METHOD FOR PREVENTING SALT PRECIPITATION IN A ZERO-GAP CO2 REDUCTION ELECTROLYZER

Description

TECHNICAL FIELD

The present invention relates to the field of electrochemical energy conversion and storage technologies, and more specifically, to a method for preventing salt precipitation in a zero-gap CO₂ reduction electrolyzer.

BACKGROUND OF THE INVENTION

Global energy supply has heavily relied on fossil fuels since the last century, leading to a dramatic increase in atmospheric CO₂ concentration. In response, scientists have actively developed various CO₂ conversion technologies, among which electrochemical CO₂ reduction (CO₂RR) has attracted significant attention due to its high efficiency and economic viability. Performing CO₂RR in a zero-gap electrolyzer offers substantial advantages for achieving high current density and high energy efficiency, thereby positioning it as a strong candidate for industrial application. A fundamental distinction of the zero-gap electrolyzer from traditional H-type and three-compartment flow cell electrolyzers is the absence of a flowing catholyte between the gas diffusion electrode (GDE) and the ion exchange membrane. This design significantly reduces ohmic resistance and effectively boosts current density. Typically, a zero-gap electrolyzer comprises a cathode chamber, an anode chamber, and an ion exchange membrane positioned between them. Depending on the ion exchange membrane's ion conduction type, it can be classified as an alkaline or neutral electrolyzer (employing an anion exchange membrane), or an acidic electrolyzer (employing a cation exchange membrane).

Alkaline or neutral electrolyzers, which utilize an anion exchange membrane, create a strongly alkaline microenvironment at the cathode, thereby promoting the CO₂RR over the competing hydrogen evolution reaction (HER). However, this strong alkaline microenvironment consumes CO₂ via its reaction with OH-to form bicarbonate (HCO₃⁻) or carbonate (CO₃²⁻) ions. Under the influence of an electric field, these HCO₃⁻ or CO₃²⁻ ions subsequently migrate through the anion exchange membrane to the anode. At the anode, they react with H⁺ generated by the oxygen evolution reaction (OER), thereby regenerating CO₂. This mechanism consequently limits the theoretical single-pass CO₂ conversion efficiency to below 50%. Furthermore, minor amounts of cations (e.g., K⁺) from the anolyte can diffuse to the cathode due to concentration gradients. These cations then react with the generated HCO₃⁻ or CO₃²⁻ ions to form KHCO₃ or K₂CO₃ salts that precipitate due to exceeding their solubility limit. This precipitation, in turn, can clog the pores of the cathode GDE, impeding CO₂ transport, which leads to a decrease in the selectivity of CO₂RR products and electrolyzer failure.

Acidic electrolyzers, which utilize a cation exchange membrane, have garnered significant attention owing to their theoretical allowance for 100% single-pass CO₂ conversion efficiency. However, the use of a cation exchange membrane creates an acidic microenvironment at the cathode. In this acidic environment, the HER is favored over the CO₂RR, thereby limiting the selectivity of CO₂RR products. To enhance CO₂RR product selectivity, researchers have introduced alkaline cations (e.g., K⁺) into the anolyte, thereby regulating the cathode microenvironment.

Although this approach improves CO₂RR product selectivity, it introduces a severe problem of KHCO₃ or K₂CO₃ salt precipitation. Similar to the issue observed in alkaline systems, this precipitation can obstruct the pores of the gas diffusion layer, thereby hindering CO₂ transport, diminishing CO₂RR product selectivity, and ultimately causing electrolyzer failure.

Consequently, both acidic CO₂ electrolyzers and alkaline/neutral CO₂ electrolyzers face the challenge of salt precipitation clogging the pores of the gas diffusion layer. Therefore, there is an urgent need for a method to significantly address this problem.

BRIEF SUMMARY OF THE INVENTION

The present invention aims to provides a method for preventing salt precipitation in zero-gap CO₂ reduction electrolyzer. This method specifically targets the issue of salt precipitation clogging the pores of GDE, a problem encountered in both acidic CO₂ electrolyzers and alkaline/neutral CO₂ electrolyzers.

