55 V and maintained excellent\nelectrocatalytic stability for 24 h. It reveals that CoNi<sub>2</sub>Se<sub>4</sub>@Ti<sub>2</sub>NbC<sub>2</sub>T<sub><i>x</i></sub> could be used as a cost-effective and efficient catalyst,\npaving the way for its application in clean hydrogen production through\noverall water splitting. Owing to its better electrochemical behavior,\nthe prepared CoNi<sub>2</sub>Se<sub>4</sub>@Ti<sub>2</sub>NbC<sub>2</sub>T<sub><i>x</i></sub> material is also used as the\nelectrode material for supercapacitor applications, and it exhibits\na specific capacitance of about 2.05 F cm<sup>–2</sup> at 2\nmA cm<sup>–2</sup>.