Method for preparing multi-carbon product by reducing carbon dioxide through acidic electro-catalysis

Abstract

The invention discloses a method for preparing a multi-carbon product through acid electrocatalysis carbon dioxide reduction and belongs to the field of chemistry and chemical engineering. An electro-catalysis carbon dioxide reduction system takes a Cu-based catalyst modified by HEDP as an electrode material, and K < + > in an electrolyte can be effectively enriched on the surface of the Cu-based catalyst due to the complexing effect of HEDP on K < + >, so that the local pH is increased, C-C coupling is promoted, and efficient conversion of CO2 to a multi-carbon product under an acidic condition is realized. According to the invention, HEDP molecules with a K < + > complexing function are introduced into the surface of a Cu-based catalyst for the first time, and the Cu-based catalyst is applied to an acidic electrocatalytic carbon dioxide reduction system with low K < + > concentration. The preparation method of the electrocatalytic system cathode catalyst is simple, mild in reaction condition and simple to operate, can effectively relieve the problem of carbonate deposition in an alkaline electrocatalytic system, and has industrial application prospects.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of chemical engineering, and relates to an acidic electrolyte system, an electrochemical method, and a method for preparing multi-carbon products from carbon dioxide as raw material BACKGROUND

[0002] Electrocatalytic CO2 reduction (ECR) converts CO2 into high-value chemicals using renewable electricity, providing a sustainable and net-zero-carbon solution to global energy and climate challenges. Currently, electrocatalytic CO2 reduction to multi-carbon products (C 2+ ) is usually carried out in neutral or alkaline aqueous electrolytes to suppress the competing hydrogen evolution reaction (HER) and promote C-C coupling on the catalyst surface. However, in alkaline and neutral electrolytes, the locally strong alkaline environment formed by electrocatalytic CO2 reduction leads to the combination of CO2 and hydroxyl ions to form carbonate. This is an exothermic and spontaneous process, and limits the single-pass conversion efficiency of CO2 to C 2+ products to below 25%. Carrying out electrocatalytic CO2 reduction in acidic electrolytes can effectively solve the above problems.

[0003] Under acidic conditions, high concentrations of protons in the electrolyte can suppress the formation of carbonate. However, due to the faster kinetics of the competing HER, catalysts in acidic electrolytes tend to promote the hydrogen evolution reaction, thereby limiting the formation of C 2+ products. Previous studies have shown that the addition of alkaline cations to acidic electrolytes can effectively solve this problem. Since then, acidic electrolytes with high concentrations of K + have been widely reported to promote C-C coupling and inhibit the hydrogen evolution reaction. Although previous studies have shown that high concentrations of alkaline cations in the electrolyte help to buffer the local pH and promote the generation of C 2+ products, it also presents some challenges. The locally high pH formed by electrocatalytic CO2 reduction and the accumulation of K + on the catalyst surface still leads to the formation of carbonate precipitates, blocking the mass transfer channels of CO2, increasing the interfacial resistance, and weakening the stability of the catalytic system. Reducing the K + concentration in the electrolyte can effectively alleviate this problem. These challenges have prompted the design of catalysts suitable for acidic electrolytes to achieve efficient C 2+ product generation under low K + concentration conditions. SUMMARY

[0004] The present application provides a method for preparing multi-carbon products by acidic electrocatalytic CO2 reduction. The reaction is carried out under acidic conditions (e.g. pH 1.0) using a hydroxyethylidene diphosphonic acid-modified Cu-based catalyst at low K +The concentration electrolyte can efficiently catalyze CO2 into multi-carbon products. This effectively alleviates the problem of carbonate deposition in the electrocatalytic reduction of carbon dioxide, provides a practical path for the industrialized electrocatalytic reduction of carbon dioxide to prepare multi-carbon products, and has important practical application value and economic benefits.

[0005] The technical solutions adopted by the present application are as follows:

[0006] A method for electrocatalytically preparing multi-carbon products under acidic conditions, using CO2 as raw material, a Cu-based catalyst modified by hydroxyethylidene diphosphonic acid as a cathode material, an acidic KCl solution with a pH of 1.0 as a cathode electrolyte, an acidic K2SO4 solution with a pH of 1.0 as an anode electrolyte, and an electrocatalytic system is formed to carry out electrocatalytic reaction to obtain multi-carbon products.

