Patent Application
20240204209
The present invention relates to an air electrode including an electric double layer containing hydrogen peroxide, and a metal-air cell or battery using the same.
Hydrogen fuel cells and metal-air cells are known as fuel cells, but hydrogen fuel cells require compressed hydrogen as a hydrogen supply source, and in the case of use in automobiles, hydrogen peroxide is proposed to be used as a fuel because there are difficulties in supplying and storing compressed hydrogen gas. In addition, although a carbon electrode is generally used as the air electrode in a metal-air cell, there is a problem that the rate of ionization of oxygen at the air electrode is slower than the rate of ionization at the anode electrode, and therefore, it is common to use porous carbon and improve it (Patent Document 1). Further, in a fuel cell, poly(3,4-ethylenedioxythiophene (PEDOT), which is a conductive polymer, is used as a cathode electrode instead of a carbon electrode, while a nickel mesh is used as an anode electrode, so that a loss due to a disproportionation reaction is not generated, and a fuel cell exhibiting an open-circuit potential ranging in 0.5˜0.6V with a 0.20˜0.30 mW cm power density has been published (Non-Patent Document 1). On the other hand, a fuel cell using copper hexacyanoferrate (CuHCF) as a cathode material and Ni grids as an anode material has also been published (Non-Patent Document 2), but there is no versatility for use as an air electrode of the metal-air cell.
As a result of intensive research to solve the problem of the air electrode of the prior art, the present inventor has found that; when hydrogen peroxide is supplied into the alkaline electrolyte of the metal-air cell, a dipole electric double layer having a separator function is formed at the interface between the metal electrode and the electrolyte solution, and short-circuiting of the electrode can be prevented. On the other hand, while in the fuel cell, when the metal electrode is used as a positive electrode, a disproportionation reaction of hydrogen peroxide occurs, and it has been considered that the metal electrode cannot be used for cathode, but the present inventor has also found that: if the electrolyte solution contains hydrogen peroxide, hydrogen peroxide can form a dipole electric double layer on the copper electrode surface, so that the copper electrode can be used as an air electrode and hydrogen peroxide can be used as a fuel. These findings were surprising. In view of the above, it is an object of the present invention to provide an air electrode or a copper or its alloy electrode including an electric double layer containing hydrogen peroxide, and secondly, to provide a metal-air cell including a copper or its alloy electrode including an electric double layer containing hydrogen peroxide as an air electrode.
That is, the present invention firstly provides a metal-air cell or a fuel cell comprising a neutral or alkaline electrolytic solution containing at least hydrogen peroxide, wherein a metal copper or an alloy thereof immersed in the electrolytic solution is used as a cathode electrode, and a dipole electric double layer formed of hydrogen peroxide is formed at the interface.
The present invention provides a metal-air cell or battery comprising a neutral or alkaline aqueous electrolytic solution containing hydrogen peroxide for forming an electric double layer at an interface with an electrode, a cathode electrode made of metal copper or an alloy thereof immersed in the electrolytic solution, and an anode electrode made of a metal or an alloy thereof having a more base electrode potential than the cathode electrode, wherein a dipole electric double layer is formed by an electrolytic solution containing hydrogen peroxide at the interface between the cathode electrode and the electrolytic solution, and can be used as an air electrode instead of a carbon electrode.
According to the present invention, hydrogen peroxide in the electrolytic solution is an electric dipole, and therefore tends to be oriented to the electrode surface and form a dipole electric double layer.
In the metal-air cell, which is supplied with hydrogen peroxide, the metal-air cell obtains electrons at the anode side by oxidation reaction of, 2Mg→2Mg2++4e−, while at the cathode side, oxygens are reduced to produce hydroxy ions by reduction reaction of O2+2H2O+4e−→4OH−, which generate electric power. However, when a copper-electrode is used as a cathode electrode in a neutral or alkaline electrolyte containing hydrogen peroxide, the amount of current increases. In view of this factor, in the battery having such a configuration, not only the ionization reaction delay, which is a neck of the metal-air battery, is eliminated by the addition of hydrogen peroxide, but also the generation of oxygen and hydrogen on the cathode side can be confirmed, so that it is considered that the fuel cell reaction in which hydrogen peroxide decomposition occurs on the surface of the copper electrode. Normally, in a hydrogen peroxide fuel cell, as disclosed in Non-Patent Document 1, in an acidic region
Cathode reaction: H2O2+2H++2e−→2H2O (1.78 V to NHE) (1)
Anode reaction: H2O2→O2+2H++2e− (0.682 V to NHE) (2)
Sum: The electrochemical reaction of 2H2O2→2H2O+O2 (1.09 V) (3).
On the other hand, in the neutral or alkaline region of the present invention to which hydrogen peroxide is added,
Cathode reaction: H2O2+2H++2OH−+2e−→2H2O+2OH− (1)
Anode reaction: H2O2+2OH−→O2+2H++2OH−+2e− (2)
It can be thought that the above electrochemical reactions are occurring at the same time.
In addition, according to the present invention, it can be thought that the dipole electric double layer containing hydrogen peroxide is caused by the decomposition of hydrogen peroxide along with the catalytic reaction on the surface of the copper cathode.
2H2O2→4OH→2O2+2H2+4e− (power generation response)
Or 4OH−→O2+2H2O+4e− (power generation response) by the decomposition of hydroxyl ions.
As shown in
An electromotive force in the configuration of an alkaline electrolyte/cathode electrode comprising an anode electrode/hydrogen peroxide, the reaction of which is as follows:
The metal-oxidation reaction of the anode-side: M→Mn++ne−,
On the other hand, it is O2+H2O+4e−→4OH− to carry out an oxygen-reducing reaction on the cathode side.
