Electrografting of stainless steel by the diazonium salt of 4-aminobenzylphosphonic acid

Stainless steel has been widely used in areas such as automotive, aeronautics, marine industry, biomedical. Particularly for the processes but also for many other industrial applications, the corrosion resistance of stainless steel needs to be improved. As well-known, surface functionalization with mono- and multi-layers of organic materials is a promising solution to prevent corrosion of metal surfaces and stainless steel as well. This paper concentrated on developing a simple one-step method to strongly attach an efficient organic inhibitor to stainless steel substrate. Benzylphosphonic acid has been reported to be easily grafted on stainless steel surface by electroreduction of the diazonium salt of 4-aminobenzylphosphonic acid in sulphuric acid medium at low reduction potential (−0.01 vs. (Ag/AgCl)/V). In combination with XPS measurements, electrochemical impedance spectroscopy recorded in sulphuric acid and sodium chloride solutions containing redox probes allowed us to evidence the presence of a polybenzylphosphonic acid covalently coated on the steel surface. The pristine steel and modified surfaces were further characterized by linear sweep voltammetry in order to bring out the anticorrosive ability of the polybenzylphosphonic layer. Beside protection against corrosion, an easy attachment of aryl layer onto stainless steel substrate notwithstanding the presence of many components on its surface, even the isolating one, as reported in this work contributed to enlarge the applications of diazonium chemistry for surface functionalization.