New Electrochemical CO2 Reduction Process to Control Emissions at Low Cost

Researchers from KAIST have demonstrated three novel methods for changing local carbon dioxide (CO₂) concentration in gas-diffusion electrode (GDE)-based flow electrolyzers.

They also empirically showed that ensuring a moderate local CO₂ concentration is effective in enabling carbon–carbon (C–C) coupling reactions for the synthesis of multi-carbon molecules.

This study was reported in the May 20^th issue of Joule and acts as a rational guide to control CO₂ mass transport for the maximum production of useful multi-carbon products.

Against the backdrop of global measures taken to decrease and recycle anthropogenic CO₂ emissions, CO₂ electrolysis exhibits a high potential to convert CO₂ into useful chemicals that were conventionally acquired from fossil fuels.

Several studies have been making efforts to enhance CO₂ selectivity for industrially and commercially high-value multi-carbon products like 1-propanol, ethanol, and ethylene as a result of their large market size and high energy density.

To realize the highly-selective conversion of CO₂ into useful multi-carbon products, earlier studies have endeavored to design catalysts and tune the local surroundings associated with cations, pH, and molecular additives.

Traditional CO₂ electrolytic systems heavily rely on an alkaline electrolyte that is often used up in huge quantities while reacting with CO₂. Thus, they lead to an increase in operational costs. Furthermore, the short lifespan of a catalyst electrode results from its inherent chemical reactivity.

As part of their recent study, a team of researchers from KAIST led by Professor Jihun Oh from the Department of Materials Science and Engineering states that the local CO₂ concentration has been a neglected factor that highly impacts the selectivity toward multi-carbon products.

In collaboration with his colleagues Dr Ying Chuan Tan, Hakhyeon Song, and Kelvin Berm Lee, Professor Oh suggested that there is a close relation between multi-carbon product selectivity and local CO₂ at the time of electrochemical CO₂ reduction reactions.

The researchers applied the mass-transport modeling of a GDE-based flow electrolyzer that uses copper oxide (Cu₂O) nanoparticles as model catalysts. Furthermore, they found and employed three methods to modify the local CO₂ concentration inside a GDE-based electrolytic system, which includes (1) feed flow rate, (2) CO₂ feed concentration, and (3) control of the catalyst layer structure.

In contrast to a common notion, the study demonstrated that ensuring a maximum CO₂ transport results in suboptimal multi-carbon product faradaic efficiency. Rather, by limiting and ensuring a moderate local CO₂ concentration, C–C coupling can be improved considerably.

The scientists experimentally illustrated that the selectivity rate improved from 25.4% to 61.9%, and from 5.9% to 22.6% for the conversion rate of CO₂. When a cost-effective, milder, near-neutral electrolyte was employed, the CO₂ electrolytic system’s stability increased considerably, enabling over 10 hours of stable selective production of multi-carbon products.

According to Dr. Tan, “Our research clearly revealed that the optimization of the local CO₂ concentration is the key to maximizing the efficiency of converting CO₂ into high-value multi-carbon products.”

Tan is also the lead author of the paper.

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. My colleagues and I hope that our study becomes a cornerstone for related technologies and their industrial applications.

Jihun Oh, PhD, Associate Professor, Department of Materials Science and Engineering, KAIST

This work was financially supported by the Korean Ministry of Science and ICT (MSIT) Creative Materials Discovery Program.

Journal Reference:

Tan, Y. C., et al. (2020) Modulating Local CO₂ Concentration as a General Strategy for Enhancing C–C Coupling in CO₂ Electroreduction. Joule. doi.org/10.1016/j.joule.2020.03.013.