The electrochemical reduction of CO₂ (eCO₂R) is a promising way to convert detrimental CO₂ emissions into sustainable fuels and chemicals, and thus to achieve a net zero or net negative carbon economy_.¹ Depending on catalyst type and reaction conditions, different gaseous and liquid products can be obtained during eCO₂R, with their production rates significantly varying over time. Thus, for any catalytic performance analysis, it becomes key to be able to assess the product distribution online during eCO₂R_.^2,3 However, while gaseous products are readily analyzed online by gas chromatography, liquid products are typically only assessed at the end of the reaction due to the lack of suitable automated liquid sampling and analysis methods. In addition, relevant reaction parameters such as CO₂ flow rates, electrolyzer temperatures and flow pressures are seldom recorded, causing the loss of significant information on catalysts, electrodes, and electrolyzer behavior.

In this work, we overcome these issues by assembling a comprehensive analytical system coupling online gas and liquid product analysis by gas and liquid chromatography (leveraging a special automated liquid sampling valve) with electrochemical protocols that assess CO₂RR performance, electrolyzer cell resistance and electrode surface area. In addition, we record CO₂ volumetric flow rates, electrolyzer temperatures, as well as gas and liquid flow pressures_.⁴ To rapidly and reproducibly handle the large and heterogeneous data volume obtained we implement a standardized data pipeline based on our own open-source software,⁵ which automatically parses the numerous different raw data files, composes a data set following FAIR practices,⁶ and post-processes and plots the data in a standard way. We validate this analytical system by carrying out eCO₂R at 200 mA/cm² on Cu gas diffusion electrodes, following the changes in selectivity with reaction time for > 12 gaseous and liquid products while recording volumetric flow rates, electrolyzer cell resistance, electrode surface area, electrolyzer temperatures and flow pressures. The modular nature of our analytical system, combined with the standardized data pipeline, allows us to freely increase the number and type of sensors used with minimal impact on the data analysis time, as well as to multiplex our analysis to 8 parallel electrolyzer cells, providing a deep understanding of the function of eCO₂R catalysts, electrodes, and electrolyzers, and paving the way to accelerated discoveries.