Carbon material / ptfe modified carbon brush cathode for magnesium alloy anode seawater battery and preparation method and application thereof

Abstract

The application discloses a carbon material / PTFE modified carbon brush cathode for a magnesium alloy anode seawater battery and a preparation method and application thereof, and belongs to the technical field of marine chemical power sources. The magnesium alloy anode seawater battery comprises a magnesium alloy anode, a seawater electrolyte and a modified carbon brush cathode. The modified carbon brush cathode comprises a three-dimensional carbon brush substrate and an oxygen reduction functional layer loaded on the surface of the three-dimensional carbon brush substrate, and the oxygen reduction functional layer comprises a porous carbon material and a PTFE bonding / hydrophobicity regulating component. The cathode is aimed at the problems of Mg 2+ OH ‑ , and the cathode is prone to magnesium-containing deposit blockage and low dissolved oxygen mass transfer limitation near the cathode. The dissolved oxygen capture and utilization capacity is improved through the porous carbon material, and the anti-flooding mass transfer channel is constructed in the carbon brush through the PTFE, so that the large-current discharge capacity and long-time discharge stability of the magnesium seawater battery are improved. The application does not depend on a noble metal catalyst, has a simple preparation process and low cost, and is especially suitable for a dissolved oxygen type seawater battery with a magnesium alloy as an anode and seawater or simulated seawater as an electrolyte.

Description

Technical Field

[0001] This invention belongs to the field of marine chemical power source technology, specifically relating to a carbon material / PTFE modified carbon brush cathode for magnesium alloy anode seawater batteries, its preparation method and application, and particularly to a three-dimensional modified carbon brush cathode that can adapt to the discharge environment of magnesium alloy anodes, improve dissolved oxygen utilization efficiency and improve long-term discharge stability. Background Technology

[0002] Magnesium-seawater batteries are a typical type of metal-dissolved oxygen seawater battery. They typically use magnesium or magnesium alloys as the anode, seawater or simulated seawater as the electrolyte, and dissolved oxygen from the seawater as the cathode reactant. During discharge, the magnesium alloy anode undergoes oxidation and dissolution, while the cathode undergoes an oxygen reduction reaction. Due to the high theoretical specific capacity of magnesium-based anodes and the direct availability of seawater as the electrolyte, magnesium-seawater batteries have potential applications in marine sensors, deep-sea exploration devices, marine buoys, emergency power supplies, and long-term marine monitoring equipment.

[0003] However, the cathode reaction environment of magnesium alloy anode seawater batteries differs from that of typical metal-air batteries or fuel cells. When the magnesium alloy anode discharges in seawater, it continuously releases magnesium... 2+ The cathode oxygen reduction reaction will continuously produce OH. - This leads to a localized increase in pH near the cathode. Mg 2+ With OH - The coupling effect easily induces the formation of Mg(OH)2 or other magnesium-containing deposits near the cathode. These deposits may cover the cathode active sites, block the three-dimensional carbon brush channels, weaken the transport of dissolved oxygen to the reaction interface, and ultimately cause a decrease in discharge voltage and long-term stability degradation. Therefore, the cathode design of magnesium alloy anode seawater batteries needs to consider not only oxygen reduction catalytic activity, but also dissolved oxygen capture, anti-flooding mass transfer, and suppression of magnesium-containing deposit blockage.

[0004] Currently, the cathodes of magnesium-containing seawater batteries typically use precious metals such as platinum and silver as oxygen reduction catalysts, distributed on corrosion-resistant substrates with high specific surface areas (such as titanium alloys). However, with increasing ocean depth, dissolved oxygen concentrations decrease significantly. Existing seawater battery cathode materials suffer from low activity and rapid performance degradation, failing to meet the long-term power supply requirements of marine equipment, especially the ultra-long-term stable operation of deep-sea instruments. Current technologies primarily address this by preparing catalysts.

[0005] Chinese patent application CN201611131494.2 discloses a hydrophilic cathode for a dissolved oxygen seawater battery, its preparation, and its application. The method involves in-situ growth of a hydrophilic, conductive polymer film with a nanostructure on the surface of a hydrophobic conductive substrate. This increases the effective active area for the oxygen reduction reaction at the cathode by improving the surface roughness of the electrode. Simultaneously, the interaction between a hydrophilic binder and the conductive polymer anchors catalyst nanoparticles within the conductive polymer nanostructure, thereby improving the cathode discharge performance of the metal seawater dissolved oxygen cathode and enhancing the battery's discharge performance and operational stability. However, this method suffers from complex processes and high manufacturing costs.

