Nickel complexes containing N4 schiff-base macrocycles dereived from diphenylamine-2,2'-dicarboxaldehyde for catalytic CO2 reduction

Abstract

In this dissertation, nickel(II) complexes featuring N4-Schiff base macrocycles derived from diphenylamine-2,2'-dicarboxaldehyde (1-Ni and 2-Ni) with a new crystal structure ([2-Ni]Me) were synthesized and investigated for electrochemical CO2 reduction (ECR). Cyclic voltammetry (CV) of two nickel complexes, 1-Ni and 2-Ni, illustrated the catalytic response whereas one, [2-Ni]Me, virtually remained peak-shaped in the presence of CO2, indicating the feasibility of ECR activity for these nickel complexes. To develop heterogeneous ECR catalysts in aqueous media, all nickel complexes were adhered on N-doped graphene (NG) through non-covalent interaction, obtaining Ni@NG hybrid catalysts. The Ni@NG catalysts showed satisfactory ECR activity with the faradaic efficiency of CO production (FECO) of 60-80% at the overpotential of 0.56 V vs. RHE. The ECR activity of Ni@NG catalysts demonstrated that the necessity of N-H functionality from the ligand is less important in the heterogeneous aqueous system owing to plenty of viable hydrogen-bond and proton donors from water and bicarbonate species. Besides, an unexpected formation of nickel complexes bearing acridine-based Schiff base ligand ([NiLACR]2+) was obtained via the rearrangement of diphenylamine-2,2'-dicarboxaldehyde. In addition, electrochemical properties and hydrogen evolution reaction of the nickel complexes were preliminary investigated.