Palladium-Catalyzed Electrocoupling of Acetylene to C ₄ –C ₁₀ Hydrocarbons

Acetylene (C2H2) is a feedstock capable of undergoing C–C coupling to yield valuable long-chain hydrocarbons. Currently, only C2 (ethylene) and C4 hydrocarbon formation has been reported from the electrochemical C2H2 reduction reaction (C2H2RR). Herein, we demonstrate that C2H2 can be further coupled to form C6, C8, and C10 hydrocarbons by using electrocatalysts with different binding strengths for carbon-containing molecules. Utilizing a palladium nanoparticle catalyst which binds to carbonaceous intermediates optimally, C2H2 was converted into hydrocarbons with total Faradaic efficiencies (FE) of up to 96%. Importantly, C6 hydrocarbons were formed with a FE of 2.9% at −0.4 V vs reversible hydrogen electrode (RHE) and a partial current density (jC6) of −3.3 mA·cm–2 at −0.7 V vs RHE. C8 and C10 products were also formed with respective FEs up to 0.8 and 0.1% at −0.4 V vs RHE. A stronger adsorption of C2H2 on a catalyst surface also results in more hydrogenated products: strong-binding ruthenium favored more hydrogenated hexanes and hexenes (isomers), while weak-binding copper yielded less hydrogenated hexadienes and hexatriene. Interestingly, cyclic hydrocarbons were formed on copper, which we attribute to copper’s ability to facilitate rearrangement of C2 intermediates into metallocycle moieties while preserving π-bond character, so that cyclization can occur.