In situ Electropolymerized 3D Microporous Cobalt‐Porphyrin Nanofilm for Highly Effective Molecular Electrocatalytic Reduction of Carbon Dioxide

Abstract Electrocatalytic CO₂ reduction reaction (CO₂RR) based on molecular catalysts, for example, cobalt porphyrin, is promising to enhance the carbon cycle and mitigate current climate crisis. However, the electrocatalytic performance and accurate evaluations remain problems because of either the low loading amount or the low utilization rate of the electroactive CoN₄ sites. Herein a monomer is synthesized, cobalt(II)‐5,10,15,20‐tetrakis(3,5‐di(thiophen‐2‐yl)phenyl)porphyrin (CoP), electropolymerized onto carbon nanotubes (CNTs) networks, affording a molecular electrocatalyst of 3D microporous nanofilm (EP‐CoP, 2–3 nm thickness) with highly dispersed CoN₄ sites. The new electrocatalyst shortens the electron transfer pathway, accelerates the redox kinetics of CoN₄ sites, and improves the durability of the electrocatalytic CO₂RR. From the intrinsic redox behavior of CoN₄ sites, the effective utilization rate is obtained as 13.1%, much higher than that of the monomer assembled electrode (5.8%), and the durability is also promoted dramatically (>40 h) in H‐type cells. In commercial flow cells, EP‐CoP can achieve a faradic efficiency for CO (FE_CO) over 92% at an overpotential of 160 mV. At a higher overpotential of 620 mV, the working current density can reach 310 mA cm⁻² with a high FE_CO of 98.6%, representing the best performance for electrodeposited molecular porphyrin electrocatalysts.