To achieve the aforementioned objectives, the present invention employs the following technical solution:

A method for preventing salt precipitation in a zero-gap CO₂ reduction electrolyzer, comprising the steps of:

• • Step 1: preparing an ammonium salt solution, wherein the ammonium salt is represented by the formula [N(R1)(R2)(R3)(R4)]X; and wherein R1, R2, R3, and R4 are each independently selected from —H, —CH₃, —CH₂CH₃;
  • Step 2: loading a catalyst onto a cathode gas diffusion layer to form a cathode gas diffusion electrode for a CO₂ reduction reaction;
  • Step 3: loading a catalyst onto an anode gas diffusion layer to form an anode gas diffusion electrode for a water oxidation reaction; and
  • Step 4: testing CO₂ reduction performance in the zero-gap CO₂ reduction electrolyzer, wherein: CO₂, the ammonium salt solution obtained in step (a), or both, are supplied to the cathode gas diffusion electrode obtained in step (b) through a cathode chamber; and the ammonium salt solution obtained in step 1 is supplied to the anode gas diffusion electrode obtained in step 3 through an anode chamber.

Preferably, in Step 4, the zero-gap CO₂ reduction electrolyzer comprises a cathode chamber, a cathode gas diffusion electrode, an anode chamber, an anode gas diffusion electrode, and an ion exchange membrane.

Preferably, in Step 1, the concentration of the ammonium salt ranges from 0.001 mol L⁻¹ to 3 mol L⁻¹.

Preferably, in Step 1, X is an anion.

Preferably, in Step 2, he cathode gas diffusion layer comprises carbon paper.

Preferably, in Step 2, the catalyst comprises a silver-based catalyst or a copper-based material.

ADVANTAGES OF THE INVENTION

Compared to the background art, the present invention offers the following advantages:

• • 1. Elimination of Salt Precipitation: The introduction of an ammonium salt solution as the electrolyte in the zero-gap CO₂ reduction electrolyzer effectively solves the problem of salt precipitation clogging the pores of the gas diffusion layers.
  • 2. Enhanced CO₂RR product selectivity: The use of ammonium cations enables tailoring of the cathode's microenvironment, leading to enhanced CO₂ electroreduction selectivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the results measured for a silver electrode in a zero-gap CO₂ reduction electrolyzer according to Example 1 of the present invention.

FIG. 2 shows the results measured for a copper electrode in a zero-gap CO₂ reduction electrolyzer according to Example 1 of the present invention.

FIG. 3 shows the results measured for a silver electrode in a zero-gap CO₂ reduction electrolyzer according to Example 2 of the present invention.

FIG. 4 shows the results measured for a copper electrode in a zero-gap CO₂ reduction electrolyzer according to Example 2 of the present invention.

FIG. 5 shows the results measured for a silver electrode in a zero-gap CO₂ reduction electrolyzer according to Example 3 of the present invention.

FIG. 6 shows the results measured for a copper electrode in a zero-gap CO₂ reduction electrolyzer according to Example 3 of the present invention.

FIG. 7 shows the results measured for a silver electrode in a zero-gap CO₂ reduction electrolyzer according to Comparative Example 1 of the present invention.

FIG. 8 shows the results measured for a copper electrode in a zero-gap CO₂ reduction electrolyzer according to Comparative Example 1 of the present invention.

FIG. 9 shows the results measured for a silver electrode in a zero-gap CO₂ reduction electrolyzer according to Example 4 of the present invention.

FIG. 10 shows the results measured for a silver electrode in a zero-gap CO₂ reduction electrolyzer according to Comparative Example 2 of the present invention.

FIG. 11 shows the results measured for a silver electrode in a zero-gap CO₂ reduction electrolyzer according to Example 5 of the present invention.

FIG. 12 shows the results measured for a silver electrode in a zero-gap CO₂ reduction electrolyzer according to Example 6 of the present invention.

FIG. 13 shows the results measured for a silver electrode in a zero-gap CO₂ reduction electrolyzer according to Comparative Example 3 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Unless otherwise defined, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The following detailed description illustrates various embodiments of the invention and is not intended to limit the scope of the invention.

