Reactivating Molecular Cobalt Catalysts for Electrochemical CO2 Conversion to Methanol

Abstract

Molecular catalysts immobilized on a carbon support have demonstrated electrocatalytic CO₂ conversion capabilities distinct from those of metallic surfaces. For instance, cobalt phthalocyanine supported on carbon nanotubes (CoPc/CNT) is capable of selective CO₂-to-methanol conversion with ∼30% selectivity, which cannot be accomplished by other metal catalysts, such as cobalt, silver, and copper. However, despite its promising methanol selectivity, the CoPc/CNT catalyst exhibits a gradual decrease in the methanol production rate during the electrochemical CO₂ reduction reaction (CO₂RR). This catalytic instability impedes its practical application, yet little is known about the origin of the activity decay and viable solutions to circumvent it. In this study, we show that the catalytic deactivation is not an irreversible process caused by the chemical degradation of the catalyst and present reactivation strategies to recover the catalytic performance for stable methanol production. We propose that formaldehyde, an intermediate generated during the CO₂RR, can act as a poisoning species, and its adsorption configuration on the cobalt site can determine the fate of its reaction pathway: carbon-down (*CH₂O) versus oxygen-down (*OCH₂) pathways. In contrast to the carbon-down configuration leading to methanol production, the oxygen-down configuration can inhibit its further reduction, poisoning the cobalt active site and causing the deactivation.