Anode material for alkaline aluminum-air battery and preparation method and application thereof

Abstract

This invention belongs to the field of air batteries and relates to an anode material for air batteries. The anode material mainly consists of the following components by weight percentage: Mg: 0.1%-0.6%, Sn: 0.1%-0.8%, Ga: 0.01%-0.1%, In: 0.01%-0.1%, Bi: 0.01%-0.1%, with impurities not exceeding 0.01%, and the balance being Al. The anode material for air batteries of this invention successfully prepares aluminum anode material by composite addition of Mg, Sn, Ga, In, and Bi elements to activate the aluminum anode, followed by composition optimization, smelting, cold rolling deformation, and stress-relief annealing. This effectively improves the utilization rate of the aluminum anode while increasing its energy density; the production process is simple and meets the needs of mass production.

Description

Technical Field

[0001] This invention belongs to the field of air batteries and relates to an anode material for air batteries. Background Technology

[0002] The growing demand for electric vehicles and large-scale energy storage is driving the development of next-generation high-energy-density battery systems. Against this backdrop, aluminum-air batteries are considered a promising candidate due to their advantages, including the extremely high theoretical specific capacity of aluminum anodes (2980 mAh g⁻¹), abundant crustal reserves, and low cost, with a mass energy density far exceeding that of existing lithium-ion batteries. However, the inherent challenges of surface passivation and hydrogen evolution corrosion in alkaline electrolytes severely hinder their practical application. Application CN 109244442 A discloses a porous aluminum anode and an aluminum-air battery. To address the surface passivation problem, Ga, with its near-room-temperature melting point (29.8℃), can form eutectic mixtures with other alloying elements, resulting in a thinner passivation film on the aluminum anode surface. This makes Ga a commonly used alloying element for improving the activity of aluminum anodes. However, Ga tends to introduce intergranular corrosion through grain boundary segregation, and excessive Ga also accelerates hydrogen evolution self-corrosion of the aluminum anode. Although this increases the discharge voltage, the anode utilization rate is low, limiting the industrial application of aluminum anodes. Therefore, to solve the above problems, it is necessary to propose an aluminum anode for aluminum-air batteries and its preparation method. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention proposes an anode material for alkaline aluminum-air batteries, its preparation method, and its application.

[0004] The technical solution of this invention is implemented as follows:

[0005] An anode material for an alkaline aluminum-air battery, the anode material being composed of the following components in weight percentage: Mg: 0.1%-0.6%, Sn: 0.1%-0.8%, Ga: 0.01%-0.1%, In: 0.01%-0.1%, Bi: 0.01%-0.1%, impurity content not exceeding 0.01%, and the balance being Al.

[0006] Preferably, the composition is Mg: 0.1%-0.3%, Sn: 0.1%-0.21%, Ga: 0.01%-0.05%, In: 0.01%-0.05%, Bi: 0.01%-0.1%, with impurity content not exceeding 0.01%, and the balance being Al.

[0007] Further, the composition is as follows: Mg: 0.25%-0.3%, Sn: 0.15%-0.21%, Ga: 0.04%-0.05%, In: 0.04%-0.05%, Bi: 0.01%-0.1%, with impurity content not exceeding 0.01%, and the balance being Al.

[0008] The above-mentioned method for preparing the anode material for alkaline aluminum-air batteries includes the following steps:

[0009] (1) Weigh out high-purity Al, high-purity Mg, high-purity Sn, high-purity Ga, high-purity In and high-purity Bi according to the proportion;

[0010] (2) Melting: Heat the high-purity aluminum block to 720-760℃ for melting. After it is completely melted, hold it at that temperature for 30-50 minutes to obtain molten liquid 1. The pure aluminum block can be melted at 720-760℃.

[0011] (3) Add high-purity Mg, high-purity Sn, high-purity Ga, high-purity In and high-purity Bi wrapped in aluminum foil to melt 1 to obtain mixed melt 2, keep it at 720-740℃ for 5-20 min; use argon to remove hydrogen from mixed melt 2 for 3-5 min;

[0012] (4) Cast the hydrogen-free mixed melt 2 from step (3) into a billet; remove the oxide scale from the surface of the billet and cold roll the billet into an aluminum anode plate; perform stress-relief annealing on the cold-rolled aluminum anode plate to obtain the desired product.

