JPS5913831B2 - electrochemical photocell - Google Patents

Description

[Detailed description of the invention] The present invention relates to electrochemical photovoltaic cells.

More specifically, the present invention relates to an electrochemical photovoltaic cell using a titanium oxide film electrode. The present inventors have previously found that when an n-type semiconductor electrode such as TiO2 or ZnO is irradiated with light, the potential of the electrolytic oxidation reaction shifts to a more base potential, and oxygen generation occurs below the equilibrium potential. It was named photosensitized electrolytic oxidation (Industrial Chemistry Magazine 7-2, 108-113 (196
9)), and the present inventors utilized this photosensitized electrolytic phenomenon to develop an electrochemical photovoltaic cell (specially In addition, he developed an electrochemical cell (Japanese Patent Application No. 49-25036) in which two monopolar chambers connected by a conductive partition wall were made of electrolyte aqueous solutions having different pH values.

The photovoltaic cell described above converts inexhaustible light energy such as sunlight into electrical energy, and at the same time decomposes water, an abundant natural resource, to provide oxygen and hydrogen. What is extremely noteworthy is that it uses a single-crystal TiO2 semiconductor for its electrodes, making it very expensive and unsatisfactory for practical use.

Attempts have been made to improve electrochemical photovoltaic cells using n-type semiconductor electrodes, but so far they have not achieved great success. In order to improve the practicality of electrochemical cells using semiconductor electrodes, we have been conducting extensive research into improving the electrochemical cell, but we have discovered that by using a titanium oxide film electrode, which is made by treating titanium metal at high temperatures to form an oxide film on its surface. The present invention was achieved by discovering that the economical efficiency can be significantly improved while the photovoltaic properties are at the same level.The purpose of the present invention is to provide an inexpensive TiO2 semiconductor electrode without impairing the photovoltaic properties.
The purpose of this is to place a titanium oxide film electrode, which is made by treating titanium metal at a high temperature to form an oxide film on its surface, and a counter electrode in a container containing a liquid to be electrolyzed, and to irradiate the surface of the titanium oxide film with light. This is achieved by obtaining electrical output from both ends of the conductors of both electrodes. The present invention will be explained in detail below.

In the present invention, a titanium metal with an oxide film formed thereon is used as the TiO2 electrode.

Generally, there are an electrolytic oxidation method and a high-temperature oxidation method as methods for forming an oxide film on titanium metal, and in the present invention, the latter is adopted. In other words, when a titanium metal oxide film obtained by oxidizing a titanium plate at high temperature under various conditions is used as an anode for an electrochemical photovoltaic cell, a rolled titanium plate is simply degreased and used as a sample, and the surface is heated to a constant potential. It shows extremely superior properties compared to the case of using a titanium anodic oxide film obtained by anodizing at constant current density, and in particular, the property value is about 10 times higher than that of the oxide film obtained by gas flame high temperature oxidation. can be obtained.

Titanium metal is treated at high temperature in a city gas or other gas flame or in an electric furnace to form an oxide film on the surface, and then the electrode is coated with epoxy resin to a surface area of 1 cd and exposed to light under different temperature conditions. We investigated the characteristics of an anode for electrochemical photocells, focusing on measuring potential and current using a potentiostat.

FIG. 1 shows the potential/current curves of a titanium oxide electrode fired in a gas flame at various temperatures for a certain period of time (5 minutes) under irradiation with a 500 W xenon lamp. In a titanium electrode that is not heat-treated, that is, in a titanium electrode in which no high-temperature oxide film is formed, almost no photocurrent flows, but the oxidation current increases as the film forms, and begins to rise slightly above 1350°C. On the other hand, if an electric furnace is used to heat the oxide film for a long time under conditions of 1000°C or less, a photosensitive film can be obtained from about 400°C, and about 75%
The best photoelectrode behavior is shown at 0° C. (not shown). FIG. 2 shows the relationship between oxidation current and firing time when the flame temperature is 1300°C. It can be seen that as the film is fired, a film with semiconductor properties grows and the current increases, but if the firing is longer than a certain period of time, oxidation progresses and resistance increases, so the current also decreases. In other words, it is understood that the oxidation current is closely related to the film composition, film thickness, etc., but the results in Figure 3, which show the relationship between the compositional analysis of the oxide film by X-ray diffraction and the oxidation current, are also similar. This shows that there is a relationship. That is, as the oxidation temperature increases, the amount of titanium decreases and the amount of ruti'-type TiO increases, a film with semiconductor properties grows and the photocurrent increases, but at 1400°C, oxidation progresses and part of the film is a high resistance rutile type T with a stoichiometric ratio.
The photocurrent becomes iO2 and decreases. This means that in order to obtain good photoelectrode behavior, it is necessary to have donors due to oxygen defects in the crystal and to have a film thickness sufficient to absorb light. It is presumed that due to insufficient supply of oxygen, the film becomes a film with oxygen defects and exhibits good photosensitivity. As mentioned above, titanium oxide films obtained by high-temperature oxidation of titanium metal, particularly films obtained by high-temperature oxidation of titanium plates in various gas flames, exhibit excellent photoelectrode behavior.

An electrode element in which an oxide film is formed by heating a titanium plate for a suitable period of time using a heat source including a large number of Bunsen Parners placed at equal intervals can be produced at low cost and easily. Next, a method for assembling an electrochemical photocell using the obtained titanium oxide film as an anode will be explained.