Example 1

In this example, a cation exchange membrane separates the cathode chamber and the anode chamber. A solution containing ammonium salt (where R1, R2, R3, and R4 are all —CH₃) is supplied to the anode chamber, and humidified CO₂ is supplied to the cathode chamber. The catalyst for the cathode gas diffusion electrode (GDE) is silver or copper, thereby enabling the CO₂ reduction reaction in a zero-gap CO₂ reduction electrolyzer. The specific steps are as follows:

Step 1: Preparation of Ammonium Salt Solution;

An ammonium salt and H₂SO₄ mixed solution is prepared, wherein the ammonium salt is [N(R1)(R2)(R3)(R4)]X, and R1, R2, R3, and R4 are all —CH₃.

Step 2: Preparation of Cathode Gas Diffusion Electrode;

A GDE is fabricated by first preparing a dispersion comprising a CO₂ reduction catalyst such as silver or copper, a binder, and a solvent selected from ethanol, isopropanol, ethylene glycol, and deionized water. The mixture is subjected to sonication and subsequently sprayed onto a gas diffusion layer composed of carbon paper.

Step 3: Preparation of Anode Gas Diffusion Electrode;

An anode GDE is prepared by loading iridium oxide onto a titanium felt substrate.

Step 4: Testing the CO₂ reduction performance of the zero-gap CO₂ reduction electrolyzer;

The humidified CO₂ is supplied to the cathode GDE obtained in Step 2 through the cathode chamber, and subsequent is converted into reduction products at the cathode GDE. In this example, the CO₂ reduction catalyst is silver or copper.

The mixed solution of ammonium salt and H₂SO₄ obtained in Step 1 is supplied to the anode GDE obtained in Step 3 through the anode chamber. Water is converted into O₂ at the anode GDE via the iridium oxide catalyst.

An ion exchange membrane is used to separate the cathode chamber and the anode chamber, wherein the ion exchange membrane is a cation exchange membrane.

As shown in FIG. 1, the CO₂ reduction performance of the system employing silver as the CO₂ reduction catalyst is demonstrated. At a current density of 100 mA cm⁻², a Faradaic efficiency of 77% toward CO₂ reduction products is achieved. As further illustrated in the inset of FIG. 1, no visible white salt precipitation is observed on the backside of the cathodic GDE after electrolysis, which ensures CO₂ transport and stable operation of the zero-gap CO₂ electrolyzer.

As shown in FIG. 2, the CO₂ reduction performance of the system employing copper as the CO₂ reduction catalyst is demonstrated. At a current density of 100 mA·cm⁻², a Faradaic efficiency of 53% toward CO₂ reduction products is achieved. As further illustrated in the inset of FIG. 2, no visible white salt precipitation is observed on the backside of the cathodic GDE after electrolysis, which ensures CO₂ transport and stable operation of the zero-gap CO₂ electrolyzer.

Example 2

In this example, a cation exchange membrane separates the cathode chamber and the anode chamber. A solution containing ammonium salt (where R1, R2, R3, and R4 are all —CH₂CH₃) is supplied to the anode chamber, and humidified CO₂ is supplied to the cathode chamber. The catalyst for the cathode GDE is silver or copper, thereby enabling the CO₂ reduction reaction in a zero-gap CO₂ reduction electrolyzer. The specific steps are as follows:

Step 1: Preparation of Ammonium Salt Solution;

An ammonium salt and H₂SO₄ mixed solution is prepared, wherein the ammonium salt is [N(R1)(R2)(R3)(R4)]X, and R1, R2, R3, and R4 are all —CH₂CH₃.

Step 2: Preparation of Cathode Gas Diffusion Electrode;

A GDE is fabricated by first preparing a dispersion comprising a CO₂ reduction catalyst such as silver or copper, a binder, and a solvent selected from ethanol, isopropanol, ethylene glycol, and deionized water. The mixture is subjected to sonication and subsequently sprayed onto a gas diffusion layer composed of carbon paper.