[0007] Further, the concentration of the cathode electrolyte KCl solution is 0-3M; the concentration of the anode electrolyte K2SO4 solution is 0.5M.

[0008] The electrocatalytic reaction applies a constant current, and the current density is-300 to-1100mA cm -2 , preferably-700mA cm -2 . The current density can be adjusted as needed; the multi-carbon products are mainly C 2+ products, including C2H5OH, C2H4, CH3COOH, and also C3H7OH.

[0009] A method for preparing a Cu-based catalyst modified by hydroxyethylidene diphosphonic acid as a cathode material, comprising the following steps:

[0010] (1) Dissolve a certain amount of borax, ascorbic acid and hydroxyethylidene diphosphonic acid in deionized water to obtain a first solution;

[0011] (2) Add a compound containing a Cu source to the first solution, stir at room temperature, then separate by centrifugation, wash, and finally dry to obtain a Cu-based pre-catalyst;

[0012] (3) Drop the above pre-catalyst on carbon paper and perform pre-reduction under a CO2 atmosphere to prepare a Cu-based catalyst modified by hydroxyethylidene diphosphonic acid as a cathode material;

[0013] Further, the amount of borax used in step (1) is 5-100mg / mL, the amount of hydroxyethylidene diphosphonic acid used is 0.5-10mg / mL, and the amount of ascorbic acid used is 1-50mg / mL.

[0014] Further, the amount of Cu source used in step (2) is 1-100mg / mL.

[0015] Furthermore, the Cu source compound in step (2) can be copper nitrate (Cu(NO3)2), copper chloride (CuCl2), copper sulfate (CuSO4), or copper acetate (Cu(CH3COO)2).

[0016] Further, in step (3), the above pre-catalyst is drop-coated onto carbon paper: the above pre-catalyst is added to an isopropanol aqueous solution (isopropanol:water is 1:1) and Nafion solution, and ultrasonically dispersed; the above dispersion is drop-coated onto an untreated gas diffusion electrode, and then in a flow cell, the above electrode containing the pre-catalyst is used as the working electrode, Pt sheet is used as the anode, 3M KCl is used as the catholyte, 0.5M K2SO4 is used as the anolyte, and the pH of both the anode and cathode electrolytes is adjusted to 1.0 with commercially available concentrated sulfuric acid, and pre-reduction is carried out under a CO2 atmosphere;

[0017] The pre-reduction process is conducted at -100 to -500 mA cm. -2 Continue at the current density for 3–10 minutes.

[0018] The beneficial effects of this invention are as follows:

[0019] Through the above technical solution, this invention provides a two-step method for preparing HEDP-modified Cu-based catalysts at room temperature. The method utilizes HEDP to modify K... + The complexation effect, in acidic, low K + High CO2 reduction activity can be achieved in electrolytes with concentrations (even zero). The method of this invention facilitates the regulation of the local microenvironment of the catalyst, reducing the Gibbs free energy of the hydrogenation step in the reaction intermediate, thereby improving the catalytic activity of the catalyst. The method disclosed in this invention is simple in procedure, operates under mild conditions, and can effectively mitigate the salting-out problem in the electrocatalytic CO2 reduction process, providing a practical pathway for the electrocatalytic conversion of acidic CO2 into multi-carbon products, and has promising prospects for industrial application. Attached Figure Description

[0020] Figure 1 This is a SEM image of the HEDP-modified Cu-based catalyst in this invention;

[0021] Figure 2 This is the ATR-IR spectrum of the HEDP-modified Cu-based catalyst in this invention;

[0022] Figure 3 In this invention, a HEDP-modified Cu-based catalyst is used as the cathode, under an application of -700 mA / cm². -2 At current densities, multi-carbon products (C) are generated in 0–3 M KCl electrolyte (pH 1.0). 2+ Faraday efficiency diagram;

[0023] Figure 4This is a Faraday efficiency diagram of the product obtained in a membrane electrode reactor at a full cell voltage of 4.0–4.4 V using a HEDP-modified Cu-based catalyst as the cathode in this invention.

