阅读说明：本技术 多层级纳米孔金属基柔性薄膜气体扩散电极及其制备方法与应用 (Multi-level nano-pore metal-based flexible thin film gas diffusion electrode and preparation method and application thereof ) 是由 林柏霖 肖彦军 钱瑶 于 2020-05-27 设计创作，主要内容包括：本发明公开了一种多层级纳米孔金属基柔性薄膜气体扩散电极的制备方法,包括以下步骤：步骤1：将柔性薄膜裁剪,依次用丙酮、乙醇、去离子水清洗、烘干备用；步骤2：用物理真空方法在柔性薄膜的一侧沉积金属膜；步骤3：使用晶格膨胀和收缩策略来构建分层的纳米孔结构：金属膜在溶液中发生阳极氧化,金属纳米粒子转化为金属盐或金属氧化物微米畴,使得金属晶格体积发生膨胀；随后的阴极还原将负离子或氧原子从金属盐或金属氧化物中去除,使其还原为金属单质,使得晶格原位收缩,导致在畴界处形成畴界通道/间隙,以及由于晶格收缩和负离子或氧原子损失而导致的畴内小孔,即得多层级纳米孔金属基柔性薄膜气体扩散电极。本发明的原料廉价,制备方法简单高效,十分有利于工业化应用。(The invention discloses a preparation method of a multilayer nano-pore metal-based flexible thin film gas diffusion electrode, which comprises the following steps: step 1: cutting the flexible film, sequentially cleaning with acetone, ethanol and deionized water, and drying for later use; step 2: depositing a metal film on one side of the flexible film by a physical vacuum method; and step 3: a lattice expansion and contraction strategy was used to build the layered nanopore structure: the metal film is subjected to anodic oxidation in the solution, and the metal nano particles are converted into metal salt or metal oxide micro domains, so that the metal lattice volume is expanded; the subsequent cathode reduction removes negative ions or oxygen atoms from metal salts or metal oxides to reduce the negative ions or oxygen atoms into metal simple substances, so that the crystal lattices contract in situ, domain boundary channels/gaps are formed at the domain boundaries, and pores in the domains are caused by the crystal lattice contraction and the loss of the negative ions or the oxygen atoms, and the multilayer nano-pore metal-based flexible film gas diffusion electrode is obtained. The raw materials of the invention are cheap, the preparation method is simple and efficient, and the invention is very beneficial to industrial application.)

1. A preparation method of a multilayer nano-pore metal-based flexible thin film gas diffusion electrode is characterized by comprising the following steps:

step 1: cutting the flexible film, sequentially cleaning with acetone, ethanol and deionized water, and drying for later use;

step 2: depositing a metal film on one side of the flexible film by a physical vacuum method;

and step 3: a lattice expansion and contraction strategy was used to build the layered nanopore structure: the metal X film is subjected to anodic oxidation in the solution, and the metal X nano particles are converted into metal salt or metal oxide micro domains, so that the metal lattice volume is expanded; the subsequent cathode reduction removes negative ions or oxygen atoms from metal salts or metal oxides to reduce the negative ions or oxygen atoms into metal simple substances, so that the crystal lattices contract in situ, domain boundary channels/gaps are formed at the domain boundaries, and pores in the domains are caused by the crystal lattice contraction and the loss of the negative ions or the oxygen atoms, and the multilayer nano-pore metal-based flexible film gas diffusion electrode is obtained.

2. The method for preparing a multi-layer nano-pore metal-based flexible thin film gas diffusion electrode as claimed in claim 1, wherein the metal comprises any one of silver, gold, copper, tin, bismuth and nickel.

3. The method for preparing a multi-layer nano-pore metal-based flexible thin film gas diffusion electrode as claimed in claim 1, wherein the flexible thin film in step 1 is a nano-porous polypropylene film.

4. The method for preparing a multi-layer nano-pore metal-based flexible thin film gas diffusion electrode as claimed in claim 1, wherein the physical vacuum method in the step 2 comprises any one of an electron beam evaporation method, a thermal evaporation method and a magnetron sputtering method.

