Active Sites under Electronic Effect Are More Sensitive to Microenvironment in CO₂ Electroreduction

Tailoring the structure of the active sites and engineering the microenvironment to tune catalytic performance are both at the forefront of catalysis. Yet, design principles bridging the two remain missing. Here, we synthesize a platform consisting of well-defined cubic Cu nanocrystals with an oxide coating of tunable porosity, here alumina. We indicate that varying the porosity modulates the relative importance of the native geometric effect and the introduced interfacial electronic effect. We link the change in porosity to the catalytic behavior in the electrochemical CO₂ reduction reaction. In particular, we use the shift in selectivity as a key descriptor to show that the electronic effect overrules the geometric effect with increasing porosity. We find that a balance between geometric and electronic effects optimizes the intrinsic catalytic reactivity. Importantly, we use this platform to propose that active sites under electronic effect are more sensitive to the change in microenvironment, here exemplified by alkali cations in the electrolyte. The fundamental insights gathered through the proposed catalytic platform stimulate future discussion on linking the nature of the active sites and the microenvironment engineering.