Redox‐Conjugated Co^II‐Phthalocyanine–Phenazine Polymer as a Robust Catalyst for Efficient Electrochemical CO₂ Conversion

This work reports the synthesis and electropolymerization of 4-aminophenoxy-substituted Co^II-phthalocyanine to prepare a phenazine (PNZ)-bridged Co^II-phthalocyanine polymer as a durable catalyst for heterogeneous electrochemical CO₂ reduction (ECO₂R). At -1.19 V versus normal hydrogen electrode, the ECO₂R under catalysis of the target polymer effectively produces CO with 94% faradaic efficiency (FE_CO), CO partial current density of 5.5 mA cm^-2, and turnover frequency of 1.1 s^-1 over 2 h. Moreover, the polymeric system exhibits remarkably higher stability than the monomeric one by achieving average FE_CO, current density and a turnover number of up to 93%, 7 mA cm^-2 and 5.3 × 10⁵, respectively, along 120-h electrolysis. Variable-frequency square wave voltammetry indicates efficient electron transfer within polymeric bulk through the PNZ linkage, while in situ Raman spectroscopy reveals a higher proportion of electrochemically active Co^I species in the polymer film than the monomer one. In addition, density functional theory calculations using the real-space GPAW framework are conducted to investigate charge penetration in the extended π-conjugated polymer network in comparison to that in the monomeric counterpart. These findings provide valuable insights for the rational design of the robust Co^II-phthalocyanine-based catalyst and contribute to the progress of an efficient CO₂-to-CO conversion.