CN113130930A

CN113130930A - Gas diffusion layer material, electrode comprising same, preparation and application

Info

Publication number: CN113130930A
Application number: CN202110419421.8A
Authority: CN
Inventors: 孙晓明; 商志成; 罗亮
Original assignee: Beijing University of Chemical Technology
Current assignee: Beijing University of Chemical Technology
Priority date: 2021-04-19
Filing date: 2021-04-19
Publication date: 2021-07-16
Anticipated expiration: 2041-04-19
Also published as: CN113130930B

Abstract

The invention belongs to the technical field of inorganic chemical industry, and particularly relates to a wood-based gas diffusion layer material, an electrode comprising the same, and preparation and application of the electrode. The surface of the gas diffusion layer material is composed of a plurality of vertical holes, and the gas diffusion layer material is carbonized wood. The invention adopts the timber crosscut material to prepare the gas diffusion layer material, and has the advantages of low cost, wide raw material sources, easy acquisition and the like. What is more important is that: gas diffusion electrodes conventional in the art typically have an uncontrolled tortuous pore structure. The carbonized wood transverse section material is adopted as the electrode substrate, the original vertical pore structure can be well maintained, the electrode substrate has the advantages of controllable pore diameter and pore distribution and the vertical pore structure, and compared with a zigzag pore structure, the wood substrate has a large number of micron-sized vertical pore structures which are more beneficial to gas conduction. And the existence of mesopores and micropores in the carbonized wood accelerates the gas conduction process.

Description

Gas diffusion layer material, electrode comprising same, preparation and application

Technical Field

The invention belongs to the technical field of inorganic chemical industry, and particularly relates to a wood-based gas diffusion layer material, an electrode comprising the same, and preparation and application of the electrode.

Background

Energy environmental problems existing in the current society cause various social circles to continuously explore new energy sources (solar energy, chemical energy, wind energy, biomass energy, hydrogen energy and the like) development and utilization ways. The method for realizing energy conversion and storage by adopting the electrochemical catalysis mode is an efficient and convenient mode, and has important significance for commercialization and civilization of new energy in the future. In order to realize efficient energy conversion, research on fuel cells, metal-air batteries, and the like has been receiving attention. In the electrochemical device with gas participating in the reaction, the gas diffusion electrode plays a role in constructing a mass transfer path and catalyzing the reaction.

The gas diffusion electrode is generally composed of a gas diffusion layer and a catalytic layer, which directly affect the power density of the cell as important components thereof. During the operation of the battery, the reaction gas needs to overcome the mass transfer resistance of the gas diffusion layer to reach the catalytic layer to perform chemical reaction. However, the current gas diffusion electrode is mostly constructed by adhering a catalyst on carbon fiber paper. Such carbon fiber paper-based gas diffusion electrodes still have a number of problematic problems. For example, since it is formed by stacking and compressing carbon fibers, it has a scattered pore structure distribution, and cannot realize regulation of a substance transport path. The transmission rate of the substance in the zigzag holes is greatly limited; secondly, the carbon fiber paper raw material has complex production process and high energy consumption, so that the carbon fiber material is expensive, and the cost of the battery is not greatly increased.

Therefore, how to develop a gas diffusion electrode that is inexpensive, has high efficiency of transport and catalytic activity of reaction, and has high mechanical strength is a significant challenge for electrochemical gas consuming reaction devices.

The present invention has been made to solve the above problems.

Disclosure of Invention

The invention discovers that the wood gradient wettability gas diffusion electrode prepared by using the carbonized wood transverse slice as the substrate greatly improves the material transmission efficiency by constructing a vertical hole mode on one hand. On the other hand, by constructing gradient wettability, the active sites of the catalyst reaction are increased, and the electrochemical performance of the electrode is improved.

The invention provides in a first aspect a wood-based gas diffusion layer material, the surface of which is composed of a number of vertical pores, the gas diffusion layer material being a carbonized wood.

Preferably, a plurality of large vertical holes and small vertical holes which penetrate through the gas diffusion layer material are distributed on the surface of the gas diffusion layer material, the diameter of each large vertical hole is 50-150 micrometers, the diameter of each small vertical hole is 5-30 micrometers, and the number of the small vertical holes is larger than that of the large vertical holes;

or only a plurality of small vertical holes with the diameter of 5-30 are distributed on the surface of the gas diffusion layer material.

