Axial Modification of Cobalt Complexes on Heterogeneous Surface with Enhanced Electron Transfer for Carbon Dioxide Reduction

Efficient electron communication between molecular catalyst and support is critical for heterogeneous molecular electrocatalysis and yet it is often overlooked during the catalyst design. Taking CO₂ electro-reduction on tetraphenylporphyrin cobalt (PCo) immobilized onto graphene as an example, we demonstrate that adding a relay molecule improves the interfacial electron communication. While the directly immobilized PCo on graphene exhibits relatively poor electron communications, it is found that diphenyl sulfide serves as an axial ligand for PCo and it improves the redox activity of PCo on the graphene surface to facilitate the generation of [PCo]^.- active sites for CO₂ reduction. Thus, the turnover frequencies of the immobilized Co complexes are increased. Systematic structural analysis indicates that the benzene rings of diphenyl sulfide exhibit strong face-to-face stacking with graphene, which is proposed as an efficient medium to facilitate the interfacial electron communication.