A study on the electrochemical behaviour of polypyrrole films in concentrated aqueous alkali halide electrolytes

The electrochemical behaviour of polypyrrole films doped with dodecyl benzene sulfonate (PPy/DBS) in LiCl aqueous electrolytes has been investigated in order to find the electrolyte concentration suitable for the operation of PPy/DBS-based soft actuators. For this investigation, PPy/DBS films deposited on gold-coated quartz crystals by electropolymerization and simultaneous cyclic voltammetry and electrochemical quartz crystal microbalance techniques were used.

During the first redox cycle, while large water movement is observed along with the counter ions in dilute electrolytes, such water transport in concentrated electrolytes is found to be very low. In dilute electrolytes, water molecules accompany counter ions as solvated molecules and due to osmotic effect.

In concentrated electrolytes, water movement is less due to limited availability of free water as well as a smaller osmotic pressure difference. In highly concentrated aqueous electrolytes, the mass of the PPy/DBS film at the end of each redox cycle is found to drift, which can be controlled by changing the concentration of the electrolyte.

The PPy/DBS films were also cycled at different scan rates in various alkali halide aqueous electrolytes of concentrations 0.1 and 1 M to determine the effective diffusion coefficients of alkali ions in the films. The effective diffusion coefficients were found to increase with the concentration of the electrolytes and decrease with the increase in size of cations.