Cathode electrode for fuel cells made of copper or copper alloy

Abstract

To provide a cathode electrode for a metal-air battery and a hydrogen peroxide fuel cell.SOLUTION: The cathode electrode for a metal-air battery and a hydrogen peroxide fuel cell is composed of a metal copper or its alloy having a function to decompose hydrogen peroxide and / or hydroxy ions in a water soluble electrolyte containing hydrogen peroxide.SELECTED DRAWING: Figure 2B

Description

[Technical Field]

[0001] The present invention relates to a cathode electrode for a fuel cell made of copper or a copper alloy. [Background technology]

[0002] In fuel cells, hydrogen peroxide has attracted attention as a fuel source that is easier to supply than hydrogen. In recent years, hydrogen peroxide fuel cells have been expected to be a promising energy conversion platform because, unlike hydrogen fuel cells, their single-compartment structure using an aqueous solution makes fuel supply easy and they can operate without a membrane separating the cathode and anode chambers.

[0003] However, because hydrogen peroxide is a high-energy-density liquid that functions as both a fuel and an oxidant, most metal electrodes catalyze the disproportionation of H2O2 to H2O and O2. As a result, this heterogeneous reaction represents a significant loss mechanism in peroxide fuel cells, and no hydrogen peroxide fuel cells with metal cathodes exist. Specifically, a hydrogen peroxide fuel cell has been reported that uses a conductive polymer, poly(3,4-ethylenedioxythiophene (PEDOT)) as the cathode electrode and a nickel mesh as the anode electrode to prevent losses due to disproportionation reactions, and that exhibits an open circuit potential in the range of 0.5 to 0.6 V at a power density of 0.20 to 0.30 mW cm (Non-Patent Document 1: "Single-Compartment hydrogen peroxide fuel cell with poly(3,4-ethylenedioxythiophene) cathodes," Chemical Communications, 2018, Vol. 54, Pages 11873-11876). On the other hand, a hydrogen peroxide fuel cell has also been reported that uses copper hexacyanoferrate (CuHCF) as the cathode material and a Ni grid as the anode material (Non-Patent Document 2: "Copper hexacyanoferrate as cathode material for hydrogen peroxide fuel cell," International Journal of Hydrogen Energy, ELSEVIER, Vol. 45, Issue 47, September 25, 2018). 2020, Pages 25708-25718). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Chemical Communications,2018, Vol.54, Pages 11873-11876 [Non-patent document 2] Journal of Hydrogen Energy, ELSEVIER, Vol.45, Issue 47, 25 September 2020, Pages 25708-25718 [Non-patent document 3] Eiji Mizuto: Progress in Physical Chemistry (1936), 10(3): 154-165 Summary of the Invention [Problem to be solved by the invention]

[0005] However, conventional cathode electrodes for hydrogen peroxide fuel cells, such as poly(3,4-ethylenedioxythiophene) (PEDOT) and copper hexacyanoferrate (CuHCF), are complex and difficult to mass-produce. Therefore, an objective of the present invention is to provide a new electrode that can be used as the cathode electrode for hydrogen peroxide fuel cells.

[0006] However, it has been discovered that hydrogen peroxide solution is alkaline and contains many hydroxy ions along with oxygen, and that immersing copper or a copper alloy in this hydrogen peroxide solution produces a gas. Since this gas contains not only oxygen but also hydrogen, the inventors speculated that the copper or copper alloy catalyzes the decomposition of hydrogen peroxide or hydroxy ions. Therefore, the inventors have proposed that in a metal-air battery, oxygen is reduced on the cathode electrode side to form hydroxy ions as follows: O2+2H2O+4e - →4OH - , Copper or copper alloys were used as the cathode electrode to form a new metal-air battery configuration or a new hydrogen peroxide fuel cell configuration using copper and its alloys as the cathode electrode. [Means for solving the problem]

[0007] Conventionally, porous carbon electrodes have been used as cathode electrodes in metal-air batteries, and poly(3,4-ethylenedioxy)thiophene (PEDOT) and copper hexacyanoferrate (CuHCF) have been proposed as cathode electrodes for hydrogen peroxide fuel cells. However, this invention focuses on the catalytic function of copper or its alloys in hydrogen peroxide, and its gist is a cathode electrode for metal-air batteries and hydrogen peroxide fuel cells, which is made of copper or a copper alloy and has the function of decomposing hydrogen peroxide or hydroxy ions in an aqueous solution containing hydrogen peroxide to produce oxygen and hydrogen. That is, the present invention relates to a cathode electrode for metal-air batteries and hydrogen peroxide fuel cells, which has a metallic copper or copper alloy surface on its surface, is used in an alkaline electrolyte containing hydrogen peroxide, and has the catalytic function of decomposing hydrogen peroxide and / or hydroxy ions in the aqueous solution. [Effects of the Invention]

