AEM electrolytic cell membrane electrode and preparation method and application thereof

Abstract

The invention discloses an AEM electrolytic cell membrane electrode and a preparation method and application thereof, the membrane electrode comprises: an anode comprising an anode catalyst growing on a porous metal substrate in situ; the cathode comprises a cathode catalyst and a cathode diffusion layer; the anion exchange membrane is arranged between the anode catalyst and the cathode catalyst; and the cathode catalyst is loaded on the cathode side of the anion exchange membrane. The self-supporting anode is formed in an in-situ growth mode, so that the self-supporting anode has the effects of being stable in performance, good in conductivity, not prone to falling off and the like, gas diffusion is guaranteed, active sites are provided for oxidation reaction, a gas diffusion layer does not need to be considered for the anode when an electrolytic cell is assembled, and assembling is easy and convenient; the cathode catalyst is sprayed on the anion exchange membrane, and the advantages of the CCM are combined, so that the mass transfer path of the cathode is reduced, the ohmic polarization is reduced, and the electrolytic efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and in particular to an AEM electrolytic cell membrane electrode and a preparation method and application thereof. Background Art

[0002] There are two types of membrane electrode preparation processes in anion exchange membranes (AEMs) electrolyzers: one is catalyst coated membrane (CCM), and the other is catalyst coated substrate (CCS). Figure 1 As shown. In the CCM method, a mixture of electrocatalyst and ionomer is prepared into a slurry, which is applied to both sides of the AEM by spraying, spin coating, etc. and dried; then it is placed between the gas diffusion layers and assembled mechanically or hot-pressed. The manufacturing process is relatively complicated. Some catalyst ink solvents will dissolve the membrane, and there is also membrane creep behavior in the CCM, which will reduce the durability of the membrane. In order to ensure the efficiency of electrolysis, platinum carbon is generally used as the cathode, which has a low precious metal loading and a light weight. The anode uses a high non-precious metal loading. It is difficult to make both sides of the membrane completely flat. If there is a problem during assembly, the performance cannot be guaranteed after disassembly and reassembly, which is not conducive to large-scale electrolytic cell assembly and maintenance. Figure 2 、 Figure 3 As shown. In the CCS method, the electrocatalyst slurry is directly deposited on the gas diffusion layer and then sintered to form an electrode. The AEM is encapsulated in the gas diffusion layer or between the electrodes to form a membrane electrode assembly. Among them, the catalyst is directly deposited on the gas diffusion layer and it is necessary to add slurry as a binder to inhibit the diffusion of bubbles and the exposure of active sites, resulting in insufficient contact between the membrane and the catalyst layer, thereby affecting the activity of the catalyst; the conductive path is long, resulting in large resistance losses during electron transmission, consuming a large amount of additional electricity, making the energy consumption of water electrolysis high and the economic benefits poor; and after adding the slurry coating, the catalyst layer cracked after 1000 hours of testing, as shown Figure 4 As shown, it is impossible to operate with high performance for a long time. Summary of the Invention

[0003] The present invention aims to solve at least one of the above-mentioned technical problems existing in the prior art. To this end, the present invention aims to provide an AEM electrolytic cell membrane electrode and its preparation method and application.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] A first aspect of the present invention provides a membrane electrode, comprising:

[0006] an anode comprising an anode catalyst grown in situ on a porous metal substrate;

[0007] a cathode, comprising a cathode catalyst and a cathode diffusion layer;

[0008] An anion exchange membrane is provided between the anode catalyst and the cathode catalyst; and the cathode catalyst is supported on the cathode side of the anion exchange membrane.

[0009] The surface energy of anion exchange membranes is generally high. Even if the same resin monomer is used as a binder, excessive addition of binder will cover the active sites of the catalyst, resulting in poor membrane electrode performance; if too little binder is added, the catalyst will fall off severely, and the membrane electrode performance will drop sharply over time. In the present invention, the anode catalyst is grown in situ on a porous metal substrate to form a self-supporting anode, without the need to add a binder. This not only avoids the aforementioned defects of poor system stability and durability caused by the addition of a binder, but also avoids the defect of inhibiting rapid diffusion of bubbles caused by the binder blocking the gas diffusion channel; this type of in situ grown anode does not need to be activated before use. The cathode side of the anion exchange membrane where the cathode catalyst is directly loaded can effectively shorten the electron transmission path, reduce ohmic polarization, and increase electrolysis efficiency. On the other hand, after loading the cathode catalyst, the anion exchange membrane is easier to spread flat under the action of surface forces, overcoming the defect of uneven spreading caused by the different amounts of catalysts on both sides of the traditional anion exchange membrane; the anode metal substrate also provides a platform for the spreading of the anion exchange membrane, preventing the anion exchange membrane from swelling during the assembly process, resulting in an uneven surface and a short circuit in the electrolyzer.

