A pH Electrode Based on Melt-Oxidized Iridium Oxide

Fabrication and characterization of a novel potentiometric pH electrode based on melt-oxidized iridium oxide film is presented. The oxide film produced in a lithium carbonate melt has the composition of and shows high chemical stability. The electrode based on this oxide film exhibits very promising pH sensing performance, with an ideal Nernstian response in the tested pH range of 1 to 13. The potential response is fast, with a 90% response time obtained in less than 1 s for all pH changes. The open-circuit potential of the electrode is almost drift-free, with an average variation over time in a pH 6.6 solution as small as 0.1 mV/day. Furthermore, the potential/pH slopes and the apparent standard electrode potentials show excellent agreement among electrodes from the same batch. A comparison is made of the present electrode and those reported in the literature with respect to fabrication method and pH sensing characteristics.