Linkage Effect in the Heterogenization of Cobalt Complexes by Doped Graphene for Electrocatalytic CO2 Reduction

Immobilization of planar Co-II-2,3-naphthalocyanine (NapCo) complexes onto doped graphene resulted in a heterogeneous molecular Co electrocatalyst that was active and selective to reduce CO2 into CO in aqueous solution. A systematic study revealed that graphitic sulfoxide and carboxyl dopants of graphene were the efficient binding sites for the immobilization of NapCo through axial coordination and resulted in active Co sites for CO2 reduction. Compared to carboxyl dopants, the sulfoxide dopants further improved the electron communication between NapCo and graphene, which led to the increase of turnover frequency of the Co sites by about 3 times for CO production with a Faradic efficiency up to 97 %. Pristine NapCo in the absence of a graphene support did not display efficient electron communication with the electrode and thus failed to serve as the electrochemical active site for CO2 reduction under the identical conditions.