[0010] In some embodiments of the present invention, the surface density of the porous metal substrate is 300 to 2000 g / m 2 , such as 500~1800g / m 2 ,800~1500g / m 2 ,900~1200g / m 2 , 1000g / m 2 In the present invention, the test method of the surface density is as follows: GB / T 20251-2006 “Nickel foam for batteries”.

[0011] In some embodiments of the present invention, the porosity of the porous metal substrate is 60-150 PPI (Pores Per Inch, i.e., pores per inch), such as 80-130 PPI, 90-120 PPI, 100-110 PPI, etc. In the present invention, the porosity is tested according to GB / T 20251-2006 "Nickel Foam for Batteries".

[0012] In some embodiments of the present invention, the average pore size of the porous metal substrate is 50 to 120 μm.

[0013] In some embodiments of the present invention, the pore volume distribution of the porous metal substrate is D10: 1-5 μm; D50: 50-75 μm; D90: 100-150 μm.

[0014] In some embodiments of the present invention, the anode catalyst is in situ grown on the surface and / or in the pores inside the porous metal substrate; preferably, the porous metal substrate has 10 to 20 g / cm 3 If the loading is too low, the effective catalytic components in the anode will be too few, which is not conducive to the oxygen evolution catalytic reaction; if the loading is too high, the structure of the anode will be too dense, which is not conducive to gas conduction, and the conductivity will be reduced, the ohmic impedance will increase, and the overpotential of the oxygen evolution reaction will increase.

[0015] In some embodiments of the present invention, the porous metal substrate comprises at least one of nickel foam, nickel mesh, nickel felt, titanium foam, and stainless steel foam.

[0016] In some embodiments of the present invention, the anode catalyst comprises iridium dioxide (IrO2), nickel ferrite (NiFeO x )

[0017] In some embodiments of the present invention, the loading amount of the cathode catalyst on the anion exchange membrane is 0.5 to 2.0 mg / cm 2 .

[0018] In some embodiments of the present invention, the cathode catalyst includes one of platinum, platinum carbon, nickel, NiMo, and NiP; wherein, when the cathode catalyst is platinum carbon, the platinum content is 10-50wt%, such as 20-40wt%, 30wt%.

[0019] In some embodiments of the present invention, the cathode diffusion layer is selected from at least one of carbon paper, carbon cloth, carbon felt, and nickel felt.

[0020] In some embodiments of the present invention, the thickness of the anion exchange membrane is 10-100 μm, such as 30-80 μm, 60 μm, 70 μm, etc.

[0021] In some embodiments of the present invention, the anion exchange membrane comprises a halogen-containing imidazole polymer, an anion exchange membrane with a polyaryl or polyolefin backbone, or other suitable materials. For example, the anion exchange membrane may be FAS from Fumatech or X37-50 from Dioxide Materials.

[0022] The second aspect of the present invention provides a method for preparing the membrane electrode, comprising the following steps:

[0023] The porous metal substrate is immersed in a metal salt solution forming an anode catalyst for in-situ growth to prepare an anode;

[0024] spraying a cathode catalyst onto the cathode side of an anion exchange membrane to prepare an anion exchange membrane coated with the cathode catalyst;

[0025] The anode, the anion exchange membrane coated with the cathode catalyst and the cathode diffusion layer are assembled in sequence to prepare the membrane electrode.

[0026] In some embodiments of the present invention, the mass concentration of the metal salt solution is 0.1 to 1.0 mol / L, such as 0.1 to 0.5 mol / L.

[0027] In some embodiments of the present invention, the metal salt includes a nickel salt and an iron salt to form nickel ferrite, and the nickel salt includes at least one of nickel chloride, nickel sulfate, and nickel nitrate; the iron salt includes at least one of ferric chloride, ferric nitrate, and polyferric sulfate.