[0013] Specifically, in step (1), the purity of high-purity Al, high-purity Mg, high-purity Sn, high-purity Ga, high-purity In and high-purity Bi are all ≥99.99%.

[0014] Specifically, in step (4), the thickness of the billet can be 35-45mm.

[0015] Specifically, in step (4), the deformation during cold rolling can be 85-90%.

[0016] Furthermore, specifically, in step (4), the stress-relief annealing temperature is 100℃-250℃, and the holding time is 1.0-3.0h.

[0017] This invention also provides the application of the above-mentioned aluminum anode material in the preparation of alkaline aluminum-air batteries.

[0018] The present invention also provides an alkaline aluminum-air battery comprising the aforementioned aluminum anode material.

[0019] The present invention has the following beneficial effects:

[0020] (1) This invention provides a novel aluminum anode formulation; by adding Mg, Sn, Ga, In and Bi elements to activate the aluminum anode and assist in stress-relief annealing, the utilization rate of the aluminum anode is effectively improved while the energy density of the aluminum anode is increased.

[0021] (2) In this invention, Mg and Sn are commonly used aluminum anode activating elements that can form segregated phases with the Al matrix, thereby activating the alloy by promoting the preferential dissolution of the aluminum anode. Ga has a melting point close to room temperature, at 29.87℃, which allows Ga to form a low eutectic mixture with other alloying elements, destroying the passivation film on the aluminum anode surface and promoting the dissolution of the aluminum matrix, thus activating the aluminum anode. In has a high hydrogen evolution overpotential, which can inhibit hydrogen evolution and reduce the self-corrosion of the aluminum anode when In is deposited on the aluminum anode surface. Bi has a relatively high hydrogen evolution overpotential, which inhibits the hydrogen evolution reaction of the aluminum anode. In and Bi are beneficial to promoting the fine and dispersed precipitation of the second phase, promoting uniform corrosion of the alloy, and improving corrosion resistance. Therefore, the problem of low utilization rate of aluminum anode is effectively improved. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 The hydrogen evolution rate graphs are for Example 2 and the comparative example.

[0024] Figure 2 Examples 2 and 3 are shown below, along with their polarization curves and corrosion current densities; the left figure is the polarization curve, and the right figure is the corrosion current density.

[0025] Figure 3 This is the second phase distribution diagram for Example 2. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] Unless otherwise specified, the experimental methods used in the following experimental examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0028] The high-purity Al, high-purity Mg, high-purity Sn, high-purity Ga, high-purity In, and high-purity Bi used in this application all have a purity of ≥99.99%.

[0029] The anode material for alkaline aluminum-air batteries disclosed in this application is composed of the following components by weight percentage: Mg: 0.1%-0.6%, Sn: 0.1%-0.8%, Ga: 0.01%-0.1%, In: 0.01%-0.1%, Bi: 0.01%-0.1%, with impurities not exceeding 0.01%, and the balance being Al.

[0030] Preferably, the composition is Mg: 0.1%-0.3%, Sn: 0.1%-0.21%, Ga: 0.01%-0.05%, In: 0.01%-0.05%, Bi: 0.01%-0.1%, with impurity content not exceeding 0.01%, and the balance being Al.

[0031] Further, the composition is as follows: Mg: 0.25%-0.3%, Sn: 0.15%-0.21%, Ga: 0.04%-0.05%, In: 0.04%-0.05%, Bi: 0.01%-0.1%, with impurity content not exceeding 0.01%, and the balance being Al.

[0032] The above-mentioned method for preparing the anode material for alkaline aluminum-air batteries includes the following steps:

[0033] (1) Weigh out high-purity Al, high-purity Mg, high-purity Sn, high-purity Ga, high-purity In and high-purity Bi according to the proportion;

[0034] (2) Smelting: The high-purity aluminum block is heated to 720-760℃ for smelting. After it is completely melted, it is kept at the temperature for 30-50 minutes to obtain molten liquid 1. The pure aluminum block can be smelted at 720-760℃. In order to save energy and improve efficiency, this application uses 730℃ for performance research.

