Natural polymer-based bimetallic electrocatalyst for preparing ethanol through electroreduction of CO2 and preparation method of natural polymer-based bimetallic electrocatalyst

Abstract

The invention discloses a natural polymer-based bimetallic electrocatalyst for preparing ethanol through electroreduction of CO2 and a preparation method thereof. The electrocatalyst is constructed by using a two-step electrochemical method, firstly, a zero-valence copper nanoparticle material anchored and dispersed by a natural polymer substrate is synthesized in situ through an electroreduction method, and then second metal tin is introduced through an electrodeposition method, so that the bimetallic electrocatalyst with the copper-tin heterojunction is prepared. The copper-tin asymmetric sites in the electrocatalyst can realize effective regulation and control of an electronic structure and oxyphilicity by changing preparation conditions, so that a remarkable synergistic effect is generated, the adsorption state of a reaction intermediate is optimized, a hydrogen evolution competitive reaction is inhibited, and the electroreduction reaction activity, the ethanol single selectivity and the catalysis long-term stability are improved. The electrocatalyst has the advantages of simple preparation process, environmental protection, low cost, high efficiency, cleanness and the like. The invention provides a new thought for development of an electrocatalyst related to electroreduction of CO2.

Description

Technical Field

[0001] The present invention belongs to the technical field of green chemistry, and particularly relates to an electrocatalyst with a copper-tin bimetallic heterostructure using a natural polymer as a carrier, its in-situ electrochemical preparation method and steps, and its use in the electroreduction of CO 2 for the preparation of ethanol. Background Art

[0002] CO 2 The excessive emission of CO is considered to be a key factor leading to environmental problems such as global warming and acid rain. Converting CO 2 into low-carbon energy chemicals and liquid fuels, especially multi-carbon hydrocarbons and oxygenates, has become a fundamental method to mitigate extreme climate change and increasing energy demand. From the perspectives of technical difficulty, maturity, and economy, the electroreduction of CO 2 reaction is considered a technical route with broad application prospects. However, in this reaction, various products such as C 1 (such as carbon monoxide, methane, formic acid, etc.), C 2 (such as ethanol, acetic acid, etc.), and C 3 are involved. Therefore, how to improve the selectivity of a single product becomes particularly important.

[0003] As one of the most important organic chemicals, ethanol is both an excellent fuel and fuel improver, and also a key precursor in the synthesis of various compounds and in the medical and food industries. Currently, the annual global production of ethanol is approximately 100 million tons, but it still does not meet the demands of various industries at this stage. Therefore, converting CO 2 into the high-value product ethanol is an effective way to realize the resource utilization of CO 2 . Currently, the Faraday efficiency of the known electroreduction of CO 2 to ethanol is generally lower than 45%, and multiple by-products are generated. This is closely related to the few active sites and poor catalytic orientation in the electrocatalyst. Therefore, designing and synthesizing an electrocatalyst with a sufficient amount of highly dispersed asymmetric sites is the key to achieving high-selectivity electroreduction of CO 2 to ethanol. Copper-based catalysts are the most effective catalysts known so far for converting CO 2 into multi-carbon products. Based on this, the single-product selectivity at the active sites can be improved by introducing a second metal, thereby increasing the ethanol yield. Therefore, this patent designs a natural polymer-based bimetallic electrocatalyst, which effectively regulates the electronic structure and surface oxygen affinity of the catalyst by introducing tin elements, causing changes in the adsorption of key active intermediates, thereby improving the reaction activity and single selectivity of ethanol in the electroreduction of CO 2 . Summary of the Invention

[0004] The present invention for the first time prepares a natural polymer-based bimetallic electrocatalyst by a two-step electrochemical method, and uses it as a cathode electrode for electro-reducing CO 2 to prepare ethanol, showing high catalyst activity, single ethanol selectivity and long-term stability, and having excellent performance.

[0005] The first aspect of the present invention discloses a natural polymer-based bimetallic electrocatalyst, which includes a natural polymer substrate material and nanoparticles with a copper-tin heterostructure grown on the substrate material.

[0006] Preferably, the natural polymer substrate is chitin, chitosan oligosaccharide, or chitosan.

[0007] Preferably, the metal sources for the copper-tin heterostructure are copper chloride, copper sulfate, stannous chloride, and stannous sulfate.

[0008] Preferably, the crystal planes exposed by the copper-tin heterostructure are Cu(111), Cu(200), and Sn(220); the size of the formed nanoparticles is 1 to 5 nanometers.

