A group of researchers led by Professor Jihun Oh from the Department of Materials Science and Engineering have presented three new approaches for modulating local carbon dioxide concentration in gas-diffusion electrode (GDE) based flow electrolyzers. Their study showed that moderate local CO₂ concentration can effectively promote carbon-carbon coupling reactions and generate multi-carbon molecules.

CO₂ electrolysis, which converts CO₂ into valuable chemicals traditionally derived from fossil fuels, has the potential to contribute significantly to the global efforts to reduce anthropogenic CO₂. In the past, studies focused on the design of catalysts and tuning of reaction conditions to achieve highly selective conversion. The new research, which focuses on local CO₂ concentration as a significant factor, provides a new approach for improving selectivity towards more useful multi-carbon products. 

The research analyzed the relationship between local CO₂ and multi-carbon product selectivity during electrochemical CO₂ reduction reactions. Using mass-transport modeling of a GDE-based flow electrolyzer, which utilizes copper oxide nanoparticles as model catalysts, the team identified that the catalyst layer structure, CO₂ feed concentration, and feed flow rate can be controlled to modulate the local CO₂ concentration within the electrolytic system. 

Furthermore, the study demonstrated that by restricting and providing moderate local CO₂ concentration, C-C coupling can be improved compared to the conventional method of providing maximum CO₂ transport, which leads to sub-optimal multi-carbon product faradaic efficiency. Their experimental evidence shows that selectivity rate increased from 25.4% to 61.9%, and from 5.9% to 22.6% for the CO₂ conversion rate. 

According to Professor Oh, “this finding is expected to deliver new insights to the research community that variables affecting local CO₂ concentration are also influential factors in the electrochemical CO₂ reduction reaction performance.” Their paper was featured in the May issue of Joule, and will serve as a valuable guide for tuning CO₂ mass transport of multi-carbon products.