[0035] (3) Add high-purity Mg, high-purity Sn, high-purity Ga, high-purity In and high-purity Bi wrapped in aluminum foil to melt 1 to obtain mixed melt 2, and keep it at 720-740℃ for 5-20 min; use argon to remove hydrogen from mixed melt 2 for 3-5 min; the purpose of keeping it at 730℃ is to ensure that each raw material is fully mixed, preferably for 10 min.

[0036] (4) Cast the hydrogen-free mixed melt 2 from step (3) into a billet; remove the oxide scale from the surface of the billet and cold roll the billet into an aluminum anode plate; perform stress-relief annealing on the cold-rolled aluminum anode plate to obtain the desired product.

[0037] Specifically, in step (1), the purity of high-purity Al, high-purity Mg, high-purity Sn, high-purity Ga, high-purity In and high-purity Bi are all ≥99.99%.

[0038] Specifically, in step (4), the thickness of the billet can be 35-45mm.

[0039] Specifically, in step (4), the deformation during cold rolling can be 85-90%, with 87% being the preferred deformation.

[0040] Furthermore, specifically, in step (4), the stress-relief annealing temperature is 100℃-250℃, and the holding time is 1.0-3.0h. The further stress-relief annealing temperature is 100℃-200℃, and the preferred stress-relief annealing temperature is 150℃.

[0041] The following examples illustrate the performance of this anode material on a specific scale:

[0042] Example 1

[0043] The Al-Mg-Sn-Ga-In-Bi microalloyed aluminum alloy anode material for alkaline aluminum-air batteries in this embodiment is composed of the following components by weight percentage: Mg: 0.25%, Sn: 0.18%, Ga: 0.04%, In: 0.04%, Bi: 0.01%, unavoidable impurities 0.01 wt.%, and the balance being Al.

[0044] The preparation method of the above-mentioned Al-Mg-Sn-Ga-In-Bi microalloyed aluminum alloy anode material for alkaline aluminum-air batteries includes the following steps:

[0045] Step 1: Prepare high-purity Al, high-purity Mg, high-purity Sn, high-purity Ga, high-purity In, and high-purity Bi according to the weight percentage of the components;

[0046] Step 2: Melt 4N pure aluminum at 730℃ to obtain molten liquid 1;

[0047] Step 3: Add high-purity Mg, high-purity Sn, high-purity Ga, high-purity In and high-purity Bi wrapped in aluminum foil to melt 1 to obtain mixed melt 2, and keep it at 730℃ for 10 min;

[0048] Step 4: Use high-purity argon gas to remove hydrogen from the mixed melt 2 for 3 minutes;

[0049] Step 5: Cast the hydrogen-removed mixed melt 2 from Step 4 into a stainless steel mold to form a billet with a thickness of 40mm.

[0050] Step 6: Remove the oxide scale from the surface of the cast billet by sanding (the same applies below), and cold roll the cast billet into an aluminum plate with a thickness of 5mm and a deformation of 87%;

[0051] Step 7: Perform stress-relief annealing on the cold-rolled aluminum sheet. The stress-relief annealing process is as follows: heat from room temperature to 150°C, hold at 150°C for 1 hour, and then air cool to obtain the final product.

[0052] Example 2

[0053] The Al-Mg-Sn-Ga-In-Bi microalloyed aluminum alloy anode material for alkaline aluminum-air batteries in this embodiment is composed of the following components by weight percentage: Mg: 0.30%, Sn: 0.21%, Ga: 0.05%, In: 0.05%, Bi: 0.05%, unavoidable impurities 0.01 wt.%, and the balance being Al.

