Gas diffusion electrode for electrochemical carbon dioxide reduction and manufacturing method therefor

Abstract

The present invention relates to a gas diffusion electrode for electrochemical carbon dioxide reduction and a manufacturing method therefor. The gas diffusion electrode for carbon dioxide reduction, according to the present invention, has the advantages of being capable of smoothly discharging moisture and salt components formed on the electrode and facilitating the supplying of carbon dioxide so as to maintain high carbon dioxide reduction performance for a long time. In addition, the excellent physical strength of a nickel foam used as a support layer enables the area of the electrode to be easily increased and thus is suitable for industrial application.

Description

Gas diffusion electrode for electrochemical carbon dioxide reduction and method for manufacturing the same

[0001] The present invention relates to a gas diffusion electrode for electrochemical carbon dioxide reduction and a method for manufacturing the same.

[0002] Electrochemical carbon dioxide reduction technology is a technology that uses electric energy with carbon dioxide as a raw material to produce useful compounds such as carbon monoxide (CO), synthesis gas, formic acid (HCOOH), ethylene (C2H), and ethanol (C2H5OH). In conventional electrochemical carbon dioxide reduction reactions, carbon-based gas diffusion electrodes are mainly used to facilitate electron movement and to smoothly supply the reactant, carbon dioxide, to the catalyst layer (Republic of Korea Patent 10-2020-0168081, Republic of Korea Patent 10-2022-0114122).

[0003] Conventional gas diffusion electrodes consist of a microporous layer formed from carbon black powder, such as Vulcan XC-72, on a support such as carbon paper or carbon cloth having large pores, and a catalyst layer is coated on the microporous layer to be used as an electrode. Although these carbon-based electrodes exhibit excellent performance in the initial stages of use, over time, the hydrophobicity of the electrode decreases, causing moisture and salt to accumulate on the electrode, resulting in a flooding phenomenon that hinders the supply of carbon dioxide to the catalyst layer. Due to this flooding phenomenon, the supply of carbon dioxide, which is a reactant, is inhibited, and the rate of the electrochemical carbon dioxide reduction reaction is limited. Furthermore, as water surrounding the catalyst participates in the reduction reaction instead of carbon dioxide and causes a hydrogen evolution reaction, the Faraday efficiency of the electrochemical carbon dioxide reduction reaction decreases.

[0004] Consequently, the flooding phenomenon continuously degrades the carbon dioxide reduction performance of carbon-based gas diffusion electrodes, hindering the commercialization of electrochemical carbon dioxide conversion technology.

[0005] Previous studies have reported that channels ranging in size from several to several hundred micrometers are created in microporous layers through pore-forming agents (J Electrochem Soc, 2017, 164, F1697-711) or laser perforation (ECS Trans, 2013, 58, 315-24) to facilitate the supply of carbon dioxide and the discharge of water, thereby mitigating flooding problems; however, this process increases the cost of fabricating electrodes.

[0006] In order to solve the problems of the electrochemical carbon dioxide reduction electrodes mentioned above, the present invention developed a gas diffusion electrode capable of maintaining a stable and high reduction reaction rate and high Faraday efficiency by suppressing or mitigating the flooding phenomenon.

[0007] The present invention provides a gas diffusion electrode for carbon dioxide reduction comprising: a porous metal substrate layer; a pore layer formed on the porous metal substrate layer comprising a carbon compound and a hydrophobic polymer; and a catalyst layer formed on the pore layer.

[0008] In addition, the present invention comprises the step of preparing a porous metal substrate layer by coating a nickel foam with a hydrophobic polymer;

[0009] A step of preparing a porous layer by coating a slurry solution mixed with a carbon compound and a hydrophobic polymer onto a porous metal substrate layer; and

[0010] The present invention provides a method for manufacturing a gas diffusion electrode for carbon dioxide reduction, comprising the step of preparing a catalyst layer by coating a slurry solution mixed with silver and Nafion ionomer onto a porous layer.

[0011] The gas diffusion electrode for carbon dioxide reduction according to the present invention has the advantage of being able to smoothly discharge moisture and salt components formed on the electrode due to its high gas permeability, and to maintain high carbon dioxide reduction performance for a long period by ensuring a smooth supply of carbon dioxide. In addition, the excellent physical strength of the nickel foam used as a support layer facilitates the expansion of the electrode area, making it suitable for industrial application.

[0012] Figure 1 shows the manufacturing process of a gas diffusion electrode according to the present invention, a schematic diagram of the gas diffusion electrode, and a surface SEM image.

