Pentlandite Catalysts for the Electrochemical Hydrogenation of Alkynols in a Zero-Gap Electrolyzer

Electrosynthetic methods are considered to be crucial in the sustainable transformation of the chemical industry. Being an integral part of many synthetic pathways, the electrification of hydrogenation reactions gained increasing interest in recent years. However, for the large-scale industrial application of electrochemical hydrogenations, low-resistance zero-gap electrolyzers operating at high current densities and high substrate concentrations, ideally applying noble-metal-free catalyst systems, are required. In this work, we demonstrate the successful development of an electrochemical hydrogenation process towards application at the example of the semi-hydrogenation of alkynols. Because of their conductivity, stability, and stoichiometric flexibility, transition metal sulfides were thoroughly investigated as promising electrocatalysts for electrochemical hydrogen evolution but remain scarcely investigated for electrochemical hydrogenations. An initial screening of a series of first-row transition metal sulfides of the pentlandite class revealed promising activity for the electrochemical hydrogenation of alkynols in water and methanol. Based on these findings, selected catalysts were incorporated into a zero-gap electrolyzer, thereby enabling the hydrogenation of alkynols at current densities of up to 1 A cm-2, Faraday efficiencies of up to 75 %, and an alkene selectivity of 90 %. In this scalable setup we demonstrate high stability of the catalyst and the electrode for at least 100 h. Altogether, we illustrate the successful integration of a sustainable catalyst into a scalable zero-gap electrolyzer establishing electrosynthetic methods in an application-oriented manner. Figure 1