Electrical double layer model reveals the possibility of electrochemical CO2 reduction in acidic environment

Shuo Liu^a, Jun Gu^b^,^c, Xile Hu^b, Sophia Haussener^a

^aLaboratory of Renewable Energy Science and Engineering, Institute of Mechanical Engineering, École Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland., Rte Cantonale, Laussane, Switzerland

^bLaboratory of Inorganic Synthesis and Catalysis, Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), EPFL-ISIC-LSCI, Rte Cantonale, Lausanne, Switzerland

^cDepartment of Chemistry, Southern University of Science and Technology, Shenzhen, Guangdong, 518055, China., 1088 Xueyuan Ave, Nanshan, Shenzhen, Guangdong Province, Shenzhen Shi, China

Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe Fall Meeting 2021 (NFM21)

#SolCat21. (Photo-)Electrocatalysis: From the Atomistic to System Scale

Online, Spain, 2021 October 18th - 22nd

Organizers: Karen Chan, Sophia Haussener and Brian Seger

Contributed talk, Shuo Liu, presentation 128
DOI: https://doi.org/10.29363/nanoge.nfm.2021.128
Publication date: 23rd September 2021

Electrochemical CO₂ reduction has the potential to contribute to a closed carbon cycle by recycling CO₂ from various sources and converting it into sustainable chemicals. The reaction environment is crucial to achieve high activity, conversion and selectivity. Hydrogen evolution is typically dominating in acidic environments (due to the sufficient presence of protons) leading to low Faradaic efficiency. Recently, it has been shown that the hydrogen evolution reaction could be suppressed by adding extra non-reactive cations, such as potassium ions in the electrolyte. We developed an electric double layer model, solving for the transport of ionic species in the diffusion layer and charge distribution in Stern layer, to describe the potential and concentration distribution in close vicinity of the electrode. We showed that the potassium cations can migrate to the electrode surface and modulate the electric field strength, and therefore, reduce the migration of protons towards the electrode. The concentration of all ionic species, the potential profile, and the hydrogen evolution current density can be quantitively obtained. This model explained the mechanism of hydrogen evolution suppression by potassium ions which was also observed and convinced in the experiment. The model reveals the possibility of electrochemical CO₂ reduction in acidic environment and proposes a possible way to overcome the depletion of CO₂ in alkaline environments.

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