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Published November 28, 2022 | Submitted + Supplemental Material
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Beyond Tafel Analysis for Electrochemical CO₂ Reduction

Abstract

The development and characterization of active and selective catalysts is critical for the simulation and optimization of electrochemical synthesis of chemicals and fuels using renewable energy. The rate of electrochemical generation of a specific product as a function of electrode potential can be described by a Tafel equation, which depends on two parameters: the Tafel slope (or the related transfer coefficient) and the exchange current density. However, common methods for calculating Tafel slopes are subjective and limited by data insufficiency resulting from challenges associated with product quantification, and, as shown here, the effects of mass transport, bulk reaction occurring in the mass-transfer boundary layer, and the occurrence of competitive surface reactions. Errors in the Tafel slope extracted from experimental data can also lead to errors in the exchange current density estimation. To address these issues, we present a technique that leverages statistical learning methods informed by physics-based modeling to calculate kinetic parameters (the transfer coefficient and exchange current density) with quantified uncertainty. The method is applied to 21 sets of data for the electrochemical reduction of CO₂ to CO and H₂ on Ag catalysts acquired under similar experimental conditions. We find that fitted values for the transfer coefficient and exchange current density do not converge to a unique set of values, and that there is an apparent correlation of these parameters; however, the most probable value of the exchange coefficient for CO and H₂ formation correspond reasonably well with the DFT-predicted values of this parameter. While the system explored is relatively simple, the techniques developed can be used to evaluate the transfer coefficient and exchange current density for many other electrochemical processes.

Additional Information

The content is available under CC BY 4.0 License. This material is based on work performed within the Liquid Sunlight Alliance, which is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Fuels from Sunlight Hub under Award Number DE-SC0021266. JCB would like to acknowledge support from the National Defense Science and Engineering Graduate Fellowship (NDSEG) supported by the Army Research Office (ARO). The authors would also like to acknowledge helpful discussions with Joy Zeng that helped guide the direction of the study. Author Contributions. JCB developed the model physics and COMSOL continuum model of CO₂ reduction on Ag used in the study. KRMC and AML developed the utilized covariance matrix adaptation MATLAB code applied to fit kinetic parameters. KRMC linked the COMSOL and MATLAB codes to fit kinetic and transport parameters in the continuum model. JCB and LMP developed the sensitivity analysis for the CO₂ reduction model. KM, AZW, and ATB provided guidance and direction for the project. KRMC and JCB prepared the original draft of the manuscript. All authors engaged in reviewing and editing the manuscript.

Attached Files

Submitted - beyond-tafel-analysis-for-electrochemical-co2-reduction.pdf

Supplemental Material - supporting-information-for-beyond-tafel-analysis-for-electrochemical-co2-reduction.pdf

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beyond-tafel-analysis-for-electrochemical-co2-reduction.pdf

Additional details

Created:
August 20, 2023
Modified:
October 18, 2023