A gas diffusion electrode and its preparation method and application

Abstract

The present invention discloses a gas diffusion electrode, a preparation method thereof, and its application as or for making an electrochemical cathode for producing hydrogen peroxide. The preparation method comprises: uniformly dispersing conductive carbon and PTFE in ethanol by ultrasonication, adding carbon felt, placing the electrode in a heatable shaker, controlling the heating temperature not to exceed 60°C, and shaking the shaker at a speed of 100 to 200 rpm, heating and shaking for more than 1 hour to evaporate the solvent to obtain dry carbon felt, and calcining the dry carbon felt to obtain a gas diffusion electrode. In the gas diffusion electrode of the present invention, a hydrophobic layer composed of conductive carbon and PTFE is distributed on the surface and interior of the carbon felt. The present invention can solve existing technical problems such as low hydrogen peroxide production caused by problems such as insufficient three-phase interface.

Description

Technical Field

[0001] The present invention relates to the field of electrocatalysis technology, and in particular to a gas diffusion electrode and a preparation method and application thereof. Background Art

[0002] The use of a gas diffusion electrode to produce hydrogen peroxide is a green alternative to the anthraquinone method. Both gaseous oxygen and dissolved oxygen gain electrons at the three-phase interface of the gas diffusion electrode to generate hydrogen peroxide.

[0003] The most common method for preparing gas diffusion electrodes is to roll or hydraulically bond a paste containing a catalyst and a binder to carbon felt or other supports. For example, patent specification CN108358282A discloses a method for preparing a modified gas diffusion electrode that can be used as a cathode in electrochemical systems. The method involves laminating a diffusion layer containing carbon black and polytetrafluoroethylene (PTFE) with the electron collection layer using a stainless steel or titanium mesh as an electron collection layer, followed by a heat treatment at 330-380°C for 20-40 minutes. However, gas diffusion electrodes prepared in this manner have a smooth surface and few exposed active sites. Furthermore, the catalytic and diffusion layers can easily fall off when hydrogen evolution occurs at the cathode.

[0004] Coating methods are also currently used. For example, patent publication number CN 112259756 A discloses a method for preparing a stepped hydrophobic gas diffusion layer. First, conductive carbon and other carbon powder materials are thoroughly mixed with additives such as PTFE through ultrasonic vibration to create a hydrophobic agent slurry. The slurry is then coated on the gas diffusion layer and dried to produce the hydrophobic gas diffusion layer. However, the coating method is prone to uneven catalyst coating, and the slurry can only be applied to the surface.

[0005] In addition, spraying is also a common method. Although the spraying method can evenly distribute the catalyst, the catalyst layer is only on the surface of the carbon felt or other support.

[0006] In addition, if the impregnation method is used, the catalyst is prone to precipitation during the impregnation process, and only a catalytic layer is formed at the bottom of the impregnation, which is unevenly distributed.

[0007] Gas diffusion electrodes require a sufficient three-phase interface to produce hydrogen peroxide. Common gas diffusion electrode fabrication methods only construct a catalytic layer and a diffusion layer on the surface of carbon felt or other supports, which lacks sufficient three-phase interface and results in low hydrogen peroxide production. Therefore, it is necessary to improve the fabrication methods of gas diffusion electrodes to ensure a sufficient three-phase interface and achieve high hydrogen peroxide production. Summary of the Invention

[0008] In response to the above-mentioned technical problems and deficiencies in the art, the present invention provides a method for preparing a gas diffusion electrode. In the prepared gas diffusion electrode, a hydrophobic layer composed of conductive carbon and PTFE is distributed on the surface and interior of the carbon felt. When used as or in the manufacture of an electrochemical cathode for preparing hydrogen peroxide, it can solve existing technical problems such as low hydrogen peroxide production caused by insufficient three-phase interface and other problems.

[0009] The specific technical solutions are as follows:

[0010] A method for preparing a gas diffusion electrode comprises: uniformly dispersing conductive carbon and PTFE in ethanol by ultrasonication, adding carbon felt, placing the mixture in a heatable shaker, controlling the heating temperature to not exceed 60° C. and the shaking speed of the shaker to be 100 to 200 rpm, heating and shaking the mixture for more than 1 hour to evaporate the solvent to obtain dry carbon felt, and calcining the dry carbon felt to obtain a gas diffusion electrode;

[0011] In the gas diffusion electrode, a hydrophobic layer composed of the conductive carbon and the PTFE is distributed on the surface and inside of the carbon felt.

