SURFACE-POLISHABLE IRIDIUM OXIDE COMPOSITE HYDROGEN ION ELECTRODE AND METHOD OF MANUFACTURING THE SAME

Abstract

Disclosed herein is a surface-polishable iridium oxide composite hydrogen ion electrode and a method of manufacturing the same, and, more particularly, a surface-polishable iridium oxide composite hydrogen ion electrode, which has a long life due to its excellent physical strength, pH dependency approximate to a theoretical value (59 mV/pH unit), and high surface renewability, and a method of manufacturing the same. The iridium oxide composite hydrogen ion electrode according to the present invention is effective in that, when the electrode is contaminated or inactivated, the surface of the electrode can be regenerated through a simple polishing process because the electrode has high surface renewability, unlike conventional electrodes. The iridium oxide composite electrode according to the present invention can be usefully used in a water-quality monitoring system for monitoring the hydrogen ion concentration of a solution for a long period, an online pH measurement system, and pH measurement for samples, which causes serious contamination of the surface of a sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a graph showing the voltage change of an iridium oxide composite electrode of the present invention to pH change (reference electrode: Ag/AgCl);

FIG. 2 is a graph showing the electrode voltage dependency of an iridium oxide composite electrode of the present invention to pH change;

FIG. 3 is a graph showing the response time of an iridium oxide composite electrode of the present invention to pH change;

FIG. 4 is a graph showing the hydrogen ion sensing slope depending on the polishing of the surface of an iridium oxide composite electrode of the present invention;

FIG. 5 is a graph showing the long-term stability of an iridium oxide composite electrode of the present invention in various storage conditions; and

FIG. 6 is a graph showing the voltage stability of an iridium oxide composite electrode of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described in detail with reference to Examples.

Here, these Examples are set forth to illustrate the present invention, but should not be construed as the limit of the present invention.

EXAMPLE 1

Formation of Inactive Conductive Material

0.5 g of (NH₄)₂IrCl₆ was put in a 200 ml round bottomed flask, and was then dissolved in water by adding 50 ml of water to the flask. Subsequently, 5 ml of ethanol was additionally added to the solution in order to improve the solubility thereof.

Subsequently, 1.7 g of glass fine powder, having a particle size of 45 μm or less, was added to the flask, and the flask, to which the glass fine powder was added, was installed in a rotary evaporator, and then the solvent present in the flask was evaporated and dried at a temperature of 80° C., thereby coating the glass fine powder with (NH₄)₂IrCl₆.

Subsequently, the glass powder, coated with (NH₄)₂IrCl₆, was charged in a boat type crucible, and the crucible, containing the glass powder coated with the (NH₄)₂IrCl₆, was installed in a tubular furnace, and then the crucible was heated to a temperature of 500° C. for 5 hours in a hydrogen atmosphere, and thus the (NH₄)₂IrCl₆ applied on the surface of the glass powder was decomposed and reduced, thereby forming fine iridium metal particles on the surface of glass.

EXAMPLE 2

Formation of Iridium Oxde

0.5 g of (NH₄)₂IrCl₆ was put in a 200 ml flask with a round bottom, and was then dissolved in water by adding 50 ml of water to the flask. Subsequently, 5 ml of ethanol was additionally added to the solution in order to improve the solubility thereof.

Subsequently, 1.7 g of glass fine powder having a particle size of 45 μm or less, or glass fine powder including iridium metal fine particles formed in Example 1, was added to the flask, and the flask, to which the glass fine powder was added, was installed in a rotary evaporator, and then the solvent present in the flask was evaporated and dried at a temperature of 80° C., thereby coating the glass fine powder with (NH₄)₂IrCl₆.

Subsequently, the glass powder, coated with (NH₄)₂IrCl₆, was charged in a boat type crucible, and the crucible, containing the glass powder coated with the (NH₄)₂IrCl₆, was installed in a tubular furnace, and then the crucible was heated to a temperature of 500° C. for 5 hours in an air or oxygen atmosphere, and thus the (NH₄)₂IrCl₆ applied on the surface of the glass powder was oxidized to iridium oxide, thereby forming a high-temperature sinterable mixture of iridium oxide/glass fine powder or iridium metal/iridium oxide/glass fine powder.

EXAMPLE 3

Preparation of Composite Electrode Material

The high-temperature sinterable mixture of iridium oxide/glass fine powder or iridium metal/iridium oxide/glass fine powder, formed in Example 2, was molded, and then the molded mixture was sintered at a temperature of 700° C. for 4 hours, thereby preparing a polishable iridium oxide/glass composite electrode material or a polishable iridium metal/iridium oxide/glass composite electrode material.

EXAMPLE 4

Evaluation of Sensitivity of Electrode

The sensitivity of the iridium oxide/glass composite hydrogen ion electrode prepared in Example 3 was measured.

A pH glass electrode and the iridium oxide/glass composite hydrogen ion electrode were immersed into 0.1 M of a universal buffer solution including phosphoric acid, boron acid, acetic acid and potassium chloride, and the pH of the solution was set to 1. Subsequently, the potentials of the iridium oxide/glass composite hydrogen ion electrode vs. Ag/AgCl (3.0 M KCl) electrode were measured while changing the pH of the solution in the range of 1 to 13 by adding potassium hydroxide and nitric acid to the solution, and the results thereof are shown in FIG. 1.

