Cationically fixed acidic membrane electrode assembly, and preparation method and application thereof

Abstract

The application relates to the technical field of catalytic materials, and discloses a cation-fixed acidic membrane electrode assembly as well as a preparation method and application thereof. The preparation method comprises the following steps: adding ion exchange resin into an alkali cation solution and stirring to obtain a mixed solution; fully precipitating the mixed solution, performing solid-liquid separation, and then drying to obtain alkali cation resin; taking carbon paper loaded with a catalyst as a cathode, uniformly laying the alkali cation resin on the surface of the cathode, taking a titanium mesh loaded with iridium oxide as an anode, separating the cathode from the anode by using a proton exchange membrane, and assembling the membrane electrode assembly. The prepared acidic membrane electrode assembly is applied to electrocatalytic carbon dioxide reduction. The resin fixed on the cathode hinders the migration of H + + from the anode to the cathode, thereby improving the local pH of the cathode, enhancing the selectivity of target products in the acidic CO2RR, avoiding salt precipitation, greatly improving the stability, and realizing efficient electrocatalytic carbon dioxide reduction for preparing CO under acidic conditions.

Description

Technical Field

[0001] This invention belongs to the field of catalytic materials technology, and specifically relates to an electrocatalytic material, namely an acidic membrane electrode assembly with cation immobilization, its preparation method and application. Background Technology

[0002] Electrochemical carbon dioxide reduction reaction (CO2RR) utilizes renewable energy to convert the greenhouse gas CO2 into high-value-added carbon-based fuels and chemicals (such as ethylene, ethanol, and formic acid), providing a promising technological pathway for solving environmental problems. Traditional CO2RR systems primarily rely on alkaline or neutral electrolytes to suppress the competitive hydrogen evolution reaction (HER), but this method has a significant problem: the presence of OH groups in the electrolyte... - It reacts with CO2 to form carbonates (CO3). 2- ) or bicarbonate (HCO3) - This reaction not only permanently consumes the reactant CO2, but also causes carbonate deposition and cross-contamination, leading to a significant decrease in carbon utilization and severely damaging the long-term stability of the CO2RR system. This phenomenon has become a serious limitation restricting the large-scale application of CO2RR technology.

[0003] To overcome the aforementioned limitations, research on CO2RR (pH ≤ 3) in acidic media based on cation exchange membranes (CEMs) has rapidly emerged in recent years. Its core advantage lies in suppressing carbon loss at its source. Even if a localized high pH environment is created at the cathode interface due to rapid proton consumption, the generated carbonates or bicarbonates will quickly react with H+ in the low pH electrolyte environment. + The H2 is then converted back into CO2. This mechanism enables in-situ regeneration and recycling of CO2, resulting in a single-pass carbon efficiency (SPCE) exceeding the theoretical maximum (50%) for alkaline systems. However, the high proton concentration in low-pH environments gives the hydrogen evolution reaction a significant thermodynamic and kinetic advantage. In unoptimized pure acid systems, H2 often accounts for over 90% of the total products, leading to extremely low CO2RR selectivity.

[0004] Previous studies have shown that alkali metal cations (such as Li) + Na + K + Cs + It is an important medium for activating CO2RR and stabilizing reaction intermediates, playing a dual role in the reaction process: on the one hand, it stabilizes key intermediates through electrostatic shielding. CO2; on the other hand, its hydrated shell properties can selectively delay HER kinetics, creating a time window for CO2 activation. Therefore, adding alkali metal salts to acidic electrolytes has become a common method to improve CO2RR selectivity. However, this method has obvious technical problems: the salting-out effect under acidic conditions, that is, alkali metal cations migrating from the anode to the cathode will react with CO3 generated locally at the cathode. 2- or HCO3 - They combine to form insoluble carbonate precipitates, such as K2CO3 and KHCO3.