[0012] The present invention involves uniformly mixing conductive carbon, ethanol, PTFE, and carbon felt, then heating and shaking the mixture to evaporate the solvent. The turbulent flow and centrifugal action generated by the shaking promote the migration of the conductive carbon and PTFE into the interior of the carbon felt. Subsequently, calcination is performed to impart a hydrophobic layer composed of conductive carbon and PTFE to both the surface and interior of the carbon felt in the prepared gas diffusion electrode, thereby producing a gas diffusion electrode with discontinuous hydrophilic and hydrophobic layers (the carbon felt itself is hydrophilic). The preparation method of the gas diffusion electrode of the present invention is simple and requires mild conditions.

[0013] The inventors have found that if the conductive carbon, ethanol, PTFE and carbon felt are directly mixed and heated without shaking, the solvent will evaporate and the conductive carbon and PTFE will sink to the bottom of the container. They will not adhere firmly to the carbon felt and will easily fall off.

[0014] Based on this, the inventors firstly controlled the heating temperature and rotation speed to ensure that the conductive carbon, PTFE and carbon felt were fully in contact with each other during the whole process of solvent volatilization under the influence of fluid movement and centrifugal force. Finally, when the solvent evaporated completely, the binder PTFE dispersed the conductive carbon on the surface and three-dimensional structure of the carbon felt. The dried carbon felt after heating and shaking was calcined to form a gas diffusion electrode with discontinuous hydrophilic and hydrophobic layers.

[0015] The preparation method of the gas diffusion electrode of the present invention has at least the following key points that need to be strictly controlled:

[0016] 1. Control the heating temperature not to exceed 60°C. If the heating temperature is too high, the solvent will evaporate too quickly, and the paste composed of conductive carbon and PTFE will form too quickly, which will easily cause the paste to only stay on the surface of the carbon felt and be unable to enter the internal three-dimensional structure of the carbon felt;

[0017] 2. Control the shaking speed of the shaker to 100-200 rpm. If the speed is too slow, the fluid turbulence and centrifugal effect provided will be too small, making it difficult to promote the conductive carbon and PTFE to effectively enter the three-dimensional structure inside the carbon felt. If the speed is too fast, the solvent will overflow the container, causing the loss of conductive carbon and PTFE.

[0018] 3. The overall heating and shaking time is controlled at more than 1 hour, and the paste formed by the conductive carbon and PTFE is formed at a moderate rate, so that there is sufficient time for the conductive carbon and PTFE to effectively enter the internal three-dimensional structure of the carbon felt.

[0019] In the method for preparing a gas diffusion electrode, the conductive carbon may be one or more of graphite, carbon black, carbon fiber, carbon nanotubes, and graphene, preferably carbon fiber. When the carbon fiber is used as the conductive carbon, the prepared gas diffusion electrode can be used as or for making an electrochemical cathode for preparing hydrogen peroxide, thereby achieving a higher hydrogen peroxide yield.

[0020] In a preferred example, in the method for preparing the gas diffusion electrode, the mass ratio of the conductive carbon to the ethanol is 1 to 3:300.

[0021] In a preferred example, in the preparation method of the gas diffusion electrode, the PTFE is added in the form of a PTFE aqueous dispersion, the mass fraction of PTFE in the PTFE aqueous dispersion is 10% to 20%, and the mass ratio of the conductive carbon to the PTFE aqueous dispersion is 1:1 to 5.

[0022] In a preferred embodiment, the heating temperature of the gas diffusion electrode preparation method is 40-60° C., ensuring the efficiency of the preparation process while allowing the paste composed of conductive carbon and PTFE to fully penetrate into the three-dimensional structure inside the carbon felt.

[0023] In a preferred embodiment, in the method for preparing the gas diffusion electrode, the heating and shaking time is 1 to 2 hours, ensuring the efficiency of the preparation process while allowing the paste composed of conductive carbon and PTFE to fully enter the three-dimensional structure inside the carbon felt.

[0024] In a preferred embodiment, the method for preparing the gas diffusion electrode is as follows: the calcination temperature is 300-340°C, the residence time is 30-60 min, and the heating rate is 5-10°C min -1 .

[0025] The present invention further provides a gas diffusion electrode prepared by the preparation method.

[0026] The present invention also provides the use of the gas diffusion electrode as or in making an electrochemical cathode for preparing hydrogen peroxide.

