Potential-Dependent Selectivity in CO2 Electroreduction over Carbon-Supported Cobalt Phthalocyanine

Abstract

Cobalt phthalocyanine (CoPc)-functionalized carbon nanotubes (CoPc/CNT) exhibit exceptional performance in the electrochemical reduction of CO2 to produce methanol, yet the atomistic origin of its potential-dependent selectivity remains elusive. Here, we employ grand canonical ensemble density functional theory calculations to unravel the potential-dependent reaction mechanisms over CoPc/CNT. We reveal that under reducing conditions, the catalyst undergoes structural evolution, with the ligand being preferentially hydrogenated to form a stable CoPcH4 species. Crucially, a potential-driven reduction of the metal center from Co(II) to Co(I) acts as an electronic trigger, dramatically enhancing CO binding affinity and enabling deep reduction. Furthermore, the product selectivity is governed by two key factors: potential-dependent surface charge accumulation induces electrostatic repulsion that modulates the stability of the formaldehyde intermediate; and the production of methane is thermodynamically prohibited due to the geometric inability of the isolated cobalt single site to stabilize the residual oxygen adatom (*O) upon C−O bond cleavage. These findings provide a unified mechanistic understanding of methanol synthesis on molecular catalysts, highlighting the pivotal roles of dynamic electronic states and local geometric constraints in directing reaction pathways.