Controlled activation of iridium film for AIROF microelectrodes

The electrochemical activation process of the activated iridium oxide film (AIROF) has been investigated on a microelectrode (the geometric surface area is 7850 μm2) with sputtered iridium in physiological saline solution (0.9% NaCl). For one activation cycle, the potential is swept from −1.0 to 1.0 V at 0.05 Hz. The activation process could be controlled by the activation cycles which are characterized by the current–time data, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). After activation, the charge storage capacity of the AIROF microelectrode is 40.07 mC/cm2, which is nearly 24 times more than that of iridium microelectrode. The impedance at 1 kHz of the AIROF microelectrode is 4064 Ω, about one-tenth of that of iridium microelectrode. The double layer capacitance of the AIROF microelectrode is 1.519 μF, about 34.5 times more than that of iridium microelectrode. The relationship between the electrochemical performance of the AIROF microelectrodes and the applied activation cycles is also investigated. In the neutral electrolyte at pH 7, the Ir(IV)/Ir(III) surface redox couple exhibits increasing separation of the oxidation/reduction peaks due to the protons released/consumed during the Ir(IV)/Ir(III) redox activity. Finally, the relationship between the separation of the redox peaks and the applied activation cycles is also studied.