[0009] The second aspect of the present invention discloses a preparation method of the natural polymer-based bimetallic electrocatalyst as described above, including the following steps:

[0010] a: Prepare a suspension of natural polymer and copper salt, continuously stir at room temperature for more than 6 hours, centrifuge and wash, and vacuum dry at 60 °C to obtain a copper ion-natural polymer chelate.

[0011] b: Prepare a potassium bicarbonate solution, and introduce CO 2 to reach a saturated state. Uniformly drop-coat the copper ion-natural polymer obtained in step a on a hydrophobic carbon paper as the working electrode, select a silver-silver chloride electrode as the reference electrode, and a platinum mesh as the counter electrode, and reduce it in a constant current mode to obtain a zero-valent copper nanoparticle precursor.

[0012] c: Prepare an acid solution containing tin ions, and continue to use the hydrophobic carbon paper loaded with the precursor in step b as the working electrode, select a silver-silver chloride electrode as the reference electrode, and a platinum mesh as the counter electrode. Perform electro-deposition in a constant current mode to finally obtain a natural polymer-based bimetallic electrocatalyst.

[0013] Preferably, in step a, the concentration of the natural polymer is 5 to 15 grams per liter; the concentration of copper ions is 0.005 to 0.075 moles per liter.

[0014] Preferably, in step b, the concentration of the potassium bicarbonate solution is 0.15 to 0.85 moles per liter; the current range in the constant current mode is -100 to -300 milliamperes, and the time is 1000 to 3000 seconds.

[0015] Preferably, in step c, the concentration of tin ions is 0.035 - 0.105 mol / L; the concentration of hydrogen ions is 0.5 - 1.5 mol / L; the current range in the constant current mode is -15 to -45 mA, and the time is 10 - 100 s.

[0016] Preferably, in steps b and c, the size of the hydrophobic carbon paper is 1.5×2.5 cm², the electrolyte in the silver-silver chloride electrode is saturated potassium chloride solution, and the size of the platinum mesh is 1×1 cm².

[0017] The third aspect of the present invention discloses the application of the natural polymer-based bimetallic electrocatalyst in electro-reducing CO 2 for the preparation of ethanol.

[0018] Preferably, the electro-reduction of CO 2 reaction of the natural polymer-based bimetallic electrocatalyst is carried out in a flow-type electrolytic cell, the electrolyte is potassium hydroxide solution with a concentration of 0.5 - 1.5 mol / L; the applied current density is 50 - 150 mA / cm².

[0019] The working principle of the present invention is as follows:

[0020] The present invention adopts a two-step electrochemical method to simply and rapidly prepare a natural polymer-based bimetallic electrocatalyst for electro-reducing CO 2 for the preparation of ethanol. This method involves in-situ synthesizing zero-valent copper nanoparticles uniformly dispersed on the natural polymer substrate by electro-reduction method. Subsequently, using the copper nanoparticles as crystal nuclei, the second metal tin is introduced by electrodeposition method to construct a rich copper-tin heterostructure.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The preparation method adopted by the present invention has low cost, good repeatability, and is non-toxic and harmless to the environment.

[0023] (2) The present invention uses natural polymer as the substrate material, and utilizes the good chelating ability of hydroxyl and amino groups in the natural polymer structure to transition metal copper to achieve uniform dispersion of catalyst active sites.

[0024] (3) By simply introducing the second metal tin by electrodeposition method to construct a rich copper-tin heterogeneous interface, it provides a new idea for developing electrocatalysts with high activity for electro-reducing CO 2 for the preparation of ethanol.

[0025] (4) The natural polymer-based bimetallic electrocatalyst described in the present invention exhibits extremely high catalytic activity, stability, and high selectivity for ethanol products, and the Faraday efficiency reaches 74.26%. Description of the Drawings

[0026] To illustrate the core solutions in the embodiments of the present invention and the prior art, the accompanying drawings required for the description of the embodiments or the prior art will be briefly introduced below. The accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other accompanying drawings can be obtained based on these drawings without creative efforts.

