A molecular material based on electropolymerized cobalt macrocycles for electrocatalytic hydrogen evolution

Abstract

An electrocatalytic material for the H₂ evolution reaction (HER) in acidic aqueous solution has been prepared by electropolymerization of Co(II) dibenzotetraaza[14] annulene (CoTAA). Chemical analysis by X-ray photoelectron spectroscopy (XPS) confirms that the structural integrity of the [Co^II–N₄] motif is preserved in the poly-CoTAA film. In acetate buffer solution at pH 4.6, an overpotential η = −0.57 V is required to attain a catalytic current density −i_k = 1 mA cm_geom⁻². The faradaic efficiency of poly-CoTAA for the HER is 90% over a period of one hour of electrolysis, but there is a decrease of the apparent concentration of Co sites after prolonged H₂ production, which we ascribe to partial demetallation of the poly-CoTAA film at negative potentials.