A field-induced poising technique for promoting convergence of standard electrode potential values of thermally oxidized iridium pH sensors

Hitchman, Michael L.; Ramanathan, Subramaniam

doi:10.1016/0039-9140(92)80008-2

Cited by 30 publications

(39 citation statements)

References 6 publications

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“…For example, sputtered IROF usually has a thickness in the 0.1 mm level. The present oxide film shows a deep black appearance, which is different from the dark blue IROFs prepared by other methods [12,18]. The deep black color of the current IROF can be attributed to the involve- ment of Li in the film from the fact that the insertion of Li causes a black color for NiO [25].…”

Section: Potential Response Measurementcontrasting

confidence: 57%

Carbonate‐Melt Oxidized Iridium Wire for pH Sensing

Wang

Yao

2003

Electroanalysis

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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.

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Section: Potential Response Measurementcontrasting

confidence: 57%

Carbonate‐Melt Oxidized Iridium Wire for pH Sensing

Wang

Yao

2003

Electroanalysis

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“…• C. 34 Both surface films of fabricated by the above conditions showed obvious cracks. We have fabricated IrO x pH sensor showing wide Nernst response range, quick pH response rate by cycling the 800…”

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confidence: 98%

“…By comparing sensitivity, Nernst response range, ion selectivity, interference of oxidation, the iridium oxide pH electrode has been demonstrated to be the most promising one among all kinds of pH sensors. [17][18][19] The reported fabrication approaches of IrO x pH electrode include electrochemical cyclic voltammetry (CV), 19-22 electrodeposition, 23-25 radio frequency (RF) magnetron sputtering deposition, 26-30 and thermal oxidation.14,31 Among which, the electrode produced by thermal oxidation exhibited excellent overall performance, including wide E-pH relationship range, fast response time and long term stability.32-36 Wang et al developed carbonate melt oxidation to coat Ir through the oxidation of Ir wires in a carbonate melt at 870• C for 5 hours.31 Hitchman et al produced IrO x -electrodes by direct thermal oxidation in air at 800• C. 34 Both surface films of fabricated by the above conditions showed obvious cracks. We have fabricated IrO x pH sensor showing wide Nernst response range, quick pH response rate by cycling the 800…”

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confidence: 99%

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The Effects of Cyclic Isothermal Oxidation on Ir/IrO_xpH Electrode and a Method to Correct the Potential Drift of Metal Oxide Electrode

Huang¹,

Wan²,

Jin³

et al. 2017

J. Electrochem. Soc.

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The present work demonstrated the effects of isothermal oxidation temperature (750 • C∼870 • C) and water quenching cycle times (1∼3) on properties of IrO x pH electrodes. Property tests of the fabricated electrodes showed that electrodes developed by 800 • C isothermal heating and water quenching for 3 times (H&Q 3) had excellent near Nernst E-pH relationship, relatively faster response rate and the minimum potential drift in long-term stability test. Surface and cross-section morphologies, confocal laser scanning microscopy, electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) were employed to characterize the electrodes to explore the reason for their excellent properties. Surface morphology showed that the iridium oxide film (IROF) made by H&Q 3 at 800 • C had larger surface roughness, and well-defined homogeneous dense inner layer and loose porous outer layer. Besides, it had the minimum reaction resistance in both acid and alkaline buffers, and contained more effective compositions compared to electrodes fabricated by other conditions. Thus H&Q 3 at 800 • C was suggested to obtain a better integrated pH sensing property. Furthermore, a potential compensation method with a specially designed probe structure was proposed to correct possible errors caused by the potential drift of IrO x pH electrode in long-term pH monitoring. pH, used to reflect the grade of solvents in chemical laboratory since 1909, is an important parameter in many fields such as chemical industry, bio-industry as well as some fundamental research like electrodeposition/electrolysis and corrosion process.1-3 The glass pH electrode is a mature routine tool presenting good sensitivity, excellent stability and long life time in pH sensing. However, some of its disadvantages restrict its usage in some particular applications due to the physical nature of the glass membrane.The alternative pH electrodes include ion-sensitive field-effect transistor (ISFET) pH sensors, 4,5 optical fiber pH sensors, 6,7 hydrogel film pH sensors, [8][9][10][11][12] metal/metal oxide sensors, 13-16 etc. By comparing sensitivity, Nernst response range, ion selectivity, interference of oxidation, the iridium oxide pH electrode has been demonstrated to be the most promising one among all kinds of pH sensors. [17][18][19] The reported fabrication approaches of IrO x pH electrode include electrochemical cyclic voltammetry (CV), 19-22 electrodeposition, 23-25 radio frequency (RF) magnetron sputtering deposition, 26-30 and thermal oxidation.14,31 Among which, the electrode produced by thermal oxidation exhibited excellent overall performance, including wide E-pH relationship range, fast response time and long term stability.32-36 Wang et al. developed carbonate melt oxidation to coat Ir through the oxidation of Ir wires in a carbonate melt at 870• C for 5 hours.31 Hitchman et al. produced IrO x -electrodes by direct thermal oxidation in air at 800• C. 34 Both surface films of fabricated by the above conditions showed obvious cracks...

