Heterogenizing molecular catalysts within multidimensional architectures is a promising strategy of developing new catalytic materials for the electrochemical CO2 reduction reaction (CO2RR). The goal is to develop multidimensional catalyst architectures that maintain the selectivity of discrete, molecular catalysts, but also possess high activity and stability of multi-site heterogeneous materials. However, developing such systems requires us to first understand how the interactions between molecular building units influence catalytic activity and selectivity in multimetallic assemblies. To this end, we have synthesized a series of homo- and heterobimetallic Co complexes with pyridyldiimine (PDI)-based ligands to investigate the interactions between the discrete building units. Through cyclic voltammetry and electrocatalytic studies, we have identified three interactions between molecular units: charge delocalization across the extended bimetallic structure, electronic coupling between the catalyst active sites, and intramolecular electrostatic effects. The catalytic activity of the homobimetallic bi-[Co(PDI)] complex is more than an order of magnitude higher than that of the monometallic parent complex, [Co(PDI)], due to the effects of these interactions. Through systematic modifications of the monometallic and bimetallic systems, we evaluated the individual effects of each interaction and concluded that the intramolecular electrostatic effects are likely the largest influence on the increased activity in the bimetallic systems. In particular, an extended bimetallic complex with weaker electronic coupling (bi-ex-[Co(PDI)]) has slight difference in catalytic activity compared to bi-[Co(PDI)]; whereas another bimetallic complex with mainly electrostatics (bi-[ZnCo(PDI)]) exhibits around two times higher activity than that of bi-[Co(PDI)]. DFT calculations of CO2 binding modes are also consistent with the observed electrochemical results. Our work highlights a promising catalyst design strategy for heterogeneous, multidimensional architectures in which catalytic capacity is enhanced by incorporating intramolecular electrostatics into the backbone of multidimensional structures.

Multidimensional catalyst architectures: Effects of interactions between molecular catalytic units on electrocatalytic CO2 conversion

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