Preparation of iridium oxide and its application in sensor-actuator systems

Acid or base concentrations can be determined by coulometric titration. A new all-iridium oxide sensor-actuator device is presented, of which the titrant is generated by a reversible redox reaction occurring in the electroactive iridium oxide actuator electrode, and the equivalence point in the titration curve is detected by the pH-sensitive iridium oxide sensor. The advantage with respect to the formerly used noble metal actuator electrode/ISFET sensor device is twofold: on the one hand, interference of Cl− ions, which oxidize at the noble metal actuator electrode during titration, is avoided and on the other hand, the preparation of the all-iridium oxide device is easier than of the ISFET-based devices. In addition to the conventional potential sweep method of oxide growth, a new current-pulse method is proposed, of which the parameters for optimal growth depend less on the pH of the solution.