CATHODE STRUCTURE, ANODE STRUCTURE AND GAS PHASE ELECTROCHEMICAL MODULE

Description

TECHNICAL FIELD

The present disclosure relates to a cathode structure of a gas-phase electrochemical module, an anode structure of a gas-phase electrochemical module, and a gas-phase electrochemical module.

RELATED ART

The core concept of carbon dioxide capture, storage, and utilization (CCSU) technology is to capture, convert and reuse carbon dioxide, the source of greenhouse gas emissions, and thereby reducing emissions to the atmosphere. The development of this technology may not only effectively control carbon emissions in the air, but also help convert carbon dioxide into valuable products, realizing carbon recycling and reuse.

In recent years, gas-phase electrochemical reduction process technology has attracted much attention due to the ability thereof to convert carbon dioxide into other industrial products. However, there is still room for improvement in the current gas-phase electrochemical module for carbon dioxide conversion.

SUMMARY

A cathode structure of a gas-phase electrochemical module of the present disclosure includes a cathode electrode plate, a gas diffusion layer (GDL), and a cathode catalyst layer. The gas diffusion layer is disposed on the cathode electrode plate, and a portion of the gas diffusion layer away from the cathode electrode plate is a hydrophilic structure. The cathode catalyst layer is formed in the hydrophilic structure of the gas diffusion layer, the depth of the cathode catalyst layer penetrating into the gas diffusion layer from this side is greater than 10 μm, and the metal content of the cathode catalyst layer is greater than 95%. The cathode catalyst layer comprises a first coating layer and a second coating layer formed on the surface of the first coating layer, and the first coating layer is a copper metal layer. The second coating layer is a single-layer or multi-layer structure, and the material of the second coating layer includes silver, gold, indium, or an alloy thereof.

The anode structure of the gas-phase electrochemical module of the present disclosure includes an anode electrode plate, a porous mesh plate, and an anode catalyst layer. The porous mesh plate is disposed on the anode electrode plate, and there are multiple pores in the porous mesh plate. The anode catalyst layer is formed on the porous mesh plate, and the depth of the anode catalyst layer penetrating into the porous mesh plate is greater than 100 μm, in which the metal content of the anode catalyst layer is greater than 95%. The material of the anode catalyst layer is palladium (Pd), zinc (Zn), tin-palladium (Sn—Pd), nickel-iron (Ni—Fe), or nickel-phosphorus (Ni—P).

The gas-phase electrochemical module of the present disclosure includes the cathode structure, the anode structure, and a separation membrane. The separation membrane has a first side and a second side opposite to each other, in which the cathode structure is disposed on the first side of the separation membrane, and the anode structure is disposed on the second side of the separation membrane.

To make the foregoing characteristics of the present disclosure more clearly understandable, exemplary implementations are described below with detailed explanations together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a cathode structure of a gas-phase electrochemical module according to the first embodiment of the present disclosure.

FIG. 2 is a partially enlarged schematic view of the cathode structure in FIG. 1.

FIG. 3 is a schematic cross-sectional view of an anode structure of a gas-phase electrochemical module according to the second embodiment of the present disclosure.

FIG. 4 is a schematic view of the gas-phase electrochemical module according to the third embodiment of the present disclosure.

FIG. 5 shows the CO conversion rate and H₂ conversion rate in Experimental Example 1.

FIG. 6 shows the reaction rate improvement curve of an anode product in Experimental Example 2.

DESCRIPTION OF THE EMBODIMENTS

The following embodiments are described in detail with reference to the accompanying drawings, but the provided embodiments are not intended to limit the scope covered by the present disclosure. Furthermore, the drawings are merely for illustrative purposes and are not drawn to scale. For ease of understanding, the same components in the following description will be explained using the same reference signs.

FIG. 1 is a schematic cross-sectional view of a cathode structure of a gas-phase electrochemical module according to the first embodiment of the present disclosure.

