(97c) Electrochemical Conversion of CO2 with Ionic Liquids In a Microfluidic Reactor

Energy storage solutions compatible with the current energy grid need to be developed for renewable and carbon neutral energy sources to replace fossil fuels.  Electrochemical conversion of CO₂ into fuels can provide a means for the storage of electrical energy in chemical form, which is important considering that most carbon neutral energy sources such as wind and solar produce electricity.  Storage of this electrical energy in a chemical form would enable the use of renewable energy in the transportation sector, which makes up a large portion of our energy use but has only 3% supplied by renewable sources [1].  Additionally, this technology could provide a means of storage for renewable energy sources such as wind and solar that are intermittent and, as a result, require output leveling.

Conversion of CO₂ into CO [2,3] is attractive due to the versatility of CO (with hydrogen) as a feedstock for the Fischer-Tropsch process, which enables the synthesis of a variety of products including liquid hydrocarbon fuels.  Presently, key challenges reducing large overpotentials and improving selectivity, thereby resulting in a search for electrolytes and catalysts that stabilize CO₂- intermediate.  Work by Rosen et al. has shown that the ionic liquids may stabilize the intermediate and lower the necessary overpotentials [4]. 

Here, we use a microfluidic reactor that employs a flowing electrolyte to investigate the influence of ionic liquids in a flowing cell [5].  In the flow cell, we found ionic liquids improve the selectivity for CO as opposed to H₂ and increase the current densities, both at low currents.  However, ionic liquids were found to be mass transport limited, thereby limiting the selectivity at high currents.  To address this limitation, we study several key parameters including, temperature, and pressure with regards to current efficiency, faradaic efficiency, current densities and overpotentials.  Additives are used to improve the selectivity for CO and minimize anodic poisoning.  massand make design changes to overcome these mass transport limitations.  The mass transport limitations can be overcome via the use of temperature as well as design and operational changes. 

References

[1] Whipple, D. T., and Kenis, P. J. A.,  J. Phys. Chem. Lett., 2010, 1, 3451.

[2] Hori, Y., Wakebe, H., Tsukamoto, T., Koga, O., Electrochim. Acta, 1994, 39, 1833.

[3] Delacourt, C., Ridgway, P. L., Kerr, J. B., Newman, J., J. Electrochem. Soc, 2008, 155, B42.

[4] Rosen, B. A., Salehi-Khojin, A., Masel, R., Artificial Photosynthesis: Conversion of CO₂ at Low Temperature and Potential Using Ionic Liquids, AIChE Annual Meeting , 2010.

[5] Whipple, D. T., Finke E. C., and Kenis, P. J. A., Electr. & Solid-State Lett., 2010, 13, B109-B111.