Spiro-linked hanging group cobalt phthalocyanine for CO2-to-methanol electrocatalysis unveiled by grand canonical density functional theory

Abstract

Heterogeneous cobalt phthalocyanine (CoPc) is one of the few favorable molecular catalysts for the electrocatalytic reduction of carbon dioxide to methanol. In-plane substituent modification of planar conjugated phthalocyanine ligands is a key way to establish the structure-activity relationship and enhance the catalytic performance of cobalt phthalocyanines. While steric hanging substituents inspired by efficient enzymes' catalytic architectures are prevalent in metalloporphyrin systems, their application in metal phthalocyanines remains underexplored. Herein, we carried out a systematic constant potential theoretical study on heterogeneous hanging group substituted CoPc electrocatalytic carbon dioxide reduction reaction. Notably, a phenol-based hanging group-modified tetra amino cobalt phthalocyanine was found to have excellent activity and selectivity for the methanol production. Intriguingly, the hanging group substituent connects to the ligand through a spirocyclic structure (rather than the conventional C-N single bond), which can reduce spatial steric hindrance and maintain hydrogen bonding. The phenolic H atoms in the hanging group form effective hydrogen bonds with the O atoms in the key structures of *CHO and *CH₂O, resulting in a strong stabilizing effect that facilitates the selectivity-determining *CO → *CHO and rate-determining *CHO → *CH₂O over a wide potential range. Our findings offer a theoretically effective hanging group substituent for metal phthalocyanine catalysts, broadening the scope and complexity of substituent design.