[0008] In the case of an air battery, hydrogen peroxide was supplied to the anode, and 2Mg was added to the anode. 2+ + 4e- and electrons are obtained through the oxidation reaction, while at the cathode, O2 + 2H2O + 4e- → 4OH - When hydrogen peroxide is released, oxygen is reduced to generate hydroxy ions, generating electricity. However, according to the present invention, by using copper or copper alloy as the cathode electrode in an electrolyte solution containing hydrogen peroxide instead of a porous carbon electrode, it is currently possible to obtain an electromotive force of 1.2 V or more when measured under load (data logger). Furthermore, in the present invention, the generation of oxygen and hydrogen on the cathode side can be confirmed, and it is believed that a fuel cell reaction occurs on the copper electrode surface, where hydrogen peroxide decomposes. Normally, in a hydrogen peroxide fuel cell, as shown in Non-Patent Document 1, in an acidic region, Cathode: H2O2+ 2H++ 2e - → 2H2O (1.78 V vs. NHE)(1) Anode: H2O2 → O2+ 2H++ 2e - (0.682 V vs. NHE)(2) The total electrochemical reaction is: 2H2O2 → 2H2O + O2 (1.09 V)(3) In the alkaline region where hydrogen peroxide is added, Cathode: H2O2+ 2H + +2OH - +2e - → 2H2O+2OH - (1) Anode: H2O2+2OH - → O2+ 2H + +2OH - + 2e - (2) Furthermore, in the present invention, a catalytic reaction on the copper cathode surface is also involved, resulting in the decomposition of hydrogen peroxide. 2H2O2→ ·4OH→ 2O2+ 2H2 + 4e - Power generation reaction or 4OH by decomposition of hydroxyl ion - →O2+2H2O+4e - This is thought to be accompanied by a power generation reaction.

[0009] Furthermore, hydrogen peroxide acts as a dipole, forming a dipole electric double layer on the surface of the cathode electrode, preventing short-circuiting even when the anode electrode comes into contact with it. Furthermore, the electric dipole forms an electric double layer capacitor with a current-collecting function (Figure 2A). Specifically, the microcapacitor formed here consists of hydrogen peroxide in the electrolyte scattered locally on the copper electrode surface, forming microcapacitors that repeatedly collect and discharge current (Figure 2B). Unlike a conventional capacitor, this microcapacitor accumulates electrons from the cathode until a predetermined charge is reached, as shown in Figure 4. When electrons begin to flow from the cathode to the anode due to the tunneling effect, they rapidly concentrate and flow locally at the opposing anode, amplifying the current like an avalanche. Therefore, in the present invention, the copper electrode installed opposite the anode electrode preferably has multiple triangular protrusions formed at regular intervals on its surface. This is because the tunneling effect facilitates avalanche amplification of the current. Furthermore, by providing an electrode surface with electrode protrusions and electrode legs that support the electrode surface at a fixed distance from the bottom of the battery tank, the reaction with hydrogen peroxide rising with the electrolyte is enhanced. Furthermore, it is preferable that the open-topped frame that surrounds the battery tank and the electrode mounting base that divides the interior of the frame into upper and lower sections at a fixed height from the bottom and has an opening through which the electrolyte flows vertically are made of metallic copper or its alloy. This is because the reaction efficiency in metal-air batteries and hydrogen peroxide fuel cells is proportional to the electrode area of ​​copper and copper alloys. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a conceptual diagram showing a basic cell reaction using copper or its alloy of the present invention as a cathode electrode. [Figure 2A] FIG. 1 is a conceptual diagram of a cathode electrode that forms a dipole electric double layer that does not short-circuit even when the anode electrode and cathode electrode come into contact with each other. [Figure 2B] 1 is a conceptual diagram of a cathode electrode in which an anode electrode and a cathode electrode are in contact with each other to form a dipole microcapacitor at the short circuit. [Figure 3A]A perspective view of a copper cathode electrode with four protruding electrodes cut out from a 10 cm square copper electrode surface. [Figure 3B] 3A is a cross-sectional view of the electrode configuration in which a magnesium anode electrode is sandwiched between copper cathode electrodes; [Figure 4A] A perspective view of a copper cathode electrode with six protruding electrodes cut out from a 10 cm square copper electrode surface. [Figure 4B] 4A is a cross-sectional view of the electrode configuration in which a magnesium anode electrode is sandwiched between copper cathode electrodes; [Figure 5A] A perspective view of a copper cathode electrode with 12 protruding electrodes cut out from a 10 cm square copper electrode surface. [Figure 5B] 5A is a cross-sectional view of the electrode configuration in which a magnesium anode electrode is sandwiched between copper cathode electrodes; [Figure 6A] This is a perspective view showing a combination of a dipole electric double layer between a magnesium and copper electrode, a copper cathode electrode, and a T-shaped copper spacer. [Figure 6B] Figure 6A shows a cross-sectional view of an electrode configuration combining a copper electrode and a magnesium electrode. [Figure 7] FIG. 1 is a perspective view showing an electrode tank composed only of a copper cathode electrode. DETAILED DESCRIPTION OF THE INVENTION

