(326c) Microenvironment and Active Site Tuning for Electrocatalytic CO2-to-Methanol Conversion on Heterogenized Molecular Cobalt Catalyst

With renewable electricity becoming more accessible and affordable, electrochemical approaches powered by renewable energy sources are expected to progressively replace large part of the current fossil fuel-based chemical industry. Among the electrochemical technologies, electrocatalytic CO₂ conversion to value-added products is particularly promising in that it enables carbon negative manufacturing of chemicals and fuels, utilizing CO₂ feedstocks from large emission point sources or direct capture from the atmosphere.

Recently, it has been demonstrated that molecular cobalt catalysts immobilized on a carbon support can selectively produce methanol (e.g., >30% selectivity) from the electrochemical CO₂ reduction reaction (CO₂RR). Methanol is a versatile chemical with wide industrial applications and a high annual demand (over 100 million metric tons per year), which can be used as a liquid energy carrier (e.g., direct methanol fuel cells) and as a small building block to synthesize more complex chemicals in downstream processes (e.g., methanol-to-olefins conversion). To decarbonize the current methanol mass production process by replacing it with electrocatalytic CO₂-to-methanol conversion, the catalytic performance including activity and selectivity needs to be further improved. In this regard, it is fundamentally important to understand (1) how the catalysts interact with their electrocatalytic microenvironment during the reaction and (2) how the active sites can be tailored to further enhance their catalytic performance.

In this talk, I will first discuss the effect of electrolyte cations on the electrocatalytic CO₂-to-methanol conversion. We show that beyond their generally acknowledged intermediate-stabilizing role, cations play a promoting role in a proton-coupled electron transfer (PCET) reaction during the rate-determining step. Through cation-dependent electrocatalytic kinetics analyses, kinetic isotope effect studies, and CO reduction experiments, we identified a rate determining step of the CO₂-to-methanol conversion, uncovering that cations and their hydration environment control the PCET kinetics, providing a proton from the hydration shell. Our study also reveals the complete catalytic cycle of the molecular cobalt catalyst during CO₂-to-methanol conversion. Second, I will discuss molecular functionalization approaches to tune the catalytic active site of the molecular catalyst through inductive effect and further discuss how it controls the catalytic performance. Overall, it will be underlined that clear understanding and careful tuning of both (1) electrocatalytic microenvironment and (2) active site are essential to bring out the full potential of electrocatalysts and realize their practical applications.