Referring to FIG. 1, a cathode structure 100 of the gas-phase electrochemical module includes a cathode plate electrode 102, a gas diffusion layer (GDL) 104, and a cathode catalyst layer 108. The gas diffusion layer 104 is disposed on the cathode electrode plate 102, and the portion of the gas diffusion layer 104 away from the cathode electrode plate 102 is a hydrophilic structure 106. In this embodiment, the gas diffusion layer 104 includes a carbon material. The thickness of the gas diffusion layer 104 is, for example, in a range of 300 μm to 500 μm. The cathode electrode plate 102 is, for example, a metal plate, a graphite plate, or a composite graphite plate. From the perspective of facilitating gas flow, the pore size of the gas diffusion layer 104 may be in a range of 10 nm to 500 nm, such as 100 nm, 200 nm, 300 nm, and 400 nm. The porosity of the gas diffusion layer 104 may be above 60%, such as 65%, 70%, 80%, 85%, or 90%, but the present disclosure is not limited thereto. The gas diffusion layer 104 may include a hydrophobic thin film formed by a C—F compound, a C—O compound, or a C—Si compound. The cathode catalyst layer 108 is formed in the hydrophilic structure 106 of the gas diffusion layer 104, and a depth d1 of the cathode catalyst layer 108 penetrating into the gas diffusion layer 104 from the side away from the cathode electrode plate 102 is greater than 10 μm, such as greater than 30 μm or greater than 50 μm, but the present disclosure is not limited thereto. A thickness t1 of the cathode catalyst layer 108 is, for example, in a range of 0.2 μm to 5 μm, but the present disclosure is not limited thereto. In the present disclosure, the thickness t1 of the cathode catalyst layer 108 refers to the size of the cathode catalyst layer 108 protruding outside the gas diffusion layer 104, and thus the portion occupied by the cathode catalyst layer 108 includes the thickness t1 range protruding outside the gas diffusion layer 104 and the depth d1 range penetrating into the gas diffusion layer 104. The depth d1 of the cathode catalyst layer 108 affects the cathode reaction rate. The deeper the depth, the larger the surface area, and the faster the cathode reaction rate.

In this embodiment, the cathode catalyst layer 108 is, for example, a continuous uniform coating, which may be observed from the partial enlarged view of FIG. 2.

Shown in FIG. 2 is the detailed structure corresponding to an enlarged area II of FIG. 1, in which the cathode catalyst layer 108 includes a first coating layer c1 and a second coating layer c2 formed on the surface of the first coating layer c1, and the first coating layer c1 is a copper metal layer. The second coating layer c2 may be a single-layer or multi-layer structure, in which the material of the second coating layer c2 includes silver (Ag), gold (Au), indium (In), or an alloy thereof. The cathode catalyst layer 108 is formed by, for example, using a chemical liquid diffusion method to first deposit a trace amount of palladium metal on the surface and inner layer of the gas diffusion layer 104, and then, copper metal is deposited through chemical copper reaction to obtain the first coating layer c1, and the second coating layer c2 is deposited on the surface of the first coating layer c1 through a displacement reaction to form a continuous uniform coating, and the metal content of the cathode catalyst layer 108 produced in this way may be greater than 95%.

FIG. 3 is a schematic cross-sectional view of an anode structure of the gas-phase electrochemical module according to the second embodiment of the present disclosure.

Referring to FIG. 3, an anode structure 300 includes an anode electrode plate 302, a porous mesh plate 304, and an anode catalyst layer 306. In this embodiment, the anode electrode plate 302 is, for example, a metal plate, a graphite plate, or a composite graphite plate. The porous mesh plate 304 is disposed on the anode electrode plate 302, and the porous mesh plate 304 has a plurality of pores. From the perspective of facilitating liquid flow, the pore size of the porous mesh plate 304 may be in a range of 10 μm to 1000 μm, such as 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 800 μm, and the porosity of the porous mesh plate 304 may be above 80%, such as 83%, 85%, 88%, or 90%, but the present disclosure is not limited thereto. In an embodiment, the porous mesh plate 304 includes a foamed copper plate, a foamed nickel plate, a foamed titanium plate, a metal fiber plate, a metal fiber felt, or a carbon fiber mesh. In another embodiment, the porous mesh plate 304 includes a fiberglass plate, a fiberglass mesh, or a polymer foam material. If the porous mesh plate 304 is a material with low electrical conductivity, then the anode catalyst layer 306 may be deposited on all surfaces of the porous mesh plate 304; that is, a depth d2 of the anode catalyst layer 306 penetrating into the porous mesh plate 304 is equal to the thickness t2 of the porous mesh plate 304.

