Investigation of Electrochemical Behavior of Stimulation/Sensing Materials for Pacemaker Electrode Applications

The electrochemical behavior, interfacial properties, and stability of Pt, Ti, smooth and rough TiN electrodes for pacemaker applications were investigated in a phosphate-buffered saline solution, by electrochemical impedance spectroscopy and cyclic voltammetry (CV), as well as surface analysis using scanning electron microscopy and X-ray photoelectron spectroscopy. The influence of surface roughness on charge-transfer characteristics was examined under fast cyclic potential sweeps. The stability of the electrodes was investigated by simulated aging through large numbers of CV cycles between to 1 V vs. open-circuit potential. The results show that these electrodes exhibit different electrochemical behavior, and surface roughness plays an important role. Although the rough-surfaced TiN provides a high interfacial capacitance, the maximum capacitance cannot be fully utilized at high CV sweep rates, because part of the effective surface area is inaccessible. As the sweep rate increases, the current-potential response becomes linear (ohmic) due to the pore-like rough surface. Upon accelerated aging, changes in surface composition and structure occurred to different extents on the electrode materials. Pt and the rough TiN electrodes were stable, whereas Ti and the smooth TiN electrodes were affected, mainly by oxidation of Ti and nitride, but also by H adsorption on Ti.