JP5546168B2 - Photoelectrochemical measurement electrode - Google Patents

Description

  The present invention incorporates a total of three electrodes, a working electrode, a counter electrode made of a conductive material, and a reference electrode, and a small light-emitting diode and its lighting circuit as a light source. The present invention relates to a photoelectrochemical measurement electrode that can measure the photoelectrochemical characteristics of a solution or a solid with a single electrode without using another light source.

  In recent years, global warming due to a large amount of carbon dioxide emission from fossil fuel combustion and abnormal weather, major floods, disappearance of permafrost, reliable melting of glaciers, sea level rise, etc. In addition, it is occurring at a high frequency, and the living environment of mankind is rapidly deteriorating and being threatened. In order to quickly solve such serious global problems, creation of new energy resources and innovative energy-saving technologies are strongly demanded. Wind power generation, solar power generation using solar cells, renewable new energy resources such as biomass use, and energy-saving systems using fuel cells are expected and becoming popular as a technology to solve these problems. .

  However, in order to implement these new energy systems economically, there are still many problems in terms of efficiency and cost, and at present, further basic research and development efforts are strongly demanded. . One of the leading and important research and development methods for this purpose is a photoelectrochemical method using a semiconductor or a dye-sensitized semiconductor as a photoelectrode. This is a method of obtaining fuel such as hydrogen or electric power from solar energy by utilizing photochemical energy conversion by a semiconductor or a dye-sensitized semiconductor. In fact, dye-sensitized solar cells invented by Prof. Gretzell at the University of Lausanne in Switzerland are attracting attention as next-generation solar cells for inorganic semiconductor solar cells such as silicon. In Australia, a dye-sensitized solar cell is sold as a product. A method for producing hydrogen fuel from water and solar energy using a photoelectrochemical reaction of a semiconductor is also attracting attention, and many researches and developments are being carried out worldwide aiming at practical use. In addition, the present inventors have proposed and verified a biophotochemical battery that can completely decompose and purify waste liquid and waste of biomass and organic matter with sunlight, and simultaneously convert the enormous energy contained in them into electric power, and promote research and development. (Masao Kaneko and Junichi Nemoto, “Biophotochemical Battery”, Industrial Research Committee (2008)) (Non-patent Document 1).

  As described above, the present inventors use various kinds of biomass, inorganic / organic compounds, and electron donating compounds such as wastes as fuels, so that photophysics capable of generating electric power simultaneously with their photolysis and purification. The idea that a chemical cell can be used for society as a new energy-saving power generation system that replaces conventional solar cells and fuel cells was obtained, and its basic patent (Patent Document 1) is “photophysical chemical cell”. As of March 9, 2006, he filed an international patent application (PCT application) as an applicant; Ibaraki University, inventor; Masao Kaneko. However, this application is an invention as a photovoltaic cell, and an apparatus for realizing it is composed of a reaction vessel (cell), a semiconductor photoelectrode, and an oxygen reduction counter electrode, and operates as a photovoltaic cell. It was impossible to measure the properties.

  The present invention relates to research and development of photochemical energy conversion, as a device or element for measuring the photocurrent, utilizing the electric power generated by photodegrading various compounds to photodecompose and generating photocurrent efficiently. It is an object of the present invention to provide a powerful and simple means for measuring photoelectrochemistry which is absolutely necessary for developing a photochemical cell. For this purpose, a semiconductor electrode or dye-sensitized electrode that responds to light is used as a working electrode, a conductor such as platinum or graphite is used as a counter electrode, and a silver-silver chloride electrode is used as a reference electrode. In addition, an ultra-compact and ultra-energy-saving light-emitting diode (LED) and its lighting circuit are incorporated into this composite electrode, and only this photoelectrochemical measurement electrode is used for cyclic voltammogram (CV) under light irradiation. ) Was successfully made possible.

  As a measuring apparatus similar to this method, there is a “specific detection method of a test substance using a photocurrent, electrodes used therefor, a measuring cell, and a measuring apparatus” (Patent Document 2). It consists only of a working electrode and a counter electrode, and detects and quantifies a test substance only by the obtained photocurrent, and measurement of photoelectrochemical characteristics is impossible. Further, although an example using an LED is also in the claims, there is no description that the LED or its lighting circuit is built in the cell, which is completely different from the present invention.