Step 3: Preparation of Anode Gas Diffusion Electrode;

An anode GDE is prepared by loading iridium oxide onto a titanium felt substrate.

Step 4: Testing the CO₂ reduction performance of the zero-gap CO₂ reduction electrolyzer;

The humidified CO₂ is supplied to the cathode GDE obtained in Step 2 through the cathode chamber, and subsequent is converted into reduction products at the cathode GDE. In this example, the CO₂ reduction catalyst is silver or copper.

The mixed solution of ammonium salt and H₂SO₄ obtained in Step 1 is supplied to the anode GDE obtained in Step 3 through the anode chamber. Water is converted into O₂ at the anode GDE via the iridium oxide catalyst.

An ion exchange membrane is used to separate the cathode chamber and the anode chamber, wherein the ion exchange membrane is a cation exchange membrane.

As shown in FIG. 3, the CO₂ reduction performance of the system employing silver as the CO₂ reduction catalyst is demonstrated. At a current density of 100 mA cm⁻², a Faradaic efficiency of 48% toward CO₂ reduction products is achieved. As further illustrated in the inset of FIG. 3, no visible white salt precipitation is observed on the backside of the cathodic GDE after electrolysis, which ensures CO₂ transport and stable operation of the zero-gap CO₂ electrolyzer.

As shown in FIG. 4, the CO₂ reduction performance of the system employing copper as the CO₂ reduction catalyst is demonstrated. At a current density of 100 mA·cm⁻², a Faradaic efficiency of 34% toward CO₂ reduction products is achieved. As further illustrated in the inset of FIG. 4, no visible white salt precipitation is observed on the backside of the cathodic GDE after electrolysis, which ensures CO₂ transport and stable operation of the zero-gap CO₂ electrolyzer.

Example 3

In this example, a cation exchange membrane separates the cathode chamber and the anode chamber. A solution containing ammonium salt (where R1, R2, R3, and R4 are all —H) is supplied to the anode chamber, and humidified CO₂ is supplied to the cathode chamber. The catalyst for the cathode GDE is silver or copper, thereby enabling the CO₂ reduction reaction in a zero-gap CO₂ reduction electrolyzer. The specific steps are as follows:

Step 1: Preparation of Ammonium Salt Solution;

An ammonium salt and H₂SO₄ mixed solution is prepared, wherein the ammonium salt is [N(R1)(R2)(R3)(R4)]X, and R1, R2, R3, and R4 are all —H.

Step 2: Preparation of Cathode Gas Diffusion Electrode;

A GDE is fabricated by first preparing a dispersion comprising a CO₂ reduction catalyst such as silver or copper, a binder, and a solvent selected from ethanol, isopropanol, ethylene glycol, and deionized water. The mixture is subjected to sonication and subsequently sprayed onto a gas diffusion layer composed of carbon paper.

Step 3: Preparation of Anode Gas Diffusion Electrode;

An anode GDE is prepared by loading iridium oxide onto a titanium felt substrate.

Step 4: Testing the CO₂ reduction performance of the zero-gap CO₂ reduction electrolyzer;

The humidified CO₂ is supplied to the cathode GDE obtained in Step 2 through the cathode chamber, and subsequent is converted into reduction products at the cathode GDE. In this example, the CO₂ reduction catalyst is silver or copper.

The mixed solution of ammonium salt and H₂SO₄ obtained in Step 1 is supplied to the anode GDE obtained in Step 3 through the anode chamber. Water is converted into O₂ at the anode GDE via the iridium oxide catalyst.

An ion exchange membrane is used to separate the cathode chamber and the anode chamber, wherein the ion exchange membrane is a cation exchange membrane.

As shown in FIG. 5, the CO₂ reduction performance of the system employing silver as the CO₂ reduction catalyst is demonstrated. At a current density of 100 mA cm⁻², a Faradaic efficiency of 59% toward CO₂ reduction products is achieved. As further illustrated in the inset of FIG. 5, no visible white salt precipitation is observed on the backside of the cathodic GDE after electrolysis, which ensures CO₂ transport and stable operation of the zero-gap CO₂ electrolyzer.

