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 VFc, 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.

Unraveling the catalytic mechanisms of H2 production with thiosemicarbazone nickel complexes

“…Hess and co-workers have reported a cobalt complex where three protons are required, with one of them acting as a pre-catalytic preparation of the complex. 25 This possibility could also take place in the kind of catalysts studied here. Table 2 shows that the p K a for a protonation of the second N d is favorable prior to a second reduction, regardless of the interactions with TFAH.…”

Electrocatalytic Hydrogen Evolution with a Cobalt Complex Bearing Pendant Proton Relays: Acid Strength and Applied Potential Govern Mechanism and Stability

“…Current challenges include the design of new catalytic platforms featuring higher activity together with increased stability. Introduction of proton relays in the second coordination sphere of the metal center − or redox-active ligands − have been proved essential to promote, tune, or enhance catalytic activity. Notable examples involve the control of the formation of cobalt-hydride derivatives as the key active species in catalysis. − Recently, cobalt­(II) polypyridyl complexes have emerged as promising catalysts for hydrogen evolution.…”

The Flexible On-Surface Self-Assembly of a Low-Symmetry Mabiq Ligand: An Unconventional Metal-Assisted Phase Transformation on Ag(111)

“…One of us has previously developed the solution chemistry of a series of mono- and bimetallic Mabiq complexes. Monometallic M-Mabiq complexes (e.g., M = Fe, Co, Ni, Cu, and Zn) with formal oxidation states ranging from 0 to III were isolated. − Our studies demonstrated that both the mono- and bimetallic compounds are photoactive. , Notably, the Co-Mabiq complex acts as an electrocatalyst for H 2 evolution, while Ni-Mabiq enables photocatalytic C–C bond formation. , …”