The titanium oxide film electrode and the smooth platinum electrode are placed in a container containing an electrolyte solution selected from water or various electrolyte aqueous solutions, such as an aqueous solution of potassium hydroxide, sodium hydroxide, sodium sulfate, sodium chloride, sulfuric acid, etc. Opposite electrodes are provided, each electrode is connected with an appropriate load or the like or with no load to form a closed circuit, and a window is provided in the container so that the titanium oxide film electrode can be irradiated with light. In this case, the membrane to be electrolyzed is an electrolyte aqueous solution, the container is divided into two, each having a monopolar chamber, the two chambers are connected with a conductive partition, and the PH value of the chamber on the titanium oxide layer electrode side is set higher than that of the other chamber. It is also possible to use a power type with higher photovoltaic efficiency. A device for collecting the generated gas may be provided above each electrode, and a collected gas storage tank may be connected thereto. To operate the resulting photovoltaic cell, the surface of the titanium oxide film electrode is irradiated with light, in which case the irradiated light has an energy higher than 3.0 eV, i.e. 4
The wavelength needs to be shorter than 15 mμ. Specifically, mercury lamps, xenon lamps, and sunlight are used. This titanium oxide film can be used as the anode of an electrochemical photovoltaic cell and operated under sunlight to produce a considerable amount of hydrogen, making it an important means of inexpensively producing hydrogen, which is said to be an ideal pollution-free fuel. It gives you a discount.

Embodiments of the present invention will be described in more detail below with reference to Examples, but the present invention does not go beyond the gist of the invention. EXAMPLES Without being limited by the following examples
1 [Manufacture of a single tank type electrochemical photovoltaic cell] Nine commercially available titanium metal plates (thickness 0.1 Twft) were arranged with Bunsen burners at equal intervals, and the flame temperature was 1300.
The mixture was heated at ℃ for various times to form a uniform film.

The obtained titanium oxide film was used as an anode, and a lead wire was connected to it using a soldering iron. A smooth platinum plate was selected as a cathode, and a lead wire was also connected to it. A light irradiation window made of a transparent quartz plate was provided at one end, and it was placed in an aquarium. A single-tank photovoltaic cell was obtained by installing them facing each other. [Manufacture of double tank type electrochemical photovoltaic cell] Put 1N-NaOH in one tank and 1N-H2SO4 in the other tank, connect both tanks using a salt bridge as a conductive partition, and apply the titanium oxide film to the NaOH tank. Installed and used as an anode room,
A smooth platinum plate was placed in a H2SO4 tank to serve as a cathode chamber.

The anode chamber was equipped with a window for light irradiation using a transparent quartz plate to obtain a double tank photovoltaic cell. (Example 1) Titanium oxide film electrodes (25 x 28wn) obtained using the obtained double tank electrochemical photocell with a flame temperature of 1300°C and varying heating times.
The current-potential curve under sunlight at the time of clear skies in July is the 4th graph.
As shown in the figure.

Even at a heating time of 30 seconds, some characteristics were exhibited, and as the heating time was increased, the characteristics improved, but saturated after about 6 to 8 minutes.
The optimal heating conditions are related to the size and thickness of the titanium plate, the heating device, etc. Table 1 shows oxide film A obtained under the above conditions and oxide film A obtained under other conditions (0.1w1n thickness, 25×28m1
1400°C 2 minutes) B1} and TiO obtained by treatment in vacuum
An example of the characteristics of two single-crystal electrodes C under the same conditions is shown below. An oxide film electrode can provide photoelectrode properties equivalent to those of a single crystal electrode, and if the heating time is appropriate, the properties will not deteriorate even if the area is increased.

The electrode heated for 8 minutes as shown in Figure 4 was heated using an electrolyte composition of 1N-NaOH.
(Anode chamber) -1N-H2SO4 (Cathode chamber) When using an electrochemical photocell, the short circuit current is 25m under sunlight.
A, and 10 yoke of hydrogen gas was obtained per hour. (Example 2) In order to increase the anode area of the titanium oxide film electrode shown in Example 1 and create a battery with high output, a plurality of oxide film electrodes were connected in parallel to the Pt electrode, and a single anode battery was obtained. A circuit current lower than the arithmetic sum for the case was obtained.

The degree of reduction increases as the light intensity and hence the current increase, and as the number of connections increases.

FIG. 5 shows the relationship between the arithmetic sum current of a single anode battery and the actual circuit current when connected in parallel. This small current range is thought to be due to voltage drop due to resistance in salt bridges, solutions, etc. When five electrochemical photovoltaic cells with four anodes in parallel were assembled and operated under short-circuit conditions, 5
A total of approximately 100,011 tons of hydrogen was collected using the platinum cathode per day (from 6 a.m. to 5 p.m.) on a sunny day in July. In this case, the light receiving area is 1700 cd, so 6 per i
t becomes 1 from the heat of combustion of hydrogen (68Kc & 1/MOl)
This corresponds to 8.2 Kca1 of energy (assuming that the energy of sunlight is 3000 Kca1 (Japan's national average) per 1w7 per day, the efficiency is 0.6%.

[Brief explanation of drawings]

Figure 1 shows the relationship between firing temperature, potential, and current.
Figure 2 shows the relationship between titanium firing time and oxidation current at 1300°C, Figure 3 shows the relationship between titanium firing temperature and current or X-ray diffraction intensity, and Figure 4 shows the relationship between titanium firing time, potential, and current. FIG. 5 shows the relationship between the actual loop current and the arithmetic sum current when the membrane electrodes are connected in parallel.

Claims (1)

[Claims] 1. A titanium oxide film electrode, which is made by heat-treating titanium metal to form an oxide film on its surface, and a counter electrode are placed in a container containing an electrolyte, and the surface of the titanium oxide film electrode is irradiated with light. An electrochemical cell characterized in that electrical output is obtained from both ends of the conductor wires of both electrodes.