Electrocatalytic Reduction of CO2 to CH4 and CO in Aqueous Solution Using Pyridine-Porphyrins Immobilized onto Carbon Nanotubes

Electrochemical reduction of carbon dioxide (CO2) is a sustainable solution to conversion of CO2 into value-added products such as hydrocarbons and carbon monoxide (CO). However, designing high-efficiency molecule-based electrocatalysts is challenging. In this work, we designed and synthesized iron-porphyrin-pyridine (Fe-TPPy) catalysts in a strategy that combined molecular design and a nanoscale approach. The catalytic activity of these compounds toward CO2 reduction was evaluated under both homogeneous and heterogeneous conditions. Tuning of Fe-TPPy with anisole electron-donating substituents improved the catalytic efficiency up to 76% with a current density of -1.3 mA/cm(2) and a turnover frequency (TOF) of 1 s(-1). The faradaic efficiency was further enhanced to 92% with a current density of -30 mA/cm(2) and a TOF of 5 s(-1) after immobilization of the porphyrins onto carbon nanotubes. Density functional theory calculations confirmed that the push-pull pyridine-anisole interaction facilitates CO2 binding, resulting in an enhancement of the overall catalytic efficiency. This work provides an effective strategy for improvement of electrocatalytic performance that could inspire the design of future molecular catalysts.