Long-term characterization of electrode materials for surface electrodes in biopotential recording.

The long-term electrical behavior of 16 different electrode materials was investigated by using continuous impedance spectroscopy over a period of 10 days. The materials included bare and electrolytically treated metals, metals coated with intrinsically conductive polymers, and polymers with conductive particles. Electrolytic treatment of metal electrodes yielded a significant impedance reduction. The lowest impedance values could be reached with the polymer-coated metal electrodes. The impedance behavior is an important aspect when choosing an electrode material, and has to be considered in signal processing. The choice of a material depends on the application of the electrode. Moreover, for long-term applications, the electrochemical stability of a material has to be considered.