In recent years, electrochemical synthesis has begun to arise as a viable alternative for the sustainable generation of valuable chemical commodities. Advancement of electrochemical synthesis hinges on the development and characterization of catalysts for these processes. A key figure of merit in characterizing electrocatalysts is the Tafel slope, defined as the requisite voltage to increase the current density towards a particular reaction by an order of magnitude. Unfortunately, common methods of evaluating the Tafel slope are incompatible with the nature of experimentation in electrochemical synthesis. Namely, the requirements of product quantification severely limit the amount of data that can be collected. Additionally, mass transport limitations encountered in these systems further limit the applicability of current Tafel analyses by necessitating further elimination of data in the plateau regime of the polarization curve. Both the data insufficiency and the arbitrary demarcation of the transport limited region lead to substantial, unquantified error in Tafel analysis for these systems.<br/><br/>Herein, we discuss a new method to characterize the Tafel slope in electrochemical synthesis systems with multiple competing reactions. By coupling the modern data analysis technique known as covariance matrix adaptation (CMA) with a multiphysics model of the mass transport boundary layer in an electrochemical synthesis device, the entire scope of the experimental data (both the kinetic and mass transport regions) for all competing reactions can be fit with a quantified band of uncertainty. Applying this algorithm to experimental data across the literature for electrochemical CO<sub>2</sub> reduction on Ag catalysts demonstrates the robustness and universality of the algorithm, while also enabling visualization of trends in Tafel slopes for Ag measured, showing that cardinality in Tafel slopes does not necessarily exist, even for a single catalyst and a single reaction product. Ultimately, this work represents a key step forward in the rigor and standardization of kinetic analysis for catalysts applied in electrochemical synthesis.

Beyond Tafel analysis for kinetic parameterization in electrochemical synthesis

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