Investigating the Intrinsic Activity, Nature, and Deactivation Pathway of a Carbon-Nanotube-Confined Molecular Co Catalyst for CO ₂ Reduction

Cathodes functionalized using molecular catalysts represent a promising approach for the efficient conversion of CO₂ into valuable products, with the potential to meet the performance metrics relevant to industrial applications. However, assessing the intrinsic activity of the metal center while maintaining the structure of the catalyst's molecular scaffold during electrolysis still remains a challenge. This work focuses on the in-depth characterization of a tetraaza-macrocyclic cobalt complex-based molecular cathode, from gaining a more accurate description of the catalyst's performance metrics to the investigation of its probable deactivation pathway during electrocatalytic CO₂ reduction (CO₂RR). Importantly, our findings confirm that lowering the surface concentration of the catalyst allows reaching a catalytic regime where the activity is not anymore limited by mass transport within the porous multiwalled carbon nanotube film but by the intrinsic activity of the immobilized catalyst, therefore allowing us to determine its TOF_max value of 4.9 s^-1. We propose that at least two populations of catalysts are present at the electrode surface, with variable contributions to the electrocatalytic process. Post <i>operando</i> studies provide key insights on the deactivation process of the immobilized catalyst via hydrogenation of both imine functions followed by demetallation.