[0054] The preparation method of the above-mentioned Al-Mg-Sn-Ga-In-Bi microalloyed aluminum alloy anode material for alkaline aluminum-air batteries includes the following steps:

[0055] Step 1: Prepare high-purity Al, high-purity Mg, high-purity Sn, high-purity Ga, high-purity In, and high-purity Bi according to the weight percentage of the components;

[0056] Step 2: Melt 4N pure aluminum at 730℃ to obtain molten liquid 1;

[0057] Step 3: Add high-purity Mg, high-purity Sn, high-purity Ga, high-purity In and high-purity Bi wrapped in aluminum foil to melt 1 to obtain mixed melt 2, and keep it at 730℃ for 10 min;

[0058] Step 4: Use high-purity argon gas to remove hydrogen from the mixed melt 2 for 3 minutes;

[0059] Step 5: Cast the hydrogen-removed mixed melt 2 from Step 4 into a stainless steel mold to form a billet with a thickness of 40mm.

[0060] Step 6: Remove the oxide scale from the surface of the cast billet by sanding (the same applies below), and cold roll the cast billet into an aluminum plate with a thickness of 5mm and a deformation of 87%;

[0061] Step 7: Perform stress-relief annealing on the cold-rolled aluminum sheet. The stress-relief annealing process is as follows: heat from room temperature to 150°C, hold at 150°C for 1 hour, and then air cool to obtain the final product.

[0062] Example 3

[0063] The Al-Mg-Sn-Ga-In-Bi microalloyed aluminum alloy anode material for alkaline aluminum-air batteries described in this embodiment is composed of the following components by weight percentage: Mg: 0.28%, Sn: 0.15%, Ga: 0.05%, In: 0.04%, Bi: 0.10%, unavoidable impurities 0.01 wt.%, and the balance being Al.

[0064] The preparation method of the above-mentioned Al-Mg-Sn-Ga-In-Bi microalloyed aluminum alloy anode material for alkaline aluminum-air batteries includes the following steps:

[0065] Step 1: Prepare high-purity Al, high-purity Mg, high-purity Sn, high-purity Ga, high-purity In, and high-purity Bi according to the weight percentage of the components;

[0066] Step 2: Melt 4N pure aluminum at 730℃ to obtain molten liquid 1;

[0067] Step 3: Add high-purity Mg, high-purity Sn, high-purity Ga, high-purity In and high-purity Bi wrapped in aluminum foil to melt 1 to obtain mixed melt 2, and keep it at 730℃ for 10 min;

[0068] Step 4: Use high-purity argon gas to remove hydrogen from the mixed melt 2 for 3 minutes;

[0069] Step 5: Cast the hydrogen-removed mixed melt 2 from Step 4 into a stainless steel mold to form a billet with a thickness of 40mm.

[0070] Step 6: Remove the oxide scale from the surface of the cast billet by sanding (the same applies below), and cold roll the cast billet into an aluminum plate with a thickness of 5mm and a deformation of 87%;

[0071] Step 7: Perform stress-relief annealing on the cold-rolled aluminum sheet. The stress-relief annealing process is as follows: heat from room temperature to 150°C, hold at 150°C for 1 hour, and then air cool to obtain the final product.

[0072] Comparative Example

[0073] The Al-Mg-Sn-Ga microalloyed aluminum alloy anode material for alkaline aluminum-air batteries described in this comparative example is composed of the following components by weight percentage: Mg: 0.30%, Sn: 0.20%, Ga: 0.05%, unavoidable impurities 0.01 wt.%, and the balance being Al.

[0074] The preparation method of the above-mentioned Al-Mg-Sn-Ga microalloyed aluminum alloy anode material for alkaline aluminum-air batteries includes the following steps:

[0075] Step 1: Prepare high-purity Al, high-purity Mg, high-purity Sn, and high-purity Ga according to the weight percentage of the components;

[0076] Step 2: Melt 4N pure aluminum at 730℃ to obtain molten liquid 1;

[0077] Step 3: Add high-purity Mg, high-purity Sn and high-purity Ga wrapped in aluminum foil to melt 1 to obtain mixed melt 2, and keep it at 730℃ for 10 min;

[0078] Step 4: Use high-purity argon gas to remove hydrogen from the mixed melt 2 for 3 minutes;

[0079] Step 5: Cast the hydrogen-removed mixed melt 2 from Step 4 into a stainless steel mold to form a billet with a thickness of 40mm.

