Electrocatalytic H₂ Evolution by the Co-Mabiq Complex Requires Tempering of the Redox-Active Ligand

H₂ is a promising fuel for sustainable energy conversion and storage. The development of effective earth abundant H₂ evolution catalysts is integral to advancing hydrogen-based technologies. H₂ evolution by molecular complexes classically involves the formation of metal hydride intermediates. Recently, the use of redox-active ligands has emerged as an alternate strategy for electron and proton storage. Herein, we examine the electrocatalytic behavior of [Co^II(Mabiq)(THF)](PF₆) (Co_Mbq), containing a redox-active macrocyclic ligand, in acidic, organic media (using para-cyanoanilinium (pCA) as the proton source). Cyclic voltammetry (CV) and Rotating Ring Disk Electrode (RRDE) voltammetry evidence a pre-catalytic process that leads to the formation of a protonated, two-electron reduced intermediate. This species evolves H₂ at potentials negative of −1.1 V_Fc, as confirmed by On-line Electrochemical Mass Spectrometry (OEMS). OEMS results further reveal a catalyst deactivation pathway. The electrochemical data denote the involvement of the redox-active Mabiq ligand in the hydrogen evolution reaction (HER), with implications for the use of such scaffolds in electrocatalytic complexes.