Strong Electron-Withdrawing Effect Activates Metal-Free Carboxylate Anion into Efficient Active Sites for Electrocatalytic Acetylene Semihydrogenation.

Abstract

The exploration of novel and high-performance organo-electrocatalysts with well-defined active sites is vital for understanding catalytic mechanisms and replacing metal-based catalysts, but remains a formidable challenge. Here, we report metal-free trifluoroacetate as a new organo-electrocatalyst, where the strong electron-withdrawing trifluoromethyl (-CF₃) group intrinsically transforms the neighboring carboxylate anions (-COO^-) into highly efficient active sites for electrocatalytic acetylene semihydrogenation. The electrophilic acetylene molecule bonds to the negatively charged O^- sites of the carboxylate anion via the σ-configuration. Benefiting from precise molecular engineering of electron-withdrawing groups, the ethylene partial current density presents a volcano relationship with the total natural charge of the -COO^- anions. In 1 M KOH aqueous solution, trifluoroacetate delivers an ethylene partial current density of 260 mA/cm² with an ethylene Faradaic efficiency of 96.8% at -0.9 V versus the reversible hydrogen electrode (RHE) under a pure acetylene atmosphere, outperforming metal-based electrocatalysts. This work presents a new type of high-activity organo-electrocatalysts with -COO^- anions as active center and promises its application in electrocatalysis.