In the present invention, in order to accelerate the reduction reaction on the cathode side of the metal-air battery, hydrogen peroxide was added to the electrolytic solution to improve and solve the reason why the ionization progress rate of the cathode side positive electrode is inferior to that of the anode side negative electrode.
In other words, the metallic copper dissolves somewhat in hydrogen peroxide as shown in the reaction of Cu+2H2O2→Cu2++2OH+2OH− and the reaction of Cu+2OH→Cu2++2OH−, but as shown in the reaction of Cu2++2HO2−→Cu+2HO2 according to Haber u. Willstatter chain (Non-Patent Document 3), the HO2 groups seems to improve and accelerate the decomposition of hydrogen peroxide.
Further, in the present invention, generation of hydrogen and oxygen gas is recognized from the cathode side, which means in addition to constituting a conventional hydrogen peroxide fuel cell (see Non-Patent Document 1), the following reaction occurrence at the same time
Cathode: H2O2+2H++2e−→2H2O (1.78 V to NHE) (1)
Anode: H2O2→O2+2H++2e− (0.682 V to NHE) (2)
Total: 2H2O2→2H2O+O2 1.099 V) (3)
It is believed that the present disclosure decomposes into hydrogen peroxide 2H2O2→·4OH along with the catalytic reaction on the copper-cathode surface to generate oxygen and hydrogen as shown in the reaction of 4OH⇒H2+O2+4e− and, or decompose the hydroxy-ion to generate oxygen and hydrogen as shown in the reaction of 4OH−⇒H2+O2+4e−, and simultaneously emit electrons.
In the present invention, although hydrogen peroxide was added to the electrolytic solution as an oxidizing agent for forming an insulating electric double layer on the cathode electrode surface, various oxidizing agents for oxidizing the metal surface, as long as it has a function of forming an electric double layer, it can be understood from the description of the present specification by those skilled in the art that the same functions and effects can be achieved even if using together with hydrogen peroxide.
In the present invention, it is preferable that a part or all of hydrogen peroxide is supplied to the aqueous electrolytic solution by sodium percarbonate. Specifically, from 0.5 to 2.0 mol of an alkali metal or alkaline earth metal halide salt, in particular from a few percent to a few tens of percent hydrogen peroxide solution (by volume %) or sodium percarbonate (by weight %) is preferably added to a neutral or alkaline aqueous solution containing sodium chloride.
The anode electrode and the cathode electrode are alternately opposed to each other with a spacer therebetween, and an electric double layer capacitor is formed by an aqueous electrolyte solution containing hydrogen peroxide at a contact portion between the anode electrode and the cathode electrode (
(Performance Comparison with and without Micro-Capacitors)
The copper-electrodes shown in
An upper open cuboid plastic container with a volume 3000 ml is used. Numerous triangle projections 11 of the height of 50 mm are formed by cutting at 150 mm to 200 mm intervals on the copper cathode electrodes sheet 10 of 100×100 mm having 1 mm thickness (photo 3A), as shown in 3B of the figure, both end copper sheet 10 are arranged with inward protrusion 11 and middle copper sheets are combined back-to-back and are arranged with outward protrusion 11. the magnesium anode electrodes sheet 20 of horizontal 100×100 mm having 2 mm thickness are sandwiched by the inward protrusion 11 and outward protrusion 11.
Using the above combined electrode, a microcapacitor can be formed on the top of the copper cathode electrode, as shown in
On the other hand, as shown in 2A of the drawing, the copper electrode plate is attached with a T-shape spacer having 3 bended ends and 2 magnesium electrode plates of 100×100 mm having a 1 mm thickness are sandwiched by a pair of the copper electrode plates with the T shaped spacer. This structure is shown as
To a 1500 ml of pure water, an electrolyte solution of 0.5 mol/l or more of sodium chloride, preferably more than 1.5 mol/l to less than 2 mol/l is added, and sodium percarbonate 50˜100 g and 30% hydrogen peroxide 50 ml are added. After a certain period of time, hydrogen peroxide is consumed and the oxygen is reduced, so 10 ml 30% hydrogen peroxide solution is added every 2-3 hours.
In the present embodiment, the performance of the electrode configurations of
While hydrogen peroxide decomposes into H2O2+2H2O+2e−→2H2O+2OH−, hydrogen peroxide not only causes an oxidation reaction of H2O2+2OH−→O2+2H2O+2e− on the cathode side, but also causes a metal oxidation reaction in an alkaline electrolyte solution of Mg→Mg2++2e−, and finally oxygen is reduced and ionized on the cathode side as shown in the reaction of O2+2H2 O+4e−→4OH−. However, it can be understood that the oxygen gas is generated in the hydrogen peroxide fuel cell and the metal air cell reaction, but not only the oxygen gas but also the hydrogen gas is generated in the present inventive configuration. That is, as suggested in Non-Patent Document 3 (Eiji Water, Physicochemical Advancement (1936), 10(3):154-165), it is understood that the catalytic function works on the surface of the copper cathode electrode, and decomposition of hydrogen peroxide or decomposition of hydroxy ions occurs, and it seems to lead to the power generation reaction of
2H2O2→4·OH→H2+O2+4e−
4OH−→H2+O2+4e−
As described above, the present invention has been described using a Mg anode electrode and a Cu cathode electrode as a pair of electrodes, even if the other anode electrode selected from the same kind of typical metals such as aluminum, zinc and the alloy thereof is used, it goes without saying that the same kind of effect can be obtained although the electrode potential difference differs.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-073490 | Apr 2021 | JP | national |
| 2021-073534 | Apr 2021 | JP | national |
| 2021-073535 | Apr 2021 | JP | national |
| 2021-142106 | Sep 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/018775 | 4/25/2022 | WO |