[0005] Therefore, existing technologies still cannot solve the above problems simultaneously. Summary of the Invention

[0006] This invention aims to address the salting-out effect of cations on the cathode surface in existing acidic MEAs, while simultaneously suppressing H+. + To address the issue of cation migration towards the cathode to increase the local pH, this paper provides an acidic membrane electrode assembly with cation immobilization, its preparation method, and its application.

[0007] This invention is achieved using the following technical solution: This invention provides a method for preparing an acidic membrane electrode assembly with cation immobilization, comprising the following steps: In this invention, the medium used for cation immobilization is Dowex 50W X8 or Dowex 1×8 type ion exchange resin; wherein the Dowex 1×8 type resin itself stably supports quaternary ammonium cation groups under covalent bonding, and therefore can also serve as a cation immobilization layer without modification or S1 / S2 operations. The Dowex 50W X8 type ion exchange resin prototype carries H+ via electrostatic interactions. + This is detrimental to CO2RR, so it is modified in the following steps.

[0008] S1. Take ion exchange resin and add it to a 0.1~0.5mol / L alkaline cation solution and stir at 800~1200rpm for 24~48h to obtain a mixed solution.

[0009] Preferably, the mass-to-volume ratio of ion exchange resin to alkaline cation solution is (1~2):(100~300), with mass expressed in g and volume expressed in ml; A basic cation solution is an aqueous solution of the basic cations sulfate, chloride, bromide, and iodide salts, where the basic cation is Na. + K + Cs + At least one of them.

[0010] S2, let the mixed solution stand at room temperature for 3-8 hours to fully precipitate, and after solid-liquid separation, dry at 50-80℃ for 6-12 hours. Solid-liquid separation is carried out by centrifugation or filtration. Specifically, the centrifugation speed is 8000-10000 rpm and the time is 3-5 minutes to obtain the alkali cation exchange resin.

[0011] S3, using carbon paper loaded with a catalyst as the cathode, the catalyst being a carbon dioxide reduction catalyst, specifically silver (Ag), the loading method including magnetron sputtering or spraying, uniformly spreading the alkaline cation exchange resin obtained in step S2 on the cathode surface, with a spreading thickness of 0.6~1.5mm, using a titanium mesh loaded with iridium oxide as the anode, and using a proton exchange membrane to separate the cathode and anode, the proton exchange membrane being a Nafion N117 proton exchange membrane, and assembling into a membrane electrode assembly.

[0012] The present invention also provides an acidic membrane electrode assembly with cation immobilization prepared by the above preparation method.

[0013] Specifically, the cathode surface of the acidic membrane electrode assembly is uniformly covered with an ion exchange resin layer carrying alkali metal cations; when using the acidic membrane electrode assembly, the anode uses pure acid with a pH of 1 to 3 as the anolyte, and the cathode uses humidified CO2 gas as the feed.

[0014] The present invention also provides the application of the above-mentioned cation-fixed acidic membrane electrode assembly in electrocatalytic carbon dioxide reduction.

[0015] Specifically, it is applied to the electrocatalytic reduction of carbon dioxide to prepare C1 and C2 products, and further, to the electrocatalytic reduction of carbon dioxide to prepare carbon monoxide; the electrocatalytic reduction of carbon dioxide is carried out at a current density of 50~300 mA·cm. -2 The following will proceed.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a cation-immobilized acidic membrane electrode assembly, its preparation method, and its application. A cation-immobilizing layer (K-type cation resin) is used to immobilize cations on the cathode. The resin immobilized on the cathode can electrostatically repel H+. + To achieve the goal of hindering H + The migration of cations increases the local pH at the cathode, enhancing the selectivity of the target product in acidic CO2RR. Simultaneously, the cation immobilization layer prevents the accumulation of cations migrating from the anode to the cathode, effectively preventing the accumulation of cations from the anode by K+. + The accumulated salt precipitation significantly improves stability, enabling efficient electrocatalytic reduction of carbon dioxide to CO under acidic conditions.

