Heterogeneous Nature of Electrocatalytic CO/CO₂ Reduction by Cobalt Phthalocyanines

Graphical Abstract

It is not what it seems: The electrocatalytic reduction of CO to methanol and CO₂ to CO by soluble cobalt phthalocyanine derivatives in aqueous media can be predominantly attributed to adsorbed molecules on the electrode surface and is therefore heterogeneous in nature.

Abstract

Molecular catalysts for electrochemical CO₂ reduction have traditionally been studied in their dissolved states. However, the heterogenization of molecular catalysts has the potential to deliver much higher reaction rates and enable the reduction of CO₂ by more than two electrons. In light of the recently discovered reactivity of heterogenized cobalt phthalocyanine molecules to catalyze CO₂ reduction into methanol, direct comparison is needed to uncover the distinct catalytic activity and selectivity in homogeneous catalysis versus heterogeneous catalysis. Herein, soluble cobalt phthalocyanine derivatives were synthesized, and their catalytic activities in the homogeneous solutions were evaluated. The results show that the observed catalytic activities for both CO₂-to-CO and CO-to-methanol conversions in aqueous solutions of the cobalt phthalocyanines are predominantly heterogeneous in nature through the adsorbed species on the electrode.