Polarization of AIROF Microelectrodes in Charge Delivery

Activated iridium oxide film (AIROF) microelectrodes have high charge delivery capacity within polarization limits that don't initiate water electrolysis at the electrode/electrolyte interface. These limits, the so-called "water window," are used to ensure that the AIROF electrodes can deliver charge reversibly in various electrolyte environments. However, strictly observing these limits may uncomfortably reduce the charge delivery capacity of AIROF microelectrodes in vivo. This paper compares the constituents of electrode polarization during in vitro and in vivo current pulsing. It shows that capacitive-like polarization is the main component of the measured electrode polarization in vitro within buffered physiological saline. In vivo, in addition to a larger ohmic polarization, a secondary electrode polarization is observed. Presently we are examining the difference between in vivo and in vitro polarization responses in an effort to optimize the iridium activation process, in order to achieve the most charge delivery with the least electrode polarization for AIROF microelectrodes.