Fe-Porphyrin-Based Metal-Organic Framework Films as High-Surface Concentration, Heterogeneous Catalysts for Electrochemical Reduction of CO₂

Realization of heterogeneous electrochemical CO₂-to-fuel conversion via molecular catalysis under high-flux conditions requires the assembly of large quantities of reactant-accessible catalysts on conductive surfaces. As a proof of principle, we demonstrate that electrophoretic deposition of thin films of an appropriately chosen metal-organic framework (MOF) material is an effective method for immobilizing the needed quantity of catalyst. For electrocatalytic CO₂ reduction, we used a material that contains functionalized Fe-porphyrins as catalytically competent, redox-conductive linkers. The approach yields a high effective surface coverage of electrochemically addressable catalytic sites (∼10¹⁵ sites/cm²). The chemical products of the reduction, obtained with ∼100% Faradaic efficiency, are mixtures of CO and H₂. These results validate the strategy of using MOF chemistry to obtain porous, electrode-immobilized, networks of molecular catalysts having competency for energy-relevant electrochemical reactions.