[0027] The gas diffusion electrode with discontinuous hydrophilic and hydrophobic layers of the present invention can produce 38.55 mg L of hydrogen peroxide by providing sufficient three-phase interface. -1 cm -2 , which is conducive to promoting practical applications.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention combines heating and shaking with calcination to produce a gas diffusion electrode with discontinuous hydrophilic and hydrophobic layers. This method is simple and inexpensive to prepare. Furthermore, the gas diffusion electrode has a sufficient three-phase interface, enabling high hydrogen peroxide production and possessing practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a scanning electron microscope image of the original carbon felt.

[0031] Figure 2 This is a scanning electron microscope photograph of the gas diffusion electrode prepared in Example 1.

[0032] Figure 3 This is a scanning electron microscope photograph of the gas diffusion electrode prepared in Example 2.

[0033] Figure 4 This is a scanning electron microscope photograph of the gas diffusion electrode prepared in Example 3.

[0034] Figure 5 This is a scanning electron microscope photograph of the gas diffusion electrode prepared in Comparative Example 1.

[0035] Figure 6 This is a scanning electron microscope photograph of the gas diffusion electrode prepared in Comparative Example 2.

[0036] Figure 7 This is a scanning electron microscope photograph of the gas diffusion electrode prepared in Comparative Example 3.

[0037] Figure 8 Graphs showing the accumulation of hydrogen peroxide over time for the gas diffusion electrodes prepared in Examples 1 to 3 and the original carbon felt.

[0038] Figure 9 This is a graph showing the accumulation of hydrogen peroxide in the gas diffusion electrodes prepared in Comparative Examples 1 to 3 after 60 minutes of reaction. DETAILED DESCRIPTION

[0039] The present invention will be further described below with reference to the accompanying drawings and specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0040] In the following examples, the operating methods without specifying specific conditions are generally carried out under conventional conditions or conditions recommended by the manufacturer.

[0041] Example 1

[0042] The preparation method of the gas diffusion electrode with discontinuous hydrophilic and hydrophobic layers of this embodiment is carried out according to the following steps:

[0043] (1) Weigh 0.1 g of graphite and 20 mL of anhydrous ethanol in a beaker and ultrasonically disperse for 5 min;

[0044] (2) Slowly drip 300 μL of 10% PTFE aqueous dispersion into the beaker and continue ultrasonication for 10 min;

[0045] (3) Add carbon felt and place it in a heated shaker at a heating temperature of 60°C, a shaking speed of 150 rpm, and a heating and shaking time of 1 h. The solvent is evaporated to dryness to obtain dry carbon felt;

[0046] (4) Place the dry carbon felt in a tubular furnace and heat it up at a rate of 5°C min -1 The calcination temperature was 300 °C and the holding time was 40 min, and finally a gas diffusion electrode with a discontinuous hydrophilic and hydrophobic layer was obtained.

[0047] Figure 1 The scanning electron microscope photo of the original carbon felt and the scanning electron microscope photo of the gas diffusion electrode with discontinuous hydrophilic and hydrophobic layers prepared in Example 1 are shown in FIG. Figure 2 As shown, from Figure 2 It can be seen that the hydrophobic layer composed of graphite and PTFE is distributed not only on the surface of the carbon felt, but also inside the carbon felt, and finally forms an intermittent hydrophilic and hydrophobic layer with the carbon felt skeleton.

[0048] Example 2

[0049] The preparation method of the gas diffusion electrode with discontinuous hydrophilic and hydrophobic layers of this embodiment is carried out according to the following steps:

[0050] (1) Weigh 0.1 g of carbon fiber and 20 mL of anhydrous ethanol in a beaker and ultrasonically disperse for 5 min;

[0051] (2) Slowly drip 100 μL of 10% PTFE aqueous dispersion into the beaker and continue ultrasonication for 10 min;

[0052] (3) Add carbon felt and place it in a heated shaker at a heating temperature of 60°C, a shaking speed of 150 rpm, and a heating and shaking time of 1 h. The solvent is evaporated to dryness to obtain dry carbon felt;

[0053] (4) Place the dry carbon felt in a tubular furnace and heat it up at a rate of 5°C min -1 The calcination temperature was 300℃ and the holding time was 40min, and finally a gas diffusion electrode with a discontinuous hydrophilic and hydrophobic layer was obtained.

