A Molecular Cobalt Hydrogen Evolution Catalyst Showing High Activity and Outstanding Tolerance to CO and O₂

There is a demand to develop molecular catalysts promoting the hydrogen evolution reaction (HER) with a high catalytic rate and a high tolerance to various inhibitors, such as CO and O₂ . Herein we report a cobalt catalyst with a penta-dentate macrocyclic ligand (1-Co), which exhibits a fast catalytic rate (TOF=2210 s^-1 ) in aqueous pH 7.0 phosphate buffer solution, in which proton transfer from a dihydrogen phosphate anion (H₂ PO₄ ^- ) plays a key role in catalytic enhancement. The electrocatalyst exhibits a high tolerance to inhibitors, displaying over 90 % retention of its activity under either CO or air atmosphere. Its high tolerance to CO is concluded to arise from the kinetically labile character of undesirable CO-bound species due to the geometrical frustration posed by the ligand, which prevents an ideal trigonal bipyramid being established.