Modulating carbon dioxide activation on carbon nanotube immobilized salophen complexes by varying metal centers for efficient electrocatalytic reduction

Electrocatalytic CO₂ reduction (ECR) into valuable chemicals, especially driven by renewable energy, presents a promising pattern to realize carbon neutrality. Site-isolated metal complexes flourish in the area of ECR as single-atom-like catalysts because of their competent and tailorable activity. In this study, salophen-based metal (Fe, Co, Ni and Cu) complexes were anchored onto carbon nanotubes (CNTs) to construct efficient catalysts for electrochemically converting CO₂ to CO. Both experimental and theoretical results verified that CO₂ activation was the rate-determining step for the catalytic performance of these hybrid molecular catalysts. The coordinate activation ability can be manipulated by varying the metal centers. The as-synthesized Fe-salophen hybrid CNT (Fe-salophen/CNT) shows the best activity and selectivity of -13.24 mA·cm^-2 current density with 86.8% Faradaic efficiency for generating CO (FE_CO) at -0.76 V vs. RHE in aqueous solution, whereas Cu-salophen/CNT only achieved a -2.22 mA·cm^-2 current density and 57.9% FE_CO under the same reaction conditions. These distinct catalytic performances resulted from the different coordination activation abilities of CO₂ on various metal centers.