5. A preparation method of a multi-layer nano-pore silver-based thin film gas diffusion electrode is characterized by comprising the following steps:

step 1: cutting the nano porous polypropylene film, sequentially washing with acetone, ethanol and deionized water, and drying for later use;

step 2: depositing a silver film on one side of the polypropylene film by a physical vacuum method;

and step 3: a lattice expansion and contraction strategy was used to build the layered nanopore structure: anodic oxidation of the silver film occurs in the hydrochloric acid aqueous solution, and Ag nano particles are converted into AgCl micro domains; subsequent cathodic reduction removes chlorine atoms from the AgCl lattice, resulting in domain boundary channels/gaps at the domain boundaries, and in-domain pinholes due to lattice shrinkage and chloride ion loss, i.e., multi-layer nanoporous silver-based thin film gas diffusion electrodes.

6. The method for preparing a multi-layer nano-porous silver-based thin film gas diffusion electrode according to claim 5, wherein the pore diameter of the nano-porous polypropylene film in the step 1 is 15-800 nm.

7. The method for preparing a multi-layer nano-porous silver-based thin film gas diffusion electrode according to claim 5, wherein the thickness of the silver film in the step 2 is 600-1800 nm.

8. The method for preparing a multi-layer nano-pore silver-based thin film gas diffusion electrode according to claim 5, wherein the silver film in the step 2 is formed by closely packing irregular silver nano-particles, and the particle size of the silver nano-particles is 10-1000 nm.

9. The method for preparing the multi-layer nano-pore silver-based thin film gas diffusion electrode according to claim 5, wherein the size of AgCl micro domain in the step 3 is 0.1-2.5 μm; the size of domain boundary channels/gaps in the step 3 is 10-1200 nm; and in the step 3, the average size of the small holes in the domains is 10-200 nm.

10. A multi-layer nanoporous silver-based thin film gas diffusion electrode prepared by the method of any one of claims 5 to 9.

11. The multi-layer nanoscale silver-based thin film gas diffusion electrode of claim 10 in CO₂Application in RR reaction.

12. Use of the multi-layer nanoporous silver-based thin film gas diffusion electrode as defined in claim 10 in OER reactions.

13. Use according to claim 11, wherein the use is of reducing CO₂Is CO, alcohol, acid, alkane or alkene.

Technical Field

The invention relates to a gas diffusion electrode and a preparation method thereof, in particular to a multilayer nano-pore metal-based flexible thin film gas diffusion electrode and a preparation method thereof.

Background

Global climate change due to mass burning of fossil fuels is aggravated and greenhouse efficiency is more severe, and in view of the current trend, the residual carbon budget to achieve the temperature control target will be rapidly exhausted within the next 10-20 years, requiring immediate action to reduce the large carbon dioxide emissions caused by human factors. The artificial photosynthesis system can simultaneously perform CO₂Reduction reaction (CO)₂RR) and water oxidation oxygen production reaction (OER), CO can be realized₂Substantial reduction in emissions and large-scale storage of intermittent solar energy in carbonaceous fuels. CO 2₂The RR products vary with the reaction potential, where CO, an ideal CO₂RR product is a good energy carrier and chemical industry intermediate. Although much progress has been made in previous research work, even in CO₂The most active gold catalysts are used in RR to CO systems, and only relatively modest electrochemical reduction of CO is achieved₂And (4) performance. Therefore, in order to efficiently use the driving force of the solar cell, it is necessary to design and develop a solar cell capable of efficiently utilizing CO₂RR and OER catalysts, methods, and systems.

Disclosure of Invention

The invention aims to solve the problem of the prior electrochemical reduction of CO₂The catalyst has the problems of high manufacturing cost, large reaction overpotential, difficult long-term high-efficiency operation and the like, and provides a novel high-efficiency electrochemical reduction method for CO₂A nano-film gas diffusion electrode and a rapid and efficient preparation method.

In order to achieve the purpose, the invention provides a preparation method of a multilayer nano-pore metal-based flexible thin film gas diffusion electrode, which is characterized by comprising the following steps:

step 1: cutting the flexible film, sequentially cleaning with acetone, ethanol and deionized water, and drying for later use;

step 2: depositing a metal film on one side of the flexible film by a physical vacuum method;

and step 3: a lattice expansion and contraction strategy was used to build the layered nanopore structure: the metal film is subjected to anodic oxidation in the solution, and the metal nano particles are converted into metal salt or metal oxide micro domains, so that the metal lattice volume is expanded; the subsequent cathode reduction removes negative ions or oxygen atoms from metal salts or metal oxides to reduce the negative ions or oxygen atoms into metal simple substances, so that the crystal lattices contract in situ, domain boundary channels/gaps are formed at the domain boundaries, and pores in the domains are caused by the crystal lattice contraction and the loss of the negative ions or the oxygen atoms, and the multilayer nano-pore metal-based flexible film gas diffusion electrode is obtained.

