Proton Sponge Tailoring of Interfacial H‐Bond Networks Enables Seawater Electrosynthesis for Concomitant Alkenol and Mg(OH) 2

ABSTRACT Seawater electrolysis provides a sustainable hydrogen source for electrocatalytic semi‐hydrogenation (ECSH) of alkynols, but it suffers from severe hydrogen evolution and a lack of effective interfacial management. Here, we construct a proton sponge (1,8‐bis(dimethylamino)naphthalene) modified PdIn intermetallic metallene (Pd 1 In 1 ene@DMAN). In situ FTIR and ab initio molecular dynamics simulations reveal that this modification disrupts the hydrogen‐bond network of interfacial water molecules, while DFT calculations indicate facilitated water dissociation and enhanced generation of active hydrogen species. The Pd 1 In 1 ene@DMAN achieves a Faradaic efficiency (FE) of 94.43% for 2‐methyl‐3‐buten‐2‐ol (MBE) production at −100 mA cm −2 , a dramatic increase from the 44.93% attained by the Pd 1 In 1 ene, with an operational stability over 500 h. In a membrane‐electrode assembly (MEA) electrolyzer, it enables the efficient conversion of alkynol to alkenol at a current of 2 A, delivering a FE of 84.16%, a selectivity of 98.54% toward MBE, and excellent stability for up to 200 h. Concurrently, the cathodically generated OH − selectively precipitates Mg 2+ as high‐purity Mg(OH) 2 by precise pH control, enabling the co‐production of value‐added MBE and Mg(OH) 2 . This work establishes a seawater‐based electrochemical system, which regulates the hydrogen bond microenvironment through molecular interface engineering, providing a new strategy for efficient electrochemical hydrogenation in complex media.