[0013] Figure 2 shows SEM images before and after coating the pore layer and the catalyst layer during the manufacturing process of the gas diffusion electrode according to the present invention.

[0014] Figure 3 is a graph of CO production Faraday efficiency and operating voltage according to current density of comparative examples and embodiments according to the present invention.

[0015] FIG. 4 shows 200 mA / cm² of the comparative example and the example according to the present invention. 2 This is a graph of 50-hour long-term driving data.

[0016] Figure 5 is a graph of contact angle measurements before and after 50 hours of long-term operation of the comparative example and the embodiment according to the present invention.

[0017] FIG. 6 is a graph of gas permeability measured under dry carbon dioxide supply conditions and carbon dioxide supply conditions containing moisture corresponding to a relative humidity of 100% or more according to the comparative example and embodiment of the present invention.

[0018] Figure 7 is a graph of the electrical conductivity measurement results of the comparative example and the embodiment according to the present invention.

[0019] The present invention will be described in detail below.

[0020] The present invention comprises a porous metal substrate layer;

[0021] A porous layer comprising a carbon compound and a hydrophobic polymer formed on the above porous metal substrate layer; and

[0022] A gas diffusion electrode for carbon dioxide reduction is provided, comprising a catalyst layer formed on the above-mentioned porous layer.

[0023] The porous metal may include nickel, and most preferably, may be in the form of nickel foam. Nickel foam is a porous solid material composed of nickel metal and has a porous form similar to a sponge.

[0024] The porous metal substrate layer may have a pore size of 100 to 1000 μm. When the pore size of the substrate layer is less than 100 μm, the movement of reactants and products may not be smooth, and when the pore size exceeds 1000 μm, there is a problem of reduced electrical conductivity.

[0025] The above porous metal substrate layer can be coated with a hydrophobic polymer.

[0026] In the present invention, the hydrophobic polymer may be one or more selected from the group consisting of polytetrafluoroethylene (PTFE), polypropylene (PP), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polyperfluoroalkoxy (PFA), ethylene tetrafluoroethylene (ETFE), polyoxymethylene (POM), and polyimide (PI). A hydrophobic polymer may be used to minimize the flooding effect, and among such hydrophobic polymers, a polymer with high electrical and chemical stability is preferred. Preferably, it may be PTFE.

[0027] The above carbon compound may be one or more selected from carbon black, graphite, and carbon fiber. Preferably, it may be carbon black (acetylene black) with a specific surface area of ​​50 to 70 m² 2 Carbon black with a characteristic of / g is more desirable.

[0028] The carbon compound and hydrophobic polymer of the above-mentioned porous layer may have a weight ratio of 9:1 to 7:3, preferably 8.5:1.5 to 7.5:2.5. When the hydrophobic polymer is 3 or more, there may be a problem of reduced electrical conductivity of the porous layer, and when it is less than 1, there may be a problem of reduced mechanical strength of the porous layer.

[0029] The above pore layer may have a pore size of 10 to 300 μm.

[0030] The catalyst layer comprises silver (Ag) and Nafion, and may contain silver (Ag) and Nafion in a weight ratio of 5:5 to 9.5:0.5. The silver (Ag) in the catalyst layer may be silver nanopowder. If the silver (Ag) content ratio exceeds 9.5 weight ratio, there may be a problem in that the shape of the catalyst layer is not maintained due to insufficient binder content, and if it is less than 5 weight ratio, there may be a problem in that the Nafion binder reduces the active surface area of ​​the catalyst, thereby reducing the carbon dioxide reduction performance. The most preferred weight ratio may be 9.5:0.5 to 8:2.

[0031] The above catalyst layer is 200 cm under dry carbon dioxide supply conditions 3 / cm 2 It can have a gas permeability of / sec / kPa or greater, and 10 cm even under carbon dioxide supply conditions containing moisture corresponding to a relative humidity of 100% or more. 3 / cm 2 It can have a gas permeability of / sec / kPa or higher (Fig. 6).

[0032] The catalyst layer has a contact angle of 125° or more and can maintain a contact angle of 125° or more even during long-term operation of 50 hours or more. In the example, compared to a commercial carbon material-based gas diffusion electrode, it was confirmed that the contact angle is maintained even after long-term operation (Fig. 5), which means that it maintains hydrophobicity for a longer period than a commercial carbon material-based gas diffusion electrode, resulting in superior carbon dioxide reduction ability.

[0033] The catalyst layer may have a pore size of 10 to 300 μm.

