Diamond Electrode

The diamond electrode has a high oxygen evolution potential and is suitable for ozone generation and decomposition of persistent organic substances. It enables electrode reactions that were not possible with platinum or DSE^®.

Flexibility

High Performance

Robustness

Long Life

Electrolysis voltage

The theoretical decomposition voltage required to cause water electrolysis is about 1.2 volts (pink line in Fig. 1), but in reality, electrolysis does not proceed at this voltage. A voltage of 1.2 volts or more is required for electrolysis, and the minimum voltage required for electrolysis of this water is called a "potential window". In Figure 1, the potential window is the difference between the potential at which oxygen evolution begins and the potential at which hydrogen evolution begins. This potential window depends on the type of electrode.

Electrochemical window of diamond electrode

It is about 2 volts for electrodes such as platinum and precious metal coated titanium electrodes (brown wire in Fig. 1). With diamond electrodes, it extends up to 3-5 volts (blue line, red line in Figure 1).

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Wide potential window

Fig.1 Measured in the current potential curve (1M-H2SO4)

If the potential window is wide, instead of the electrolysis reaction of water, the oxidation and reduction reactions of substances that are normally difficult to electrolyze can proceed preferentially. This property enables the decomposition and synthesis of substances that were not possible with conventional electrochemical systems.

Diamond electrodes can be given electrical conductivity by boron doping. Semiconductors, conductors, and superconductors can be manufactured according to the boron concentration, and the "diamond electrode" that uses conductive diamonds doped at a relatively high concentration (about 10²³cm^-3) as electrochemical electrodes is a conventional noble metal. It is attracting attention as a next-generation electrode material that can be expected to have many applications by substituting electrodes and carbon electrodes. It can be seen that our diamond electrodes are densely distributed with polycrystalline particles of 0.1 to 10 μm (see Fig. 2).

Fig. 2 SEM image of diamond electrode and image by laser microscope

Fig3. Raman spectral diagram (1333 cm-1 is the peak indicating diamond)

Lineup of diamond electrodes

We not only manufacture and sell diamond electrodes (BDD: Boron Doped Diamond) alone, but also offer two types of product lineup that apply BDD.

１）BDD spiral module

Introducing the BDD spiral module for ozone water generation using an ion exchange membrane. This product was developed in collaboration with Professor Kitaori of Tokyo National College of Technology. The electrolytic part (membrane-electrode assembly) is shown in [Figs. 4 and 5].
It has a structure in which an ion exchange membrane and a cathode ray are wound around a rod-shaped BDD anode, and has the following features.

1) This module features an one-chamber cell structure that does not separate hydrogen, ozone, and oxygen.

2) Since it has an one-chamber cell structure, it is electrolyzed in the neutral region, so hardness components such as Ca and Mg do not easily adhere, and tap water can be used as a raw material.

3) Using tap water as a raw material, ozone water of 1 to 2 mg dm^-3 can be stabilized for 300 hours under the conditions shown below.

When tap water is used as a raw material and electrolyzed at a constant voltage of 15 V (repeated operation of 8 minutes ON + 2 minutes OFF), a current of about 0.5 A is stably applied, and 1 to 2 mg dm^-3 ozone water is applied for 300 hours. You can get stable over.

The current efficiency is reduced to about one-third compared to the case of pure water raw material, but this is due to the decrease in ozone current efficiency due to changes in the current distribution and impurities such as chloride ions, effective chlorine and hardness components. It is presumed that the generated ozone is decomposed due to the presence and reaction with the alkaline component generated at the cathode.

Fig.4 Appearance of BDD spiral module

Fig.5 Changes in electrolytic characteristics in tap water electrolysis

Fig.7 Appearance of BDD clip

2）BDD clip module

Small size BDD clip module improved and developed for application to portable devices (spray, bottle type, etc.) that generate electrolyzed water containing ozone, hydrogen peroxide, hypochlorous acid, etc. (Reference: Patent 5710691) Introducing. This BDD clip module has the following features because it uses a new clip-type membrane-electrode assembly structure in place of the conventional winding electrode, that is, the BDD spiral module.

１）The compact size (BDD length is only 8mm) and the large degree of freedom in installation space expand the possibilities of equipment for customers.

２）Stable performance can be maintained because the ion exchange membrane can be held at a stable pressure with respect to the anode.

３）Even if it is compact, it is possible to stably obtain 0.05 to 0.5 mg dm^-3 ozone water.

The BDD clip module with the above features has a shape suitable for incorporation into various spray-type ozone water generators that are convenient for use at home or on the go.

The figure below shows the result of electrolyzing the applied current under three conditions of 50, 100, and 150mA.

The electrolysis conditions are that the raw water is ion-exchanged water, the raw water capacity is 30 ㎖, the electrolysis time is 30 seconds, and the liquid temperature is 15 ° C.

Fig.8 Average and standard deviation of ozone water concentration at each current value