Unraveling the Electrochemical Mechanism of Cobalt Phthalocyanine for CO 2 and CO Reduction under Heterogenized Conditions

Cobalt phthalocyanine supported on multiwalled carbon nanotubes (CoPc/MWCNTs) represents a benchmark molecular electrocatalyst for the reduction of CO 2 and CO. However, the exact nature of its redox states and their catalytic functions remains uncertain. In this work, we elucidate the successive electrochemical transformations of CoPc/MWCNTs under Ar, CO 2, and CO atmospheres. Cyclic voltammetry combined with in situ spectroscopic measurements reveals several reduction steps that occur prior to substrate activation. The second reduction is ligand-based and pH-dependent, coinciding with the onset of hydrogen evolution and the formation of a cobalt–hydride intermediate─identified experimentally for the first time. Neither the singly nor doubly reduced CoPc species react with CO 2 or CO, demonstrating that a 2e – /2H + process does not suffice for CO 2 -to-CO conversion or subsequent CO activation at near-neutral pH. Additional overpotentials of approximately 40–90 mV and 350–400 mV are required for CO 2 -to-CO and CO-to-CH 3 OH conversion, respectively. Catalytic activity primarily arises from redox-active CoPc sites, whereas redox-inactive species contribute marginally.