[0017] The preparation method of this invention is simple. It prepares ion exchange resin materials loaded with basic cations through an ion exchange reaction, requiring no complex synthesis or expensive reagents. It is compatible with existing MEA assembly processes and has advantages such as low cost, controllable conditions, and simple process. Furthermore, it has strong versatility and is suitable for C... 2+ Products (such as ethylene and ethanol) also have application potential, indicating that they can be extended to multi-carbon product systems.

[0018] The membrane electrode assembly prepared by this invention, in an acidic MEA, at 100 mA·cm -2 At current densities of 50–250 mA·cm⁻¹, CO exhibits a Faraday efficiency as high as 98.4%, and this efficiency remains high in the range of 50–250 mA·cm⁻¹. -2 Maintaining a stability of over 90% across a wide current range demonstrates the crucial role of the cation immobilization layer in achieving efficient CO2 reduction under harsh acidic conditions (pH=1). The Dowex 1×8 type ion exchange resin MEA system achieved the longest stability, reaching 150 hours in pure acid and 460 hours in an ultra-low potassium composite electrolyte (pH≈1) composed of 0.05 mmol / L H2SO4 and 1 mmol / L K2SO4 as the anolyte. This significantly surpasses the level of similar technologies reported to date, demonstrating groundbreaking long-term operational stability. Attached Figure Description

[0019] Figure 1 The graph shows the CO Faraday efficiency test results for Examples 1-4.

[0020] Figure 2 The graph shows the performance test results of Example 1 under different current densities.

[0021] Figure 3 The figure shows the stability test results of Example 4 under pure acid.

[0022] Figure 4 The figure shows the stability test results of Example 4 in a low-potassium acidic solution. Detailed Implementation

[0023] The specific embodiments of the present invention will be described in detail below. Example 1

[0024] A method for preparing a cation-immobilized acidic membrane electrode assembly includes the following steps: S1. Take 1g of ion exchange resin and add it to 0.4mol / L K2SO4 solution. Stir at 1000rpm for 24h to obtain a mixed solution.

[0025] S2, after the mixed solution has fully precipitated, filtered, and dried at 60℃ for 8 hours, the alkali cation exchange resin is obtained.

[0026] In step S3, silver (Ag) is deposited on the surface of hydrophobic carbon paper using vapor deposition to form an Ag catalyst layer as the cathode. The alkaline cation exchange resin obtained in step S2 is evenly spread on the cathode surface with a thickness of 0.8 mm. A titanium mesh loaded with iridium oxide is used as the anode. A Nafion N117 proton exchange membrane is used to separate the cathode and the anode. The resin layer is evenly spread between the cathode electrode and the ion exchange membrane to assemble a membrane electrode assembly.

[0027] The Dowex 50W X8 ion exchange resin used in this embodiment is an ion exchange resin with a negatively charged backbone. Its functional group is a sulfonic acid group (-SO3H), and the supported cation is a potassium ion (K). + ).

[0028] CO2RR performance was tested at room temperature and pressure using 0.05 mol / L sulfuric acid as the anolyte.

[0029] Performance tests show that Ag, after being added to the K-type cation exchange resin, has a viscosity of 100 mA·cm⁻¹ in pure acid (pH≈1). -2 Faraday efficiency (FE) of CO at current density CO The percentage reached 98.4%. Example 2

[0030] A method for preparing an acidic membrane electrode assembly with cation immobilization differs from Example 1 in that, in step S1, the alkaline cation solution is a Na2SO4 solution, while the rest is completely consistent with Example 1.

[0031] The Dowex 50W X8 ion exchange resin used in this embodiment is an ion exchange resin with a negatively charged backbone. Its functional group is a sulfonic acid group (-SO3H), and the supported cation is a sodium ion (Na). + ).

[0032] CO2RR performance was tested at room temperature and pressure using 0.05 mol / L sulfuric acid as the anolyte.

