NATURE OF ION SENSITIVITY OF POLYPYRROLE ELECTRODES

The ion sensitivity of polypyrrole (PPy) films deposited electrochemic ally onto Pt, glassy carbon and SnO2 substrate was studied by potentio metric measurements. The influence of electrochemical (overoxidation, reduction and potentiodynamic cycling) and chemical (alkaline solution ) pre-treatment on the potentiometric behaviour of PPy electrodes was determined. The dependence of the potential of the PPy electrode after long-term conditioning on the log of electrolyte activity of conditio ning solution is characterised by low negative (solutions of NaSCN, Na NO3, KCl, or NaF) and low positive (Cd2SO4, Na2SO4 or Li2SO4) slopes. The exceptionally low exchange rate of anions between sulphate-doped P Py films and solution was established by electron probe microanalysis. Short-term (2-5 min) potential responses of PPy electrodes to the cha nge of composition and concentration of electrolyte were studied. PPy electrodes conditioned in NaSCN, NaNO3, KCl, and NaF solutions possess anion sensitivity, and electrodes conditioned in Cs2SO4, Na2SO4 and L i2SO4 solutions, cation sensitivity, independent of the composition of the solution used for the preparation of the PPy film. The short-term response is generally not selective and depends on the arrangement of the ions in the Hofmeister lyophilic series. This potential response is interpreted as the result of asymmetric movement of anions or catio ns through the PPy solution boundary.