In Situ Electrosynthesis of MAX‐Derived Electrocatalysts for Superior Hydrogen Evolution Reaction

Abstract MAX phases are frequently dominated as precursors for the preparation of the star material MXene, but less eye‐dazzling by their own potential applications. In this work, the electrocatalytic hydrogen evolution reaction (HER) activity of MAX phase is investigated. The MAX‐derived electrocatalysts are prepared by a two‐step in situ electrosynthesis process, an electrochemical etching step followed by an electrochemical deposition step. First, a Mo 2 TiAlC 2 MAX phase is electrochemically etched in 0.5 m H 2 SO 4 electrolyte. Just several hours, electrochemical dealloy etching of Mo 2 TiAlC 2 MAX powders by applying anode current can acquire a moderated HER performance, outperforming most of reported pure MXene. It is speculated that in situ superficially architecting endogenous MAX/amorphous carbide (MAC) improves its intrinsic catalytic activity. Subsequently, highly active metallic Pt nanoparticles immobilized on MAC (MAC@Pt) shows a transcendental overpotential of 40 mV versus RHE in 0.5 m H 2 SO 4 and 79 mV in 1.0 m KOH at the current density of 10 mA cm −2 without iR correction. Ultrahigh mass activity of MAC@Pt (1.5 A mg pt −1 ) at 100 mV overpotential is also achieved, 29‐folds than those of commercial PtC catalysts.