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Insights into the Carbon Balance for CO2 Electroreduction on Cu using Gas Diffusion Electrode Reactor Designs

preprint
submitted on 13.12.2019 and posted on 17.01.2020 by Ming Ma, Ezra Lee Clark, Kasper T. Therkildsen, Sebastian Dalsgaard, Ib Chorkendorff, Brian Seger
In this work, the carbon balance during high-rate CO2 reduction in flow electrolyzers is rigorously analyzed. The CO2 consumption at gas-diffusion electrodes due to electrochemical reduction and reaction with OH- at the electrode-electrolyte interface leads to a substantial reduction in the volumetric flowrate of gas flow out of the electrolyzer, especially when highly alkaline electrolytes and elevated current densities are utilized, mainly owing to elevated pH at cathode/electrolyte interface. Without considering the CO2 consumption, the Faradaic efficiencies for major gas products could be significantly overestimated during high current density CO2 reduction conditions, particularly in the case of high pH electrolyte. In addition, a detailed carbon balance path is elucidated via a two-step procedure of CO2 reaction with OH- at cathode/electrolyte interface and subsequent CO2 generation at anode/electrolyte interface caused by a relatively low pH in the vicinity of the anode. Based on the proposed two-step carbon balance path, a systemic exploration of gases released in anolyte reveals the transformation of a HCO3- or OH- catholyte to a CO32- catholyte, which was further confirmed by pH measurement.

Funding

Villum Foundation V-SUSTAIN grant 9455 to the Villum Center for the Science of Sustainable Fuels and Chemicals;

ECOEthylene project from the Innovation Fund Denmark (Grant# 8057-00018B)

History

Email Address of Submitting Author

mingma@fysik.dtu.dk

Institution

Surfcat, Department of Physics, Technical University of Denmark

Country

Denmark

ORCID For Submitting Author

0000-0003-3561-5710

Declaration of Conflict of Interest

There are no conflicts to declare.

Exports