[0028] In some embodiments of the present invention, the metal salt comprises an iridium salt to form iridium dioxide, and the iridium salt comprises at least one of chloroiridic acid, sodium chloroiridate, and iridium nitrate. In some embodiments of the present invention, the solvent of the metal salt solution is an organic solvent, and the organic solvent comprises at least one of methanol, ethanol, and propanol, and the propanol comprises n-propanol and isopropanol.

[0029] In some embodiments of the present invention, the method for preparing the metal salt solution comprises dissolving the metal salt in water, adjusting the pH to 1 to 7, adding the organic solvent, and stirring and / or ultrasonicating to a homogeneous system; preferably, the stirring and / or ultrasonicating time is 1 to 6 hours.

[0030] In some embodiments of the present invention, the in situ growth time is 24 to 96 hours, such as 48 hours, 72 hours, etc.

[0031] In some embodiments of the present invention, the method for preparing the membrane electrode further includes pretreating the porous metal substrate; preferably, the specific operation of the pretreatment includes ultrasonic treatment with hydrochloric acid, acetone, and ethanol in sequence; preferably, the ultrasonic treatment time is 10 to 30 minutes.

[0032] The third aspect of the present invention provides an electrolytic cell comprising the membrane electrode.

[0033] A fourth aspect of the present invention provides a method for producing hydrogen by electrolysis of water, comprising using the membrane electrode or the electrolyzer to produce hydrogen by electrolysis of water.

[0034] The beneficial effects of the present invention are:

[0035] The present invention forms a self-supporting anode by in-situ growth, which has the advantages of stable performance, good conductivity, and non-detachment. It not only ensures gas diffusion but also provides active sites for oxidation reaction. When assembling the electrolytic cell, there is no need to consider the gas diffusion layer for the anode, and the assembly is simple. The cathode catalyst is sprayed on the anion exchange membrane, combining the advantages of CCM to ensure that the mass transfer path of the cathode is reduced, the ohmic polarization is reduced, and the electrolysis efficiency is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the traditional membrane electrode preparation process.

[0037] Figure 2 A physical diagram of the swelling problem in the traditional CCM method.

[0038] Figure 3 A physical diagram of the swelling problem in the traditional CCM method.

[0039] Figure 4 The cracking phenomenon of the surface catalytic layer after 1000 hours of testing by traditional CCS method spraying on nickel felt substrate.

[0040] Figure 5 Schematic diagram of the membrane electrode structure of an embodiment of the present invention.

[0041] Figure 6 This is a photo of the cathode side of the anion exchange membrane after spraying cathode catalyst on it in Example 1 of the present invention.

[0042] Figure 7 These are membrane electrode polarization curves of Example 1 of the present invention and Comparative Examples 1 and 2.

[0043] Figure 8 Graph showing changes in membrane electrode electrolysis voltage over time for Example 1 of the present invention and Comparative Examples 1 and 2.

[0044] Figure markings: 1. anode; 2. anion exchange membrane; 3. cathode catalyst; 4. cathode diffusion layer. DETAILED DESCRIPTION

[0045] The present invention is further described in detail below using specific examples. Unless otherwise specified, the raw materials, reagents, and apparatus used in the examples and comparative examples are available from conventional commercial sources or by conventional methods. Unless otherwise specified, all experimental or testing methods are conventional in the art.

[0046] In the following examples or comparative examples, the anion exchange membrane is X37-50 from Dioxide Materials.

[0047] Example 1

[0048] This embodiment prepares a membrane electrode, the structural diagram of which is shown in FIG. Figure 5 The specific process is as follows:

[0049] S1: Anode substrate pretreatment: select a surface density of 1000g / cm 2 , 110PPI nickel foam (effective area 5*5cm 2 ). Use 3M hydrochloric acid, acetone, and ethanol to treat in sequence, ultrasonicate for 10 minutes each to remove the oxide layer on the surface of the metal substrate, and air dry naturally;

[0050] S2: Preparation of anode side gas diffusion electrode: Weigh 7g nickel sulfate and 2g iron sulfate, first dissolve in 50mL deionized water, the solution pH range is 4-7, after the solution becomes a homogeneous system, react for 2h, add 100mL n-propanol, stir at a stirring rate of 40rpm, stir for 4h, finally the solution becomes a homogeneous system, completely immerse the metal substrate in the homogeneous solution, immerse and react for 24h to obtain the final anode catalyst-loaded gas anode;

[0051] S3: Cathode side - CCM form: The cathode catalyst uses a Pt-containing alloy catalyst (Pt / C) and is sprayed on the surface of the anion exchange membrane using a spray device; the Pt content in the cathode catalyst is about 20wt%, and the catalyst loading range is 0.5mg / cm 2 ;

[0052] S4: Assembling the prepared anode, the anion exchange membrane sprayed with the cathode catalyst, and carbon paper to prepare the membrane electrode.

