JPS58516B2 - Koden Henkansu Isohatsu Seisouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photoelectric conversion hydrogen generation device that directly converts light energy into electrical energy and decomposes an aqueous solution as an electrolyte to generate hydrogen.

In this type of device, a pair of electrodes (one of which may use a platinum electrode as a counter electrode), consisting of an n-type semiconductor as an anode and an n-type semiconductor as a cathode, is immersed in an aqueous electrolyte, and the semiconductor is attached to the semiconductor electrode. When irradiated with light having energy greater than the forbidden band width, the electrode potential increases to n due to the photovoltaic effect.
The electrode potential shifts to noble in type semiconductors and to base in n-type semiconductors, and the transition of the electrode potential shows a value that depends on the intensity of the irradiated light.

Therefore, if an n-type semiconductor electrode and a conductive electrode such as platinum are used as a pair of electrodes, a negative potential appears on the n-type semiconductor electrode and a positive potential appears on the conductive electrode due to light irradiation. If , a positive potential appears on the n-type semiconductor electrode and a negative potential appears on the conductive electrode.

Furthermore, in a combination of an n-type semiconductor electrode and an n-type semiconductor electrode, the phenomenon in which a positive potential appears on the former and a negative potential appears on the latter is used to directly convert light energy into electrical energy.

Also, in this conversion process, the aqueous solution as the electrolyte is decomposed, and hydrogen is generated at the cathode by a cathode reaction, while oxygen is generated at the anode by an anodic reaction.

In recent years, energy shortages have become a major social problem, and hydrogen is seen as a promising alternative fuel to petroleum and the like, and various methods of producing it are being studied.

Under these current circumstances, it is industrially extremely interesting to effectively utilize sunlight, which is natural energy, to cause water decomposition and to produce hydrogen using the photoelectric conversion hydrogen generator as described above.

From this point of view, the present inventor has conducted various studies on the composition of electrodes and electrolyte solution with the aim of reducing the cost of this type of device, increasing the generated electromotive force, and increasing the amount of hydrogen generated, and has discovered the device of the present invention. It is.

That is, in order to effectively utilize sunlight as a cathode, the device of the present invention has a forbidden band width of 1 to 100 which corresponds to the sunlight spectrum region.
Among n-type semiconductor materials with 3ev characteristics, p-type Ga-based compound semiconductors such as p-type Gap or p-type GaAs, which have particularly good unipolar characteristics, are used, and as an anode, they react with a water-soluble electrolyte to release hydrogen. It is characterized by the use of metal electrodes that exhibit a base potential, such as generated Zn and Li-A1 alloys,
By combining these pair of electrodes, a higher discharge pressure can be obtained as a photovoltaic cell, and a large amount of hydrogen can be obtained through the combination of hydrogen generation from the cathode and hydrogen generation from the anode.

The configuration of the device of the present invention will be shown below.

Example 1 In the configuration diagram shown in FIG. 1, 1 is a p-type GaP single crystal thin plate (surface area 15 cm, thickness 0.4 mm), and a copper lead wire 3 is connected to a zinc-indium alloy deposited on the back side of the plate. The electrode 1 is arranged in the cathode chamber of the H-shaped glass container 4.

2 is a Zn electrode (reactive surface area: 5 cm 2 ) used as a counter electrode, to which a copper lead wire 3 is spot-welded and placed in the anode chamber of the H-shaped glass container 4 .

5 is an electrolytic solution made of a specified aqueous sulfuric acid solution; 6 is an asbestos diaphragm that divides the glass container 4 into a cathode chamber and an anode chamber; 7 is a quartz plate provided at the light receiving window; 8 and 9 are hydrogen outlet ports; This is a sealing plate that closes the opening of the glass container 4.

Light irradiation uses sunlight and uses a Fresnel lens to magnify it 400 times (
The light was focused at 40 W/cm2).

Figure 2 shows the battery system (solid line) of the device of the present invention with the above configuration.
This is a characteristic comparison diagram of the battery system (broken line) using P-type GaP for the cathode and n-type GaP2 for the anode, and curves I and ■
The curve (2) shows the monopolar characteristics of the cathode and anode versus the saturated calomel electrode when assembled as a battery, and the curve (2) shows the battery voltage. It can be seen from the figure that an extremely high discharge pressure can be obtained in the device of the present invention.

In addition, water is decomposed in the process of converting light energy into electrical energy, and at the Zn electrode, the anode reaction is Zn+H2O- + ZnO + 2H++2e, and at the P-type GaP electrode, the cathode reaction is 2e+2.
H+→H2, and overall Zn+H20→ZnO+H2, hydrogen is generated from the cathode, and Zn (zinc) is oxidized to Zn0 (zinc oxide) at the anode.

This inactive ZnO is sequentially removed by dissolving the Zn electrode, and the Zn electrode surface is always maintained in an active state.In the three-pronged anode, an infinite percent of the Zn electrode is mixed with an electrolyte (sulfuric acid aqueous solution) during the photoelectric conversion process, as shown below. Reacts and generates hydrogen.