[0006] Chinese patent application 202211559963.6 discloses a method for preparing a multi-layered composite oxygen reduction cathode material. This method employs a scalable multi-step electrodeposition process to prepare a multi-layered PPy@PtNi composite oxygen reduction cathode with high stability and high catalytic activity. However, this method also suffers from complex processes and high manufacturing costs.

[0007] In addition, the cathode materials used in existing seawater batteries are not sufficiently targeted at the magnesium alloy anode in seawater batteries. 2+ / OH - The coupled deposition process leads to cathode mass transfer blockage. Therefore, it is necessary to develop a low-cost, simple-process modified carbon brush cathode that can be matched with the discharge environment of magnesium alloy anode seawater batteries, so that it can maintain high dissolved oxygen utilization efficiency and long-term discharge stability even under conditions of low dissolved oxygen, saline electrolyte, and easy formation of magnesium-containing deposits. Summary of the Invention

[0008] This invention aims to address the problems of high cost, complex manufacturing process, limited mass transfer due to low dissolved oxygen, easy submersion of the cathode, and insufficient long-term discharge stability caused by magnesium-containing deposits clogging the cathode in existing magnesium alloy anode seawater batteries. It provides a carbon material / PTFE modified carbon brush cathode for magnesium alloy anode seawater batteries, its preparation method, and its application.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A carbon material / PTFE modified carbon brush cathode for a magnesium alloy anode seawater battery is characterized in that the modified carbon brush cathode is used in conjunction with a magnesium alloy anode and a seawater electrolyte to form a magnesium alloy anode seawater battery; the modified carbon brush cathode includes a three-dimensional carbon brush substrate and an oxygen reduction functional layer loaded on the surface of the three-dimensional carbon brush substrate; the oxygen reduction functional layer includes a porous carbon material and a PTFE binding / hydrophobic control component; the porous carbon material is used to capture dissolved oxygen in seawater, and the PTFE binding / hydrophobic control component is used to form anti-flooding mass transfer channels inside the three-dimensional carbon brush substrate to generate Mg during discharge at the magnesium alloy anode. 2+And the reduction of oxygen at the cathode produces OH - Under these conditions, the blockage of cathode channels and active sites by magnesium-containing deposits is alleviated and the discharge stability is improved. The three-dimensional carbon brush substrate is a carbon fiber brush, a three-dimensional carbon bundle, a spiral carbon fiber brush, or a three-dimensional conductive matrix composed of carbon fiber bundles; the porous carbon material is selected from one or more of Ketjen black, acetylene black, conductive carbon black, conductive graphite, graphene, carbon nanotubes, and activated carbon.

[0010] Furthermore, the PTFE bonding / hydrophobic regulating component is derived from a PTFE emulsion, which contains 50-65 wt% solids; the oxygen reduction functional layer contains 8-20 wt% PTFE; and the mass ratio of the porous carbon material to PTFE is 10:1-5:1.

[0011] Furthermore, the dry weight of the PTFE binder / hydrophobic modulator component accounts for 0.01%-0.5% of the total mass of the overall cathode containing the three-dimensional carbon brush substrate; the oxygen reduction functional layer has a loading of 1-5 mg / cm³ on the surface of the three-dimensional carbon brush substrate. 3 .

[0012] A magnesium alloy anode seawater battery, characterized in that it comprises a magnesium alloy anode, a seawater electrolyte, and a modified carbon brush cathode as described in any one of claims 1-3; wherein the magnesium alloy anode is selected from one of Mg-Al magnesium alloy, Mg-Zn magnesium alloy, Mg-Al-Zn magnesium alloy, Mg-Mn magnesium alloy, Mg-Ca magnesium alloy, AZ31 magnesium alloy, AZ61 magnesium alloy, or AZ91 magnesium alloy; the seawater electrolyte is natural seawater, simulated seawater, or a chloride-containing salt aqueous solution, and the dissolved oxygen in the seawater electrolyte serves as the cathode reactant of the modified carbon brush cathode.

[0013] A carbon material / PTFE modified carbon brush cathode for a magnesium alloy anode seawater battery and its preparation method, the method comprising the following steps: (1) Place the carbon powder and PTFE emulsion in ethanol or a mixture of ethanol and water, and form a uniform slurry by ultrasonic dispersion, mechanical stirring or magnetic stirring. (2) Load the slurry obtained in step (1) onto the surface of the carbon brush; (3) Dry at 60-80℃ for 1-2 hours to allow ethanol to evaporate, and obtain carbon powder / PTFE binder composite material.

[0014] Furthermore, the carbon brush is a three-dimensional spiral carbon fiber matrix, and its surface is subjected to high-temperature heat treatment and acid etching treatment to remove surface organic impurities and inert substances.

