Electrochemical Etching Engineering Toward Ti Vacancy‐Confined Pt Single‐Atom MXene Catalyst for Alkaline Hydrogen Evolution

Metal vacancies in MXene catalysts are beneficial for modulating electronic structures and enhancing metal‐support interactions for single‐atom (SA) immobilization, but controlling their concentration and understanding their synergy with SAs remains challenging. Here, we develop a two‐step electrochemical etching strategy in a deep eutectic solvent to create tunable Ti vacancies within MXene (Ti V ‐Ti 3‐ x C 2 T y ) and confine Pt single atoms (Pt SA ‐Ti V ‐Ti 3‐ x C 2 T y ). The vacancy concentration is precisely controlled, and the dynamic etching‐deposition process prevents Pt SAs aggregation. The resulting catalyst with only Pt content of 0.57 wt.% exhibits excellent alkaline hydrogen evolution reaction (HER) performance: an overpotential of 31 mV at 10 mA cm −2 , a turnover frequency of 12.22 H 2 s −1 , and a mass activity of 11.95 A mg Pt −1 at 100 mV, outperforming commercial Pt/C. The coexistence of Pt SAs and adjacent Ti vacancies synergistically tunes the local electronic structure of Pt sites and modulates metal‐support bonding, lowering the water dissociation barrier and optimizing hydrogen adsorption energy to boost alkaline HER. This work offers a controllable strategy for engineering metal vacancies in MXenes for efficient single‐atom catalysts and establishes a platform for investigating vacancy‐SA synergistic mechanisms.