As shown in FIG. 6, the CO₂ reduction performance of the system employing copper as the CO₂ reduction catalyst is demonstrated. At a current density of 100 mA·cm⁻², a Faradaic efficiency of 13% toward CO₂ reduction products is achieved. As further illustrated in the inset of FIG. 6, no visible white salt precipitation is observed on the backside of the cathodic GDE after electrolysis, which ensures CO₂ transport and stable operation of the zero-gap CO₂ electrolyzer.

Comparative Example 1

In this example, a cation exchange membrane separates the cathode chamber and the anode chamber. A solution containing potassium ion (K⁺) is supplied to the anode chamber, and humidified CO₂ is supplied to the cathode chamber. The catalyst for the cathode GDE is silver or copper, thereby enabling the CO₂ reduction reaction in a zero-gap CO₂ reduction electrolyzer. The specific steps are as follows:

Step 1: Preparation of Potassium Salt Solution;

A potassium salt and H₂SO₄ mixed solution is prepared.

Step 2: Preparation of Cathode Gas Diffusion Electrode;

A GDE is fabricated by first preparing a dispersion comprising a CO₂ reduction catalyst such as silver or copper, a binder, and a solvent selected from ethanol, isopropanol, ethylene glycol, and deionized water. The mixture is subjected to sonication and subsequently sprayed onto a gas diffusion layer composed of carbon paper.

Step 3: Preparation of Anode Gas Diffusion Electrode;

An anode GDE is prepared by loading iridium oxide onto a titanium felt substrate.

Step 4: Testing the CO₂ reduction performance of the zero-gap CO₂ reduction electrolyzer;

The humidified CO₂ is supplied to the cathode GDE obtained in Step 2 through the cathode chamber, and subsequent is converted into reduction products at the cathode GDE. In this example, the CO₂ reduction catalyst is silver or copper.

The mixed solution of potassium salt and H₂SO₄ obtained in Step 1 is supplied to the anode GDE obtained in Step 3 through the anode chamber. Water is converted into O₂ at the anode GDE via the iridium oxide catalyst.

An ion exchange membrane is used to separate the cathode chamber and the anode chamber, wherein the ion exchange membrane is a cation exchange membrane.

As shown in FIG. 7, the CO₂ reduction performance of the system employing silver as the CO₂ reduction catalyst is demonstrated. At a current density of 100 mA cm², a Faradaic efficiency of 66% toward CO₂ reduction products is achieved. As further illustrated in the inset of FIG. 7, white KHCO₃ or K₂CO₃ deposits accumulated on the backside of the cathodic GDE after electrolysis, obstructing CO₂ transport and ultimately causing the failure of the zero-gap CO₂ electrolyzer.

As shown in FIG. 8, the CO₂ reduction performance of the system employing copper as the CO₂ reduction catalyst is demonstrated. At a current density of 100 mA cm⁻², a Faradaic efficiency of 39% toward CO₂ reduction products is achieved. As further illustrated in the inset of FIG. 8, white KHCO₃ or K₂CO₃ deposits accumulated on the backside of the cathodic GDE after electrolysis, obstructing CO₂ transport and ultimately causing the failure of the zero-gap CO₂ electrolyzer.

The technical solutions disclosed in Examples 1, 2, and 3 effectively address the issue of salt precipitation that clogs the pores of the gas diffusion layer, as mentioned in the background art. Notably, in Example 1, an ammonium salt solution was employed as the electrolyte in the zero-gap CO₂ electrolyzer. Compared with the potassium salt solution used in Comparative Example 1, this approach significantly improved the selectivity toward CO₂ reduction products.