[0011] In the present invention, as shown in FIG. 1, an Al or Mg anode electrode and a Cu cathode electrode are disposed facing each other and immersed in a neutral or alkaline electrolyte containing hydrogen peroxide. The electromotive force in a metal-air battery configuration consisting of an anode electrode, an alkaline electrolyte containing hydrogen peroxide, and a cathode electrode is as follows: The oxidation reaction on the anode side is M → Mn+ + ne-. On the other hand, the reduction reaction on the cathode side is O2 + H2O + 4e- → 4OH-. In the present invention, hydrogen peroxide is added to the electrolyte to promote the reduction reaction on the cathode side of the metal-air battery, thereby improving the cause of the slower ionization rate at the cathode side positive electrode compared to the anode side negative electrode. That is, metallic copper is Cu+2H2O2 → Cu2++2OH+2OH- and Cu+2OH→Cu 2+ +2OH - and partially dissolves in hydrogen peroxide, Cu 2+ +2HO2 - →Cu+2HO2 and the HO2 group forms a Haber u. Willstatter chain This is thought to be because it promotes the decomposition of hydrogen peroxide (Non-Patent Document 3).

[0012] Furthermore, in the present invention, hydrogen and oxygen gases are generated from the cathode side, so that the present invention constitutes a normal hydrogen peroxide fuel cell (see Non-Patent Document 1). Cathode: H2O2+ 2H + + 2e- → 2H2O (1.78 V vs. NHE)(1) Anode: H2O2 → O2+ 2H++ 2e- (0.682 V vs. NHE)(2) Total: 2H2O2→ 2H2O + O2(1.09 V)(3) In the present invention, hydrogen peroxide 2H2O2 decomposes to 4OH through a catalytic reaction on the copper cathode surface, generating oxygen and hydrogen as 4OH → H2 + O2 + 4e-↑, or hydroxy ions 4OH- → 2H2 + 2O2 + 4e- decompose to generate oxygen and hydrogen, simultaneously releasing electrons.

[0013] Furthermore, according to the present invention, the electric double layer formed on the surface of the cathode electrode contains hydrogen peroxide and is formed by its dipole function. Therefore, even when the counter anode electrode comes into contact with the cathode electrode, a short circuit does not occur (Fig. 2A). When the opposing anode and cathode electrodes are contacted by protrusions or the like arranged at regular intervals in a dotted pattern, the tips of the dotted protrusions have an electric double layer microcapacitor structure (Fig. 2B). Many microcapacitors are scattered on the electrode surface, and the microcapacitor effect more than doubles the power generation capacity. In the present invention, hydrogen peroxide is added to the electrolyte as an oxidizing agent that forms an insulating electric double layer on the surface of the cathode electrode. However, a person skilled in the art will understand from the description in this specification that any oxidizing agent that oxidizes a metal surface and has the function of forming an electric double layer can be used together with hydrogen peroxide to achieve the same function and effect.

[0014] In the present invention, it is preferable to supply part or all of the hydrogen peroxide to the aqueous electrolyte solution by sodium percarbonate. Specifically, it is preferable to add several to several tens of percent of aqueous hydrogen peroxide (volume %) or sodium percarbonate (weight %) to a neutral or alkaline aqueous solution containing 0.5 to 2.0 moles of an alkali metal or alkaline earth metal halide salt, particularly sodium chloride.

[0015] The anode electrode is made of magnesium or its alloy, and the battery configuration is (-)Mg / NaCl+H2O2 / Cu(+), which provides the decomposition voltage required to decompose hydrogen peroxide or the hydroxyl radicals produced by its decomposition between the anode electrode and the copper cathode electrode.

[0016] The anode and cathode electrodes are alternately arranged facing each other at a fixed distance via spacers, and an electric double layer capacitor is formed at the contact point between the anode and cathode electrodes using an aqueous electrolyte containing hydrogen peroxide (Figure 2A).If the spacer is made of the same metal as the cathode electrode, copper or copper alloy, and has dot-like protrusions spaced at regular intervals on the surface of the counter electrode (Figure 2B), it will have the effect of a microcapacitor. [Industrial Applicability]