[0033] Performance tests show that Ag added to the Na-type cation exchange resin has a viscosity of 100 mA·cm⁻¹ in pure acid (pH≈1). -2 FE at current density CO It reached 93.2%. Example 3

[0034] A method for preparing an acidic membrane electrode assembly with cation immobilization differs from Example 1 in that, in step S1, the alkaline cation solution is a Cs2SO4 solution, while the rest is completely consistent with Example 1.

[0035] The Dowex 50W X8 ion exchange resin used in this embodiment is an ion exchange resin with a negatively charged backbone. Its functional group is a sulfonic acid group (-SO3H), and the supported cation is a cesium ion (Cs). + ).

[0036] CO2RR performance was tested at room temperature and pressure using 0.05 mol / L sulfuric acid as the anolyte.

[0037] Performance tests show that Ag added to the Cs-type cation exchange resin has a viscosity of 100 mA·cm⁻¹ in pure acid (pH=1). -2 FE at current density CO It reached 92.7%. Example 4

[0038] A method for preparing a cation-fixed acidic membrane electrode assembly differs from Example 1 in that the ion exchange resin used is a Dowex 1×8 type ion exchange resin. Because it inherently and covalently supports quaternary ammonium cation groups, it is directly used as the cation fixation layer without modification. Steps S1 and S2 are omitted.

[0039] In step S3, Dowex 1×8 type ion exchange resin is used instead of the alkaline cation exchange resin prepared in step S2 and is evenly spread on the cathode surface. The rest is completely consistent with Example 1.

[0040] The Dowex 1×8 type ion exchange resin used in this embodiment is an ion exchange resin with a positively charged backbone, and its functional groups are quaternary ammonium cation groups (-N). + (CH3)3, being inherently positively charged, was not modified in any way. Infrared spectroscopy results showed that the structure of the modified resin polymer did not change significantly compared to the unmodified version.

[0041] Using 0.05 mol / L sulfuric acid as the anolyte, CO2RR performance was tested at room temperature and pressure. The performance tests showed that Ag, after being added to the Dowex 1×8 resin, achieved a CO2RR of 100 mA·cm⁻¹ in pure acid (pH=1). -2 FE at current density CO It reached 84.6% and ran stably for 150 hours.

[0042] A 0.05 mol / L sulfuric acid solution was supplemented with 1 mmol / L potassium sulfate as the anolyte, and CO2RR performance was tested at room temperature and pressure. The performance tests showed that the Ag added to the Dowex 1×8 resin exhibited good performance at 100 mA·cm⁻¹. -2 The CO2RR can operate stably for 460 hours at the specified current density. Comparative Example

[0043] A method for preparing an acidic membrane electrode assembly involves depositing silver (Ag) onto the surface of hydrophobic carbon paper using vapor deposition to form an Ag catalyst layer as the cathode. Dowex 50W X8 ion exchange resin is then uniformly spread on the cathode surface with a thickness of 0.8 mm. A titanium mesh loaded with iridium oxide is used as the anode. A Nafion N117 proton exchange membrane separates the cathode from the anode. The resin layer is uniformly spread between the cathode electrode and the ion exchange membrane, assembling the membrane electrode assembly.

[0044] The Dowex 50W X8 ion exchange resin used in this embodiment is a negatively charged ion exchange resin with a sulfonic acid group (-SO3H) as its functional group. It has not undergone the aforementioned alkaline cation modification operation, and its own loaded cation is hydrogen ion (H+). + ).

[0045] 0.05 mol / L sulfuric acid was used as the anolyte, and CO2RR performance was tested at room temperature and pressure.

[0046] Performance tests show that the Ag added to the Dowex 50W X8 ion exchange resin has a strength of 100 mA·cm⁻¹ in pure acid (pH=1). -2 FE at current density CO Almost zero.

[0047] like Figure 1 , 2 As shown, Example 1 (using K-type cation exchange resin) exhibited the best CO product selectivity in acidic MEA, and within the range of 50–250 mA·cm⁻¹. -2 The CO faradaic efficiency was maintained at over 90% within the current density range.

