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

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 -ik = 1 mA cmgeom(-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.