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

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.