[0048] like Figure 3 , 4 As shown, the Dowex 1×8 type ion exchange resin MEA system in Example 4 achieved the longest stability, reaching 150 h in pure acid (0.05 mmol / L H2SO4, pH=1); when tested with an ultra-low potassium composite electrolyte (pH≈1) composed of 0.05 mmol / L H2SO4 and 1 mmol / L K2SO4 as the anolyte, its stability reached 460 h, exceeding most existing acidic CO2RR studies. The cations in the resin are the main reason for the enhanced performance, as they can inhibit H+ ions. + Migration to the cathode surface creates a highly alkaline local environment and activates CO2RR.

[0049] In summary, this invention provides an acidic membrane electrode assembly with cation immobilization. The immobilized cation layer avoids excessive accumulation of cations at the cathode and creates a higher local pH, providing favorable conditions for CO2RR in an acidic environment. This invention also provides a reference for the design of high-performance CO2RR catalytic systems in acidic MEAs in the future.

[0050] The scope of protection claimed by this invention is not limited to the specific embodiments described above. Moreover, for those skilled in the art, this invention can have various modifications and alterations. Any modifications, improvements, and equivalent substitutions made within the concept and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for preparing an acidic membrane electrode assembly with cation immobilization, characterized in that, Includes the following steps: S1, add ion exchange resin to a 0.1~0.5mol / L alkaline cation solution and stir at 800~1200rpm for 24~48h to obtain a mixed solution; S2, the mixed solution is allowed to stand at room temperature for 3-8 hours to fully precipitate, and after solid-liquid separation, it is dried at 50-80℃ for 6-12 hours to obtain the alkali cation exchange resin; S3, using carbon paper loaded with catalyst as the cathode, uniformly spreading the alkaline cation exchange resin obtained in step S2 on the cathode surface with a spreading thickness of 0.6~1.5mm, using a titanium mesh loaded with iridium oxide as the anode, and using a proton exchange membrane to separate the cathode and anode, assembling a membrane electrode assembly.

2. The method for preparing a cation-immobilized acidic membrane electrode assembly according to claim 1, characterized in that, In step S1, the mass-to-volume ratio of the ion exchange resin to the alkaline cation solution is (1~2):(100~300), with mass expressed in g and volume expressed in ml. The ion exchange resin is a Dowex 50W X8 type ion exchange resin; The alkaline cation solution is an aqueous solution of sulfate, chloride, bromide, or iodide salts of alkaline cations, wherein the alkaline cation is Na. + K + Cs + At least one of them.

3. The method for preparing a cation-immobilized acidic membrane electrode assembly according to claim 1, characterized in that, In step S2, solid-liquid separation is performed by centrifugation or filtration. The centrifugation speed is 8000-10000 rpm and the time is 3-5 min.

4. The method for preparing a cation-immobilized acidic membrane electrode assembly according to claim 1, characterized in that, In step S3, the catalyst is a carbon dioxide reduction catalyst, and the loading method includes magnetron sputtering or spraying. The proton exchange membrane is a Nafion N117 proton exchange membrane.

5. The cation-fixed acidic membrane electrode assembly prepared by the preparation method according to any one of claims 1 to 4.

6. The cation-immobilized acidic membrane electrode assembly according to claim 5, characterized in that, The cathode surface is uniformly covered with an ion exchange resin layer carrying alkali metal cations.

7. The cation-immobilized acidic membrane electrode assembly according to claim 5, characterized in that, When the acidic membrane electrode assembly is used, the anode uses pure acid with a pH of 1 to 3 as the anolyte, and the cathode uses humidified CO2 gas as the feed.

8. The application of the cation-fixed acidic membrane electrode assembly of claim 5 in electrocatalytic carbon dioxide reduction.

9. The application according to claim 8, characterized in that, It is applied to the electrocatalytic reduction of carbon dioxide to prepare C1 and C2 products.

10. The application according to claim 8, characterized in that, The electrocatalytic carbon dioxide reduction is performed at a current density of 50~300 mA·cm⁻¹ -2 The following will proceed.

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