Insight into Impacts of π-π Assembly on Phthalocyanine Based Heterogeneous Molecular Electrocatalysis

Electrochemical CO₂ reduction (CO₂R) to feedstocks competes with the hydrogen evolution reaction (HER). Cobalt phthalocyanine (CoPc) immobilized onto carbon driven by π-π interaction represents a classical type of heterogeneous molecular catalyst for CO₂R. However, the impacts of π conjugation on the electrocatalysis have not been clarified. Herein, the electrochemical properties of CoPc were investigated by comparison of its analogue to 2,3-naphthalocyanine cobalt (NapCo) having extended π conjugation. It is found that CoPc is redox-active on carbon to provide low oxidized Co sites for improving the CO₂R activity and selectivity, while NapCo on carbon turned out to be redox-inert leading to lower performance. In addition, the redox-mediated mechanism for CO₂R on CoPc tends to operate with increasing electrolyte alkalinity, which further enhances the reaction selectivity. We speculated that moderate π conjugation allows the redox-mediated mechanism on CoPc, which is critical to promote CO₂R performance while depressing the competing HER.