Preferably, the metal includes silver, gold, copper, tin, bismuth, nickel, and the like.

Preferably, the flexible film in step 1 is a rice porous polypropylene film (nanoPP).

Preferably, the physical vacuum method in step 2 includes an electron beam evaporation method, a thermal evaporation method and a magnetron sputtering method.

A preparation method of a multi-layer nano-pore silver-based thin film gas diffusion electrode (npm-Ag) is characterized by comprising the following steps:

step 1: cutting a nano porous polypropylene film (nano PP), sequentially washing with acetone, ethanol and deionized water, and drying for later use;

step 2: depositing a silver film on one side of the polypropylene film by a physical vacuum method;

and step 3: a lattice expansion and contraction strategy was used to build the layered nanopore structure: anodic oxidation of the silver film occurs in the hydrochloric acid aqueous solution, and Ag nano particles are converted into AgCl micro domains; subsequent cathodic reduction removes chlorine atoms from the AgCl lattice, resulting in domain boundary channels/gaps at the domain boundaries, and in-domain pinholes due to lattice shrinkage and chloride ion loss, i.e., multi-layer nanoporous silver-based thin film gas diffusion electrodes.

Preferably, the pore diameter of the nano-porous polypropylene film (nano PP) in the step 1 is 15-800 nm.

Preferably, the physical vacuum method in step 2 includes an electron beam evaporation method, a thermal evaporation method and a magnetron sputtering method.

More preferably, the physical vacuum method in step 2 is an electron beam evaporation method.

Preferably, the thickness of the silver film in the step 2 is 600-1800 nm.

More preferably, the silver film thickness in step 2 is 600nm, 1200nm or 1800 nm.

Preferably, the silver film in the step 2 is formed by closely packing irregular silver nanoparticles, and the particle size of the silver nanoparticles is 10-1000 nm.

Preferably, the size of the AgCl micro domain in the step 3 is 0.1-2.5 μm.

Preferably, the domain boundary channels/gaps in step 3 have a size of 10-1200 nm.

Preferably, the size of the small holes in the domains in the step 3 is 10-200 nm.

The invention also provides a multi-layer nano-pore silver-based film gas diffusion electrode prepared by the method.

The invention also provides the application of the multi-level nano-pore silver-based film gas diffusion electrode in CO₂Application in RR reaction.

Preferably, the application is the reduction of CO₂Is CO, alcohol, acid, alkane or alkene.

More preferably, the application is to reduce CO₂Is CO.

The invention also provides application of the multi-level nano-pore silver-based film gas diffusion electrode in water oxidation oxygen generation reaction (OER).

The invention selects silver as CO₂The RR electrocatalyst is targeted because it is about one percent of gold and has been successfully used in large-scale industrial processes such as chloralkali electrolysis and ethylene epoxidation. Furthermore, the technical economic analysis shows that the use of silver electrodes in the cell is comparable in cost to the overall system using non-noble metal electrodes, while the use of gold as the reaction electrode catalyst in the cellThe reagent adds significantly to the cost. However, although some nano-silver electrocatalysts with better catalytic activity have been reported, they are at lower overpotentials (<300mV), the electrocatalytic activity is weak, i.e.there is not a sufficiently large current density (>10mA·cm^-2). In addition, in the lower overpotential interval, the Faradaic Efficiency (FE) of carbon monoxide tends to be much lower than 100% due to the existence of a competing reaction, the hydrogen evolution reaction.

