(414f) Design, Characterization and Testing Of Catalysts For Electrochemical Reduction Of CO2 To CO

During the past few decades, the increasing level of CO₂ in the atmosphere has led to a number of undesired climate effects, including global warming, rising sea levels, and more unpredictable weather patterns.  The amounts of CO₂ being produced are so large that multiple approaches need to be implemented simultaneously, including switching to renewable energy sources, increasing the energy efficiency of buildings, switching from coal to the less carbon-producing natural gas, natural gas, and underground carbon sequestration to curb the increase in atmospheric CO₂ levels.^[1]  An additional approach that can be employed to overcome this daunting challenge is the electrochemical reduction of CO₂ into useful chemicals such as formic acid, carbon monoxide, hydrocarbons, or alcohols.^[2-4]  This process can be driven, for example, by the vast amount of excess renewable power that frequently is available from intermittent sources such as solar and wind.  Furthermore, by utilizing CO₂ as the starting material for chemical production, this process reduces our dependency on fossil fuels.

Despite the potential of electrochemical reduction of CO₂, current performance levels are insufficient for commercialization.^[5]  The catalysts, electrode structures, as well as operation conditions need to be improved such that sufficient selectivity for the desired product (Faradaic efficiency >95%), sufficient energetic efficiency (>60%), and sufficient conversion (current density >250 mA/cm²) can be achieved.^[6-8]

This paper will report some of our recent efforts to understand and improve catalysts, electrode structure,^[9] and operation conditions.^[10]   For example, we have developed organometallic catalysts that exhibit identical performance to Ag nanoparticles, but at a significantly lower loading, as well as multiwall carbon nanotube-supported catalysts and metal-free catalysts that exhibit current densities larger than 180 mA/cm², thus vastly exceeding state-of-the-art performance of Ag nanoparticles. The results of these efforts start to approach the aforementioned specified performance metrics needed for an economically viable process.

[1]      S. Pacala, R. Socolow, Science 2004, 305, 968-972.
[2]      D. T. Whipple, E. C. Finke, P. J. A. Kenis, Electrochem. Solid-State Lett. 2010, 13, B109-B111.
[3]      Y. Hori, in Handbook of Fuel Cells, Vol. 2, John Wiley & Sons, Ltd, 2010, pp. 720-733.
[4]      H.-R. M. Jhong, S. Ma, P. J. A. Kenis, Curr. Opin. Chem. Eng. 2013, accepted.
[5]      E. J. Dufek, T. E. Lister, M. E. McIlwain, Electrochem. Solid-State Lett. 2012, 15, B48-B50.
[6]      C. E. Tornow, M. R. Thorson, S. Ma, A. A. Gewirth, P. J. A. Kenis, J. Am. Chem. Soc. 2012, 134, 19520-19523.
[7]      A. Salehi-Khojin, H.-R. M. Jhong, B. A. Rosen, W. Zhu, S. Ma, P. J. A. Kenis, R. I. Masel, J. Phys. Chem. C 2012, 117, 1627-1632.
[8]      B. A. Rosen, A. Salehi-Khojin, M. R. Thorson, W. Zhu, D. T. Whipple, P. J. A. Kenis, R. I. Masel, Science 2011, 334, 643-644.
[9]      H.-R. M. Jhong, F. R. Brushett, P. J. A. Kenis, Advanced Energy Materials 2013, accepted.
[10]    M. R. Thorson, K. I. Siil, P. J. A. Kenis, J. Electrochem. Soc. 2013, 160, F69-F74.