[0015] Furthermore, the magnesium alloy anode seawater battery is used in marine instruments, deep-sea sensors, marine buoys, emergency power supply devices, or marine monitoring equipment.

[0016] The technical solution of this invention is a magnesium seawater battery cathode based on carbon brushes modified with carbon materials and PTFE binder, including a carbon brush substrate (carbon fiber brush / three-dimensional carbon bundle) and an oxygen reduction functional layer (carbon material + PTFE binder phase); it abandons expensive precious metal catalysts and makes pure use of the high specific surface area of ​​carbon materials and the excellent hydrophobicity of PTFE, which not only greatly reduces the cost, but also significantly reduces the mass transfer resistance of the oxygen reduction reaction. Attached Figure Description

[0017] Figure 1 This is an optical photograph of the cathode of a magnesium seawater battery based on a carbon brush modified with PTFE binder in Example 1 of the present invention.

[0018] Figure 2 These are contact angle test images of carbon brushes modified with PTFE binder in Embodiment 1 of the present invention.

[0019] Figure 3 This is a long-term discharge curve of the magnesium alloy anode seawater battery assembled in Example 1.

[0020] Figure 4 The graph shows the rate discharge curve of the magnesium alloy anode seawater battery assembled in Example 2.

[0021] Figure 5 This is a long-term discharge curve of the magnesium alloy anode seawater battery assembled in Example 2. Detailed Implementation

[0022] The present invention will be described in detail below with reference to specific embodiments, but the present invention is not limited to these embodiments. Example

[0023] A method for preparing and applying a magnesium seawater battery cathode based on a carbon brush modified with carbon materials and PTFE binder includes the following steps: (1) The carbon brush is ultrasonically cleaned repeatedly for 15 minutes with anhydrous ethanol, acetone and ultrapure water to remove surface dust and residual acid, while making the carbon fiber bundles spread evenly. (2) Ketjenblack and PTFE emulsion (mass ratio 5:1) were placed in a mixed solvent of ethanol and water and ultrasonically dispersed for 30 minutes to form a homogeneous slurry. The catalyst concentration in the Ketjenblack-PTFE mixed slurry was 3 mg·ml. −1 ; (3) Coat the obtained slurry onto the carbon brush surface, with a Ketjen black loading of 1-5 mg / cm³. −3 ; (4) Dry at 60-80℃ for 1-2 hours to evaporate the ethanol and obtain Ketjen black-PTFE binder composite material, which is the cathode.

[0024] The discharge test process for the magnesium-seawater battery is as follows: A self-made battery kit was used for the magnesium-seawater battery test. The anode was a magnesium metal rod with a diameter of 8*60mm. The cathode used a modified carbon fiber brush electrode with a diameter of 40*40mm. The volumetric current density was calculated based on the cathode.

[0025] Taking the Ketjenblack / PTFE binder composite material in this embodiment as an example, an optical photograph of the carbon brush electrode modified with the Ketjenblack / PTFE binder composite material is attached. Figure 1 As shown.

[0026] The changes in hydrophilicity and hydrophobicity of unmodified carbon brushes and carbon brushes modified with Ketjenblack / PTFE binder composites were analyzed using contact angle testing. Figure 2 It can be seen that the hydrophobicity of the carbon brush modified with Ketjenblack / PTFE binder composite material is significantly improved compared with the blank carbon brush.

[0027] from Figure 3 It can be seen that after assembling the modified carbon brush cathode with a magnesium alloy anode to form a magnesium alloy anode seawater battery, the carbon brush modified with Ketjenblack / PTFE binder composite material exhibits better long-term discharge performance than the unmodified carbon brush. The optimized three-phase interface reduces the mass transfer resistance of the oxygen reduction reaction and increases the discharge voltage in seawater environments. Under the same dissolved oxygen concentration, the discharge voltage is 0.3V higher than that of the traditional carbon brush. Example

[0028] A method for preparing and applying a magnesium seawater battery cathode based on a carbon brush modified with carbon materials and PTFE binder includes the following steps: The carbon material used was Ketjen Black, and the solvent and dispersion process were the same as in Example 1. Commercial platinum carbon was used as a control sample.

[0029] The testing and assembly methods for magnesium seawater batteries are the same as in Example 1.

[0030] from Figure 4 It can be seen that after assembling carbon brushes with magnesium alloy anodes into a magnesium alloy anode seawater battery, the rate discharge performance of the carbon brush modified with Ketjenblack-PTFE binder composite material is better than that of the carbon brush modified with platinum-carbon-PTFE binder composite material at high current density.