Generally, increasing the catalyst loading can directly increase the current density of the catalytic reaction to a certain extent; but with the continuous increase of the loading capacity or thickness of the catalyst, the limitation on the mass transfer of active substances in the process of the carbon dioxide electrocatalytic reaction is gradually enhanced; it also results in insufficient contact of the catalyst active sites with the electrolyte, thereby reducing the electrocatalytic activity of the electrode. In the copper-based catalyst PTFE electrode reported by Sargent, its catalytic activity is significantly inhibited as the thickness of the catalyst increases, probably due to the long and narrow diffusion path in the nanomaterial of the catalyst, which limits CO₂Interfacial active species transfer, a key step of the RR reaction. In addition, the PTFE nano film is high in manufacturing cost, so that the PTFE nano film is not beneficial to large-scale popularization and application. Therefore, a silver-based nano film electrocatalyst (npm-Ag) with a multi-level pore structure and a nano polypropylene film (nanoPP) as a substrate is designed and prepared, a small pore structure in a film catalyst layer of the silver-based nano film electrocatalyst has active sites with higher geometric density, and macropores and channels in the silver-based nano film electrocatalyst can realize the rapid transfer of active substances on a reaction interface, and the synergistic action of the catalyst can ensure that a photosynthesis system has ideal and efficient energy conversion efficiency; in addition, the nano polypropylene film (nano PP) has more uniform pore structure, stronger hydrophobicity and higher heat-resistant temperature, and is more suitable for electrocatalytic reduction of CO₂The gas diffusion electrode of the reaction can ensure the stability of the electrocatalytic reaction to a certain extent.

The invention has the beneficial effects that:

1. the polypropylene film adopted by the invention has the advantages of low cost, uniform structure and stable property, and is used for electrocatalytic reduction of CO₂Gas of reactionThe diffusion electrode can provide a better and more stable gas-liquid-solid three-phase interface;

2. the multi-layer nano-pore silver-based polypropylene film gas diffusion electrode (npm-Ag) is applied to alkaline CO₂RR reaction, excellent performance and high efficiency reduction of CO₂Is CO;

3. CO in 1M KOH of the invention₂When the overpotential of RR is as low as 40mV, the CO Faraday conversion efficiency can reach 80%; at slightly higher overpotentials (90-290mV), the Faraday efficiency reached 100%, while the cell current density reached about 18.4mA cm^-2(ii) a The performance is far better than other reported catalysts.

4. The catalyst prepared by the invention shows excellent stability at 15.2 mA-cm^-2Under the condition of continuously carrying out electrochemical reduction of CO_·After reacting for 28h, no obvious fading phenomenon is shown.

5. The raw materials for preparing the catalyst are all cheap raw materials, the preparation method is simple and efficient, the electrode preparation efficiency is improved, the electrode preparation cost is greatly reduced, and the method is very beneficial to industrial application.

Drawings

FIG. 1 is a scanning electron microscope image, pore size distribution, and flooding resistance of three types of breathable base materials; (A) carbon paper treated with polytetrafluoroethylene (Dongli TGP-H-60); (B) (E), (H) and (K) a nano polyethylene film (nanoPE); and (C), (F), (I) and (L) a nano polypropylene film (nano PP). Since the critical breakthrough pressure is inversely proportional to the membrane pore size, the average pore size (36.5 μm) and maximum pore size (165.7 μm) of the carbon paper are much larger than those of the NanoPE membrane (average: 166.5nm, maximum: 1.52 μm) and the NanoPP membrane (average: 131.5nm, maximum: 806.6 nm).

FIG. 2 (A) useful in the electrochemical reduction of CO in the present invention₂The multilayer nano-porous silver-based polypropylene film gas diffusion electrode (npm-Ag); (B) scanning electron microscope images of the multi-level nano-pore structure silver film gas diffusion electrode (npm-Ag) show that after constant current reduction, the prepared AgCl film can simultaneously form rich large channels (about 534 +/-153 nm) and small pores (about 68.5 +/-26.0 nm), and the AgCl film can be inserted into the large channels and the small poresThe figure shows a high resolution scanning electron microscope image; (C) cross-sectional Scanning Electron Microscope (SEM) images showed that npm-Ag had more large channels/gaps at the bottom than at the top; inset shows a high resolution SEM image.

FIG. 3 is a silver film deposited on the surface of a NanoPP film by an electron beam evaporation method; (A) scanning electron microscope images of the top view of the vacuum deposited silver film; (B) a cross-sectional view of a deposited silver film; (C) and (3) a silver particle size distribution diagram based on a scanning electron microscope image.