In FIG. 3, the anode catalyst layer 306 is formed on the porous mesh plate 304, and the depth of the anode catalyst layer 306 penetrating into the porous mesh plate 304 is greater than 100 μm. The material of the anode catalyst layer 306 is palladium (Pd), zinc (Zn), tin-palladium (Sn—Pd), nickel-iron (Ni—Fe), or nickel-phosphorus (Ni—P). The anode catalyst layer 306 is formed by, for example, depositing the anode metal catalyst material through the porous mesh plate 304 to form a non-granular or special-shaped continuous uniform coating, as shown in the partial enlarged view shown on the left side of FIG. 3, and the metal content of the anode catalyst layer 306 produced in this way may be greater than 95%. In this embodiment, a thickness t3 of the anode catalyst layer 306 is, for example, in a range of 1 μm to 100 μm, but the present disclosure is not limited thereto.

FIG. 4 is a schematic view of the gas-phase electrochemical module according to the third embodiment of the present disclosure, in which the same reference signs as those in the first and second embodiments are used to represent the same or similar parts and components, and the relevant content of the same or similar parts and components may also be referred to the content of the above embodiments, so details will not be repeated here.

In FIG. 4, a gas-phase electrochemical module 400 includes the cathode structure 100, the anode structure 300, and a separation membrane 402. The separation membrane 402 has a first side 402a and a second side 402b opposite to each other. The cathode structure 100 in the first embodiment is disposed on the first side 402a of the separation membrane 402, and the anode structure 300 in the second embodiment is disposed on the second side 402b of the separation membrane 402, but the present disclosure is not limited thereto. In other embodiments, the anode structure in the gas-phase electrochemical module 400 may use a general anode structure. The cathode catalyst layer 108 of the cathode structure 100 is close to the first side 402a, and the anode catalyst layer 306 of the anode structure 300 is close to the second side 402b.

Based on the above, the cathode catalyst layer of the cathode structure of the present disclosure can penetrate a portion of the gas diffusion layer and has a high metal composition ratio with a specific metal composition, which increases the carbon dioxide reaction rate of the gas-phase electrochemical module. Moreover, in the anode structure of the present disclosure, the anode catalyst layer may coat the surface of the porous mesh plate and has a high metal concentration ratio with a specific material composition, which can reduce the reaction potential and energy consumption of the gas-phase electrochemical module through a special catalyst, and liquids such as ethanol or ethanol may be introduced into the anode to produce high-value products such as acetic acid or formic acid, and the reaction rate of the anode product can be increased through the catalytic reaction. In the present disclosure, the gas-phase electrochemical module having both the foregoing cathode structure and anode structure can naturally further increase the carbon dioxide reaction rate.

The following experiments are provided to verify the implementation effect of the present disclosure, but the present disclosure is not limited to the following content.

Experimental Example 1

1. Raw Materials:

• • 1. Gas diffusion layer: W1S1011 (made in Taiwan), thickness 410 μm, both sides have a hydrophobic surface (water contact angle approximately) 140°, porosity 60%.
  • 2. Oxidizing agent

• • 3. Adhesive material

Adhesive material used: polyurethane type UV tack-reducing adhesive.