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“…[1][2][3] Among a dozen studied metal/metal oxide electrodes, [4][5][6][7][8] the iridium oxide (IrO x ) electrode is suggested to be the most promising one for pH detection, 2,9-14 by synthetically comparing their sensitivity, Nernst response range, ion selectivity, and potential drift.…”

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confidence: 99%

Nafion Modification of Thermal-Oxidized IrO_xElectrode

Huang

Jin

Wen

et al. 2018

J. Electrochem. Soc.

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IrO x electrodes suffer from large potential drift in solutions in the presence of strong reductive anions such as S 2− , I − , etc. resulting in the inaccuracy of pH measurement. Our homemade IrO x electrode developed by cycling heat-treatment and quenching process for three times with excellent response property showed the same problem. In-situ/ex-situ XAFS study showed the composition of the IrO x film changes in strong reductive solution. At the meantime, XPS survey of the IrO x electrode also verified the composition change of Ir 4+ /Ir 3+ before and after its immersion in these solutions. In order to solve the above problem, the porous-structured IrO x electrodes were modified by being dipped into Nafion solution for 1∼3 times. Surface and cross section characterizations, EIS tests as well as the pH detection property evaluations were conducted to identify the modification effect and determine a better modification process. Nafion modification for just once is suggested to prevent the electrode from potential drift in solutions containing strong reductive anions. Finally, the pH response mechanism of the modified IrO x electrode in reductive solutions was discussed. Metal/metal oxide pH electrodes have been widely investigated because of their advantages in fabrication, miniaturization, maintenance, cost, as well as their excellent performance in pH response. 1-3Among a dozen studied metal/metal oxide electrodes, 4-8 the iridium oxide (IrO x ) electrode is suggested to be the most promising one for pH detection, 2,9-14 by synthetically comparing their sensitivity, Nernst response range, ion selectivity, and potential drift.Different from the simple ion exchange mechanism for glass pH electrode, the pH response mechanism for IrO x electrode is the transformation among different valences of Ir. 1,10,15,16 It was found that large potential drift toward negative direction occurred as IrO x pH electrodes were immersed in the environment containing strong reductive anions such as S 2− , I − etc., leading to inaccuracy of pH detection, which restricted their application in reductive environment. 17Similar situation was encountered for the other metal/metal oxide electrodes.11,18 Therefore, it is necessary to account for this problem and find proper solution for this phenomenon to broaden the application field of the metal/metal oxide electrodes, among which, surface modification is believed to be an effective approach. Nafion (perfluorosulfonic ionomer) polymer has the properties of good conductivity, excellent temperature stability, chemically inert, high corrosion resistance, non-electroactive, hydrophilic and insoluble in water etc.19 Moreover, Nafion is also an excellent cation exchanger with good ion selectivity, i.e., only exchanges cations, excludes neutral molecules and anions. Accordingly, Nafion has been widely applied in the field of analytical chemistry due to its enriched electrocatalysis and ion selectivity, i.e., voltammetric analysis, sensoring, electrocatalysis, chromatographic analysis. [20][21]...

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A field-induced poising technique for promoting convergence of standard electrode potential values of thermally oxidized iridium pH sensors

Cited by 30 publications

References 6 publications

Carbonate‐Melt Oxidized Iridium Wire for pH Sensing

Carbonate‐Melt Oxidized Iridium Wire for pH Sensing

The Effects of Cyclic Isothermal Oxidation on Ir/IrO_xpH Electrode and a Method to Correct the Potential Drift of Metal Oxide Electrode

Nafion Modification of Thermal-Oxidized IrO_xElectrode

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A field-induced poising technique for promoting convergence of standard electrode potential values of thermally oxidized iridium pH sensors

Cited by 30 publications

References 6 publications

Carbonate‐Melt Oxidized Iridium Wire for pH Sensing

Carbonate‐Melt Oxidized Iridium Wire for pH Sensing

The Effects of Cyclic Isothermal Oxidation on Ir/IrOxpH Electrode and a Method to Correct the Potential Drift of Metal Oxide Electrode

Nafion Modification of Thermal-Oxidized IrOxElectrode

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The Effects of Cyclic Isothermal Oxidation on Ir/IrO_xpH Electrode and a Method to Correct the Potential Drift of Metal Oxide Electrode

Nafion Modification of Thermal-Oxidized IrO_xElectrode