[0034] The gas diffusion electrode according to the present invention has a power of 200 mA / cm² 2 It can have an operating voltage of less than 2.4 V at a current density. In the examples, a lower operating voltage was exhibited compared to a commercial carbon-based gas diffusion electrode at the same current density (Fig. 3), which means that a high carbon dioxide reduction reaction rate can be achieved with a small amount of electrical energy. In addition, the gas diffusion electrode has a current density of 200 mA / cm² 2 At a current density, it can achieve a CO production Faraday efficiency of over 95%. In addition, it can be confirmed that it shows a CO production Faraday efficiency of over 88% even after 50 hours of long-term operation (Fig. 4).

[0035] The gas diffusion electrode according to the present invention may have an electrical conductivity of 300 to 400 S / m, preferably 340 to 360 S / m. Due to this high electrical conductivity, a high carbon dioxide reduction reaction rate can be achieved with such a low operating voltage, that is, with a small amount of electrical energy (Fig. 7).

[0036] The present invention also comprises the step of preparing a porous metal substrate layer by coating a nickel foam with a hydrophobic polymer;

[0037] A step of preparing a porous layer by coating a slurry solution mixed with a carbon compound and a hydrophobic polymer onto a porous metal substrate layer; and

[0038] The present invention provides a method for manufacturing a gas diffusion electrode for carbon dioxide reduction, comprising the step of preparing a catalyst layer by coating a slurry solution mixed with silver and Nafion ionomer onto a porous layer.

[0039] The terms of the above manufacturing method may be applied mutatis mutandis to the contents of the above gas diffusion electrode.

[0040] The step of manufacturing the above-mentioned porous metal substrate layer may include a step of coating a hydrophobic polymer and then heat-treating at 300 to 350°C. Stronger hydrophobicity may be imparted during heat treatment.

[0041] The present invention will be explained in detail below through the following experimental examples and / or manufacturing examples. However, the following experimental examples and / or manufacturing examples are merely illustrative of the present invention, and the scope of the present invention is not limited by the following experimental examples and / or manufacturing examples. Furthermore, since these experimental examples and / or manufacturing examples are intended only to aid in understanding the present invention, the scope of the present invention is not limited by them in any way.

[0042] <Preparation Example> Preparation of a porous metal-based gas diffusion electrode for carbon dioxide reduction with excellent gas permeability

[0043] The porous metal-based gas diffusion electrode for carbon dioxide reduction according to the present invention was manufactured as follows (see FIG. 1).

[0044] 1) Nickel foam (Purity > 99.99%, Porosity ≥ 95, 80 to 110 Pores per Inch, Average pore diameter approx. 0.25 mm, Thickness 500 μm) 4 cm 2 It is cut into (2cm x 2cm) pieces, washed with acetone and distilled water to remove impurities, spray-coated with a water-repellent polymer PTFE emulsion, and heat-treated at 330°C to impart hydrophobicity.

[0045] 2) A slurry solution prepared by mixing carbon black powder (acetylene black) and PTFE emulsion in an 8:2 weight ratio using isopropyl alcohol as a solvent is spray-coated onto a porous metal to form a porous layer.

[0046] 3) A gas diffusion electrode was prepared by spray coating a slurry mixed in a 9:1 weight ratio of silver (Ag) catalyst powder (Ag nanoparticles (<100 nm, Sigma)) and Nafion ionomer (Nafion® perfluorinated ion-exchange resin, 5 wt. % solution in a mixture of lower aliphatic alcohols and water (20%)) onto a porous layer using isopropyl alcohol as a solvent (this was named Example 1).

[0047] 4) As comparative examples, an electrode fabricated through process 3) on SGL’s 39BB product having a microporous layer (named Comparative Example 1), an electrode fabricated through processes 2) and 3) on Toray’s TGPH060 product (named Comparative Example 2), and an electrode fabricated by creating a porous layer using a heat press method with the slurry solution prepared in process 2 on the nickel foam prepared in process 1) and then creating a catalyst layer through fixation in process 3) (named Comparative Example 3).

[0048] SEM images of the above-prepared Example 1 and Comparative Examples 1, 2, and 3 before and after coating are shown in FIG. 2 (from left to right: Example 1, Comparative Examples 1, 2, and 3; based on the arrow, the top is before coating (when only the substrate layer exists), and the bottom is after coating).

[0049] Two types of commercial carbon material-based gas diffusion electrodes and one type of porous metal-based gas diffusion electrode were fabricated, and their physical properties and performance were compared.

