Co-Co and Co-Zn bimetallic complexes for electrocatalytic CO2 reduction: The role of interrelated intramolecular effects on activity

A key knowledge gap in developing multimetallic architectures for electrochemical CO₂ reduction reaction (CO₂RR) is the difference in per-site activity compared to their molecular catalyst analogs. Here, we have carefully designed a model system of homo- and heterobimetallic catalysts to study how intramolecular effects such as internal electrostatics and electronic coupling influence catalytic activity. We demonstrate that intramolecular electrostatics is a crucial influence on the per-site activity. The larger electrostatics exerted by Zn²⁺ in heterobimetallic [Zn(PDI)-(PDI)Co] results in higher catalytic activity for CO₂RR compared to the other catalysts, especially compared to the parent monometallic [Co(PDI)]: > 2 orders of magnitude larger TOF_cat and > 7 orders of magnitude larger TOF₀. Notably, replacing a possible Co active site in homobimetallic [Co(PDI)-(PDI)Co] with a redox-inert Zn²⁺ leads to an increase, not decrease, in activity, which provides a promising design strategy for multimetallic assemblies incorporating both redox-active and redox-inert metal sites.