[0031] from Figure 5 As shown in the long discharge performance data, under the same dissolved oxygen concentration, the carbon brush modified with Ketjenblack / PTFE binder composite material exhibits significantly better long discharge performance at a current density of 500 mA / L than the carbon brush modified with platinum-carbon / PTFE binder composite material.

[0032] The above results indicate that in magnesium alloy anode seawater batteries, cathode performance depends not only on the intrinsic activity of the oxygen reduction catalyst but also on the combined effects of dissolved oxygen mass transfer, cathode flood resistance, and magnesium-containing deposit blockage behavior. Although Pt / C exhibits high intrinsic oxygen reduction activity, magnesium-containing deposits generated near the cathode during discharge in magnesium alloy anode seawater batteries tend to cover noble metal active sites and increase mass transfer resistance. In contrast, the Ketjenblack / PTFE modified carbon brush cathode enhances dissolved oxygen capture capacity through porous carbon materials and maintains open mass transfer channels through PTFE hydrophobic regulation, making it more suitable for the long-term discharge environment of magnesium alloy anode seawater batteries.

Claims

1. A carbon material / PTFE modified carbon brush cathode for a magnesium alloy anode seawater battery, characterized in that, The modified carbon brush cathode is used in conjunction with a magnesium alloy anode and a seawater electrolyte to form a magnesium alloy anode seawater battery; the modified carbon brush cathode includes a three-dimensional carbon brush substrate and an oxygen reduction functional layer loaded on the surface of the three-dimensional carbon brush substrate; The oxygen reduction functional layer includes porous carbon material and PTFE binder / hydrophobic control component; the porous carbon material is used to capture dissolved oxygen in seawater for the cathode, and the PTFE binder / hydrophobic control component is used to form anti-flooding mass transfer channels inside the three-dimensional carbon brush substrate. The three-dimensional carbon brush substrate is a carbon fiber brush, a three-dimensional carbon bundle, a spiral carbon fiber brush, or a three-dimensional conductive matrix composed of carbon fiber bundles; the porous carbon material is selected from one or more of Ketjen black, acetylene black, conductive carbon black, conductive graphite, graphene, carbon nanotubes, and activated carbon.

2. The modified carbon brush cathode as described in claim 1, characterized in that, The PTFE binder / hydrophobic modifier is derived from a PTFE emulsion containing 50-65 wt% solids; the oxygen reduction functional layer contains 8-20 wt% PTFE in its solids; and the mass ratio of the porous carbon material to PTFE is 10:1-5:

1.

3. The modified carbon brush cathode as described in claim 1, characterized in that, The dry weight of the PTFE binder / hydrophobic modulator component accounts for 0.01%-0.5% of the total mass of the overall cathode containing the three-dimensional carbon brush substrate; the oxygen reduction functional layer has a loading of 1-5 mg / cm³ on the surface of the three-dimensional carbon brush substrate. 3 .

4. A magnesium alloy anode seawater battery, characterized in that, The invention includes a magnesium alloy anode, a seawater electrolyte, and a modified carbon brush cathode as described in any one of claims 1-3; wherein the magnesium alloy anode is selected from one of Mg-Al magnesium alloys, Mg-Zn magnesium alloys, Mg-Al-Zn magnesium alloys, Mg-Mn magnesium alloys, Mg-Ca magnesium alloys, AZ31 magnesium alloys, AZ61 magnesium alloys, or AZ91 magnesium alloys; the seawater electrolyte is natural seawater, simulated seawater, or a chloride-containing salt aqueous solution, and the dissolved oxygen in the seawater electrolyte serves as the cathode reactant of the modified carbon brush cathode.

5. A carbon material / PTFE modified carbon brush cathode for magnesium alloy anode seawater batteries and its preparation method, the method comprising the following steps: (1) Place the carbon powder and PTFE emulsion in ethanol or a mixture of ethanol and water, and form a uniform slurry by ultrasonic dispersion, mechanical stirring or magnetic stirring. (2) Load the slurry obtained in step (1) onto the surface of the carbon brush; (3) Dry at 60-80℃ for 1-2 hours to allow ethanol to evaporate, and obtain carbon powder / PTFE binder composite material.

6. The method for preparing a carbon powder / PTFE binder composite material as described in claim 5, characterized in that, The carbon brush is a three-dimensional spiral carbon fiber matrix, and its surface is subjected to high-temperature heat treatment and acid etching to remove organic impurities and inert substances.

7. The application of the magnesium alloy anode seawater battery as described in claim 4 in marine instruments, deep-sea sensors, marine buoys, emergency power supply devices, or marine monitoring equipment.

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