(124a) The Electrochemical Kinetics of Hydrocarbon Synthesis from CO2: A Unified Picture of Surface Intermediates and Their Interaction with Electrolyte Ions

Producing fuels and chemicals from CO₂promises to close the anthropogenic carbon cycle. However, the synthesis of attractive hydrocarbon products such as ethylene and methane still requires high overpotentials and is plagued by low selectivity. In this talk, I will shed light onto the catalytic networks which govern the electrosynthesis of hydrocarbons and will show how this understanding allows us to rationally control hydrocarbon selectivity and overpotentials.

Kinetic and spectroscopic studies of CO₂ reduction have been limited to aqueous environments where water serves as both the solvent and proton donor. This constrains fundamental investigations by precluding control of proton transfer kinetics, limiting the alkalinity to the pKa of water and rendering independent studies of solvent effects impossible. To overcome these limitations, we designed non-aqueous model systems. These environments allowed us to precisely control the structure of electrochemical interfaces and elucidate their impact on the electrochemical kinetics of CO₂ and CO reduction reactions. Through precise structure activity-relationships we were able to identify the rate-limiting steps governing the electrosynthesis of hydrocarbons, as well as the fundamental origin of the impact of electrolyte cations on CO₂ reduction processes. Our data also demonstrate that selectivity between methane, ethylene and parasitic hydrogen generation is governed by competition between adsorbed H and CO for surface sites. Based on our findings, I will show how the variation of proton donor pKa values opens a new avenue for controlling hydrocarbon selectivity in the electrochemical reduction of CO.

Finally, I will present evidence that the mechanism observed in our non-aqueous model systems is preserved in aqueous environments and will show how our kinetic insights enable rational control of catalyst materials with high selectivity towards ethylene formation.