[0027] Figure 1 Scanning electron microscope image of the natural polymer-based bimetallic electrocatalyst in Embodiment 1 of the present invention

[0028] Figure 2 Transmission electron microscope image of the natural polymer-based bimetallic electrocatalyst in Embodiment 1 of the present invention

[0029] Figure 3 High-magnification transmission electron microscope image of the natural polymer-based bimetallic electrocatalyst in Embodiment 1 of the present invention

[0030] Figure 4 X-ray diffraction pattern of the natural polymer-based bimetallic electrocatalyst in Embodiment 1 of the present invention

[0031] Figure 5 Element distribution map of the natural polymer-based bimetallic electrocatalyst in Embodiment 1 of the present invention

[0032] Figure 6 Transmission electron microscope image of the natural polymer-based bimetallic electrocatalyst (10 seconds) in Embodiment 2 of the present invention

[0033] Figure 7 Transmission electron microscope image of the natural polymer-based bimetallic electrocatalyst (30 seconds) in Embodiment 3 of the present invention

[0034] Figure 8 Transmission electron microscope image of the natural polymer-based bimetallic electrocatalyst (60 seconds) in Embodiment 4 of the present invention

[0035] Figure 9 Transmission electron microscope image of the natural polymer-based bimetallic electrocatalyst (90 seconds) in Embodiment 5 of the present invention

[0036] Figure 10 Electroreduction of CO by the natural polymer-based bimetallic electrocatalyst in Embodiment 1 of the present invention 2 Performance graph

[0037] Figure 11 Electroreduction of CO by the electrocatalyst at a current density of 100 mA / cm² in Embodiments 1-5 of the present invention 2 Performance graph

[0038] Figure 12 Electroreduction of CO by the natural polymer-based bimetallic electrocatalyst in Embodiment 1 of the present invention 2Long-term stability graph of ethanol product, test current density is 100 milliamperes per square centimeter Detailed implementation manners

[0039] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope protected by the present invention.

[0040] Example 1:

[0041] a: Prepare a copper chloride solution with a concentration of 0.04 mol / L. Disperse 0.2 g of low-viscosity (100 - 200 mPa·s) chitosan in the above solution, continuously stir at room temperature for more than 6 hours, centrifuge and wash, and vacuum dry at 60 °C to obtain a copper ion-low-viscosity chitosan chelate.

[0042] b: Prepare a potassium bicarbonate solution with a concentration of 0.5 mol / L, and introduce CO 2 to reach a saturated state. Uniformly drop-coat the copper ion-low-viscosity chitosan chelate obtained in step a on a hydrophobic carbon paper as the working electrode, select a silver-silver chloride electrode as the reference electrode, and a platinum mesh as the counter electrode, and react in a constant current mode of -200 mA for 1000 s to obtain zero-valent copper nanoparticles as the precursor.

[0043] c: Prepare a solution containing 0.2 mol / L of copper chloride dihydrate, 0.07 mol / L of anhydrous stannous chloride, and 1 mol / L of hydrochloric acid. Continue to use the hydrophobic carbon paper with the growth precursor in step b as the working electrode, select a silver-silver chloride electrode as the reference electrode, and a platinum mesh as the counter electrode, and electro-deposit for 15 s in a constant current mode of -30 mA to finally obtain a natural polymer-based bimetallic electrocatalyst. See the scanning electron microscope, transmission electron microscope, high-magnification transmission electron microscope, X-ray diffraction, and element distribution maps in Figure 1 、 2 、3, 4, 5 respectively.

[0044] Example 2:

[0045] Change the electro-deposition time in step c of Example 1 to 10 s to obtain a natural polymer-based bimetallic electrocatalyst (10 s). See the transmission electron microscope image in Figure 6 .

[0046] Example 3:

[0047] Change the electro-deposition time in step c of Example 1 to 30 s to obtain a natural polymer-based bimetallic electrocatalyst (30 s). See the transmission electron microscope image in Figure 7 .

[0048] Example 4:

[0049] Change the electrodeposition time in step c of Example 1 to 60 seconds to obtain a natural polymer-based bimetallic electrocatalyst (60 seconds), and its transmission electron microscopy image is shown in Figure 8 .

[0050] Example 5:

[0051] Change the electrodeposition time in step c of Example 1 to 90 seconds to obtain a natural polymer-based bimetallic electrocatalyst (90 seconds), and its transmission electron microscopy image is shown in Figure 9 .

[0052] Example 6:

[0053] The electroreduction of CO of the natural polymer-based bimetallic electrocatalyst of the present invention was tested using a three-electrode system: the reference electrode was a mercury-mercuric oxide electrode, the counter electrode was a nickel foam electrode, and the working electrode was the hydrophobic carbon paper carrying the electrocatalyst in Examples 1-5. The test was carried out in a flow-type electrolytic cell, and the electrolyte was a 1 mol / L potassium hydroxide solution. The electroreduction of CO performance of the natural polymer-based bimetallic electrocatalyst in Example 1 is shown in 2 . It can be seen from 2 that with the change of the applied current density, there are obvious changes in the distribution of the CO Figure 10 reduction products. When the current density is 100 mA / cm², the Faraday efficiency of ethanol reaches 74.26%, and the partial current density is 74.26 mA / cm². The performance of the electrocatalysts in Examples 1-5 at a current density of 100 mA / cm² is shown in Figure 10 . It can be seen from 2 that by controlling the electrodeposition time, the proportion of the copper-tin heterostructure can be changed, thereby effectively regulating the selectivity of the electrocatalyst for the electroreduction of CO Figure 11 to the target product ethanol of the reaction; when the electrodeposition time is 15 seconds, the Faraday efficiency of ethanol reaches the highest. Figure 11 2

