Electroreduction of CO 2 (eCO 2 RR) is a potentially sustainable approach for carbon-based chemical production. Despite significant progress, performing eCO 2 RR economically at scale is challenging. Here we report meeting key technoeconomic benchmarks simultaneously through electrolyte engineering and process optimization. A systematic flow electrolysis studyperforming eCO 2 RR to CO on Ag nanoparticles as a function of electrolyte composition (cations, anions), electrolyte concentration, electrolyte flow rate, cathode catalyst loading, and CO 2 flow rate -resulted in partial current densities of 417 and 866 mA/cm 2 with faradaic efficiencies of 100 and 98 % at cell potentials of À 2.5 and À 3.0 V with full cell energy efficiencies of 53 and 43 %, and a conversion per pass of 17 and 36 %, respectively, when using a CsOH-based electrolyte. The cumulative insights of this study led to the formulation of system design rules for high rate, highly selective, and highly energy efficient eCO 2 RR to CO.[a] S.
The renewable electricity-powered electrolysis of CO 2 could be a viable carbon-neutral method for producing carbon-based value-added chemicals like carbon monoxide, formic acid, ethylene, and ethanol. A typical CO 2 electrolyzer suffers, however, from the high power requirements, mainly due to the energy-intense anode reaction. In this work, we decrease the anode overpotential and thus reduce the overall cell energy consumption by using a NiFe-based bimetallic catalyst at the anode and applying a magnetic field. For a CO 2 electrolysis process producing CO in a gas diffusion electrode-based flow electrolyzer, we demonstrate that power savings in the range from 7% to 64% can be achieved at CO partial current densities exceeding −300 mA/cm 2 using a NiFe catalyst at the anode and/or by using a magnetic field at the anode. We achieve a maximum CO partial current density of −565 mA/cm 2 at a full cell energy efficiency of 45% with 2 M KOH as the electrolyte.
The Cover Feature illustrates how mechanistic insights can used to engineer the electrolyte composition and formulate system design rules for intensified electroreduction of CO2 to CO. More information can be found in the Aricle by S. S. Bhargava et al.
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 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. https://www.esrl.noaa.gov/gmd/ccgg/trends/ (accessed 12 November 2019). S. Pacala and R. Socolow, Science, 2004, 305, 968. 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. B. Endrődi, G. Bencsik, F. Darvas, R. Jones, K. Rajeshwar and C. Janáky, Progress in Energy and Combustion Science, 2017, 62, 133-154. S. Verma, B. Kim, H.-R. M. Jhong, S. Ma and P. J. A. Kenis, Chemsuschem, 2016, 9, 1972-1979. M. Jouny, W. Luc and F. Jiao, Industrial & Engineering Chemistry Research, 2018, 57, 2165-2177.
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