Steering Active Hydrogen and Intermediate Adsorption via Hydrogen-Bond Microenvironment on Electron-Deficient Pd Sites for Electrocatalytic Semihydrogenation of Alkynol

Electrocatalytic semihydrogenation of alkynols to alkenols with water offers an environmentally benign alternative to conventional thermal methods. However, its efficiency is largely limited by the sluggish active hydrogen (*H) supply from water dissociation and the difficulty in fine-tuning intermediate adsorption. Here, we develop tannic acid (TA)-modified Pd metallene nanoribbons (TA-Pd MNRs) as an efficient electrocatalyst for selective semihydrogenation of alkynols to alkenols. TA functionalization induces electron-deficient Pd sites and creates a local hydrogen-bond microenvironment, which (i) strengthens 2-methyl-3-butyn-2-ol (MBY) adsorption, (ii) expedites H2O dissociation to regulate *H supply, and (iii) weakens *H adsorption ability to suppress both the competitive hydrogen evolution and overhydrogenation reactions. As a result, TA-Pd MNRs deliver an impressive 2-methyl-3-buten-2-ol (MBE) production rate of 493 gMBE gcat−1 h−1 with 96.5% selectivity at an industrially relevant current density of −200 mA cm−2 in a continuous-flow cell. This work establishes a synergistic strategy of electronic and hydrogen-bond engineering for selective electrocatalytic semihydrogenation.