Ionic Liquid-Mediated Selective Conversion of CO₂ to CO at Low Overpotentials

Ionic Liquid-Mediated Selective Conversion of CO₂ to CO at Low Overpotentials

29 September 2011 | Brian A. Rosen, Amin Salehi-Khojin, Michael R. Thorson, W. Zhu, Devin T. Whipple, Paul J. A. Kenis, Richard I. Masel
This study presents an electrocatalytic system for the selective conversion of CO₂ to CO at low overpotentials using ionic liquids. The system uses an ionic liquid electrolyte to lower the energy of the (CO₂)⁻ intermediate, likely through complexation, thereby reducing the initial reduction barrier. The silver cathode then catalyzes the formation of CO. CO is first observed at 1.5 V, slightly above the equilibrium potential of 1.33 V. The system produced CO for at least 7 hours with Faradaic efficiencies over 96%. CO₂ activation has been challenging compared to water splitting. While some homogeneous catalysts show initial activity, they often lose activity under reaction conditions. The proposed system aims to lower the potential for forming the (CO₂)⁻ intermediate, which then reacts with H⁺ on the silver cathode to produce CO. If Bockris' proposal is correct, lowering the free energy of the (CO₂)⁻ intermediate should reduce the overpotential for CO₂ conversion. The study tested 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF₄) as a potential co-catalyst. Experiments showed that CO is produced at 1.5 V, compared to 2.1 V without the ionic liquid. The Faradaic efficiency for CO formation was over 96%, with hydrogen formation less than 3%. The energy efficiency was 87% at 1.5 V, dropping as voltage increased due to resistive losses. The system demonstrated a turnover rate of about 26,000 turnovers over 7 hours, showing robustness. However, the observed rates are lower than needed for commercial processes. Further development is needed to increase turnover numbers and scale up the system. The current cathode has a much smaller electrochemical surface area compared to commercial cells, limiting production rates. The study highlights the potential of ionic liquids in improving CO₂ conversion efficiency and suggests further research for commercial applications.This study presents an electrocatalytic system for the selective conversion of CO₂ to CO at low overpotentials using ionic liquids. The system uses an ionic liquid electrolyte to lower the energy of the (CO₂)⁻ intermediate, likely through complexation, thereby reducing the initial reduction barrier. The silver cathode then catalyzes the formation of CO. CO is first observed at 1.5 V, slightly above the equilibrium potential of 1.33 V. The system produced CO for at least 7 hours with Faradaic efficiencies over 96%. CO₂ activation has been challenging compared to water splitting. While some homogeneous catalysts show initial activity, they often lose activity under reaction conditions. The proposed system aims to lower the potential for forming the (CO₂)⁻ intermediate, which then reacts with H⁺ on the silver cathode to produce CO. If Bockris' proposal is correct, lowering the free energy of the (CO₂)⁻ intermediate should reduce the overpotential for CO₂ conversion. The study tested 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF₄) as a potential co-catalyst. Experiments showed that CO is produced at 1.5 V, compared to 2.1 V without the ionic liquid. The Faradaic efficiency for CO formation was over 96%, with hydrogen formation less than 3%. The energy efficiency was 87% at 1.5 V, dropping as voltage increased due to resistive losses. The system demonstrated a turnover rate of about 26,000 turnovers over 7 hours, showing robustness. However, the observed rates are lower than needed for commercial processes. Further development is needed to increase turnover numbers and scale up the system. The current cathode has a much smaller electrochemical surface area compared to commercial cells, limiting production rates. The study highlights the potential of ionic liquids in improving CO₂ conversion efficiency and suggests further research for commercial applications.
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