Formation of a Dodecanethiol Film on an Oxide-Free Nickel Electrode from Aqueous and Aqueous-Alcoholic Solutions Under Electrochemical Control

In contrast to gold, ferromagnetic metals have a strong tendency toward oxidization in air and solutions. The self-assembly of alkanethiols on these metals is limited by difficulties connected with the presence of oxide films on the surface. Oxide-free Ni surfaces are prepared by electrochemical reduction of the superficial oxide. To create dodecanethiol (DDT) self-assembled monolayers (SAMs) on oxide-free nickel surfaces, we combine the techniques of surface renewal by the electrochemical procedure of removing the native oxide, thiol adsorption, and electrochemical control of SAMs properties in a thiol-containing aqueous solution. The electrochemical adsorption of DDT is monitored using chronoamperometry, and SAMs are characterized by cyclic voltammetry. The electrochemical self-assembly of DDT on Ni and the insulating properties of DDT SAMs strongly depend on the contact time of the electrode with a thiol-containing solution, the concentration of DDT in the solution, and the presence of dissolved oxygen. The introduction of ethanol into a dodecanethiol-containing solution of sodium perchlorate leads to the substantial acceleration of DDT self-assembly on nickel. The best insulating properties of Ni/DDT electrodes are obtained in aqueous-alcoholic solutions with an ethanol concentration of 40-60%. The approach used in this study allows one to use aerated low-concentration thiol-containing solutions for preparing electrochemically stable DDT films that well insulate the Ni surface within a broad potential range. The electrochemical self-assembly of dodecanethiol on an oxide-free nickel electrode from aqueous and aqueous-alcoholic solutions can be an effective way to modify Ni surfaces.