Example 4

In this example, a cation exchange membrane separates the cathode chamber and the anode chamber. A solution containing ammonium salt (where R1, R2, R3, and R4 are all —CH3) is supplied to the cathode chamber, and a H₂SO₄ solution is supplied to the anode chamber. The catalyst for the cathode GDE is silver, thereby enabling the CO₂ reduction reaction in a zero-gap CO₂ reduction electrolyzer. The specific steps are as follows:

Step 1: Preparation of Ammonium Salt Solution;

Prepare a solution of tetramethylammonium bicarbonate ((CH₃)₄NHCO₃);

Prepare a solution of H₂SO₄;

Step 2: Preparation of Cathode Gas Diffusion Electrode;

A GDE is fabricated by first preparing a dispersion comprising a CO₂ reduction catalyst silver, a binder, and a solvent selected from ethanol, isopropanol, ethylene glycol, and deionized water. The mixture is subjected to sonication and subsequently sprayed onto a gas diffusion layer composed of carbon paper.

Step 3: Preparation of Anode Gas Diffusion Electrode;

An anode GDE is prepared by loading iridium oxide onto a titanium felt substrate.

Step 4: Testing the CO₂ reduction performance of the zero-gap CO₂ reduction electrolyzer;

During CO₂ electrolysis process, the ammonium salt solution obtained in Step 1 is supplied to the cathode chamber and brought into contact with the cathodic GDE prepared in Step 2. At the cathode, bicarbonate ions (HCO₃⁻) react with protons (H⁺) transported across the cation exchange membrane to regenerate CO₂ in situ at the cathode. The regenerated CO₂ is subsequently reduced at the surface of the cathodic GDE. In this example, silver is used as the CO₂ reduction catalyst.

During CO₂ electrolysis process, the H₂SO₄ solution obtained in Step 1 is supplied to the anode GDE obtained in Step 3 through the anode chamber. Water is converted into O₂ at the anode GDE via the iridium oxide catalyst.

An ion exchange membrane is used to separate the cathode chamber and the anode chamber, wherein the ion exchange membrane is a cation exchange membrane.

As shown in FIG. 9, the CO₂ reduction performance of the system employing silver as the CO₂ reduction catalyst is demonstrated. At a current density of 100 mA cm⁻², a Faradaic efficiency of 12% toward CO₂ reduction products is achieved.

Comparative Example 2

In this example, a cation exchange membrane separates the cathode chamber and the anode chamber. A solution containing potassium ion (K⁺) is supplied to the cathode chamber, and a H₂SO₄ solution is supplied to the anode chamber. The catalyst for the cathode GDE is silver, thereby enabling the CO₂ reduction reaction in a zero-gap CO₂ reduction electrolyzer. The specific steps are as follows:

Step 1: Preparation of Potassium Salt Solution;

Prepare a solution of potassium bicarbonate (KHCO₃);

Prepare a solution of H₂SO₄;

Step 2: Preparation of Cathode Gas Diffusion Electrode;

A GDE is fabricated by first preparing a dispersion comprising a CO₂ reduction catalyst silver, a binder, and a solvent selected from ethanol, isopropanol, ethylene glycol, and deionized water. The mixture is subjected to sonication and subsequently sprayed onto a gas diffusion layer composed of carbon paper.

Step 3: Preparation of Anode Gas Diffusion Electrode;

An anode GDE is prepared by loading iridium oxide onto a titanium felt substrate.

Step 4: Testing the CO₂ reduction performance of the zero-gap CO₂ reduction electrolyzer;

During CO₂ electrolysis process, the KHCO₃ solution obtained in Step 1 is supplied to the cathode chamber and brought into contact with the cathodic GDE prepared in Step 2. At the cathode, bicarbonate ions (HCO₃⁻) react with protons (H⁺) transported across the cation exchange membrane to regenerate CO₂ in situ at the cathode. The regenerated CO₂ is subsequently reduced at the surface of the cathodic GDE. In this example, silver is used as the CO₂ reduction catalyst.

During CO₂ electrolysis process, the H₂SO₄ solution obtained in Step 1 is supplied to the anode GDE obtained in Step 3 through the anode chamber. Water is converted into O₂ at the anode GDE via the iridium oxide catalyst.

An ion exchange membrane is used to separate the cathode chamber and the anode chamber, wherein the ion exchange membrane is a cation exchange membrane.