[0054] The scanning electron microscope photograph of the gas diffusion electrode with discontinuous hydrophilic and hydrophobic layers prepared in Example 2 is as follows: Figure 3 As shown, from Figure 3 It can be seen that the hydrophobic layer composed of carbon fiber and PTFE is distributed not only on the surface of the carbon felt, but also inside the carbon felt, and finally forms an intermittent hydrophilic and hydrophobic layer with the carbon felt skeleton.

[0055] Example 3

[0056] The preparation method of the gas diffusion electrode with discontinuous hydrophilic and hydrophobic layers of this embodiment is carried out according to the following steps:

[0057] (1) Weigh 0.1 g of carbon fiber and 20 mL of anhydrous ethanol in a beaker and ultrasonically disperse for 5 min;

[0058] (2) Slowly drip 300 μL of 10% PTFE aqueous dispersion into the beaker and continue ultrasonication for 10 min;

[0059] (3) Add carbon felt and place it in a heated shaker at a heating temperature of 60°C, a shaking speed of 150 rpm, and a heating and shaking time of 1 h. The solvent is evaporated to dryness to obtain dry carbon felt;

[0060] (4) Place the dry carbon felt in a tubular furnace and heat it up at a rate of 5°C min -1 The calcination temperature was 300℃ and the holding time was 40min, and finally a gas diffusion electrode with a discontinuous hydrophilic and hydrophobic layer was obtained.

[0061] The scanning electron microscope photograph of the gas diffusion electrode with discontinuous hydrophilic and hydrophobic layers prepared in Example 3 is as follows: Figure 4 As shown, from Figure 4 It can be seen that the hydrophobic layer composed of carbon fiber and PTFE is distributed not only on the surface of the carbon felt, but also inside the carbon felt, and finally forms an intermittent hydrophilic and hydrophobic layer with the carbon felt skeleton.

[0062] Comparative Example 1

[0063] The preparation method of the gas diffusion electrode of this comparative example is carried out according to the following steps:

[0064] (1) Weigh 0.1 g of carbon fiber and 20 mL of anhydrous ethanol in a beaker and ultrasonically disperse for 5 min;

[0065] (2) Slowly drip 300 μL of 10% PTFE aqueous dispersion into the beaker and continue ultrasonication for 10 min;

[0066] (3) Add carbon felt and place it in a heated shaker at a heating temperature of 80°C, a shaking speed of 150 rpm, and a heating and shaking time of 0.6 h. The solvent is evaporated to dryness to obtain dry carbon felt;

[0067] (4) Place the dry carbon felt in a tubular furnace and heat it up at a rate of 5°C min -1 The calcination temperature was 300 °C and the holding time was 40 min, and finally a gas diffusion electrode was obtained.

[0068] The scanning electron microscope photo of the gas diffusion electrode prepared in Comparative Example 1 is as follows: Figure 5 As shown, from Figure 5 It can be seen that due to the high heating temperature, the ethanol evaporates too quickly, and the PTFE forms a large paste in a short time. The hydrophobic layer composed of carbon fiber and PTFE cannot enter the interior of the carbon felt and can only exist on the surface of the carbon felt.

[0069] Comparative Example 2

[0070] The preparation method of the gas diffusion electrode of this comparative example is carried out according to the following steps:

[0071] (1) Weigh 0.1 g of carbon fiber and 20 mL of anhydrous ethanol in a beaker and ultrasonically disperse for 5 min;

[0072] (2) Slowly drip 300 μL of 10% PTFE aqueous dispersion into the beaker and continue ultrasonication for 10 min;

[0073] (3) Add carbon felt and place it in a heated shaker at 60°C without shaking for 1.5 hours. The solvent is evaporated to dry carbon felt.

[0074] (4) Place the dry carbon felt in a tubular furnace and heat it up at a rate of 5°C min -1 The calcination temperature was 300 °C and the holding time was 40 min, and finally a gas diffusion electrode was obtained.

[0075] The scanning electron microscope photo of the gas diffusion electrode prepared in Comparative Example 2 is as follows: Figure 6 As shown, from Figure 6 It can be seen that due to the absence of fluid turbulence caused by shaking and the participation of centrifugal action, the catalyst and PTFE both sink to the bottom, and only a thin hydrophobic layer is formed at the bottom of the carbon felt.