[0024] Figure 5 This is a diagram of the membrane electrode cathode chamber after the electrocatalytic CO2 reduction reaction. Detailed Implementation

[0025] The technical solution of the present invention will be further described below with reference to the accompanying drawings in the embodiments of the present invention. In the present invention, the raw materials and equipment used are all commercially available. Unless otherwise specified, the methods in the embodiments are conventional methods in the art.

[0026] The electrolysis experiment was conducted in a commercial flow electrolyzer with a three-electrode system. The HEDP-modified Cu-based catalyst prepared in this invention was used as the working electrode, the Pt sheet as the counter electrode, and Ag / AgCl as the reference electrode. The anode and cathode were separated by a proton exchange membrane.

[0027] Example 1

[0028] A method for preparing an HEDP-modified Cu-based catalyst includes the following steps:

[0029] a. Preparation of precatalyst

[0030] 2.0 g of borax was dissolved in 70 mL of deionized water at 90 °C. Then, 0.8 g of ascorbic acid and 1.2 g of HEDP were added to the boric acid solution to obtain solution A. 0.4 g of copper chloride was added to solution A, and the mixture was stirred at room temperature for 2 h. After the reaction was complete, the product was separated by centrifugation, washed three times with deionized water, and then vacuum dried at 60 °C for 12 h to obtain the pre-catalyst.

[0031] b. Preparation of HEDP-modified Cu-based catalysts

[0032] 2.4 mg of the precatalyst was added to 480 μL of isopropanol aqueous solution (isopropanol:water ratio 1:1) and 2.4 μL of 5 wt% Nafion solution, and ultrasonically dispersed. The dispersion was drop-coated onto an untreated gas diffusion electrode. Subsequently, in a flow cell, the electrode containing the precatalyst was used as the working electrode, with a Pt sheet as the anode, 3 M KCl (pH 1.0) as the catholyte, and 0.5 M K₂SO₄ (pH 1.0) as the anolyte, and pre-reduction was performed under a CO₂ atmosphere.

[0033] The pre-reduction process is conducted at -100 to -500 mA cm. -2 Continue at the current density for 3–10 minutes.

[0034] Figure 1The image shows a SEM image of the HEDP-modified Cu-based catalyst obtained in Example 1. As can be seen from the image, the catalyst has a nanoparticle structure. Figure 2 The ATR-IR spectrum of the HEDP-modified Cu-based catalyst obtained in Example 1 is shown at ~1099 cm⁻¹. -1 The peak at 1145 cm⁻¹ corresponds to the symmetric stretching vibration of PO. -1 The peak at 1645 cm⁻¹ corresponds to ν (P = O). -1 The peak at that point corresponds to ν(P-OH). The presence of PO, P=O, and P-OH bonds indicates that phosphonic acid groups still exist on the surface of the HEDP-modified Cu-based catalyst, and that HEDP can stably exist on the surface of the Cu-based catalyst after electrochemical pre-reduction.

[0035] Example 2

[0036] A highly efficient electrocatalytic method for preparing multi-carbon products from CO2 mainly includes the following steps:

[0037] In an electrochemical flow cell, 3M KCl was used as the cathode electrolyte (pH 1.0), and 0.5M K₂SO₄ was used as the anolyte (pH 1.0). Constant current electrolysis was performed under a stable CO₂ gas flow of 40 sccm, with an applied current density of -300 to -1100 mA / cm⁻¹. -2 Gaseous products were collected using gas bags and analyzed using gas chromatography. Liquid products in the electrolyte were analyzed using proton nuclear magnetic resonance spectroscopy.

[0038] The catalyst of this invention exhibits high reactivity towards multi-carbon products; in this embodiment, at -700 mA cm⁻¹ -2 The Faradaic efficiency for generating multi-carbon products at the current density can reach ~80%, with ethylene being the main gaseous product and ethanol being the main liquid product. The Faradaic efficiency for ethanol reaches 38.2%, and that for ethylene reaches 33.9% (see Table 1 for results).