[0080] Step 6: Remove the oxide scale from the surface of the cast billet by sanding (the same applies below), and cold roll the cast billet into an aluminum plate with a thickness of 5mm and a deformation of 87%;

[0081] Step 7: Perform stress-relief annealing on the cold-rolled aluminum sheet. The stress-relief annealing process is as follows: heat from room temperature to 150°C, hold at 150°C for 1 hour, and then air cool to obtain the final product.

[0082] The difference between this comparative example and Examples 1-3 is that no elements In and Bi were added to the aluminum anode material.

[0083] Implementation effect analysis

[0084] Performance testing

[0085] Polarization curves were tested using 4 mol / L NaOH electrolyte, and the corrosion current density results obtained from the polarization curves are shown in Table 1.

[0086] As shown in Table 1, the corrosion current density of the aluminum anode materials in Examples 1-3 of this invention ranges from 4.960 to 9.714 mA·cm⁻¹. -2 Between [specific values]. In contrast, the corrosion current density of the comparative aluminum anode material is between 22.270 mA·cm⁻¹. -2 The results are greater than those in Examples 1-3, indicating that the addition of In and Bi elements can significantly improve the corrosion resistance of aluminum anodes.

[0087] Table 1 Corrosion current density of aluminum anode materials in the examples and comparative examples

[0088]

[0089] Hydrogen evolution corrosion tests were conducted using 4 mol / L NaOH electrolyte. The hydrogen evolution rate of each aluminum anode material was calculated based on the amount of hydrogen evolved. The hydrogen evolution rate results of the comparative example and Examples 1-3 are shown in Table 2.

[0090] As shown in Table 2, the hydrogen evolution rate of the aluminum anode materials in Examples 1-3 of this invention ranges from 0.075 to 0.212 mL / cm². 2 The hydrogen evolution rate was between [value missing] / min. In contrast, the hydrogen evolution rate of the comparative aluminum anode material was 1.050 mL / cm². 2 / min, which is greater than that of Examples 1-3, indicating that the addition of In and Bi elements can significantly reduce the hydrogen evolution rate. Figure 1The hydrogen evolution rate graphs for Example 2 and the comparative example are provided by [the relevant authority / organization]. Figure 1 It can be seen that the hydrogen evolution rate in Example 2 is significantly lower than that in the comparative example.

[0091] Constant current discharge tests were conducted using 4 mol / L NaOH electrolyte and a commercial MnO2 / C air electrode. The reaction area was 1 cm × 1 cm. The average discharge voltage, discharge capacity, and aluminum anode mass before and after the reaction were recorded. The aluminum anode utilization rate and energy density were calculated. The discharge performance of the comparative example and Examples 1-3 are shown in Table 2.

[0092] Table 2. Constant current discharge performance of aluminum anode materials in the examples and comparative examples

[0093]

[0094] As can be seen from Table 2, Examples 1-3 were at 40 mA / cm 2 The average discharge voltage, utilization rate, and energy density of the constant current discharge were 1.231-1.258V, 72.71%-80.67%, and 2667.4-2859.1 mWh / g, respectively. In comparison, the discharge performance of the comparative examples was worse than that of Examples 1-3, at 1.333, 26.95%, and 1070.9 mWh / g, respectively. This indicates that the addition of 0.05 wt.% In and 0.05 wt.% Bi can effectively improve the low anode utilization rate by inhibiting hydrogen evolution corrosion, while also improving the discharge performance of the aluminum anode.

[0095] Examples 1-3 at 80 mA / cm 2 The average discharge voltage, utilization rate, and energy density of the constant current discharge were 1.004-1.117V, 88.89%-94.33%, and 2659.6-3067.4 mWh / g, respectively. In comparison, the discharge performance of the comparative examples was worse than that of Examples 1-3, at 1.130, 76.87%, and 2588.8 mWh / g, respectively. This indicates that adding 0.05 wt.% In and 0.05 wt.% Bi can improve the anode utilization rate and the discharge performance of the aluminum anode.

[0096] Figure 2 The polarization curves and corrosion current density comparison diagrams of Example 2 and the comparative example show that the corrosion voltage of Example 2 is more positive than that of the comparative example, but its corrosion current density is significantly lower than that of the comparative example, indicating that the corrosion resistance of Example 2 is significantly improved.