Zn+H2SO4→ZnSO4+H2 Example 2 In the block diagram of FIG. 1, the Zn plate of the anode was replaced with an AI plate (reaction surface area: 5 crit), and the electrolyte in the cathode chamber and anode chamber was replaced with 1N NaOH.

The cathode and other components are the same as in Example 1. In the case of this example, the anode reaction 2Al+60H-)2Al(OH)3. +6e,
In the P-type GaP electrode, the cathode reaction 6H20+6e→
3H2+60H, and the overall result is 2Al+6H20→2AI(OH)s+3H2,
Hydrogen is generated from the cathode and AI (
aluminum) is converted to AI(OH)3 (aluminum hydroxide).

This Al(OH)3 is also sequentially removed by dissolving the AI electrode.

Further, at the anode, the AI electrode reacts with the electrolytic solution (sodium hydroxide aqueous solution) as described below, and hydrogen is generated.

2Al+2NaOH → 2NaA102+3H2 Example 3 In the configuration diagram of Fig. 1, the Zn plate of the anode is replaced with Li-Al.
It was replaced with an alloy plate (reaction surface area 5i), and 3% NaCl (saline solution) was used only as the electrolyte in the anode chamber.

The rest is the same as in Example 1. In the case of this example, Lt
In the A1 alloy electrode, the anode reaction 2Li+2H! 20→2LtOH+2H++2e, and in the P-type GaP electrode, the cathode reaction is 2e+2H+→H2 as in Example 1, and the overall reaction is 2Li+2H20→2LiOH+H2.

In addition, at the anode, the Li-AI electrode is connected to an electrolyte (saline solution).
reacts with hydrogen as shown below and generates hydrogen.

2Li+2H20→2LiOH+H2 Example 4 In Example 3, the Li-Al alloy plate of the anode was
-Al alloy plate (reaction surface area: 5 cm2) was used, and the rest was the same as in Example 3.

In the case of this example, in the Mg-Al alloy electrode, the anode reaction is Mg+2H20→Mg(OH)2+2H++2e, and in the P-type GaP electrode, the cathode reaction is 2e+2H+→
H2, and the total becomes Mg+2H20→Mg(OH)2+H2.

Further, the Mg-Al alloy electrode reacts with the electrolytic solution (saline solution) in the anode as described below to generate hydrogen.

Mg+2H20→Mg(OH)2+H2 Figures 3 and 4 show an example in which a metal electrode with a base potential that reacts with an aqueous electrolyte to generate hydrogen is used as an anode, as shown in the various examples above. Inventive device and n-type GaP
A comparison diagram of battery voltage characteristics and hydrogen production amount when P-type GaP is used as a cathode and a conventional device using a semiconductor as an anode is shown, and it is recognized that the characteristics of the device of the present invention are excellent.

As described above, the present invention relates to a photoelectric conversion hydrogen generation device that converts light energy into electrical energy and decomposes water in an aqueous electrolyte in the conversion process, and has a forbidden band on the cathode corresponding to the solar spectral region. Among P-type semiconductors with width characteristics, P-type G has particularly good unipolar characteristics.
A metal electrode that uses a P-type Ga-based compound semiconductor such as aP or P-type GaAs, exhibits a base potential at the anode, has smaller polarization than a semiconductor electrode, and generates hydrogen by reacting with an aqueous electrolyte. Therefore, a high discharge pressure can be obtained and the amount of hydrogen produced at the cathode can also be increased.

Furthermore, since hydrogen is also generated at the anode, a large amount of hydrogen can be obtained in combination with hydrogen generation from the cathode.

Regarding the aging characteristics, metal electrodes are limited because they involve dissolution and corrosion reactions, but since low-lying metal electrodes are used, they can be replaced with new ones and operated continuously.

As described above, the device of the present invention, which can reduce the cost of the device, increase the generated electromotive force, and increase the amount of hydrogen produced in this type of device that effectively uses sunlight, which is a natural energy, is extremely useful in terms of industrial contribution. It is.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of the device of the present invention, and Figure 2 is a diagram of the device of the present invention (Z
n/P-type GaP system) and conventional equipment (n-type GaP/P-type GaP system) and conventional equipment (n-type GaP/P-type GaP system)
Figures 3 and 4 are comparison diagrams of voltage-current characteristics and hydrogen generation characteristics between the device of the present invention and a conventional device. 1... Cathode electrode, 2... Anode electrode, 3...
・Copper lead wire, 4... Glass container, 5... Water-soluble electrolyte, 6... Asbestos diaphragm, 7... Quartz plate, 8,
9... Hydrogen outlet, 10... Sealing plate.

Claims (1)

[Claims] 1. In an apparatus in which a pair of electrodes, at least one of which is made of a semiconductor, is immersed in an aqueous electrolytic solution and the semiconductor electrodes are irradiated with light to generate an electromotive force and decompose water, the cathode is a p-type Ga-based compound. A photoelectric conversion hydrogen generation device comprising a semiconductor electrode, and an anode comprising an electrode made of a metal or an alloy that generates hydrogen by reacting with an electrolyte.