2. Preparation of Cathode Structure:

First, adhesive is applied on the back surface of the gas diffusion layer to protect the back surface of the gas diffusion layer. Then, an oxidizing agent is used to treat the front surface of the gas diffusion layer, in which the pore size of the front surface of the gas diffusion layer is approximately in a range of 105 nm to 855 nm. The treatment method involves soaking in the oxidizing agent at room temperature for 2 hours. The front surface of the treated gas diffusion layer is measured and the water contact angle thereof becomes in a range of 50° to 80° (hydrophilic).

Then, the treated gas diffusion layer is soaked in a tin-palladium colloid with a palladium ion concentration of 48 ppm at room temperature for 4 minutes. The chemical reaction formula is as follows:

Next, copper/silver metal is deposited on a cathode carbon cloth through a wet process. In detail, the sample soaked in tin-palladium colloid is placed in water for cleaning, the adhesive material on the back surface is removed, and the cathode carbon cloth is placed in the chemical copper coating solution (at a temperature of 40° C. to 45° C.). After 2 to 5 minutes of reaction, the cathode carbon cloth sample is washed with water and then placed into the chemical silver coating solution (at a temperature of 52° C. to 54° C.) for 10 to 15 minutes of reaction. Analyzed using X-ray fluorescence (XRF) analyzer (XRF) (with a sample size of 100 cm² for measurement and averaging 10 data points), the average thickness of copper on the cathode structure is 0.2±0.05 μm, and the average thickness of silver is 0.6±0.05 μm. The depth of the cathode catalyst layer penetrating into the gas diffusion layer may be confirmed using a destructive cross-section method (for example, SEM cross-section).

Then, the gas diffusion layer coated with the cathode catalyst layer is disposed on the cathode electrode plate to obtain a cathode structure similar to as shown in FIG. 1.

3. Conversion Rate Measurement

A carbon dioxide gas-phase electrochemical conversion module is fabricated, in which the cathode structure uses the prepared cathode structure, the anode structure is anode foam metal (material characteristics: thickness: 0.6 mm, surface density: 280 g/m², porosity>80%, ductility: longitudinal>5%, transverse>12%, pore size: 110 PPI), and together with the separation membrane (model HA-K1025), a gas-phase electrochemical module similar to FIG. 4 is formed. Regarding the cathode/anode electrolyte (each approximately 50 mL), the flow rate is 30 mL/min, and the electrolyte solution is 1M KOH.

Converted CO gas product analysis method: the CO gas flowing through the cathode structure is connected to a gas chromatograph (Agilent 7890B) for analysis. The instrument is equipped with a thermal conductivity analyzer (TCD) and a flame ionization detector (FID). In order to ensure the reproducibility of the experiment, the potential is applied for more than 200 seconds in each set of experiments, and the gas composition measurement and analysis starts after the system enters a steady state. Then, after performing Faradaic efficiency analysis on the obtained product, the conversion rate of CO₂ converted into CO is measured and calculated. The results are shown in FIG. 5.

FIG. 5 shows the CO conversion rate and H₂ conversion rate in Experimental Example 1. It may be seen from FIG. 5 that the cathode structure of the gas-phase electrochemical module of the present disclosure can increase the efficiency of converting CO₂ into CO by more than 85%.

Experimental Example 2

1. Raw Materials:

1. Porous Mesh Plate (Nickel Foam Fiber Mesh)

• • (1) Porous foam metal (UBIQ, NF960A): thickness 0.6 mm, surface density 280 g/m², porosity>80%, pore size 110PPI.
  • (2) Porous metal fiber felt (Brand: Koolon): thickness 0.6 mm, fiber width 30 to 100 μm, porosity>70%, unit weight 500 g/m².

2. Preparation of Anode Structure:

1. Preparation Method for 30% Pd Coating

Using the liquid electrochemical deposition method, an anode catalyst layer is formed on the surface of the porous mesh plate. The composition, properties, and process parameters of the palladium coating solution for the liquid electrochemical deposition method are listed in Table 1 below. The electroplating time is 1 hour, the catalyst thickness is measured using XRF, and the result is 5 μm to 10 μm.