[0097] Figure 3The left figure shows the second phase distribution diagram of the comparative example, and the right figure shows the second phase distribution diagram of Example 2. As can be seen from the figures, the size and content of the second phase in Example 2 are both lower than those in the comparative example. On the one hand, the refinement of the second phase is beneficial to improving the corrosion resistance of the anode; on the other hand, although the reduction in the second phase content will reduce the number of activation points and decrease the discharge activity of the alloy, the content of the second phase at the anode grain boundaries will also decrease, thereby improving the alloy's resistance to localized corrosion and inhibiting hydrogen evolution corrosion. Therefore, compared with the comparative example, the discharge activity of Example 2 is reduced, but the corrosion resistance is improved, hydrogen evolution corrosion is effectively inhibited, and thus the utilization rate of the anode is significantly improved.

[0098] In summary, it is evident that by optimizing and controlling the addition of In and Bi alloying elements and their preparation process in the aluminum alloy anode, this invention can effectively improve the low utilization rate of aluminum alloy anodes in aluminum-air batteries and enhance the discharge performance of aluminum anodes.

[0099] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An anode material for alkaline aluminum-air batteries, characterized in that, The anode material mainly consists of the following components by weight percentage. Composition: Mg: 0.1%-0.6%, Sn: 0.1%-0.8%, Ga: 0.01%-0.1%, In: 0.01%-0.1%, Bi: 0.01%-0.1%, impurity content not exceeding 0.01%, balance Al.

2. The anode material for alkaline aluminum-air batteries according to claim 1, characterized in that, The anode material mainly consists of the following components by weight percentage. Composition: Mg: 0.1%-0.3%, Sn: 0.1%-0.21%, Ga: 0.01%-0.05%, In: 0.01%-0.05%, Bi: 0.01%-0.1%, impurity content not exceeding 0.01%, balance Al.

3. The method for preparing the anode material for an alkaline aluminum-air battery according to claim 1 or 2, characterized in that, The steps are as follows: (1) Weigh out high-purity Al, high-purity Mg, high-purity Sn, high-purity Ga, high-purity In and high-purity Bi according to the proportions of claim 1 or 2; (2) Heat and melt the high-purity aluminum block, and keep it at the temperature after it is completely melted to obtain molten liquid 1; (3) Add high-purity Mg, high-purity Sn, high-purity Ga, high-purity In and high-purity Bi wrapped in aluminum foil to melt 1 to obtain mixed melt 2. After heat preservation and dehydrogenation treatment, casting liquid is obtained. (4) Cast the casting liquid into a billet, remove the oxide scale on the surface of the billet, cold roll the billet into an aluminum anode plate, and obtain the anode material for alkaline aluminum-air batteries by stress relief annealing.

4. The method for preparing the anode material for an alkaline aluminum-air battery according to claim 2, characterized in that: In step (1), the purity of high-purity Al, high-purity Mg, high-purity Sn, high-purity Ga, high-purity In and high-purity Bi is ≥99.99%.

5. The method for preparing the anode material for an alkaline aluminum-air battery according to claim 4, characterized in that: The melting temperature in step (2) is 720-760℃, and the holding time is 30-50min.

6. The method for preparing the anode material for an alkaline aluminum-air battery according to claim 5, characterized in that: In step (3), the temperature for heat preservation is 720-740℃ and the time is 5-20 min; the gas used for hydrogen removal is argon and the treatment time is 3-5 min.

7. The method for preparing the anode material for an alkaline aluminum-air battery according to claim 6, characterized in that: In step (4), the thickness of the billet is 35-45mm, and the deformation during cold rolling is 85-90%.

8. The method for preparing the anode material for an alkaline aluminum-air battery according to claim 7, characterized in that: The stress-relief annealing process in step (4) is carried out at a temperature of 100℃-250℃ for 1.0-3.0h.

9. The application of the anode material for alkaline aluminum-air batteries according to claim 1 or 2 in the preparation of alkaline aluminum-air batteries.

10. An alkaline aluminum-air battery, characterized in that: The anode material as described in claim 1 or 2 is used as the anode.

Images