[0053] Among them, the actual picture after the cathode side is sprayed with catalyst is as follows Figure 6 As shown, it can be seen that it is spread flat.

[0054] Example 2

[0055] This embodiment prepares a membrane electrode, and the specific process is as follows:

[0056] The preparation method of Example 1 is referred to, except that the catalyst loading on the cathode side is about 15 wt %, and the catalyst loading range is 0.45 mg / cm 2 , the rest are consistent with Example 1.

[0057] Example 3

[0058] This embodiment prepares a membrane electrode, and the specific process is as follows:

[0059] The preparation method is the same as that in Example 1, except that 8 g of nickel sulfate and 0.5 g of iron sulfate are used in S3. The rest is the same as that in Example 1.

[0060] Example 4

[0061] This embodiment prepares a membrane electrode, and the specific process is as follows:

[0062] Refer to the preparation method of Example 1, except that the NF substrate is 420g / cm 2 ,85PPI nickel foam, and the rest are consistent with Example 1.

[0063] Comparative Example 1

[0064] This comparative example prepared a membrane electrode, and the specific process was as follows:

[0065] S1: Pretreatment of cathode and anode substrate: select a surface density of 1000g / cm 2 , 110PPI nickel foam (effective area 5*5cm 2 ). Use 3M hydrochloric acid, acetone, and ethanol to treat in sequence, ultrasonicate for 10 minutes each to remove the oxide layer on the surface of the metal substrate, and air dry naturally;

[0066] S2: Preparation of cathode side CCS electrode: A Pt-containing alloy catalyst (Pt / C) was sprayed onto the surface of a nickel foam substrate using a spraying device. The Pt content in the cathode catalyst was about 20 wt%, and the catalyst loading range was 0.5 mg / cm 2 ;

[0067] S3: Preparation of CCS electrode on the anode side: Weigh 7 g of nickel sulfate and 2 g of iron sulfate, first dissolve them in 50 mL of deionized water, the pH range of the solution is 1-7, after the solution becomes a homogeneous system, react for 2 hours, add 100 mL of n-propanol, stir at a stirring rate of 40 rpm, and stir for 4 hours. Finally, the solution becomes a homogeneous system, and the metal substrate is completely immersed in the homogeneous solution. The immersion reaction time is 24 hours to obtain the final anode catalyst-loaded gas anode;

[0068] S4: Assembling the prepared cathode, anode and anion exchange membrane to obtain the membrane electrode.

[0069] Comparative Example 2

[0070] This comparative example prepared a membrane electrode, and the specific process was as follows:

[0071] S1: Anion exchange membrane treatment: The anion exchange membrane needs to be replaced by placing it in 1M KOH at 50°C for 12 hours for ion replacement. After 12 hours, replace it with new alkaline solution and continue soaking for another 12 hours to complete the replacement;

[0072] S2: Preparation of anode catalyst: Weigh 7g nickel sulfate and 2g iron sulfate, first dissolve in 50mL deionized water, the solution pH range is 1-7, after the solution becomes a homogeneous system, the reaction time is 2h, add 100mL n-propanol, stir at a stirring rate of 40rpm, stir for 4h, after stirring the solution becomes a homogeneous system, then filter to obtain nickel-iron based catalyst

[0073] S3: CCM preparation: The cathode side of the anion exchange membrane is sprayed with a Pt-containing alloy catalyst (Pt / C), where the Pt content is about 25 wt% and the catalyst loading range is 0.5 mg / cm 2 The anode side of the anion exchange membrane is sprayed with a filtered nickel-iron based catalyst with a catalyst loading range of 0.5 mg / cm 2 ;

[0074] S4: Assembling the cathode side of the anion exchange membrane with carbon paper, and assembling the anode side of the anion exchange membrane with nickel felt to prepare the membrane electrode.

