Electrolyte Engineering for Improved Selectivity of Electrochemical CO2 Reduction
Authors: Yoo Ji Mun , Trapp Katharina , Lukatskaya Maria R. 
Published: February 2024

Electrochemical CO2 reduction reaction (eCO2RR) offers a promising solution to produce valuable chemical building blocks especially when coupled with renewable energy sources. However, its practical application faces significant challenges including low production selectivity due to competing hydrogen evolution reactions (HER). As both reactions are highly sensitive to the chemical environment formulated around active sites within electrochemical double layer (EDL), a comprehensive understanding is required on the role of electrolyte components, such as cation, anion, local pH, and water molecules, in tailoring chemical environment and thereby determining selectivity between eCO2RR and HER kinetics on the same catalyst surface.

In this context, recent studies have shown that electrolyte engineering can largely control eCO2RR/HER selectivity.[2,3] For instance, different alkali cations have been shown to largely determine CO2 conversion kinetics due to their different hydrated structure within EDL structures.[4] Moreover, an increased cation population within EDL can promote effective eCO2RR over HER even under highly acidic conditions through charge screening effect.[5] Nevertheless, a lack of dynamic information from conventional experimental approaches (e.g. gas chromatography-mass spectrometry) is largely limiting our efforts to comprehensively understand electrolyte engineering effects. To advance our knowledge in electrolyte engineering for high eCO2RR selectivity, it is essential to investigate the functional correlation between electrolyte properties and eCO2RR/HER competition occurring at the electrochemical interface in operando manner.[6,7]

In this work, we utilized in situ Differential Electrochemical Mass Spectrometry (DEMS) to monitor the effects of various electrolyte engineering on eCO2RR/HER selectivity in a dynamic manner. Based on the online collection of product molecules and CO2 from Au catalyst surface, in situ DEMS can provide detailed information on both reaction competition between eCO2RR and HER and local CO2 concentration on catalyst surface on electrified catalyst surface. Based on the strength of in situ DEMS analysis, the critical role of electrolyte components will be addressed in terms of eCO2RR/HER kinetics and the local chemical environment. Overall, this work will highlight importance of understanding specific role of electrolyte engineering toward designing efficient eCO2RR systems for carbon-neutral energy technology.

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