One-step formation of ultra-thin chemically functionalized redox-active Langmuir–Schaefer Nafion films

Abstract

A novel “one-step procedure” to incorporate different cationic redox-active species within ultra-thin Nafion films is reported. Ultra-thin films of Nafion containing trimethylammonioferrocene (FA⁺), tris(2,2′-bipyridyl)ruthenium(II), Ru(bpy)₃²⁺, and hexaaminoruthenium(III), [Ru(NH₃)₆]³⁺, were prepared using the Langmuir–Schaefer (LS) technique. The morphology and thickness of the films were evaluated with atomic force microscopy (AFM). Film thicknesses were 1.9 ± 0.7, 1.8 ± 0.9, 1.5 ± 0.9 nm per layer for Nafion–FA⁺, Nafion–Ru(bpy)₃²⁺and Nafion–[Ru(NH₃)₆]³⁺, respectively. Electrochemical data confirmed the successful incorporation of the mediators into the films and proved that the redox activity was maintained during extensive voltammetric cycling. Key parameters such as surface coverage, concentration of the mediator within the films and apparent diffusion coefficients were extracted using cyclic voltammetry. To demonstrate the utility of the redox-active films for sensing applications, films with Ru(bpy)₃²⁺ incorporated were utilized for the electrocatalysis of oxalate in aqueous solution.