(Industrial Electrochemistry and Electrochemical Engineering Division Student Achievement Award Address) System-Level Approaches for Intensifying the CO2 Electrolysis Process
Authors: Bhargava Saket , Azmoodeh Daniel , Gewirth Andrew A. , Kenis Paul J.A. 
Published: May 2020

Every year about 14.7 Gigatons of net CO2 are added to the atmosphere.1 Atmospheric CO2 concentrations measured at the ESRL (NOAA, Mauna Loa HI) show an increase from 316 ppm to 409 ppm over the past 60 years.2 For the remediation of excess CO2, various studies suggest that one approach is to capture the excess CO2 emissions and subsequently utilize them to make value-added products.3 Electroreduction of CO2 (CO2RR) is a potential method for utilizing a fraction of the excess CO2 emissions by converting them into various carbon-based chemicals such as methanol, formic acid, ethylene, and carbon monoxide.4

Research efforts in academia and industry have developed catalysts, electrodes, electrolytes, and have also optimized reactor configurations and associated operating conditions to allow for high-rate and selective CO2RR.5 However, significant improvements in electrolyzer performance (catalyst activity and selectivity) are still needed for CO2RR to be technoeconomically feasible at scale.6, 7

This talk will cover multiple system-level approaches that can be further explored to intensify the performance of a flow electrolyzer for CO2RR.

The first part will discuss how electrolyte engineering based on the role of electrolyte composition and the rate determining step (RDS) can guide the systematic process optimization of CO2RR to CO on Ag nanoparticles (NPs). The effects of pH and of cation identity as well as the identity of the RDS explain how CsOH as the electrolyte can be used to optimize CO2RR performance, resulting in CO partial current densities (jCO) exceeding 850 mA/cm2 at a cathode potential of -1 V vs. RHE with 98% Faradaic efficiency (FE) and full cell energetic efficiency for CO production (EE) exceeding 40% at a conversion per pass of CO2 to CO of 36%. These process optimization insights led to the formulation of system design rules pertaining to jCO, CO FEs, CO EEs, cathode overpotentials, catalyst mass activities, conversion per pass, and system costs for CO2RR to CO on Ag NPs.

The second part briefly discusses the effects of using multiple alkali metals or multivalent cations in the electrolyte composition and the effect of electrolyte composition on performance stability over multiple hours for CO2RR to CO on Ag NPs.

The third part focuses on improving the overall cell performance by intensifying the anode performance with approaches such as using a Ni and Fe based bimetallic anode catalyst instead of the typically used IrO2 catalyst or using a magnet at the anode to enhance mass transport. These approaches led to about 200 mV reduction in cell overpotential and thus, enhanced CO EEs.

Lastly, the fourth part will discuss the effect of operating temperature on jCO, CO FEs, and CO EEs to understand the role of temperature as a process lever for process intensification of CO2RR.

References

1. IPCC, Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2013.

2. https://www.esrl.noaa.gov/gmd/ccgg/trends/ (accessed 12 November 2019).

3. S. Pacala and R. Socolow, Science, 2004, 305, 968.

4. O. S. Bushuyev, P. De Luna, C. T. Dinh, L. Tao, G. Saur, J. van de Lagemaat, S. O. Kelley and E. H. Sargent, Joule, 2018, 2, 825-832.

5. B. Endrődi, G. Bencsik, F. Darvas, R. Jones, K. Rajeshwar and C. Janáky, Progress in Energy and Combustion Science, 2017, 62, 133-154.

6. S. Verma, B. Kim, H.-R. M. Jhong, S. Ma and P. J. A. Kenis, Chemsuschem, 2016, 9, 1972-1979.

7. M. Jouny, W. Luc and F. Jiao, Industrial & Engineering Chemistry Research, 2018, 57, 2165-2177.