In-Situ XAS and Eqcm Investigations of Redox Mechanisms in IrO₂ Thin Film Electrodes

Bio-stimulating electrodes are recognized to be one of the most critical components for implantable biomedical electronic devices. In order to activate neurons for therapeutic functions, a desirable bio-stimulating electrode requires specific attributes including a large amount charge storage and high charge injection capacity along with a low impedance at the operating frequency of the device. Among the many electrode materials studied to date, iridium oxide has emerged as an especially promising candidate with superior characteristics for charge storage, biocompatibility and chemical inertness. In this presentation, we describe our studies on the interrelationships between charge transfer and structural changes in IrO2. In-situ X-ray absorption spectroscopy was used to determine the changes occurring in the oxidation states of IrO2 during cyclic voltammetry (CV) scans. These results are correlated with the structural changes occurring as determined by X-ray diffraction. In addition, we carried out eQCM measurements to better identify the electrochemical reactions associated with the redox peaks generated by the CV scans. The results of this study lead to a much better understanding of the operation of iridium oxide as a bio-stimulating electrode.