As shown in FIG. 10, the CO₂ reduction performance of the system employing silver as the CO₂ reduction catalyst is demonstrated. At a current density of 100 mA cm⁻², a Faradaic efficiency of 9% toward CO₂ reduction products is achieved.

Accordingly, in Example 4, the use of an ammonium salt solution as the electrolyte in a zero-gap CO₂ electrolyzer significantly enhanced the selectivity toward CO₂ reduction products compared to the potassium salt solution used in Comparative Example 2, thereby overcoming limitations associated with conventional electrolytes. This example thus discloses a method that improves upon prior art by employing an ammonium salt solution to enhance product selectivity during CO₂ electroreduction.

Example 5

In this example, an anion exchange membrane separates the cathode chamber and the anode chamber. A solution containing ammonium salt (where R1, R2, R3, and R4 are all —CH₃) is supplied to the anode chamber, and humidified CO₂ is supplied to the cathode chamber. The catalyst for the cathode gas diffusion electrode is silver, thereby enabling the CO₂ reduction reaction in a zero-gap CO₂ reduction electrolyzer. The specific steps are as follows:

Step 1: Preparation of Ammonium Salt Solution;

An ammonium salt solution is prepared, wherein the ammonium salt is [N(R1)(R2)(R3)(R4)]X, and R1, R2, R3, and R4 are all —CH₃.

Step 2: Preparation of Cathode Gas Diffusion Electrode;

A GDE is fabricated by first preparing a dispersion comprising a CO₂ reduction catalyst such as silver, a binder, and a solvent selected from ethanol, isopropanol, ethylene glycol, and deionized water. The mixture is subjected to sonication and subsequently sprayed onto a gas diffusion layer composed of carbon paper.

Step 3: Preparation of Anode Gas Diffusion Electrode;

An anode GDE is prepared by loading iridium oxide onto a titanium felt substrate.

Step 4: Testing the CO₂ reduction performance of the zero-gap CO₂ reduction electrolyzer;

The humidified CO₂ is supplied to the cathode GDE obtained in Step 2 through the cathode chamber, and subsequent is converted into reduction products at the cathode GDE. In this example, the CO₂ reduction catalyst is silver.

The ammonium salt solution obtained in Step 1 is supplied to the anode GDE obtained in Step 3 through the anode chamber. Water is converted into O₂ at the anode GDE via the iridium oxide catalyst.

An ion exchange membrane is used to separate the cathode chamber and the anode chamber, wherein the ion exchange membrane is an anion exchange membrane.

As shown in FIG. 11, the CO₂ reduction performance of the system employing silver as the CO₂ reduction catalyst is demonstrated. At a current density of 100 mA cm², a Faradaic efficiency of 97% toward CO₂ reduction products is achieved. As further illustrated in the inset of FIG. 11, no visible white salt precipitation is observed on the backside of the cathodic GDE after electrolysis, which ensures CO₂ transport and stable operation of the zero-gap CO₂ electrolyzer.

Example 6

In this example, an anion exchange membrane separates the cathode chamber and the anode chamber. A solution containing ammonium salt (where R1, R2, R3, and R4 are all —H) is supplied to the anode chamber, and humidified CO₂ is supplied to the cathode chamber. The catalyst for the cathode gas diffusion electrode is silver, thereby enabling the CO₂ reduction reaction in a zero-gap CO₂ reduction electrolyzer. The specific steps are as follows:

Step 1: Preparation of Ammonium Salt Solution;

An ammonium salt solution is prepared, wherein the ammonium salt is [N(R1)(R2)(R3)(R4)]X, and R1, R2, R3, and R4 are all —H.

Step 2: Preparation of Cathode Gas Diffusion Electrode;

A GDE is fabricated by first preparing a dispersion comprising a CO₂ reduction catalyst such as silver, a binder, and a solvent selected from ethanol, isopropanol, ethylene glycol, and deionized water. The mixture is subjected to sonication and subsequently sprayed onto a gas diffusion layer composed of carbon paper.

Step 3: Preparation of Anode Gas Diffusion Electrode;

An anode GDE is prepared by loading iridium oxide onto a titanium felt substrate.

