JPS5826623B2 - photocell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an energy conversion device that converts light energy into electrical energy.

Photoelectrodes that exhibit electrochemical behavior when the electrode is irradiated with light have been well known for a long time, and many semiconductors have been used as photoelectrodes.

In general, n-type semiconductors have photoresponsiveness in anode reactions,
P-type semiconductors have photoresponsiveness in cathode reactions.

Among various semiconductors, when titanium oxide (rutile structure), which is an n-type semiconductor, is used as an anode,
The electrode potential is lower than that of other semiconductor electrodes, and it is insoluble and stable in a relatively wide range of electrolytes.
The electrode itself does not change in any way; only the substance in the solution changes.
It has been discovered to this day that it has a very unique property of being able to participate in electrochemical reactions.

By using rutile titanium oxide as an anode and combining it with a suitable cathode, various photovoltaic cells can be constructed.

One example of this is the combination with air (oxygen) diffusion type electrodes used in fuel cells.

In this case, a caustic alkaline solution is used as the electrolyte, and its battery characteristics are approximately 1. By obtaining IV and irradiating the anode with sufficient light, a certain amount of electricity can be extracted, and there are high expectations for its feasibility as a new type of photovoltaic cell.

The reaction of this photocell is as follows at the anode: hν (light) → e + p (h Nyblank constant) 4 p + 40H− → 2H20+ 02↑(
C: Frequency of light) At the cathode (e: Electron) 02+2H2
It is thought that a reaction of 0+4e→40H (p: electron hole) proceeds.

Therefore, at the anode, water is decomposed by light irradiation to generate oxygen, and at the cathode, oxygen is consumed.

Since this battery uses light and oxygen in the air as active materials, it can operate semi-permanently without being recharged, so like silicon solar cells, it does not require any complicated maintenance.

However, in such a photovoltaic cell, when a semiconductor electrode such as rutile-type titanium dioxide is used, the current cannot be increased by one current.

The reasons for this are: (1) the conversion efficiency of light into electrons on the semiconductor surface is low (less than a few);

(j2), 1 The reaction surface of the semiconductor electrode becomes the light irradiation surface,
For convenience of light irradiation, the counter electrode must be placed on the opposite side of the light irradiation surface, and therefore the reactive ions must go around the photoelectrode, resulting in a very large electrolyte resistance.

(3) The reaction surface of a semiconductor electrode is a surface layer, and is limited to only one reaction surface.

(4) The electrical resistance of the rutile type titanium dioxide semiconductor is large, so the IR (current x resistance: drop) in the electrode is very large, and the internal resistance of the battery is very large.

(5) When the metal conductive to the photoelectrode comes into contact with the electrolyte, it forms a local battery and causes internal loss, so the photoelectrode cannot be formed by mixing titanium dioxide powder and a conductive agent.

etc.

These factors make it extremely difficult to put it into practical use, but on the other hand, if the above-mentioned problems can be improved, the possibility of practical application can be expected to increase.

In the present invention, we focus on these problems, and in particular, the above (2)
The purpose of the present invention is to improve the points (3) and to realize a photovoltaic cell with even better discharge characteristics.

That is, conventionally, a single crystal of rutile titanium dioxide or a sintered powder thereof is used, but in the present invention, instead of this, a sponge with a titanium dioxide layer formed on the surface by oxidation is used. A porous electrode made of titanium or titanium powder sintered body is used.

In this case, since it is porous, the electrolyte can freely pass through the electrode plate even if the light irradiation surface and the surface facing the counter electrode are front and back, facilitating ion diffusion and connecting the reaction part. The solution resistance between the electrode and the counter electrode is very small, and the reaction area of the electrode plate has a three-dimensional structure, so it increases significantly.

Furthermore, since it is a porous electrode, it is possible for light to pass into the inside of the electrode plate, and diffuse reflection into the inside of the porous electrode plate also contributes to the reaction, making it possible to fully utilize light energy.

On the other hand, from the viewpoint of conductivity, since the rutile-type titanium dioxide layer is directly formed on the continuous titanium metal conductive network, the proximity distance from the reaction point to the current collecting metal W4 is smaller than that of the conventional oxide. The electrode resistance is significantly smaller than that of a sintered electrode.

Now, as an electrode having an acetylated layer on the surface, it is possible to use a screen-shaped electrode, an expanded electrode, or a punched plate-shaped electrode.In this case, the ion permeability is improved, but The reaction area of the electrode plate becomes small, and since the electrode plate is flat, the amount of light passing through the holes in the electrode plate is lost.

Therefore, it is not necessarily effective.

For these reasons, the titanium metal porous electrode of the present invention, whose surface is oxidized to form a titanium dioxide layer, can extract a much higher current than the conventional electrode.

The features and effects of the present invention will be explained below with reference to Examples.

First, the photoelectrode of the present invention is shown in FIG.

In the figure, 1 is a metal titanium layer, 2 is a titanium dioxide layer, 3 is a hole, and 4 is a lead.

The photoelectrode 5 shown in FIG. 1 is made of titanium sponge having pores ranging from several microns to several nanometers and heat-treated at a temperature of 1200° C. in an oxygen atmosphere.

Here, the heat treatment temperature was set at 1200°C, but any temperature may be used as long as it is 1040°C or higher.