PCT / JP2006 / 305185 JP 2006-119111

Masao Kaneko and Junichi Nemoto, “Bio-Photochemical Battery”, Industrial Research Committee (2008)

  In order to measure the photoelectrochemical properties of various compounds for the purpose of photochemical energy conversion, so far, three working electrodes that absorb light, such as a semiconductor, and a counter electrode and a reference electrode, such as a conductor, are separated. In addition, it was necessary to prepare a light source for external irradiation such as a xenon lamp or pseudo-sunlight and to irradiate the light, so the device was very large and laborious, and the light source for external irradiation was 100W ~ Since a lamp (electric power) with a strong energy of about 5 KW was required, the energy and cost required for the measurement were not stupid, and it was not easy for both beginners and experts in the field to measure.

  The present invention provides a working electrode such as a semiconductor, a counter electrode, a reference electrode, and an ultra-small and ultra-energy-saving light emitting diode light source (LED) in order to make photoelectrochemical measurement extremely simple and energy-saving. All of these are installed on a small electrode of a book, and photoelectrochemical measurement can be performed very easily by using only one electrode for photochemical measurement.

According to the present invention, the following inventions are provided.
(1) (i) a semiconductor electrode or (ii) a dye-sensitized electrode as a working electrode, a conductive material as a counter electrode, and in addition to them, a reference electrode made of silver-silver chloride, and these electrodes can be exchanged A plug-in type composite electrode;
The light-emitting diode (LED) as a light source and its lighting circuit are housed in a transparent cylindrical protective tube so that the liquid does not come into contact with the light-emitting diode (LED) light source. It consists of an internal irradiation type light source part in which the tube is immersed in the liquid,
An electrode device for photoelectrochemical property measurement with a light source, wherein the composite electrode is disposed in the vicinity of a light source of a light source unit accommodated in the protective tube.

(2) The electrode device for photoelectrochemical property measurement according to claim 1, wherein the working electrode is a dye-sensitized electrode that adsorbs a dye to a semiconductor and can absorb and use visible light.

(3) Examples semiconductor electrode is a working electrode, applying a nanoparticulate powder of the semiconductor material, photoelectrochemical characteristics measuring electrode device according to claim 1 is used one made of ultra-porous semiconductor thin film obtained by sintering .

  According to the present invention, the photoelectrochemical characteristics of various biomass, organic, and inorganic compound solutions are used without using a special light source, and one super-energy-saving small electrode that does not use much energy is used. Therefore, measurement can be performed very simply and efficiently with an inexpensive apparatus. As a result, research and development for creating sustainable energy from sunlight can be greatly promoted.

It is a figure of the example of a photoelectrochemical measurement electrode. a) Image view, a ', b) Image view seen from below It is the cyclic voltammogram (CV) at the time of LED light irradiation and darkness in Example 2. FIG. The horizontal axis is the potential (vs. Ag-AgCl), and the vertical axis is the current value. It is a cyclic voltammogram (CV) with and without stirring (1200 rpm) under LED irradiation in Example 4. The horizontal axis is the potential (vs. Ag-AgCl), and the vertical axis is the current value.

Supplementary description of the embodiment of the present invention is as follows.
The characteristics of the photoelectrochemical measurement electrode can be summarized as follows.
(I) In order to easily measure the photoelectrochemical reaction without using an external light source, a semiconductor or dye-sensitized semiconductor electrode as a working electrode, a counter electrode made of a conductor, a reference electrode such as silver-silver chloride, and Photoelectrochemical measurement electrode that incorporates a small, energy-saving light-emitting diode (LED) and its lighting circuit.

(Ii) In order to make it possible to measure photoelectrochemical reactions at various irradiation light wavelengths, LEDs are made of ultraviolet light, visible light (typically, the three primary colors of blue, green, and red light), Various other wavelengths of visible light, white light and, if necessary, near-infrared LEDs are used together with the lighting circuit.

(Iii) The value of the current flowing through the LED is variable so that measurement at various light intensities is possible.

(Iv) Electrodes can be easily exchanged so that various electrodes can be used freely according to the purpose.