[0054] Example 7:

[0055] In the electroreduction of CO 2 test device of Example 6, the long-term catalytic stability of the natural polymer-based bimetallic electrocatalyst in Example 1 was tested. The stability test was carried out at a current density of 100 mA / cm², and the curve graph of voltage, ethanol Faraday efficiency and time is shown in Figure 12 . It can be seen from Figure 12 that the natural polymer-based bimetallic electrocatalyst can still maintain good catalytic activity after 24 hours of testing.

[0056] The description of the above embodiments is only used to help understand the method and its core idea of the present invention, and is not used to limit the present invention. The protection scope of the present invention is defined by the claims. Those skilled in the art can make various modifications or equivalent replacements to the present invention within the essence and protection scope of the present invention, and such modifications or equivalent replacements should be regarded as falling within the protection scope of the present invention.

Claims

1. A natural polymer-based bimetallic electrocatalyst for efficient electroreduction of CO2 to produce ethanol, characterized in that: The catalyst is a metal copper nanoparticle half-coated with a second metal tin. The nanoparticle is grown on a natural polymer substrate and has a copper-tin heterogeneous structure and a size of 1 to 5 nanometers.

2. According to claim 1, it is characterized in that: Natural polymers include chitin, chitooligosaccharides, and chitosan.

3. According to claim 1, it is characterized in that: The salts used to synthesize the metal copper nanoparticles are copper chloride and copper sulfate; the salts used to synthesize the second metal tin are stannous chloride and stannous sulfate.

4. A method for preparing a natural polymer-based bimetallic electrocatalyst for efficient electroreduction of CO2 to produce ethanol as described in claims 1 to 3, characterized in that: The steps include: a: preparing a suspension of a natural polymer and a copper salt, stirring the suspension at room temperature for more than 6 hours, centrifuging and washing the suspension, and vacuum drying the suspension to obtain a copper ion-natural polymer chelate; b: Prepare potassium bicarbonate solution, introduce CO2 to reach saturation. Apply the copper ion-natural polymer obtained in step a on hydrophobic carbon paper as the working electrode, select silver-silver chloride electrode as the reference electrode, and platinum mesh as the counter electrode, and reduce in constant current mode to obtain zero-valent copper nanoparticle precursor; c: Prepare an acid solution containing tin ions, use the hydrophobic carbon paper loaded with the precursor in step b as the working electrode, select the silver-silver chloride electrode as the reference electrode, and the platinum mesh as the counter electrode, and perform electrodeposition in a constant current mode to finally obtain a natural polymer-based bimetallic electrocatalyst.

5. The preparation method according to claim 4, characterized in that: In step a, the concentration of the natural polymer is 5 to 15 g / L; the concentration of the copper ion is 0.005 to 0.075 mol / L.

6. The preparation method according to claim 4, characterized in that: The concentration of the potassium bicarbonate solution in step b is 0.15 to 0.85 mol / L; the current range of the constant current mode is -100 to -300 mA, and the duration is 1000 to 3000 seconds.

7. The preparation method according to claim 4, characterized in that: In step c, the concentration of tin ions is 0.035 to 0.105 mol / L; the concentration of hydrogen ions is 0.5 to 1.5 mol / L; the current range of the constant current mode is -15 to -45 mA, and the time is 10 to 100 seconds.

8. The preparation method according to claim 4, characterized in that: In steps b and c, the size of the hydrophobic carbon paper is 1.5×2.5 square centimeters, the electrolyte in the silver-silver chloride electrode is a saturated potassium chloride solution, and the size of the platinum mesh is 1×1 square centimeter.

9. Use of the natural polymer-based bimetallic electrocatalyst according to claims 1 to 3 for electroreduction of CO2 to produce ethanol.

10. The use according to claim 9, characterized in that: The natural polymer-based bimetallic electrocatalyst is used for the electroreduction of CO2 in a flow-type electrolytic cell, wherein the electrolyte is a potassium hydroxide solution with a concentration of 0.5 to 1.5 mol / L; The applied current density is 50 to 150 mA per square centimeter.

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