Designing Molecular and Two Dimensional Metalloporphyrin Catalysts for the Electrochemical CO2 Reduction Reaction

A computational investigation of the electrocatalytic CO2 reduction (CO2R) on metalloporphyrin (M-POR) catalysts, featuring varying metal centres (Ni, Fe, Cu, and Co), oxidation states, and anchoring ligands, was conducted using density functional theory calculations. The evaluation of the thermodynamic and electrochemical stability of the M-POR systems concluded that neutral systems are more stable than charged systems, with the doubly reduced systems being the most unstable. The reaction free energy profiles for CO2R to the C1 products CO and HCOOH were computed according to two possible mechanisms: coupled proton-coupled electron transfer (PCET) and proton transfer – electron transfer (PT-ET). The PCET pathways was found to be by far the most favourable, leading to the preferential formation of HCOOH over CO. Among the catalysts, Fe-POR exhibited the best catalytic performance for CO/HCOOH formation. To evaluate competition with the competitive hydrogen evolution reaction (HER), overpotentials of the CO2R and HER were compared for all systems. This comparison, along with the PCET analysis, revealed that most systems favour HCOOH production. The most promising M-PORs were then to generate models of two-dimensional (2D) carbonaceous frameworks, exploring their potential for CO2R, with 2D Fe-PORs being active towards C1 formation.