[0050] <Experimental Example> Confirmation of Characteristics of Porous Metal-Based Gas Diffusion Electrode for Carbon Dioxide Reduction

[0051] Experimental Example 1. Confirmation of Surface SEM Image

[0052] Surface SEM images of Comparative Examples 1, 2, 3 and Example 1 prepared in the above preparation examples were examined and are shown in Fig. 2. Comparative Examples 1, 2, and 3 can be seen to have completely blocked surfaces during preparation, whereas Example 1 can be seen to maintain a porous structure, which is believed to have increased mass transfer.

[0053] Experimental Example 2. Evaluation of Electrochemical Carbon Dioxide Reduction CO2 Production Performance

[0054] An experiment to verify the electrochemical carbon dioxide reduction CO2 production performance of the gas diffusion electrode of the present invention was conducted under the following conditions.

[0055] - Reduction electrode: Electrode of Comparative Examples 1, 2, 3 and Example 1 prepared above

[0056] - Oxidation electrode: Nickel foam electrode

[0057] - Ion exchange membrane: Toray AEM

[0058] - Reduction electrode reactant: Humidified CO2 gas 30 ml / min

[0059] - Oxidation electrode reactant: 1M KOH aqueous solution 3 ml / min

[0060] - Reaction temperature: 60℃

[0061] - Current density: 50 ~ 500 mA / cm² 2

[0062] This is illustrated in FIG. 3. Looking at FIG. 3 (A), it can be seen that Example 1 according to the present invention exhibits superior CO production Faraday efficiency compared to Comparative Examples 1 and 2. In particular, the fact that it exhibits high CO production Faraday efficiency even under high current density conditions can be attributed to the smooth supply of carbon dioxide to the catalyst layer.

[0063] Looking at Fig. 3 (B), it can be seen that due to the high electrical conductivity of Example 1, it exhibits a lower operating voltage compared to Comparative Examples 1 and 2 under the same current density conditions. In other words, it has been confirmed that the porous metal-based gas diffusion electrode according to the present invention can achieve a high carbon dioxide reduction reaction rate with a small amount of electrical energy.

[0064] To verify whether the performance of the gas diffusion electrode of the present invention is maintained during long-term operation, the current density is 200 mA / cm² under the above conditions. 2 After fixing, it was performed for 50 hours and is shown in Fig. 4. Current density 200 mA / cm² 2 When operating continuously for 50 hours under these conditions, it was confirmed that while Example 1 maintained a stable high CO production Faraday efficiency, Comparative Examples 1 and 2 showed a rapid decline in CO production Faraday efficiency, thus confirming that flooding phenomena can be effectively inhibited.

[0065] Experimental Example 3. Confirmation of electrode surface contact angle

[0066] The surface contact angles of Comparative Examples 1 and 2 and Example 1 prepared above were confirmed and are shown in Fig. 5.

[0067] As shown in FIG. 5, Example 1 maintains a contact angle of 129° even after long-term operation, while Comparative Examples 1 and 2 show a decrease from an initial contact angle of 130° to the 110° range. Comparative Examples 1 and 2 indicate that hydrophilicity has increased due to the flooding phenomenon caused by long-term operation; in other words, the gas diffusion electrode of the present invention (Example 1) has high resistance to the flooding phenomenon.

[0068] Experimental Example 4. Verification of electrode gas permeability

[0069] Gas permeability was measured under dry carbon dioxide supply conditions and carbon dioxide supply conditions containing moisture corresponding to a relative humidity of 100% or more of Comparative Examples 1, 2, 3 and Example 1 prepared above, and is shown in Fig. 6.

[0070] Referring to Fig. 6, under dry carbon dioxide supply conditions, 235.8 cm 3 / cm 2 11.4 cm under carbon dioxide supply conditions containing moisture corresponding to / sec / kPa and relative humidity of 100% or more 3 / cm 2 Gas permeability of / sec / kPa was shown, and it was confirmed that the gas permeability of Example 1 under two conditions was higher than that of Comparative Examples 1, 2, and 3. This demonstrates that the carbon dioxide mass transfer capability of the gas diffusion electrode of the present invention (Example 1) is high even when flooding occurs under actual reaction conditions where moisture is present.

[0071] In particular, in Comparative Example 3, which used the same nickel foam as the substrate layer but did not have pores of 10 to 300 μm in the pore layer, 6.8 cm each under carbon dioxide supply conditions containing dry carbon dioxide and moisture 3 / cm 2 / sec / kPa and 1.6 cm 3 / cm 2 It was confirmed that it exhibits a low gas permeability of / sec / kPa.

[0072] Experimental Example 5. Verification of electrical conductivity

[0073] The through-plane electrical conductivity of a gas diffusion electrode was measured using the 2-wire Kelvin measurement method. The method is as follows.

