Electrocatalytic Hydrogen Evolution in Acidic Water with Molecular Cobalt Tetraazamacrocycles

A series of water-soluble molecular cobalt complexes
of tetraazamacrocyclic
ligands are reported for the electrocatalytic production of H2 from pH 2.2 aqueous solutions. The comparative data reported
for this family of complexes shed light on their relative efficiencies
for hydrogen evolution in water. Rotating disk electrode voltammetry
data are presented for each of the complexes discussed, as are data
concerning their respective pH-dependent electrocatalytic activity.
In particular, two diimine–dioxime complexes were identified
as exhibiting catalytic onset at comparatively low overpotentials
relative to other reported homogeneous cobalt and nickel electrocatalysts
in aqueous solution. These complexes are stable at pH 2.2 and produce
hydrogen with high Faradaic efficiency in bulk electrolysis experiments
over time intervals ranging from 2 to 24 h.