Investigating the impact of CO₂ dilution and O₂ presence in the feed stream on the electrochemical reduction of CO₂ to C₂ products with a flow-by electrolyzer

Climate change is proving to be one of the greatest challenges for humankind in recent years, impacting various aspects of human life, including health and the economy. Carbon capture and utilization technologies play a crucial role in reducing GHG emissions, offering a reliable approach to treating flue gases from sources where immediate decarbonization is impractical. Among the others, electrochemical CO₂ conversion has particularly interesting features since it closes the anthropogenic carbon cycle while storing energy from renewable sources into chemical bonds. This work aims to develop an industrially viable configuration of a CO₂ electrolyzer, investigating the effects of impurities in the fed gas stream on reactor performance. Initially, the study consists of testing different commercially available copper-based nanoparticles to find the catalyst with the lowest overpotential, the best stability of the system, and the highest selectivity towards ethylene and ethanol. Then, current density screenings are conducted to study the influence of current on product distribution and the effects of local CO₂ depletion. Once the optimal configuration is found, the investigation addresses the introduction of impurities, specifically N₂ and O₂, in the gas stream through two distinct experiments. Nitrogen, being inert, does not induce side reactions but can dilute CO₂, thus affecting product distribution by altering the coverage of intermediate species on the catalyst surface. On the other hand, even a low O₂ concentration proves detrimental, as its unwanted reduction to water easily displaces the CO₂ reduction reaction. This study proposes a new type of gas diffusion electrode configuration that can mitigate this selectivity shift, coupled with an increased applied current density. In this way, CO₂ reduction starts to take place after achieving a condition of local O₂ depletion. This approach makes the reactor able to withstand flue gas-like O₂ concentrations.