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

Electrocatalytic CO 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 CO to CO. Both experimental and theoretical results verified that CO 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 current density with 86.8% Faradaic efficiency for generating CO (FE) at -0.76 V vs. RHE in aqueous solution, whereas Cu-salophen/CNT only achieved a -2.22 mA·cm current density and 57.9% FE under the same reaction conditions. These distinct catalytic performances resulted from the different coordination activation abilities of CO on various metal centers.