[0039] Table 1

[0040]

[0041]

[0042] Example 3

[0043] A highly efficient electrocatalytic method for preparing multi-carbon products from CO2 mainly includes the following steps:

[0044] In an electrochemical flow cell, 3M KCl was used as the cathode electrolyte (pH 1.0), and 0.5M K₂SO₄ was used as the anolyte (pH 1.0). Constant current electrolysis was performed under a stable CO₂ gas flow of 40 sccm, with an applied current density of -700 mA / cm⁻¹. -2 Gaseous products were collected using gas bags and analyzed using gas chromatography. Liquid products in the electrolyte were analyzed using proton nuclear magnetic resonance spectroscopy.

[0045] The catalyst of the present invention has high reactivity for multi-carbon products. In this embodiment, the Faraday efficiency for generating multi-carbon products can reach up to ~80% (results are shown in Table 1).

[0046] Example 4

[0047] A highly efficient electrocatalytic method for preparing multi-carbon products from CO2 mainly includes the following steps:

[0048] In an electrochemical flow cell, 1M KCl was used as the cathode electrolyte (pH 1.0), and 0.5M K₂SO₄ was used as the anolyte (pH 1.0). Constant current electrolysis was performed under a stable CO₂ gas flow of 40 sccm, with an applied current density of -700 mA / cm⁻¹. -2 .

[0049] The catalyst of the present invention has high reactivity for multi-carbon products. In this embodiment, the Faraday efficiency for generating multi-carbon products can reach up to ~68% (results are shown in Table 1).

[0050] Example 5

[0051] A highly efficient electrocatalytic method for preparing multi-carbon products from CO2 mainly includes the following steps:

[0052] In an electrochemical flow cell, 0.1 M KCl was used as the cathode electrolyte (pH 1.0), and 0.5 M K₂SO₄ was used as the anolyte (pH 1.0). Constant current electrolysis was performed under a stable CO₂ gas flow at 40 sccm, with an applied current density of -700 mA / cm⁻¹. -2 .

[0053] The catalyst of the present invention is at a lower K + The product still exhibits high reactivity towards multi-carbon products at certain concentrations. In this example, the Faraday efficiency for generating multi-carbon products can reach up to ~65% (results are shown in Table 1).

[0054] Example 6

[0055] A highly efficient electrocatalytic method for preparing multi-carbon products from CO2 mainly includes the following steps:

[0056] In an electrochemical flow cell, 0.05 M KCl was used as the cathode electrolyte (pH 1.0), and 0.5 M K₂SO₄ was used as the anolyte (pH 1.0). Constant current electrolysis was performed under a stable CO₂ gas flow at 40 sccm, with an applied current density of -700 mA / cm⁻¹. -2 .

[0057] The catalyst of the present invention in K + Even with further reductions in concentration, it still exhibits high reactivity towards multi-carbon products. In this example, the Faraday efficiency for generating multi-carbon products can reach up to ~63% (results are shown in Table 1).

[0058] Example 7

[0059] A highly efficient electrocatalytic method for preparing multi-carbon products from CO2 mainly includes the following steps:

[0060] In an electrochemical flow cell, with K-free + H₂SO₄ was used as the cathode electrolyte (pH 1.0), and 0.5M K₂SO₄ was used as the anolyte (pH 1.0). Constant current electrolysis was performed under a stable CO₂ gas flow of 40 sccm, with an applied current density of -700 mA / cm⁻¹. -2 .

[0061] The catalyst of the present invention is in the absence of K + In the acidic electrolyte, it still has CO2 reduction activity, and the Faraday efficiency of generating multi-carbon products in this example can reach ~16% (the results are shown in Table 2).

[0062] Table 2

[0063]

[0064] Example 8

[0065] A highly efficient electrocatalytic method for preparing multi-carbon products from CO2 mainly includes the following steps:

[0066] To verify the industrial application prospects of the catalyst prepared in this invention, electrolysis was carried out in a membrane electrode electrolyzer with an area of ​​1cm*1cm, using 1mM H2SO4 as the anolyte and a humid CO2 gas flow of 30sccm, with a full cell voltage of 4.0 to 4.4V applied.