The invention provides a gradient wettability gas diffusion electrode based on wood, which comprises a gas diffusion layer material and a catalyst loaded on the gas diffusion layer material, wherein the thickness of the gas diffusion layer material is 200-1000 micrometers, the surface of the gas diffusion layer material is provided with a through vertical pore structure, and the contact angle of the gas diffusion layer material is in gradient change in the thickness direction of the gas diffusion layer material. I.e. the wettability behavior of the gdl material varies in a gradient in the thickness direction from one side to the other.

The contact angle of the gas diffusion layer material is changed in a gradient manner in the thickness direction of the gas diffusion layer material, which means that the contact angle of the gas diffusion layer material is gradually increased or decreased in the thickness direction of the gas diffusion layer material.

Preferably, a plurality of large vertical holes and small vertical holes which penetrate through the gas diffusion layer material surface of the gas diffusion electrode are distributed on the gas diffusion layer material surface of the gas diffusion electrode, the diameter of each large vertical hole is 50-150 micrometers, the diameter of each small vertical hole is 5-30 micrometers, and the number of the small vertical holes is larger than that of the large vertical holes;

Preferably, the contact angle distribution range of the hydrophilic side of the gas diffusion layer material is 60-90 degrees, and the contact angle of the hydrophobic side is 120-180 degrees.

Preferably, the gas diffusion layer material is carbonized wood.

Preferably, the carbonized wood species are selected from cherry wood, pine wood, white oak.

Preferably, the carbonized wood also has a three-level pore structure with micron-sized pores, 6-10 nm mesopores and 1-5 nm small pores.

The third aspect of the invention provides a preparation method of a wood-based gradient wettability gas diffusion electrode, which comprises the following steps:

(1) preparing carbonized wood: the method of interlayer fixation is adopted to carry out high-temperature carbonization on the wood transverse section material in the atmosphere of protective gas, so as to obtain carbonized wood transverse sections;

(2) loading a catalyst: loading a catalyst on the carbonized wood cross-cut sheet obtained in the step (1);

(3) gradient wettability modification: and (3) placing one side of the carbonized wood transverse slice loaded with the catalyst obtained in the step (2) on a low-surface-energy substance solution film for a period of time, blowing off redundant PTFE solution from the dry side to the wet side of the carbonized wood transverse slice, and roasting to obtain the gas diffusion electrode.

The low surface energy substance solution is selected from: one or more of PTFE solution, PVDF (polyvinylidene fluoride) solution and polypropylene (PP) solution.

PTFE solutions, PVDF (polyvinylidene fluoride) solutions, and polypropylene (PP) solutions are commercially available as mixtures of PTFE particles, PVDF particles, PP particles, and water, respectively.

Preferably, in the step (1), the thickness of the wood cross-section is 200-1000 microns.

Preferably, in the step (1), the carbonized wood cross-section is a gas diffusion layer material, and a plurality of large vertical holes and small vertical holes are distributed on the surface of the carbonized wood cross-section, the diameter of each large vertical hole is 50-150 micrometers, the diameter of each small vertical hole is 5-30 micrometers, and the number of the small vertical holes is larger than that of the large vertical holes.

Preferably, in step (1), the high-temperature carbonization process is as follows: the inert gas is argon or nitrogen, the gas flow rate is 50mL/min, the heating rate is 5 ℃/min, the temperature is increased to 800 ℃, the carbonization time is 2 hours, and the product is naturally cooled.

Preferably, the catalyst loading process in step (2) is as follows: and (2) ultrasonically treating the methanol solution dissolved with the cobalt salt and the methanol solution dissolved with the urea, transferring the methanol solution dissolved with the cobalt salt and the methanol solution dissolved with the urea to a reaction kettle, and meanwhile, placing the carbonized wood cross section in the step (1) in the reaction kettle and sealing. Carrying out hydrothermal reaction in a closed reaction kettle to prepare the carbonized wood cross section loaded with pink substances. The material is subjected to vapor deposition by adopting melamine under the protective atmosphere to obtain the carbonized wood cross section loaded with the cobalt-nitrogen carbon nano tube.

More preferably, in the step (2), the cobalt salt is selected from at least one of cobalt nitrate hexahydrate and cobalt sulfate heptahydrate. In the step (2), the molar ratio of the cobalt salt to the urea is 10: 1.

more preferably, in step (2), the hydrothermal reaction is carried out under the following conditions: the temperature is 120 ℃, the pressure is autogenous pressure, and the reaction time is 12 hours. In the step (2), the vapor deposition process is as follows: the inert gas is argon, the flow rate of the argon is 80mL/min, the heating rate is 5 ℃/min, the temperature is increased to 600 ℃, the reaction time is 0.5 hour, and the reaction is naturally cooled.

