Time-Resolved Analysis of CO2 Reduction Products on Copper and Oxide-Derived Copper Electrodes

Abstract

Electrochemical conversion of excess carbon dioxide to useful chemicals and fuels is one way of lowering the anthropogenic carbon footprint, and realizing a route to synthetic reactions. Seminal work from Hori and coworkers1, 2 found that copper stands out from a plethora of materials to catalyze the formation of hydrocarbons such as methane or ethylene. More recent efforts were made to give a more complete description of the product distribution, to selectively direct the reaction towards the formation of C2 and C3 products, and to suppress the competing hydrogen evolution reaction in aqueous electrolytes3-7. Li and Kanan succeeded in promoting the C-C bond formation on an oxide-derived copper electrode, prepared by thermal annealing of copper in air, followed by reduction of the formed oxide8, 9. The performance of such systems is most commonly assessed in steady-state electrolysis by ex situ analytics such as online gas chromatography, or nuclear magnetic resonance7, 10. These techniques have proven useful to obtain quantitative information about the product distribution on a time scale of minutes to hours. To capture transient events on dynamic interfaces, to detect short-living products, and for fast screening of catalysts, we developed the electrochemical real-time mass spectrometry (EC-RTMS)11.Herein, we present a novel and straight-forward approach to quantify the liquid products of the CO2 electrochemical reduction in real time, just seconds after their formation on the electrode. We successfully couple mass spectrometry to an electrolytic flow cell and we monitor seven liquid reaction products at unique mass ion signals. The rate of formation of products is resolved down to a time interval of a few seconds. Polycrystalline and oxide-derived copper catalysts are compared and the role of intermediately formed products on both catalysts is discussed.