The growth and the surface properties of polypyrrole on single crystal graphite electrodes as studied by insitu electrochemical scanning probe microscopy


1 Introduction 150

2 Experimental 151

3 Results and discussion 152

4 Conclusions 156

5 References 157

Summary. The growth of polypyrrole (PPy) films on highly oriented pyrolytic graphite (HOPG) electrodes is investigated by in-situ electrochemical scanning tunneling microscopy (STM) and in-situ atomic force microscopy (AFM) both applied in modified electrochemical cells. The PPy film formation at electrodes is studied in aqueous solutions with and without phosphate buffer in the range of pH 5 and pH 7 and with toluene-4-sulfonic acid (tosylate) as supporting electrolyte. Polymer films produced at lower pH are much smoother than films produced in buffer-free solution, i.e., they show a lower surface roughness. At pH 7 no film deposition can be observed. All films are deposited under conditions of low current density where the first nucleation centers are formed at a close distance to steps on the HOPG surface. These nuclei are in the nanometer range. Their growth leads to islands of PPy with a surface area in the micrometer range during the polymerization. Entire PPy films deposited at the electrode were studied in blank electrolyte solutions with respect to their surface morphology. A dependence of the PPy surface roughness on the applied electrode potential was found caused by surface processes in the PPy film.

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