  FIG. 1 is an example (a) of an electrode configuration image for photoelectrochemical measurement of the present invention, and also shows diagrams (a ′, b) of examples of mutual arrangement of electrodes as viewed from below. The working electrode, counter electrode, and reference electrode are interchangeable plug-in types, and the LED is housed in a protective tube so that liquid does not come into contact with it. The protection tube is partially or entirely transparent, and when UV-LED is used as the light source, the protection tube is partially or entirely made of a material that can transmit ultraviolet light. Quartz is preferable as the material through which the ultraviolet light is transmitted, but Pyrex (registered trademark) glass is sufficient because it is expensive. It also has a built-in LED lighting circuit that is connected to a 100V AC power supply. The electrodes can be arranged in various ways, but the working electrode and the counter electrode are preferably close to each other so that the liquid resistance between the working electrode and the counter electrode is small, and the reference electrode should be close to the working electrode. This is shown in FIG. 1 as an example.

(Working electrode)
What can be used as the working electrode is a semiconductor or dye-sensitized electrode. Examples of the semiconductor include a crystalline or ultraporous ultraviolet semiconductor electrode or (b) a visible semiconductor. More specifically, (a) as an ultra-porous semiconductor electrode in the ultraviolet region, titanium dioxide gives good results, but in addition, ultra-porous ultraviolet region such as zinc oxide, tin dioxide, tungsten oxide, silicon carbide, etc. A semiconductor is used. At that time, since the surface of the semiconductor made of crystals is flat, the surface of the semiconductor that is effectively used for the photochemical reaction is extremely small and the current value does not increase. In order to increase the contact area of the photoanod / liquid phase in which the photoelectrochemical reaction occurs, it is preferable to use a superporous semiconductor material having an effective surface area of several hundred times to 1000 times the apparent electrode area.

  As the visible region semiconductor, silicon, gallium arsenide, cadmium selenide, cadmium sulfide, gallium phosphide, or the like can be used as the working electrode.

  In order to use a semiconductor as a superporous electrode, for example, it is preferable to apply a nano-particle powder of a semiconductor material onto a substrate made of a transparent conductive material and then sinter to form a superporous semiconductor film. As the transparent conductive substrate material, various materials such as transparent conductive glass (ITO, etc.), metal, metal thin film, and carbon can be used. Moreover, the electrical conductivity of the conductive glass as the substrate may decrease due to heating during sintering after coating. In that case, it is preferable to use a fluorine-doped transparent conductive material (FTO) because the decrease in electrode conductivity can be reduced.

  The dye-sensitized working electrode is an electrode that adsorbs and absorbs a dye capable of absorbing visible light on the electrode so that visible light can be used. For example, when a tris (bipyridine) ruthenium complex or a derivative thereof is adsorbed on a porous semiconductor thin film electrode, it can be used as a photoelectrode that responds to visible light.

(Counter electrode)
If it is a material that can flow a sufficient current, platinum, carbon, porous carbon, graphite, or a mixture or compression of these in any composition, transparent conductive glass, or electrodes carrying platinum fine particles on them, A platinum black electrode is not particularly limited, and any of them can be used. A metal complex or the like may be modified on the electrode.

(Built-in light source: Light emitting diode LED)
The present invention is characterized in that various light-emitting diodes (LEDs) of energy saving type are used as an internal irradiation type light source. Thus, photoelectrochemical measurement can be easily performed with one main electrode without preparing another light source, and the working electrode can be irradiated with light energy without waste. In order to respond to various purposes of photoelectrochemistry, LEDs are ultraviolet (UV), various wavelengths in the visible region, especially not only white light, but also three primary colors of blue, green and red light, near infrared It can contain diodes that emit electromagnetic waves of various wavelengths such as light and infrared light.

(Position of electrode and LED)
The LED is generally installed in the position or direction where light is irradiated directly or directly below, and the working electrode is installed so as to receive light perpendicular to the irradiation direction, but this is not a limitation. Absent.

Hereinafter, the present invention will be specifically described with reference to examples, but the technical scope of the present invention is not limited thereto. These examples clearly show that the photoelectrochemical measurement electrode is extremely suitable for measuring the photoelectrochemical characteristics of the working electrode. In the examples, M is the molar concentration (moldm ^-3 ).