Preferably, in step (3), the PTFE concentration is 5 wt%.

Preferably, in step (3), the calcination process is as follows: the heating rate is 5 ℃/min, the temperature is raised to 350 ℃, the reaction time is 0.5 hour, and the mixture is naturally cooled.

Preferably, step (1) adopts a sandwich fixing mode in the carbonization process, wherein the splint is made of a porous and breathable material which has high temperature resistance and is not easy to deform, and is preferably foamed nickel.

In a fourth aspect, the present invention provides a metal-air battery, the negative electrode material of which comprises the gas diffusion electrode of any one of the second aspects.

A fifth aspect of the invention provides a fuel cell whose anode material comprises the gas diffusion electrode according to any one of the second aspects.

A sixth aspect of the present invention provides a carbon dioxide reduction device, the anode material of which comprises the gas diffusion electrode according to any one of the second aspects.

The seventh aspect of the invention provides the use of a wood-based gradient wettability gas diffusion electrode which can increase the current density of the electrode and accelerate gas conduction.

Compared with the prior art, the invention has the following beneficial effects:

(1) the art generally uses carbon fiber paper as a carrier for catalysts to construct gas diffusion electrodes. The invention adopts the wood transverse cutting sheet material to prepare the gas diffusion layer material, and has the advantages of low cost, wide raw material sources, easy acquisition and the like. What is more important is that: gas diffusion electrodes conventional in the art typically have an uncontrolled tortuous pore structure. The carbonized wood transverse section material is adopted as the electrode substrate, the original vertical pore structure can be well maintained, the electrode substrate has the advantages of controllable pore diameter and pore distribution and the vertical pore structure, and compared with a zigzag pore structure, the wood substrate has a large number of micron-sized vertical pore structures which are more beneficial to gas conduction. And the existence of mesopores and micropores in the carbonized wood accelerates the gas conduction process.

(2) In the electrode wettability modification process in the field, the electrode is generally immersed into a PTFE solution, and is subjected to a full hydrophobic treatment by using PTFE. In a preferred technical scheme, the invention provides a novel gradient wettability modification method, and the two sides of the prepared gas diffusion layer material have wettability difference, namely the contact angle of the gas diffusion layer material shows gradient change in the thickness direction of the gas diffusion layer material, so that the length of a three-phase contact line is greatly increased, more reaction active sites are created, and the electrochemical performance of an electrode is improved.

In addition, the gradient wettability of the gas diffusion layer is more favorable for the directional transport of the gas. When the electrode is used as the cathode of the aluminum-air battery, the hydrophilic side of the electrode is contacted with the electrolyte, and the hydrophobic side of the electrode is contacted with the air, so that the electrolyte can enter and the air can be transmitted more favorably.

(3) The gas diffusion layer material is carbonized wood and has high strength. However, the existing method cannot artificially synthesize the material with the three-level pore structure of micron-sized pores, 6-10 nm mesopores and 1-5 nm micropores, such as carbonized wood, wherein in the micron-sized pores, the macropores are dispersedly distributed on a substrate mainly composed of the micropores. In addition, if the material having a pore structure is synthesized using a spin-on freezing method, the strength of the material is much lower than that of carbonized wood, and the material is not durable.

(4) Compared with the traditional carbon fiber paper-based air electrode loaded with the cobalt-nitrogen carbon nano tube, the gradient wettability gas diffusion electrode based on wood prepared by the invention not only has good air permeability and aperture improved, but also has obviously improved oxygen reduction performance under an alkaline system. When the method is used for preparing the electrode material of the aluminum-air battery, the power density of the battery is good.

Drawings

FIG. 1 is a schematic view of the process flow of the present invention for preparing a wood-based gradient wettability gas diffusion electrode.

Fig. 2 is a SEM top view of the carbonized wood material obtained in step a of example 2.

Fig. 3 is a SEM side view of the carbonized wood material obtained in step a of example 2.

FIG. 4 is a SEM top view of a wood-based gradient wettability gas diffusion electrode prepared in example 2.

FIG. 5 is an SEM side view of a wood-based gradient wettability gas diffusion electrode made in example 2.

FIG. 6 is the contact angle of the wood-based gradient wetting gas diffusion electrode prepared in example 2.

