Carbonate‐Melt Oxidized Iridium Wire for pH Sensing

Abstract

A new approach to the preparation of an iridium oxide film for pH sensing is demonstrated. A thick, uniform and dense ceramic oxide layer was grown on the surface of an iridium wire by oxidizing the wire in a molten alkali metal carbonate at high temperature. The alkali metal ion from the carbonate melt was incorporated into the oxide, resulting in a highly stable oxide compound. After treated in acid solution, the oxide layer became hydrated. SEM, XRD, TGA and element analysis were carried out to characterize the oxide film, and a possible formula of the oxide was computed as Li 0.86 IrO 2.34 (OH) 0.76 ¥ 0.39H 2 O. The electrode made with this new type of oxide film exhibited good pH sensitivity and stability, even in strong acid/base solutions, or in strong corrosive solution such as hydrofluoric acid. Furthermore, the electrode showed excellent long-term stability over the test period of two and a half years. In addition, individual electrodes prepared from the same batch exhibited remarkable agreement with respect to potential/pH slopes and apparent standard electrode potentials. The performance of the electrodes depends on the properties of the oxide film, such as composition, hydration state and oxidation state.

Effects of Thermal Oxidation Cycle Numbers and Hydration on IrOxpH Sensor

“…24,25 Our XPS survey of the hydrated electrode surface demonstrated the existence of Ir 4+ and Ir 6+ (Fig. 7).…”

“…It is noted that "oxygen intercalation" mechanism does not take into account the hydration of iridium oxide film. Most pH response mechanism studies for the iridium oxide electrode were concentrated on the electrode reaction and thermodynamic equation, 4,6,24,25 however, the kinetic response process was rarely mentioned. Accordingly, iridium oxide electrode fabrication is still under development.…”

The Influences of Quenching Times on the Property of Thermal Oxidized Iridium pH Sensor

“…The transformation among different valences of IrO x leads to the ability for pH response. (19,20). Thus, the pH response reaction is dominantly the reaction [5].…”

Solution of the heavily stacking faulted crystal structure of the honeycomb iridate H3LiIr2O6

“…1 The pH electrode is a promising supplement for glass electrodes, as thin glass membranes are incompatible with high pressures and temperatures, as well as with extreme alkaline and hydrofluoric media. [2][3][4] IrO x -based solid state electrodes can be produced by the carbonate melt oxidation process [5][6][7] in which iridium wires are oxidized in an excess of molten lithium carbonate. This process leads to the formation of α-Li 2 IrO 3 .…”