The reason is that the titanium dioxide of the photoelectrode is preferably a rutile type, and the temperature at which the rutile type is obtained is 1040° C. or higher.

A photovoltaic cell combining the thus obtained photoelectrode and an oxygen (air) electrode is designated as A.

A schematic diagram of this photovoltaic cell is shown in FIG.

5 is the photoelectrode mentioned above, and its size is 10s long x 10u wide
x Thickness: 2u.

6 is an air electrode, which is 10n long by 10m wide.

7 is a 1N KOH aqueous solution, 8 is an epoxy resin container, 9 is quartz glass for transmitting light, 10 is the lid of the container, and 11 is the lead of the electrode 5, which is covered with epoxy resin.

12 is a lead of the air electrode 6, 13 is a light source, which is a 500W high-pressure mercury lamp, and 14 is a gas vent hole.

For comparison, a single crystal of rutile titanium dioxide, which is conventionally said to be photoelectrochemically active, was crushed and sintered to form a porous body with dimensions of 10 mm long x 10 mm wide x 2 fi thick. A photovoltaic cell was assembled in the same manner as in A by adhering a titanium net as a current collector to this via silver paste on the opposite side of the light-receiving surface.

Let this be B. Furthermore, even if we similarly oxidize the metal titanium surface to form a photoelectrochemically active oxide of titanium on the metal, how effective is it that the original base metal is porous? For comparison, the thickness is 2n
The surface of a titanium metal plate was oxidized at 1200'C in an oxidizing atmosphere, and this was used as an electrode.

A photovoltaic cell constructed in the same manner using this electrode is designated as C.

First, these batteries were stabilized by discharging them at a current of 0.1 mA, and then their polarization characteristics were measured.

The results are shown in FIG.

As is clear from Figure 3, the polarization characteristics of humans are higher than B and C.
Like it's much better.

In comparing A and B, even though they are porous, the conductor forms the skeleton of the entire porous body, and is directly connected to the surface of the skeleton itself to form photoelectrochemically active rutile titanium dioxide. This has been shown to reduce polarization and lead to better battery characteristics.

In the comparison of C and C, even if the surface of the titanium skeleton of the conductor is oxidized to the rutile type, if the substrate is plate-shaped, it is difficult to use it in pairs with other electrodes as in the example. This indicates that consideration must be given to the battery configuration.

Since it is a photoelectrode, it is impossible to place obstacles on the side of the irradiation surface, and the counter electrode must be placed on the side opposite to the irradiation side.
If a plate-shaped conductor is present between the irradiated surface and the counter electrode at that time, even if the characteristics on the irradiated surface are excellent, the polarization resistance will eventually be poor.

In this regard, in the case of the present invention, since the entire body including the base is porous, there is no obstacle to ion conduction between the light irradiation side and the counter electrode on the back side, unlike metals.

In this manner, when designing a battery, it is necessary to discuss the structure of the element itself in relation to other electrodes and constituent materials, rather than simply discussing the activity of the element itself.

Additionally, in order to compare the activity of the element itself, if a platinum counter electrode is arranged in a ring shape on the irradiation side and polarized so as not to interfere with the irradiation light, the electrode used in battery C is the same as the electrode used in battery A. This shows that the electrochemical activity itself is high even with C, except for the drawbacks due to the plate shape.

However, the current value at the same polarization value tends to be slightly lower by 80 to 90% compared to the case of electrode A. This is because electrode A, which originally had a rough surface made by oxidizing the porous substrate, has a smooth surface. It is presumed that this is because the reflectance is lower than that of C which is an oxidized plate, and the absorption efficiency is correspondingly higher.

In addition, although titanium sponge was used in this example, when a sintered body of titanium powder is used, it can be treated in the same way as titanium sponge, that is, heat treated in an oxidizing atmosphere at a temperature of 1040'C or higher. As a result, almost the same results as A were obtained as a photoelectrode.

In this case, titanium powder with a particle size of 5oμ to 500μ is filled into an alumina mold with dimensions of 1 drawer (vertical) x 10+m (horizontal) x 2 (depth), and baked in a vacuum at a temperature of 1200°C for 1 hour. After that, oxygen is added at a rate of It/min to about 2
The electrode was fed for 0 minutes to bring the actual surface of the electrode into a good oxidation state, and this was used as a photoelectrode.

From the above, the photovoltaic cell of the present invention has significantly improved cell characteristics compared to conventional cells, and has extremely great industrial value in terms of effective utilization of light energy.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a photoelectrode in an embodiment of the present invention, and FIG.
The figure is a schematic cross-sectional view of a photovoltaic cell using the same photoelectrode, and FIG. 3 is a diagram showing polarization characteristics. DESCRIPTION OF SYMBOLS 1...Metal titanium layer, 2...Curved titanium dioxide layer, 3...Vacancy, 5...Light opening electrode.

Claims (1)

[Scope of Claims] 1. A photovoltaic cell characterized by using a photoelectrode made of a porous titanium material having a three-dimensional three-dimensional structure and having a titanium dioxide layer formed on its surface. 2. The photovoltaic cell according to claim 1, wherein the titanium porous body is made by heat-treating titanium sponge in an oxidizing atmosphere at a temperature of 1040° C. or higher. 3 The titanium porous body heats the sintered body of titanium powder to 1040°C.
The photovoltaic cell according to claim 1, which has been heat-treated in an oxidizing atmosphere at a temperature above.