[0076] Comparative Example 3

[0077] The preparation method of the gas diffusion electrode of this comparative example is carried out according to the following steps:

[0078] (1) Weigh 0.1 g of carbon fiber and 20 mL of anhydrous ethanol in a beaker and ultrasonically disperse for 5 min;

[0079] (2) Slowly drip 300 μL of 10% PTFE aqueous dispersion into the beaker and continue ultrasonication for 10 min;

[0080] (3) Add carbon felt and place it in a heated shaker at a heating temperature of 60°C, a shaking speed of 50 rpm, and a heating and shaking time of 1.2 h. The solvent is evaporated to dry carbon felt;

[0081] (4) Place the dry carbon felt in a tubular furnace and heat it up at a rate of 5°C min -1 The calcination temperature was 300 °C and the holding time was 40 min, and finally a gas diffusion electrode was obtained.

[0082] The scanning electron microscope photo of the gas diffusion electrode prepared in Comparative Example 3 is as follows: Figure 7 As shown, from Figure 7 It can be seen that due to the low rotation speed, sufficient fluid turbulence and centrifugal effect cannot be formed, and a hydrophobic layer cannot be formed inside the carbon felt. A hydrophobic layer can only be formed at the bottom of the carbon felt.

[0083] Test Case

[0084] The gas diffusion electrodes with discontinuous hydrophilic and hydrophobic layers prepared in Examples 1 to 3, the gas diffusion electrodes prepared in Comparative Examples 1 to 3, and the original carbon felt electrode were used as cathodes to investigate the amount of hydrogen peroxide accumulated by different electrodes. The reactor volume was 100 mL, and a titanium-based tin antimony oxide electrode was used as the anode. The dimensions of the anode and cathode were both 2 cm × 2 cm, the distance between the electrodes was 2 cm, and the applied constant current was 40 mA.

[0085] The results of hydrogen peroxide accumulation in different electrode systems are shown in Figure 8 At 60 min of reaction, compared with the original carbon felt without interrupted hydrophilic and hydrophobic layers (13.12 mg L -1 cm -2 ), the hydrogen peroxide production of the gas diffusion electrodes with discontinuous hydrophilic and hydrophobic layers prepared in Examples 1 to 3 was significantly improved, and was 33.18 mg L -1 cm -2 、28.25mg L -1 cm -2 、38.55mg L -1 cm -2 .

[0086] When the reaction was carried out for 60 min under the same reaction conditions, the results of hydrogen peroxide accumulation using the gas diffusion electrodes prepared in Comparative Examples 1 to 3 were shown in FIG. Figure 9 Since the comparative example did not form a discontinuous hydrophilic and hydrophobic layer, the accumulated amount of hydrogen peroxide was lower than that of Examples 1 to 3, which were 18.89 mg L -1 cm -2 、15.00mg L -1 cm -2 、16.65mg L -1 cm-2 .

[0087] It can be seen that the gas diffusion electrode with discontinuous hydrophilic and hydrophobic layers prepared in the present invention can efficiently generate hydrogen peroxide and is suitable for promotion to practical applications.

[0088] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A method for preparing a gas diffusion electrode, characterized in that: include: Conductive carbon and PTFE are uniformly dispersed in ethanol by ultrasonication, carbon felt is added, and the mixture is placed in a heatable shaker. The heating temperature is controlled to be 40-60°C, and the shaking speed of the shaker is 100-200 rpm. The mixture is heated and shaken for 1-2 hours to evaporate the solvent to obtain dry carbon felt, and the dry carbon felt is calcined to obtain a gas diffusion electrode. In the gas diffusion electrode, a hydrophobic layer composed of the conductive carbon and the PTFE is distributed on the surface and inside of the carbon felt.

2. The preparation method according to claim 1, characterized in that The conductive carbon is one or more of graphite, carbon black, carbon fiber, carbon nanotube, and graphene.

3. The preparation method according to claim 1, characterized in that The added mass ratio of the conductive carbon to the ethanol is 1 to 3:

300.

4. The preparation method according to claim 1, characterized in that The PTFE is added in the form of a PTFE aqueous dispersion, the mass fraction of PTFE in the PTFE aqueous dispersion is 10% to 20%, and the mass ratio of the conductive carbon to the PTFE aqueous dispersion is 1:1 to 5.

5. The preparation method according to claim 1, characterized in that The calcination temperature is 300-340°C, the residence time is 30-60 min, and the heating rate is 5-10°C min -1 .

6. A gas diffusion electrode prepared according to the preparation method according to any one of claims 1 to 5.

7. Use of the gas diffusion electrode according to claim 6 as or for manufacturing an electrochemical cathode for producing hydrogen peroxide.

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