Carbon-Supported NiZnO Nanoparticles for Electrochemical Reduction of CO2 to Hydrocarbons

Abstract

A compelling approach to close the carbon cycle is electrochemical CO2 reduction. Recently, it was demonstrated that polarized Ni catalysts can form value-added hydrocarbon products like ethylene in this reaction. However, the competing hydrogen evolution reaction significantly lowers their selectivity. We investigate the effects of ZnO on the catalytic performance of well-defined carbon-supported NiO nanoparticles of 5–6 nm. Adding small amounts of ZnO to the highly dispersed NiO nanoparticles (in 20:1 Ni:Zn ratio) initially improves the Faradaic efficiency to C1−3 hydrocarbons from 4.6% to 5.7% at −1.1 V vs RHE, but adding more ZnO (10:1 Ni:Zn) favors the competing hydrogen evolution reaction. CO was detected only for the ZnO catalyst, suggesting electronic interaction between the nickel and zinc (oxide). After 2 h, the NiO catalyst outperforms the NiZnO catalysts in hydrocarbon selectivity. We attribute this to ZnOx promoting the hydrocarbon selectivity, whereas full ZnO reduction over time results in the formation of a NiZn alloy that favors hydrogen formation. Structural characterization after catalytic testing shows leaching of zinc but a high structural stability for the nickel nanoparticles. These results demonstrate that electronic promotion offers an interesting approach to modulate the catalytic performance of nickel toward long-chain hydrocarbons.