Electrochemical Characterization of Commercial Electroencephalography Bioelectrodes in Isotonic Saline Solution

The electrochemical performance of eight commercially available bioelectrodes for electrophysiological measurements was systematically evaluated in isotonic saline solution. The studied bioelectrodes included sintered Ag/AgCl pellet, cup and ring, an Ag/AgCl multipin, tin (Sn) ring and disc, a gold cup, and a stainless-steel needle. Open circuit potential (OCP) and drift rate, electrochemical impedance spectroscopy (EIS), and electrochemical noise (ECN) measurements were performed to assess interfacial stability, impedance behavior, and generated noise in time and frequency domains. Scanning electron microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDS) were used to study the morphology and chemical composition of the bioelectrodes. Ag/AgCl-based bioelectrodes exhibited the highest OCP stability and potential reproducibility, lowest impedance, and electrochemical noise, attributed to the fast and reversible Ag/AgCl electrochemical equilibrium, and high area related to roughness and porosity. EIS analysis showed predominantly low-resistance charge-transfer behavior and high capacitance for Ag/AgCl bioelectrodes, while tin, gold, and stainless-steel bioelectrodes displayed higher impedance and mixed capacitive/resistive responses associated with passive oxide films and slower interfacial kinetics. Tin, gold, and stainless-steel bioelectrodes also presented substantially higher low-frequency noise and OCP drift rate. Among all tested bioelectrodes, sintered Ag/AgCl bioelectrodes demonstrated the most favorable electrochemical characteristics for electrophysiological signal acquisition, particularly for low-amplitude and low-frequency biosignals.