[0074] 1. Place a circular gas diffusion electrode sample with a diameter of 9 mm between two nickel electrode substrates and apply current to the electrode to measure the voltage.

[0075] 2. Using the measured voltage and applied current, the electrical resistance was calculated by applying Ohm's law, and the electrical conductivity was calculated using the following Equation 1 considering the area and thickness of the electrode, and this is shown in Fig. 7.

[0076] [Formula 1]

[0077] Electrical conductivity (S / m) = (Electrode thickness) / (Electrical resistance) * (Electrode area)

[0078] It can be confirmed that the electrical conductivity of Example 1 is incomparably higher than that of Comparative Examples 1 and 2 manufactured above. Due to this high electrical conductivity, the gas diffusion electrode of the present invention can achieve a high carbon dioxide reduction reaction rate with a small amount of electrical energy.

Claims

1. Porous metal substrate layer; A porous layer comprising a carbon compound and a hydrophobic polymer formed on the above porous metal substrate layer; and A gas diffusion electrode for carbon dioxide reduction comprising a catalyst layer formed on the above-mentioned porous layer.

2. In Paragraph 1, The above gas diffusion electrode is 200 cm under dry carbon dioxide supply conditions 3 / cm 2 Gas diffusion electrode having a gas permeability of / sec / kPa or greater.

3. In Paragraph 1, The above gas diffusion electrode is 10 cm under carbon dioxide supply conditions containing moisture corresponding to a relative humidity of 100% or more. 3 / cm 2 Gas diffusion electrode having a gas permeability of / sec / kPa or greater.

4. In Paragraph 1, The above porous metal is a gas diffusion electrode that is a porous metal containing nickel.

5. In Paragraph 1, The above porous metal substrate layer is a gas diffusion electrode having a pore size of 100 to 1000 μm.

6. In Paragraph 1, The above porous metal substrate layer is a gas diffusion electrode coated with a hydrophobic polymer.

7. In either Paragraph 1 or Paragraph 6, A gas diffusion electrode in which the hydrophobic polymer is one or more selected from the group consisting of polytetrafluoroethylene (PTFE), polypropylene (PP), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polyperfluoroalkoxy (PFA), ethylene tetrafluoroethylene (ETFE), polyoxymethylene (POM), and polyimide (PI).

8. In Paragraph 1, A gas diffusion electrode in which the carbon compound is one or more selected from carbon black, graphite, and carbon fiber.

9. In Paragraph 1, A gas diffusion electrode in which the carbon compound and hydrophobic polymer of the above-mentioned porous layer are in a weight ratio of 9:1 to 7:

3.

10. In Paragraph 1, The BET specific surface area of ​​the above porous layer is 50 m² 2 / g to 300 m 2 / g gas diffusion electrode.

11. In Paragraph 1, The above porous layer is a gas diffusion electrode having a pore size of 10 to 300 μm.

12. In Paragraph 1, The catalyst layer above is a gas diffusion electrode comprising silver (Ag) and Nafion.

13. In Paragraph 12, A gas diffusion electrode in which the silver (Ag) and Nafion of the catalyst layer are in a weight ratio of 9.5:0.5 to 5:

5.

14. In Paragraph 1, The catalyst layer is a gas diffusion electrode having a contact angle of 125° or more.

15. In Paragraph 1, The catalyst layer is a gas diffusion electrode having a pore size of 10 to 300 μm.

16. In Paragraph 1, The above gas diffusion electrode is a gas diffusion electrode having an electrical conductivity of 300 to 400 S / m.

17. A step of preparing a porous metal substrate layer by coating a nickel foam with a hydrophobic polymer; A step of preparing a porous layer by coating a slurry solution mixed with a carbon compound and a hydrophobic polymer onto a porous metal substrate layer; and A method for manufacturing a gas diffusion electrode for carbon dioxide reduction according to claim 1, comprising the step of preparing a catalyst layer by coating a slurry solution mixed with silver and Nafion ionomer onto a porous layer.

18. In Paragraph 17, The above hydrophobic polymer is one or more selected from the group consisting of polytetrafluoroethylene (PTFE), polypropylene (PP), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polyperfluoroalkoxy (PFA), ethylene tetrafluoroethylene (ETFE), polyoxymethylene (POM), and polyimide (PI).

19. In Paragraph 17, The above carbon compound is one or more selected from carbon black, graphite, and carbon fiber.

20. In Paragraph 17, In the step of manufacturing the above porous metal substrate layer, A method further comprising the step of heat-treating at 300 to 350°C after coating with a hydrophobic polymer.

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