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

Abstract

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 [CoII(Mabiq)(THF)](PF6) (CoMbq), 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\u2005VFc, 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.