EQCM STUDIES ON POLYPYRROLE IN AQUEOUS-SOLUTIONS

Electrochemical quartz crystal microbalance (EQCM) studies revealed th at the electrochemical properties of polypyrrole (PPY) in aqueous solu tions are greatly dependent on the solution pH. A PPY film immersed in an aqueous KCl solution shows redox processes which involve not only anion transport but also cation transport if the solution pH is greate r than 3-4, whereas at lower pH values only anion transport prevails a s has been widely recognized. It has been found from comparative studi es using poly(N-methylpyrrole) that protonation and deprotonation at n itrogen atoms of PPY play a key role in the observed pH-dependent elec trochemical behavior. Deprotonated PPY allows transient incorporation of hydrated cations upon reduction in weak alkaline aqueous solutions, followed by slow ejection of the incorporated cations when convention al electrolytes such as KCl and NaClO4 are used, but not in NH4Cl solu tion. Discussion on the cation transport in PPY is made in terms of de protonation and protonation of nitrogen atoms of pyrrole subunits in P PY.