The effect of extended conjugation on electrocatalytic CO2 reduction by molecular catalysts and macromolecular structures

Homogenous molecular catalysts have shown significant promise for the selective reduction of CO2 to single products. However, their practical application in emerging CO2 reduction technologies is hindered by their limited solubility and stability in aqueous solutions, their diffusion-dependent kinetics, and their poor recyclability. Incorporating discrete molecular catalysts into macromolecular architectures such as covalent organic frameworks is one solution to these limitations that allows for the synthesis of heterogeneous materials with increased activity and stability but that still maintain the selectivity and active-site tunability of discrete molecular catalysts. Forming such macromolecular materials necessarily extends the ligand pi-conjugated network, which can have important effects on the electrocatalytic activity. In this review, we discuss recent studies on the effect of extended pi-conjugation on the catalytic activity of molecular catalyst and extended macromolecular architectures, with an emphasis on how activity is influenced by charge delocalization, electrostatic effects, and electronic coupling between active sites.