(69b) Electrochemical Conversion of CO2 into Value-Added Chemicals

The full utilization of sustainable energy sources such as solar and wind often is hampered by their intermittent nature, resulting in supply not meeting or exceeding demand.  Large scale energy storage capacity is needed in order to maximize utilization of these sources, especially to avoid large amounts of renewable energy being wasted when their supply exceeds demand.  Furthermore, at some point in the future large scale CO₂ producers such as energy companies and the chemical industry will be required to sequester or otherwise mitigate their CO₂ emissions.   When coupled to renewable energy sources such as wind and solar, electroreduction of CO₂ can produce low-carbon fuels or commodity chemicals, possibly providing a method for storage of otherwise wasted excess energy from intermittent renewable sources and a method to mitigate CO2 emissions [1].

Over the last years we have studied the electroreduction of to various value-added chemicals such as carbon monoxide (CO), formic acid, ethylene oxide, and ethanol.  For this process to become economically feasible, more active and stable catalysts as well as better electrodes are necessary such that CO₂ electrolyzers can be operated at sufficient conversion (current density >250 mA/cm²), reasonable energetic efficiency (>60%), and sufficient product selectivity (Faradaic efficiency >90%).   For CO production, which can serve as a feedstock for Fischer-Tropsch fuel production, the best performance reported to date is current densities on the order of 90 mA/cm² and energy efficiencies up to 45%, when operating at ambient conditions [2].  This presentation will focus on the study of new catalysts systems for efficient electroreduction of CO₂ in electrochemical cells and in electrolyzers  For CO₂ to CO conversion we studied: (i) Ag nanoparticles supported on TiO₂ [3]; (ii) Au nanoparticles supported on multiwall nanotubes; and (iii) metal-free N-doped carbons.  When these cathode catalysts are used in combination with IrO₂-based anodes current densities as high as 450 mA/cm² as well as energy efficiencies of up to 70% can be obtained.  

Furthermore, for CO₂ to ethylene and ethanol conversion we studied a variety of Cu-based catalysts, which have the unique property of being able to help produce C2 and higher hydrocarbons, but are challenging with respect to achieving product selectivity. We also performed economic as well as a life-cycle analyses of some of these processes, to determine whether this technology currently is, or can become, economically viable for large scale application in the storage of energy from renewable sources or in the reduction of greenhouse gas emissions.

References

[1] H.R. Jhong, S. Ma, P.J.A. Kenis, Current Opinion in Chemical Engineering 2 (2013) 191.

[2] H.R. Jhong, F.R. Brushett, P.J.A. Kenis, Advanced Energy Materials 3 (2013) 589.

[3] S. Ma, Y. Lan, G.M.J. Perez, S. Moniri, P.J.A. Kenis, ChemSusChem 7 (2014) 866.

[4] S. Ma, R. Luo, S. Moniri, Y. Lan, P.J.A. Kenis, JECS 161 (2014), F1124.