Electrochemical formation of thin polyacetonitrile films on a Pt surface

Abstract The modifications occurring on an anodically polarized Pt surface in CH 3 CN-MClO 4 -[M=Li + or N + (R 4 )] or CH 3 CN-LiBF 4 are studied in situ by p.m.t. Under potentiostatic control ( E =2.6 V), formation of a film whose thickness increases over time is observed. For thickness 10–150 nm the friction coefficient is constant ( f =1.5 f 0 ), whereas beyond a thickness of 200 nm, it is very high and fluctuates heavily, thereby expressing not only a major lack of homogeneity in the film surface, but also the weak adherence of the film to the metal substrate. I.r., x.p.s. and s.i.m.s. analysis show the film to be of the polyacetonitrile variety doped with ClO 4 − or BF 4 − ions. When the film is left in a moist atmosphere, partial destruction of the polymer chains occurs and a deposit made up mostly of amides or amide salts is obtained. Polymerization is initiated by radicals ClO 4 . and BF 4 . ; its propagation due to H + ions acting on acetonitrile, leads to the polymer chain Download full-size image . The films are hydrophilic and prove to be heat-resistant when subjected to temperatures up to 200°C for 30 min, but decompose beyond this temperature. Out of the solution these films are non-conductive, but in an electrolytic medium they are highly conductive, as they are easily permeated by the usual ions.