Fluorine···π Induced Alkyne Concentrating and Orderly Arranged Sulfonate-Adjusted Interfacial Water Structure Promote Alkene Electrosynthesis at Large Current Densities

Abstract

Electrocatalytic semihydrogenation of alkynes to alkenes with water at nearly industrial current densities is highly important. However, a low interfacial alkyne–water ratio leads to severe hydrogen evolution, making it extremely challenging to obtain alkenes with a high Faradaic efficiency (FE). Here, a strategy involving fluorine···π interaction-induced alkyne concentration and orderly arranged sulfonate-repelled interfacial water-cation is developed over commercial Nafion-modified palladium nanotips, enabling electrolysis of 2-methyl-3-buten-2-ol (MBE) with up to 83% FE under −100 mA cm⁻². The fluorine···π effect concentrates the alkyne via its adsorption enhancement, promotes electron transfer, and lowers the activation energy, thus accelerating hydrogenation kinetics. Under the bias potential, the side chain of Nafion undergoing rearrangement from disordered to nearly ordered significantly decreases the interfacial free water coverage and activity, thereby reducing the amount of in situ-generated surface-active hydrogen, which contributes to suppressing hydrogen evolution and improving the FE. An 82% FE and 18.9 mmol h⁻¹ reaction rate of MBE is achieved in a 10 h continuous electrosynthesis at 1.25 A, demonstrating potential utility. Furthermore, the hydrogenation and deuteration of different alkynes with improved Faradaic efficiencies at −100 mA cm⁻² rationalize the design concept.