FIG. 4 is a schematic diagram of lattice expansion and contraction strategy during the synthesis of a multi-layer nano-porous silver-based polypropylene film gas diffusion electrode (npm-Ag); (A) the silver nanoparticles of the silver film in the aqueous solution are anodized through Cl^-Injecting metal silver crystal lattices, and converting the metal silver crystal lattices into AgCl crystals to cause lattice expansion; (B) the AgCl film undergoes reduction, removing chloride ions from the AgCl lattice, resulting in lattice shrinkage, forming a large number of large channels/gaps and small pores at the micrometer domain boundaries.

FIG. 5. topographic characterization of AgCl deposited on a NanoPP film; (A) scanning an electron microscope image of a top view of the AgCl film; (B) high resolution SEM images of AgCl films; (C) AgCl micron domain size distribution graph based on scanning electron microscope images.

FIG. 6 XRD diffraction pattern patterns of AgCl/NanoPP with thicknesses of 1.44 μm (black), 2.80 μm (red) and 4.50 μm (blue), respectively; after anodic oxidation in aqueous HCl, most of the silver was converted to AgCl (JCPDS #31-1238, heart mark), but a trace of silver phase was still visible in the XRD spectrum (JCPDS #04-0783, diamond mark).

FIG. 7. AgCl cross-section SEM images for three different thicknesses: (A)1.44 μm, (B)2.80 μm and (C) 4.50. mu.m.

FIG. 8. multi-layer nano-porous silver-based polypropylene film gas diffusion electrode nmp-Ag-2.80 μm micro-domain size distribution (A), large channel/slit size distribution (B) and nano-pore size distribution (C).

FIG. 9 CO of gas diffusion electrode of multi-layer nano-porous silver-based polypropylene film₂Electrochemical performance of RR. (A) Ar or CO of multi-level nano-pore silver-based polypropylene film gas diffusion electrode under standard atmospheric pressure₂Linear sweep voltammogram under atmosphere (sweep rate: 10 mv. multidot.s)-1); (B) selectively generating the current distribution density of CO by the three silver film electrodes with different thicknesses; (C) the multi-level nano-pore silver-based polypropylene film gas diffusion electrode selectively produces the change relation of the real current density of CO along with the potential; (D) the faradaic efficiency and total current density of the sample nmp-Ag-1.44 μm for selective CO generation varied with potential and overpotential; (E) the Faraday efficiency and the total current density of a sample nmp-Ag-2.80 mu m for selectively generating CO are in the change relation with the potential and the overpotential; (F) the faradaic efficiency and total current density of sample nmp-Ag-4.50 μm selective CO generation varied with potential and overpotential.

FIG. 10 (A) sample nmp-Ag-2.80 μm in CO₂Representative of electrolyte solutions after RR test¹H-NMR spectra, in which DMSO was added as an internal standard of the solution. Determination of H by gas chromatography₂(B) And selectivity for CO (C), H₂And the retention times of CO were 0.88min and 5.08min, respectively.

FIG. 11 is a morphological feature of a multi-layer nano-porous silver-based polypropylene film gas diffusion electrode: (A) (D) and (G) nmp-Ag-1.44 μm; (B) (E) and (H) nmp-Ag-2.80 μm; (C) (F) and (I) nmp-Ag-4.50 μm.

FIG. 12 is an X-ray diffraction pattern (XRD) of a multi-level nano-porous silver-based polypropylene film gas diffusion electrode with different thicknesses: 1.44 μm (black), 2.80 μm (red) and 4.50 μm (blue), only the metallic phase of silver (JCPDS #04-0783) is present in the X-ray diffraction spectrum, and the silver films of these three different thicknesses have similar crystal plane orientations.

FIG. 13 electrochemical surface area (ECSA) testing of gas diffusion electrodes of multi-layer nanoporous silver-based polypropylene films of different thicknesses. The electric double layer of the electrode is tested by cyclic voltammetry within the potential range without obvious electrochemical reaction, and the capacitance (Cdl) and the electrochemical surface area of the electric double layer can be determined by linear fitting of the current density difference of the anode and the cathode under different scanning rates; the Cdl and ECSA of nmp-Ag-1.44/2.80/4.50 μm were determined to be: 2.44 mF. cm^-2，4.60mF·cm^-2，9.82mF·cm^-2；97.6cm²，184.0cm²，392.8cm²。

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.