Electrostatic Secondary-Sphere Interactions That Facilitate Rapid and Selective Electrocatalytic CO2 Reduction in a Fe-Porphyrin-Based Metal-Organic Framework

Metal-organic frameworks (MOFs) are promising platforms for heterogeneous tethering of molecular CO2 reduction electrocatalysts. Yet, to further understand electrocatalytic MOF systems, one also needs to consider their capability to fine-tune the immediate chemical environment of the active site, and thus affect its overall catalytic operation. Here, we show that electrostatic secondary-sphere functionalities enable substantial improvement of CO2-to-CO conversion activity and selectivity. In situ Raman analysis reveal that immobilization of pendent positively-charged groups adjacent to MOF-residing Fe-porphyrin catalysts, stabilize weakly-bound CO intermediates, allowing their rapid release as catalytic products. Also, by varying the electrolyte's ionic strength, systematic regulation of electrostatic field magnitude was achieved, resulting in essentially 100 % CO selectivity. Thus, this concept provides a sensitive molecular-handle that adjust heterogeneous electrocatalysis on demand.

Automated summary

This study demonstrates the significant enhancement of CO2 reduction activity and selectivity by electrostatic secondary-sphere functionalities in MOF materials. In situ Raman analysis reveals that immobilizing pendent positively-charged groups adjacent to MOF-residing Fe-porphyrin catalysts stabilizes weakly-bound CO intermediates and allows for control of the catalytic reaction by varying the ionic strength of the electrolyte.