Table S1. Summary of Reported Heterogeneous Molecular Catalyst Performances. Data from graphs were extracted using WebPlotDigitizer [1] and should have an error less than 5%. Catalyst loading, current density, and TOF are related via Equation S1, allowing the calculation of unreported values if the other two values are reported. Catalyst loadings are listed as the amount deposited unless otherwise indicated. Potentials in aqueous solution are referenced to SHE rather than RHE since several studies have shown a pH-independent mechanism for ECR to CO on immobilized molecular catalysts. Please see the notes at the end of the table for definitions of acronyms and symbols. Catalyst Electrode Deposition Solvent Electrolyte Catalyst Loading (mol/cm 2 ) Voltage (V vs. SHE)

The Tafel slope is a key parameter often quoted to characterize the efficacy of an electrochemical catalyst. In this paper, we develop a Bayesian data analysis approach to estimate the Tafel slope from experimentally-measured current-voltage data. Our approach obviates the human intervention required by current literature practice for Tafel estimation, and provides robust, distributional uncertainty estimates. Using synthetic data, we illustrate how data insufficiency can unknowingly influence current fitting approaches, and how our approach allays these concerns. We apply our approach to conduct a comprehensive re-analysis of data from the CO2 reduction literature. This analysis reveals no systematic preference for Tafel slopes to cluster around certain "cardinal values” (e.g. 60 or 120 mV/decade). We hypothesize several plausible physical explanations for this observation, and discuss the implications of our finding for mechanistic analysis in electrochemical kinetic investigations.

Inductive and electrostatic effects were found to both play important roles for heterogeneous electrocatalytic CO2 reduction on cobalt porphyrins.

The mechanism for carbon dioxide reduction (CO 2 RR) to carbon monoxide (CO) at immobilized cobalt phthalocyanine (CoPc) in aqueous electrolytes has been widely debated. In this work, we investigated the mechanism of CO 2 RR to CO on CoPc via experimental reaction kinetics coupled with model fitting. Unexpectedly, reactant order dependences and Tafel slopes deviate from commonly expected values and change depending on the testing conditions. For example, (1) the effect of bicarbonate deviates from power law kinetics and transitions from inhibitory to promotional with increasingly reductive potential, and (2) the CO 2 order dependence deviates from unity at more-reductive potentials. We propose a kinetic model, chosen from more than 15 candidate models, that is able to quantitatively fit all of the experimental data. The model invokes (1) catalyst poisoning via bicarbonate electrosorption, (2) mixed control between concerted proton− electron transfer (CPET) and sequential electron transfer-proton transfer (ET-PT), and (3) both water and bicarbonate as kinetically relevant proton donors. The proposed model also predicts that the relative importance of the above factors changes depending on the reaction conditions, highlighting the potential downfalls of broadly applying reaction mechanisms that were inferred from kinetic data collected in a narrow range of testing conditions. This study emphasizes the importance of cohesively using kinetic data collected over a wide range of operating conditions to test and formulate kinetic models of electrocatalytic reactions.