Electrochemical reduction of aryldiazonium salts tin acetonitrile or acidic aqueous medium) on an iron or mild steel surface permits the strong bonding (which resists an ultrasonic cleaning) of aryl groups on these surfaces. Attachment of aryl groups was demonstrated by the combined used of electrochemistry, infrared spectroscopy and polarization modulation infrared reflection spectroscopy (PMIRRAS), Rutherford backscattering, X-ray photoelectron spectroscopy, and capacity measurements. The substituents of aryl groups, which can be widely varied, include NO2, I, COOH, and long alkyl chains. It is shown that the attachment of the aryl groups is to an iron and not to an oxygen atom and that the bond is covalent.