Step 4: Testing the CO₂ reduction performance of the zero-gap CO₂ reduction electrolyzer;

The humidified CO₂ is supplied to the cathode GDE obtained in Step 2 through the cathode chamber, and subsequent is converted into reduction products at the cathode GDE. In this example, the CO₂ reduction catalyst is silver.

The ammonium salt solution obtained in Step 1 is supplied to the anode GDE obtained in Step 3 through the anode chamber. Water is converted into O₂ at the anode GDE via the iridium oxide catalyst.

An ion exchange membrane is used to separate the cathode chamber and the anode chamber, wherein the ion exchange membrane is an anion exchange membrane.

As shown in FIG. 12, the CO₂ reduction performance of the system employing silver as the CO₂ reduction catalyst is demonstrated. At a current density of 40 mA cm⁻², a Faradaic efficiency of 75% toward CO₂ reduction products is achieved. As further illustrated in the inset of FIG. 12, no visible white salt precipitation is observed on the backside of the cathodic GDE after electrolysis, which ensures CO₂ transport and stable operation of the zero-gap CO₂ electrolyzer.

Comparative Example 3

In this example, an anion exchange membrane separates the cathode chamber and the anode chamber. A solution containing potassium ion (K⁺) is supplied to the anode chamber, and humidified CO₂ is supplied to the cathode chamber. The catalyst for the cathode gas diffusion electrode is silver or copper, thereby enabling the CO₂ reduction reaction in a zero-gap CO₂ reduction electrolyzer. The specific steps are as follows:

Step 1: Preparation of Potassium Salt Solution;

A potassium salt solution is prepared.

Step 2: Preparation of Cathode Gas Diffusion Electrode;

A GDE is fabricated by first preparing a dispersion comprising a CO₂ reduction catalyst such as silver, a binder, and a solvent selected from ethanol, isopropanol, ethylene glycol, and deionized water. The mixture is subjected to sonication and subsequently sprayed onto a gas diffusion layer composed of carbon paper.

Step 3: Preparation of Anode Gas Diffusion Electrode;

An anode GDE is prepared by loading iridium oxide onto a titanium felt substrate.

Step 4: Testing the CO₂ reduction performance of the zero-gap CO₂ reduction electrolyzer;

The humidified CO₂ is supplied to the cathode GDE obtained in Step 2 through the cathode chamber, and subsequent is converted into reduction products at the cathode GDE. In this example, the CO₂ reduction catalyst is silver.

The potassium salt solution obtained in Step 1 is supplied to the anode GDE obtained in Step 3 through the anode chamber. Water is converted into O₂ at the anode GDE via the iridium oxide catalyst.

An ion exchange membrane is used to separate the cathode chamber and the anode chamber, wherein the ion exchange membrane is an anion exchange membrane.

As shown in FIG. 13, the CO₂ reduction performance of the system employing silver as the CO₂ reduction catalyst is demonstrated. At a current density of 100 mA cm⁻², a Faradaic efficiency of 88% toward CO₂ reduction products is achieved. As further illustrated in the inset of FIG. 13, white KHCO₃ or K₂CO₃ deposits accumulated on the backside of the cathodic GDE after electrolysis, obstructing CO₂ transport and ultimately causing the failure of the zero-gap CO₂ electrolyzer.

Therefore, the technical solutions disclosed in Examples 5 and 6 effectively address the issue of salt precipitation that clogs the pores of the gas diffusion layer, as mentioned in the background art. Notably, in Example 5, an ammonium salt solution was employed as the electrolyte in the zero-gap CO₂ electrolyzer. Compared with the potassium salt solution used in Comparative Example 3, this approach significantly improved the selectivity toward CO₂ reduction products.

The foregoing description is merely illustrative of preferred embodiments of the present invention and is not intended to limit the scope of the invention. Various modifications, substitutions, or alterations may be readily conceived by those skilled in the art without departing from the spirit and scope of the invention as disclosed. Accordingly, the scope of the present invention should be defined by the appended claims.