In this case, the pH of the solution was increased stepwise to 13, and was then decreased to 1 by adding nitric acid to the solution.

As shown in FIG. 1, it can be seen that the potentials of the electrode stabilized at new potentials rapidly depending on the change in the pH of the solution.

Meanwhile, the potential of the electrode depending on the pH of the solution is shown in FIG. 2.

As shown in FIG. 2, it can be seen that the iridium oxide composite hydrogen ion electrode of the present invention exhibits a slope of 59.9 mV/pH unit, and the slope approximates to a theoretical value of 59.2 mV/pH unit.

EXAMPLE 5

Evaluation of Responsivity of Electrode

In order to evaluate the response time of the iridium oxide/glass composite hydrogen ion electrode prepared in Example 3, the time that it takes for the potential of the electrode to reach 90% of the final potential of the electrode, was measured while the pH of the solution was changed, and the results thereof were shown in FIG. 3.

As shown in FIG.3, it can be seen that, when the pH of the solution was changed from 6.05 to 2.10, the time T₉₀ that it took for the potential of the electrode to reach 90% of the final potential was 7 seconds or less, and thus the electrode exhibits high responsivity.

EXAMPLE 6

Evaluation of Surface Renewability of Electrode

The surface of the electrode (containing 13% of iridium oxide) prepared in Example 3 was finely polished using a 2000 grit SiC paper, and then the potential of the electrode was measured in solutions of pH 4, 7, and 10. The response slope was evaluated for seven trials. Between each set of measurements the surface of the electrode was re-polished completely. Thereafter, the pH sensitivity of the electrode was measured in each case (referring to FIG. 4).

As shown in FIG. 4, it can be seen that the average response of the pH sensitivity of the electrode is −58.6 mV/pH unit, and the relative standard deviation (rsd) thereof is 0.76%, which is excellent.

EXAMPLE 7

Evaluation of Stability of Electrode

FIGS. 5 and 6 show the changes in the responsivity of iridium oxide composite pH electrode depending on the length of the period of use thereof.

FIG. 5 shows the response slope of the electrode to hydrogen ion concentration when the solution is neutral (pH 7), that is, when the electrode is left in air or is stored in distilled water or a neutral buffer solution for a long time.

In FIG. 5, it can be seen that the deviation in the responsivity of the electrode was 1 mV/pH unit, which is very small.

In FIG. 6, it can be seen that 3 mV of electrode voltage drift is exhibited as the result of measuring electrode voltage for 6 hours.

As described above, an iridium oxide composite electrode according to the present invention is effective in that the electrode has very high physical strength because it has a glass or ceramic medium, unlike conventional electrodes, and, when the electrode is contaminated or inactivated, the surface of the electrode can be regenerated through a simple polishing process because iridium oxide, which is a sensing material, is uniformly included in the entire electrode medium.

Accordingly, the iridium oxide composite electrode according to the present invention can be usefully used in a water-quality monitoring system for monitoring the hydrogen ion concentration of a solution for a long period, an online measurement system, and pH measurement for samples causing serious contamination on the surface of sensor.

Claims

1. A method of manufacturing a surface-polishable iridium oxide composite hydrogen ion electrode, comprising: a first step of forming an inactive conductive material on a surface of high-temperature sinterable glass fine powder, ceramic powder or ceramic precursor powder;a second step of preparing high-temperature sinterable glass fine powder, ceramic powder or ceramic precursor powder, including metal/iridium oxides or iridium oxides alone, by dispersing the high-temperature sinterable glass fine powder, ceramic powder or ceramic precursor powder coated on the surface thereof with the inactive conductive material formed in the first step or high-temperature sinterable glass fine powder, ceramic powder or ceramic precursor powder in an iridium and metal containing compound solution, evaporating and drying a solvent from the solution, thus applying the iridium compound on the surface of glass fine powder, ceramic powder or ceramic precursor powder, and then pyrolyzing compounds applied at below the sintering temperature; anda third step of molding the high-temperature sinterable glass fine powder, ceramic powder or ceramic precursor powder, including metal/iridium oxides or iridium oxides alone, and then high-temperature sintering or high-temperature high-pressure sintering the molded glass fine powder, ceramic powder or ceramic precursor powder.

2. The method according to claim 1, wherein the inactive conductive material in the first step is selected from the group consisting of platinum (Pt), iridium (Ir), palladium (Pd), and gold (Au).

3. The method according to claim 1, wherein, in the first step, the inactive conductive material is formed using a pyrolysis reduction method, a simple mixing method, or an electroless plating method.

4. The method according to claim 1, wherein the pyrolysis temperature of the applied compounds is in the range of 200 to 700° C.

5. The method according to claim 1, wherein, in the third step, the glass fine powder, ceramic powder or ceramic precursor powder, further including a binder, is molded.

6. The method according to claim 1, wherein, in the third step, the sintering temperature is in the range of 400 to 1,000° C.

7. A surface-polishable iridium oxide composite hydrogen ion electrode manufactured using the method according to claim 1.