Electrocatalytic CO2 Reduction by Self-Assembled Monolayers of Metal Porphyrins

Abstract

The main issue hindering the successful utilization of CO2 electroreduction processes in industry is the lack of selective, durable, and efficient catalysts. We design a new heterogenous molecular architecture for CO2 electrocatalysts by attaching alkyne-terminated metal (Fe, Co) porphyrins via click chemistry to azide-terminated alkyl phosphate self-assembled monolayers (SAMs) on ITO and FTO electrodes. The electrochemistry of these CO2 reduction systems is studied using cyclic voltammetry and chronoamperometry, and products are quantified through NMR and GC techniques. Additionally, AFM is used to characterize the morphology of the electrode surfaces. Experiments show that CO2 reduction is highly sensitive to the surrounding environment and choices of electrode, SAM length, metal porphyrin or external potential greatly affect reduction products. Our results indicate that FTO is a more electrochemically stable substrate and an intermediate length SAM such as an 11 carbon chain length optimize CO2 reduction conditions towards formate and carbon monoxide with our metal porphyrins. The chemical tunability of SAMs allows for a high degree of control over the surface modification of CO2 electrocatalysts, potentially enabling the design of superior catalysts.