Quantification of Gaseous Products Evolved at Industrially Relevant Current Densities During CO ₂ Electroreduction and Water Electrolysis Using Online Gas Chromatography

The quantification of gaseous chemicals such as CO and H 2 , obtained during the electrochemical reduction of CO 2 or water using online gas chromatography (GC), is extremely relevant for the evaluation of an electrolysis system's performance. Herein, the causes that may hinder the proper calculation of Faraday efficiencies, when applying industrially relevant current densities, are demonstrated for both water electrolysis and CO 2 electroreduction (eCO 2 RR). The findings highlight that rigorous calibration and an understanding of GC linearity and detection limits are essential for accurate measurement and quantification. Furthermore, the implementation of product dilution immediately after the electrocatalytic reactor, prior to GC analysis, is introduced as a versatile approach that enables reliable product quantification across different applied current densities and GC systems.