[0075] Test Example 1

[0076] The membrane electrodes prepared in the examples and comparative examples were assembled in an electrolytic cell to conduct a formation test. The specific process was as follows:

[0077] The electrolyzer is mainly composed of a membrane electrode and a carbon paper cathode. The polarization curve is tested using a charge and discharge instrument. The step current method is adopted to supply power to the electrolyzer to cause a reaction. The current in the system can be increased from 0A to 5A. After treatment, a polarization curve can be obtained. The cycle stability is tested using a CHI760 electrochemical workstation using the chronopotentiometry and a constant current of 1A / cm 2 , under 80℃ test conditions, the stability test curve can be obtained after data processing.

[0078] The results are as follows Figure 7 、 Figure 8 shown.

[0079] Figure 7 The polarization curve shows that the performance of the double-sided CCS of comparative example 1 is poor, which is due to the obstruction of mass transfer, and the poor initial performance indicates that the ohmic resistance of the component is too high, resulting in a high electrolysis voltage; Figure 7 At medium and high current densities, the double-sided CCM of Comparative Example 2 performs better because the catalyst and membrane in the CCM are tightly bonded, reducing the contact resistance between the electrodes and the membrane. This allows electrons to conduct more smoothly between the catalyst, membrane, and external circuit. Especially at high current densities, the lower ohmic resistance effectively reduces energy loss, allowing the voltage applied to the electrodes to be used more to drive the electrochemical reaction rather than consumed in resistive heating, thereby maintaining a lower operating voltage. Figure 7The reason why Example 1 has a better effect at medium and low current densities is that the anode adopts a self-supporting electrode. The catalyst self-grown on the nickel foam substrate does not need to add resin as a binder, has more active sites, optimizes the electrode reaction kinetics, and has a better mass transfer effect.

[0080] Constant current 1A / cm 2 , Under 80℃ test conditions, the electrolysis voltage changes with time as shown in the figure Figure 8 As shown, after 5000 hours of continuous testing, the voltage of Example 1 only increased from 1.64V to 1.73V. Comparative Example 1 increased steadily in the first 1000 hours, from 1.742V to 1.762V, but after 1000 hours, the electrode decayed, and the decay rate gradually increased, reaching 1.95V at 3000 hours of testing. Comparative Example 2 operated smoothly in the first 1000 hours, but decayed more sharply after 1000 hours. This was due to severe binder shedding in an alkaline environment, resulting in loss of catalyst on both sides. The voltage rose from 1.63V to 2.0V after 2000 hours of testing. These test results demonstrate the high long-term operational stability of Example 1.

[0081] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A membrane electrode, characterized in that: include: an anode comprising an anode catalyst grown in situ on a porous metal substrate; a cathode, comprising a cathode catalyst and a cathode diffusion layer; An anion exchange membrane is provided between the anode catalyst and the cathode catalyst; and the cathode catalyst is supported on the cathode side of the anion exchange membrane.

2. The membrane electrode according to claim 1, characterized in that: The surface density of the porous metal substrate is 300 to 2000 g / m 2 .

3. The membrane electrode according to claim 1, characterized in that: The porosity of the porous metal substrate is 60 to 150 PPI.

4. The membrane electrode according to claim 1, characterized in that: The anode catalyst is in situ grown on the surface and / or in the pores inside the porous metal substrate; preferably, 10 to 20 g / cm 2 anode catalyst.

5. The membrane electrode according to claim 1, characterized in that: The loading amount of cathode catalyst on the anion exchange membrane is 0.5-2.0 mg / cm 2 .

6. The membrane electrode according to claim 1, characterized in that: The anode catalyst includes one of iridium dioxide and nickel ferrite.

7. The membrane electrode according to claim 1, characterized in that: The porous metal substrate includes at least one of foamed nickel, nickel mesh, nickel felt, foamed titanium, and foamed stainless steel.

8. A method for preparing a membrane electrode according to any one of claims 1 to 7, comprising the following steps: The porous metal substrate is immersed in a metal salt solution forming an anode catalyst for in-situ growth to prepare an anode; spraying a cathode catalyst onto the cathode side of an anion exchange membrane to prepare an anion exchange membrane coated with the cathode catalyst; The anode, the anion exchange membrane coated with the cathode catalyst, and the cathode diffusion layer are assembled in sequence to prepare the membrane electrode according to any one of claims 1 to 7.

9. An electrolytic cell, characterized in that: The membrane electrode comprises the membrane electrode according to any one of claims 1 to 7.

10. A method for producing hydrogen by electrolysis of water, characterized in that: The method comprises using the membrane electrode according to any one of claims 1 to 7 or the electrolyzer according to claim 9 to electrolyze water to produce hydrogen.

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