Molecular Cobalt Pentapyridine Catalysts for Generating Hydrogen from Water

Abstract

A set of robust molecular cobalt catalysts for the generation of hydrogen from water is reported. The cobalt complex supported by the parent pentadentate polypyridyl ligand PY5Me₂ features high stability and activity and 100% Faradaic efficiency for the electrocatalytic production of hydrogen from neutral water, with a turnover number reaching 5.5 × 10⁴ mol of H₂ per mole of catalyst with no loss in activity over 60 h. Control experiments establish that simple Co(II) salts, the free PY5Me₂ ligand, and an isostructural PY5Me₂ complex containing redox-inactive Zn(II) are all ineffective for this reaction. Further experiments demonstrate that the overpotential for H₂ evolution can be tuned by systematic substitutions on the ancillary PY5Me₂ scaffold, presaging opportunities to further optimize this first-generation platform by molecular design.