Boosting the Efficiency and Selectivity of Electrocatalytic Reduction of CO₂ to C1 Products by Mn-Porphyrin via Axial Ligation

The urgency to address climate change hinges on developing efficient, selective, low-cost, and durable catalysts for effective CO2 reduction, enabling the conversion of greenhouse gases into valuable resources. This study evaluates the performance of manganese porphyrin (MnPr) and its tailored derivatives that are designed by its axial ligation with imidazole, carbene, and pyridine groups (MnPr-Im, MnPr-NHC, and MnPr-Py) for the electrocatalytic reduction of CO2 into value-added chemicals. The energetics and mechanism of the CO2 reduction reaction (CO2RR) have been explored using the density functional theory-based computational approach. The goal is to devise strategies that improve the CO2RR efficiency while minimizing the competing hydrogen evolution reaction (HER). The primary reduction product is HCOOH, and the minimum overpotential (ηHCOOH) values to lead to this product are 0.22, 0.45, 0.82, and 0.12 V on MnPr, MnPr-Im, MnPr-NHC, and MnPr-Py, respectively. In particular, electrocatalysis by MnPr-Py (ηHCOOH = 0.12 V) surpasses the catalytic activity of the state-of-the-art metal surfaces Pt(111) (η = 0.46 V) and Cu(211) (η = 0.77 V). The in-depth analysis of energy profiles, scaling relationships, electrode potentials, and pH provides a rationalization of the excellent reactivity and selectivity of the designed catalysts for the CO2RR over the competing HER. The study provides conclusive evidence that axial ligation of MnPr provides a highly efficient electrocatalyst that exhibits the advantage of excellent product selectivity, high activity, and minimum overpotential, prompting further experimental investigations in this direction.