Study on Horn-Shaped Polypyrrole Electrodes Prepared By Pulse Potential

Recently, many research in alternative biopotential sensor technologies for electrocardiograms (ECG) and electroencephalograms (EEG) applications was carried out due to skin irritation or inflammations often caused by the conventional Ag/AgCl electrode. The electrode material is a key to development of new biopotential sensor. Polypyrrole (PPy) is considered as one of most potential electrode material for biopotential sensor and artificial muscles due to its high electronic conductivity, long-term environmental stability, environmental friendliness and the relatively easy synthesis process. The preparation of PPy electrode by electrochemical method offers several advantages including high conductivity, easy controllability of its thickness and morphology However, this method does not provide horn with high distribution density on the surface of PPy film. Thus, further development of this method is needed.

Polypyrrole (PPy) films were prepared by direct current (DC), pulse current (PC) and pulse potential (PP) in aqueous solutions. The scanning electron microscope (SEM) images of PPy films indicated that a lot of horn-shaped PPy was formed during PP-PPy polymerization process. The top-end of horn-shaped PPy exhibits both open and closed structures. The body of horn-shaped PPy has a hollow structure with a thin wall. The micelles composed by PPy monomer and p-toluenesulfonate anions (PTS^-) was formed when pyrrole monomer was dispersed in aqueous solution containing PTS^- anions by mechanical stirring. In PP polymerization, the micelles with negative charge were repelled and hence leave the surface of PPy films at switch off time. As a result, the PTS^- anions on the surface of micelles were effectively supplied, and thus stabilized the micelles. This process results in the continuous growth of horn-shaped PPy. The hollow horn-shaped PPy films showed big specific capacitance, high charging/discharging rate and better stability.