Electrolyte-modulated electrochemistry and electrocatalysis on ferrocene-terminated polyelectrolyte brushes

We prepared a responsive polyelectrolyte (ferrocene-terminated poly[1-ethyl 3-(2-methacryloyloxyethyl)imidazolium chloride], PEMEImCl) brush on an Au surface through a three-step procedure consisting of surface-initiated atom transfer radical polymerization, followed by treatment with NaN₃ and by a reaction with ethynylferrocene via azide-alkyne Huisgen cycloaddition reaction, known as 'click' chemistry. The interfacial resistance of the polyelectrolyte brush was characterized with electrochemical impedance spectroscopy (EIS) using [Fe(CN)₆]^3-/4- as the redox probe in different electrolyte solution. Moreover, the redox behavior of ferrocene (Fc) at the terminus of polyelectrolyte brushes in different electrolyte solutions was characterized by cyclic voltammetry (CV). The electrochemical properties depended on the distance between redox probes (Fc at the terminus) and the substrate, which were affected by the conformation of the polyelectrolyte brush triggered by external environments. The electrocatalysis behavior of the Fc-terminated polyelectrolyte brush also can be modulated via the conformation of the brush. It is interesting that all the electrochemical behavior of the polyelectrolyte brush can be mediated by the kind and concentration of anion.