The electrochemical reduction of diazonium salts on iron electrodes. The formation of covalently bonded organic layers and their effect on corrosion

Electrochemical reduction of aryldiazonium salts on an iron electrode in acetonitrile leads to the attachment of aryl groups to the iron surface. We investigated aryl groups substituted with 4-alkyl chains (-CH3, -C4H9, -C12H25, -OC12H25, -OC16H33), with 4-halogeno substituents (-I, -F, -CF3, -OCF3, or -C6F13), or with five fluorine atoms (pentafluoro phenyl, -C6F5). Attachment of these groups was characterized by FTIR, XPS, and capacity measurements. It is shown by measuring the polarization resistance and the corrosion current that these layers provide a significant protection against corrosion.