Then, the porous mesh plate coated with the anode catalyst layer is disposed on the anode electrode plate to obtain an anode structure similar to as shown in FIG. 3.

2. Preparation Method for 60% Pd Coating

The same method as 30% Pd coating is applied on the surface of the porous mesh plate, but the coating time is changed to 3 hours. The thickness of the anode catalyst layer is measured to be 10 μm to 20 μm.

3. Pd/C

Using the spraying method, palladium is sprayed onto the surface of the porous mesh plate. In detail, 3 g of nanopalladium particles are mixed with 100 g of carbon powder slurry to achieve a catalyst slurry for spraying with 3% nanopalladium catalyst, then a spray tool is used to spray onto the nickel foam, and then baking is performed at 100° C. to remove the solvent to form a Pd/C catalyst layer with a sprayed coating thickness of 2 μm to 3 μm.

3. Efficiency Analysis

Experimental Example 2 uses ethanol oxidation reaction as a catalytic reaction to perform the anode half-reaction test.

The anode half-reaction test is to form an electrolytic cell, in which the reference electrode (RE) is chosen as a silver chloride electrode Ag/AgCl (3 M KCl solution), the counter electrode (CE) is a platinum wire ($1 mm), and the working electrode (WE) is the anode structure prepared above. Also, the reactive area is quantitatively controlled at 1×1 cm² to standardize the analysis of the energy consumption per unit current density and the corresponding half-reaction potential.

The electrochemical system chosen is Biologic-VSP300 potentiostat, which is used for measuring linear sweep voltammetry (LSV), cyclic voltammetry (CV), and chronoamperometry for different experiments. The analysis focuses on catalytic current and reaction kinetics, as well as the performance of the surface catalytic environment. At the same time, the system impedance measurements are corrected for potential drop (iR-drop compensation). The reversible hydrogen electrode (RHE) potential conversion is performed according to the following equation:

E RHE = E WE + 0.21 ( Ag / AgCl , 3 ⁢ M ⁢ KCl ) + 0.0591 × pH - 0.85 × iR Compensate .

The selected reactants are standard anhydrous ethanol (>99.5%), 1M potassium hydroxide (electrolyte), and high-purity deionized water (18.2MΩ).

According to the experimental requirements, the voltage value is measured at constant current. At the same time, the current performance in a certain potential range is measured by scanning voltammetry.

Different amounts of ethanol are added for testing according to experimental requirements. The electrolyte is circulated in the system through a peristaltic pump at a flow rate of 20 mL min⁻¹; and a flow controller is used for real-time monitoring. In order to determine the selectivity of the acetic acid liquid product, the electrolyte after the reaction is taken out and quantitatively analyzed by high-performance liquid chromatography (Agilent 1260 Infinity II). The instrument is equipped with a refractive index detector and a variable wavelength detector to conduct quantitative analysis of different liquid analytes. In order to ensure the stability and reproducibility of the system, each set of potentials accumulates a total charge of more than 100 coulombs before starting the liquid phase product analysis, and after calculating the Faradaic efficiency, the change of the reversible hydrogen electrode potential (RHE) on the current density is measured. The results are shown in FIG. 6.

It may be seen from FIG. 6 that the anode structure of the present disclosure, when introduced to an ethanol solution, also has the additional value of improving the efficiency of conversion into acetic acid. That is, compared with the general Pd/C anode structure, the reaction current (maximum current density) can be increased by up to two times.

In summary, the gas-phase electrochemical module of the present disclosure uses a cathode or anode structure with specific structural characteristics, which can significantly improve, for example, the conversion rate and the reaction current. Moreover, the cathode structure of the gas-phase electrochemical module of the present disclosure can convert carbon dioxide into CO; and the anode structure can convert ethanol into acetic acid.

Although the present disclosure has been disclosed above through embodiments, the embodiments are not intended to limit the present disclosure. Persons with ordinary knowledge in the relevant technical field may make some changes and modifications without departing from the spirit and scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be determined by the appended claims.