(664c) Automated Platform for Quantitative Kinetic Analysis of CO2 Electroreduction Mechanisms at Immobilized Metal Tetrapyrroles

In electrocatalysis, mechanistic analysis of reaction rate data often relies on linearization of relatively simple rate equations; this is the basis for typical Tafel and reactant order dependence analyses. However, for more complex reaction phenomena, such as surface coverage effects or mixed control between multiple pathways, these common linearization strategies will yield incomplete or uninterpretable results. Cohesive kinetic analysis, which is often used in thermocatalysis and involves quantitative model fitting for data collected over a wide range of reaction conditions, provides a more robust strategy for interrogating electrocatalytic reaction mechanisms. However, this analysis strategy requires substantially more experimental rate data. In this work, we report a robotic system that automates collection of electrochemical reaction rate data. To be more tailored toward the application of kinetic analysis, our robotic system automatically performs queued electrochemical experiments that can accommodate a different electrode, electrolyte, and gas-phase reactant for each individual experiment. We use this system to investigate the mechanism of carbon dioxide electroreduction (CO₂RR) to carbon monoxide (CO) at various immobilized metal tetrapyrroles. We first study immobilized cobalt phthalocyanine, where cohesive kinetic analysis of reaction data collected over a wide range of reaction conditions has previously been reported. We then extend the kinetic analysis to additional metal tetrapyrroles, such as cobalt and iron tetraphenyl porphyrins, commonly used as catalysts for CO₂RR to CO. Our analyses suggest that complex reaction mechanisms involving electrolyte adsorption and potential-dependent degrees of rate control are prevalent across this class of electrocatalysts.