After mixing titanium dioxide (P-25) nanoparticles with an average particle size of 20nm, acetylacetone and surfactant well, kneading to make a paste, and applying this onto conductive glass (FTO) , Firing at 100 ° C., repeating this, and finally firing at 450 ° C. for 30 minutes to form a superporous film (thickness of about 10 μm, area of 1 cm ² ) on the conductive glass to form an n− type semiconductor electrode It was. This working electrode has an effective interface of about 1000 times the apparent area. Using this as a working electrode, using a counter electrode made of platinum black (1cmx1cm) coated with platinum black, using Ag-AgCl electrode as a reference electrode, built-in UV-LED (Nichia Chemical NCCU033) and its lighting circuit A photoelectrochemical measurement electrode having a structure similar to that shown in FIG. 1 was prepared.

The photoelectrochemical measurement electrode prepared in Example 1 was immersed in 5 ml (pH 14) of an aqueous solution in which 1M ammonia and 0.1M Na ₂ SO ₄ were dissolved, and the three types of electrodes were connected to a commercially available electrochemical measurement device with wires. Connected to form an external circuit, and swept the potential range of -1.1V to + 0.7V vs. Ag-AgCl at a sweep rate of 20mVs ^-1 with and without LED (current 15mA) irradiation and cyclic voltammogram (CV) was measured and the result is shown in FIG. Both showed typical semiconductor electrode characteristics. As is clear from FIG. 2, almost no current was generated under non-LED irradiation, but a clear photocurrent rose from around −0.8 V under LED irradiation, just like using an external light source with only one electrode. A good photoelectrochemical CV could be measured.

In Example 2, the LED current value was set as high as 50 mA, and in other cases, the CV under LED irradiation was measured in the same manner as in Example 2. As a result, a clear rise in photocurrent was observed. The photocurrent value was about 1.6 times that of the case of Example 2 (about 0.35 mAcm ⁻² ) (about 0.55 mAcm ⁻² at 1M concentration), and a photocurrent corresponding to the LED light intensity was obtained.

In Example 2, the CV under LED (15 mA) irradiation was measured when the aqueous solution was electromagnetically stirred (1200 rpm) and not shown in FIG. Under the agitated condition, the equilibrium value of the photocurrent is a little low, and the potential at which the curve crosses the X-axis (-0.7V vs, Ag-AgCl) does not stir, which approximates the flat band potential (E _fb ) of the semiconductor. The condition was clearly as low as −0.8 V, which clearly showed that the stirring condition probably affected the adsorption state of the semiconductor surface and changed the characteristics of the semiconductor.

  In Example 4, CV under light irradiation was measured with and without agitation as in Example 2 except that the ammonia concentration was reduced to 300 mM. The equilibrium photocurrent value was, for example, 0.31 mA for ammonia 1M and 0.28 mA for 300 mM, reflecting the concentration.

  In Example 1, a commercially available paste, Ti-nanoxide T / SP, was applied as it was on the FTO by the squeegee method, sintered at 450 ° C. for 30 minutes, and nano-porous with a thickness of about 10 μm. A thin film working electrode was prepared. Using this, the equilibrium photocurrent value was measured by CV in exactly the same manner as in Example 2. As a result, it was about half of the photocurrent value in Example 2. From this, it is clear that the titanium dioxide thin film in Example 1 is superior to that in Example 6, and the photoelectrochemical measurement electrode allows various photoelectrochemicals to be carried out easily and under extremely low power consumption. You can get experimental facts.

1 Working electrode (FTO / TiO ₂ )
2 Counter electrode (Pt / Pt-Black)
3 Reference electrode (Ag-AgCl)
4 UV-LED

Claims (3)

(I) a semiconductor electrode or (ii) a dye-sensitized electrode as a working electrode, a conductive material as a counter electrode, a reference electrode made of silver-silver chloride in addition to them, and a plug-in type in which these electrodes can be exchanged Composite electrode,
The light-emitting diode (LED) as a light source and its lighting circuit are housed in a transparent cylindrical protective tube so that the liquid does not come into contact with the light-emitting diode (LED) light source. It consists of an internal irradiation type light source part in which the tube is immersed in the liquid,
An electrode device for photoelectrochemical property measurement with a light source, wherein the composite electrode is disposed in the vicinity of a light source of a light source unit accommodated in the protective tube.   2. The electrode device for photoelectrochemical property measurement according to claim 1, wherein a dye-sensitized electrode that adsorbs a dye to a semiconductor and absorbs visible light is used as the working electrode.   The electrode device for photoelectrochemical property measurement according to claim 1, wherein the semiconductor electrode as the working electrode is made of a superporous semiconductor thin film formed by applying and sintering a nanoparticle powder of a semiconductor material.