Electrochemical Self-Assembly of Alkanethiolates on Ni from Acid Solutions: an Electrochemical and X ray Photoelectron Spectroscopy (XPS) Study

M. FONTICELLI; B. BLUM; R. C. SALVAREZZA; G. BENITEZ; N. VASILJEVIC; W. SCHWARZACHER; R. NICHOLS

Manchester

Conferencia; Electrochem09 Conference.; 2009

Alkanethiol Self-assembled monolayers on metal surfaces have attracted increasing interest due to their wide range of application in nanoscience and nanotechnology. These layers are easily self-assembled on Au, Ag and Cu, but fail to be formed on Fe and Ni surfaces due to the presence of stable oxides. Recently, it has been shown that alkanethiol self-assembly can be done on Ni and carbon steel in a one step method involving oxide electroreduction and molecule adsorption in aqueous alkaline solutions. Here, we present results for alkanethiol self-assembly on Ni surfaces using a similar approach but, in this case, using an aqueous acid electrolyte. The electrochemical formation of alkanethiolate self-assembled monolayers (SAMs) on electrodeposited Ni films from alkanethiol-containing aqueous 0.05 M Na2SO4 (pH=3) solutions was studied by XPS and electrochemical techniques. Alkanethiols were adsorbed onto oxide free surfaces, under potential control (E = ‑0.60 V vs, SCE). XPS data analysis of S 2p3/2 signal on butanethiol and hexanethiol surfaces were fitted with three components associated with the following sulphur surface species: sulphide (161.4 eV), thiolate (162.3 eV) and dialkyl disulphide (164 eV). Although the main component corresponds to thiolate (about 67%), a significant amount of sulphide has been found (20±5%), which may be relevant to the electrochemical behavior of the modified surfaces.                 Electrochemical data show that these adlayers exhibit hydrocarbon chain-length dependent barrier properties, like those formed on Au and Ag. In fact, the hydrogen evolution reaction has been clearly hindered when dodecanethiol was adsorbed on Ni.