Electrocatalytic Hydrogen Production with a Molecular Cobalt Complex in Aqueous Solution

Herein, we present the synthesis of a cobalt complex with a pentadentate ligand platform and its application in the electrochemical hydrogen evolution reaction (L-CF3=2,6-bis(methoxybis(4-trifluormethyl-1H-imidazol-2-yl)methyl)pyridine). The complex is active in neutral to acidic solvent mixtures containing 50 % water. Electronic tuning in the ligand backbone, that is introduction of electron-withdrawing CF3-groups, shifts the onset potential of the catalytic wave to less negative potentials. NMR and UV/Vis studies indicate that the Co-III complex is deprotonated twice in the ligand backbone under neutral conditions. Reduction is accompanied by protonation, as indicated by pH-dependent CV measurements, and the Co-I state initiates catalysis. The result suggests that the pentadentate ligand is an ideal platform for cobalt catalysts in the oxidative and reductive water splitting reaction.