[0017] (Performance comparison) The copper electrodes shown in Figures 3-5 and 6 were used to compare the performance of the battery with and without the microcapacitor concept shown in Figure 2B. A 3000 ml open-top rectangular plastic container is used. In Figures 3A, 4A, and 5A, a copper cathode electrode plate 10 having a thickness of 1 mm and dimensions of 100 x 100 mm has numerous triangular protrusions 11 of 50 mm in height cut into it at intervals of 150 mm to 200 mm on both sides, and as shown in Figures 3B, 4B, and 5B, the copper plates 10 are attached at both ends with the protrusions 11 facing inward, and in the middle with the copper electrodes 10 attached back to back, and a magnesium anode electrode plate 20 having a thickness of 2 mm and dimensions of 100 x 100 mm is sandwiched between these copper electrodes 10. Using this combination electrode, a microcapacitor can be formed on the surface of the copper cathode electrode, as shown in Figure 2B. On the other hand, as shown in Figure 6A, a copper cathode electrode plate 10, 1 mm thick and 100 x 100 mm long and wide, is cut into a T-shape and fitted with a spacer S formed by bending the end portion. This cathode electrode plate is then sandwiched between both sides of a 2 mm thick Mg anode electrode plate 20, 100 x 100 mm long and wide, with the spacer S interposed between them. When two Mg anode electrode plates 20 are alternately sandwiched between three copper cathode electrode plates 10 with the spacer S interposed between them, the top end view shown in Figure 5B is obtained. Using this combined electrode results in Figure 2A, and does not form the microcapacitor shown in Figure 2B.

[0018] In a plastic container, prepare an electrolyte solution of 0.5 mol / L or more, preferably 1.5 mol / L to 2 mol / L, of sodium chloride in approximately 1500 mL of pure water, and add 50 to 100 g of sodium percarbonate and 50 mL of 30% hydrogen peroxide solution. After a certain period of time, the hydrogen peroxide will be consumed and the light will decrease, so add 10 ml of 30% hydrogen peroxide every 2 to 3 hours.

[0019] In this example, the performance of the electrode configurations A and B in FIGS. 3 to 5 was compared with that of the electrode configurations A and B in FIGS. 6A and B to compare the performance when a microcapacitor is formed on the surface of a copper cathode electrode and when it is not. Since the conditions were the same except for the electrode configuration, the hydrogen peroxide fuel cell reaction in alkaline electrolyzed water was accompanied by a magnesium-air battery reaction. While hydrogen peroxide decomposes to H2O2 + 2H2O + 2e- → 2H2O + 2OH-, the oxidation reaction of H2O2 + 2OH- → O2 + 2H2O + 2e- occurs on the cathode electrode side, and In alkaline electrolyte, the metal oxidation reaction is Mg → Mg2++2e-, and oxygen is released from the cathode. The typical metal-air battery reaction occurs when hydrogen peroxide is reduced and ionized: O2 + 2H2O + 4e- → 4OH-. However, while it is understood that oxygen gas is generated in hydrogen peroxide fuel cell and metal-air battery reactions, the above configuration generates not only oxygen gas but also hydrogen gas. This suggests that, as suggested in Non-Patent Document 3 (Mizuto Eiji, Advances in Physical Chemistry (1936), 10(3): pp. 154-165), the catalytic function operates on the surface of the copper cathode electrode, causing the decomposition of hydrogen peroxide or hydroxy ions, leading to the power generation reaction. 2H2O2 → 4·OH → H2 + O2 + 4e- 4OH- → H2 + O2 + 4e-

[0020] Considering the above experimental results, it was found that, depending on the configuration of the microcapacitor, fuel cells forming the microcapacitors shown in Figures 3 to 5 showed an increase in current value of more than twice that of fuel cells not forming the microcapacitors shown in Figure 6. It is clear that the current collection and discharge effect associated with microcapacitors has a significant impact on the amount of electricity generated by the battery. Therefore, the configuration of the present invention is groundbreaking because it can provide a new and useful configuration for a single-compartment hydrogen peroxide fuel cell.

Claims

1. A cathode electrode for metal-air batteries and hydrogen peroxide fuel cells, which is used in an alkaline electrolyte containing hydrogen peroxide and has, on its surface, a metallic copper or alloy surface having a catalytic function of decomposing hydrogen peroxide and / or hydroxy ions in the electrolyte, characterized in that the cathode electrode has a plurality of electrode protrusions standing up at regular intervals on the electrode surface placed opposite the anode electrode surface, and exhibits electronic conductivity to the anode electrode via an electric double layer capacitor.

2. 2. The cathode electrode according to claim 1, comprising an electrode surface forming an electrode projection and electrode legs for holding said electrode surface upright at a fixed distance from the bottom of the electrolytic cell.

3. 2. The cathode electrode according to claim 1, wherein the electrode mounting frame has an open-top frame surrounding the battery cell and an electrode mounting base portion through which the electrolyte flows at a certain height from the bottom of the frame, and the electrode mounting frame is made of metallic copper or an alloy thereof.

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