[0067] The catalyst of the present invention is in the absence of K + In the existing membrane electrode electrolysis cell, the reaction activity for multi-carbon products remains high. In this example, the Faraday efficiency for generating multi-carbon products can reach up to 50% (results shown in Table 3), and no carbonate precipitation occurs on the cathode side after electrolysis (results shown in Table 3). Figure 5 ).

[0068] Table 3

[0069]

[0070] The above results clearly demonstrate that the method of the present invention can effectively enrich K in the electrolyte on the catalyst surface. + At lower K + High concentrations of acidic electrolytes exhibit high Faraday efficiency for multi-carbon products, avoiding the presence of K+ in the electrolyte. + The problem of carbonate deposition caused by excessively high concentrations. And in the absence of K... + The efficient conversion of CO2 to multi-carbon products can still be achieved in the existing membrane electrode. These results demonstrate that the method described in this invention has certain industrial application prospects.

[0071] Although embodiments of the present invention have been described above, any modifications and substitutions made by those skilled in the art without departing from the principles and spirit of the present invention are within the scope of protection claimed by the present invention.

Claims

1. A method for the electrocatalytic preparation of multi-carbon products by carbon dioxide under acidic conditions, characterized in that, Using CO2 as a raw material, a Cu-based catalyst modified with hydroxyethylidene diphosphonic acid is used as the cathode material, an acidic KCl solution with a pH of 1.0 is used as the cathode electrolyte, and an acidic K2SO4 solution with a pH of 1.0 is used as the anolyte to form an electrocatalytic system for electrocatalytic reaction to obtain multi-carbon products. The concentration of the KCl solution in the cathode electrolyte is 0–3 M.

2. The method according to claim 1, characterized in that, The concentration of the K2SO4 solution in the anolyte is 0.5M.

3. The method according to claim 1, characterized in that, A constant current is applied to the electrocatalytic reaction, with a current density of -300 to -1100 mA / cm². -2 Preferably -700mA cm -2 . The current density can be adjusted as needed.

4. The method according to claim 1, characterized in that, A method for preparing Cu-based catalyst cathode materials modified with hydroxyethylidene diphosphonic acid includes the following steps: (1) Dissolve a certain amount of borax, ascorbic acid and hydroxyethylidene diphosphonic acid in deionized water to obtain the first solution; (2) The Cu-based precatalyst was obtained by adding the Cu-based compound to the first solution, stirring at room temperature, centrifuging, washing, and finally drying. (3) The above pre-catalyst was drop-coated onto carbon paper and pre-reduced under CO2 atmosphere to obtain Cu-based catalyst cathode material modified with hydroxyethylidene diphosphonic acid.

5. The method according to claim 4, characterized in that, In step (1), the amount of borax used is 5-100 mg / mL, the amount of hydroxyethylidene diphosphonic acid used is 0.5-10 mg / mL, and the amount of ascorbic acid used is 1-50 mg / mL.

6. The method according to claim 4, characterized in that, The amount of Cu source used in step (2) is 1-100 mg / mL; In step (2), the Cu source compound can be copper nitrate (Cu(NO3)2), copper chloride (CuCl2), copper sulfate (CuSO4), or copper acetate (Cu(CH3COO)2).

7. The method according to claim 4, characterized in that, In step (3), the pre-catalyst is drop-coated onto carbon paper: the pre-catalyst is added to an isopropanol aqueous solution (isopropanol:water ratio of 1:1) and Nafion solution, and ultrasonically dispersed; the dispersion is drop-coated onto an untreated gas diffusion electrode, and then in a flow cell, the electrode containing the pre-catalyst is used as the working electrode, with a Pt sheet as the anode, 3M KCl as the catholyte, and 0.5M K2SO4 as the anolyte. The pH of both the anode and cathode electrolytes is adjusted to 1.0 with commercially available concentrated sulfuric acid, and pre-reduction is carried out under a CO2 atmosphere.

8. The method according to claim 7, characterized in that, The pre-reduction process is conducted at -100 to -500 mA cm. -2 Continue at the current density for 3–10 minutes.

9. The method according to claim 7, characterized in that, The multi-carbon products are mainly C 2+ The products include C2H5OH, C2H4, CH3COOH, and also C3H7OH.

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