Fig. 7 is a SEM top view of the carbon fiber paper-based gas diffusion electrode prepared in comparative example 1.

Fig. 8 is a SEM side view of the carbon fiber paper-based gas diffusion electrode prepared in comparative example 1.

FIG. 9 is N of the electrode obtained in example 2 and comparative example 1₂Adsorption-desorption isotherms, inset pore size distribution (from N using BJH method)₂Isotherm adsorption branching calculated).

Fig. 10 is a comparative graph of gas permeability analysis of the electrodes prepared in example 2 and comparative example 1.

Fig. 11 is a graph of a linear scan of the F element of the electrode produced in example 2.

FIG. 12 is a fluorescence distribution diagram of a fluorescence confocal microscope of the electrodes prepared in example 2 and comparative example 1.

FIG. 13 is a physical digital image of the electrode prepared in example 2 in a liquid immersion test

FIG. 14 is a physical photograph of an electronic digital image of the electrode prepared in comparative example 1 in a liquid immersion test

FIG. 15 is a graph comparing ORR polarization curves of electrodes prepared in example 2 and comparative example 1.

Fig. 16 is a graph comparing the performance of the electrodes prepared in example 2 and comparative example 1 in an aluminum-air battery.

Fig. 17 is a test chart of practical application of the aluminum-air battery using the wood-based gradient wettability gas diffusion electrode cathode prepared in example 2.

Fig. 18 is an SEM top view of the gas diffusion electrode made of pine as a raw material according to example 4.

Fig. 19 is an SEM side view of the gas diffusion electrode made of white oak wood as a raw material according to example 4.

Fig. 20 shows the contact angle of the gas diffusion electrode made of pine as a starting material in example 4.

Figure 21 is the contact angle of the gas diffusion electrode made in example 4 as a white oak raw material.

FIG. 22 is a graph showing the gas permeability of two gas diffusion electrodes prepared in example 4 using pine and white oak as raw materials.

Fig. 23 is a comparative graph of ORR polarization curve tests for floating on electrolyte using two gas diffusion electrodes made from pine and white oak as raw materials, as made in example 4.

Detailed Description

The present invention will be described below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

The present invention is further illustrated by the following examples, but is not limited to these examples. The experimental methods not specified in the examples are generally commercially available according to the conventional conditions and the conditions described in the manual, or according to the general-purpose equipment, materials, reagents and the like used under the conditions recommended by the manufacturer, unless otherwise specified. The starting materials required in the following examples and comparative examples are all commercially available.

Example 1

The method of the present invention is described in detail with reference to the flow chart of the manufacturing process shown in fig. 1.

Firstly, high-permeability hard high-temperature-resistant materials such as foam metal and the like are assembled with selected wood to form a sandwich structure and fixed to form interlayer fixation. The purpose of the sandwich structure is to prevent the wood from generating a tortuous phenomenon caused by volatilization of substances in the carbonization process. And (3) naturally cooling the sandwich structure at the flow rate of protective gas argon gas of 50mL/min, the heating rate of 5 ℃/min, the temperature of 800 ℃, the carbonization time of 2 hours. Cutting the obtained carbonized wood substrate into 2 x 2cm pieces²Size material.

Then, 0.036-0.06 mol/L of methanol solution of cobalt salt and 0.36-0.6 mol/L of methanol solution of urea are mixed according to the volume ratio of 1: 1 preparing reaction mother liquor by a mixing and ultrasonic method, and putting the carbonized wood substrate material and the reaction mother liquor into a closed reaction kettle for hydrothermal reaction to obtain the carbonized wood material loaded with pink substances. And placing melamine at the bottom of the porcelain boat as a carbon source and a nitrogen source for reaction, wrapping the mouth of the porcelain boat with foamed nickel, placing the carbonized wood material loaded with pink substances on the foamed nickel, then covering the foamed nickel with another porcelain boat, raising the temperature to 600 ℃ in a tubular furnace at a heating rate of 5 ℃/min under the protection of argon gas, roasting for 60min, and naturally cooling to obtain the carbonized wood material loaded with the plush substances. The catalyst is grown by vapor deposition in the process, so that the catalyst can be uniformly dispersed on the surface and in the wood pore structure.

Next, the side of the carbonized wood material loaded with the fluff-like substance obtained was placed on a film of 5% strength PTFE solution for 5 min. And (3) after blowing the redundant PTFE solution from the dry side to the wet side by using a blower, raising the temperature of the sample to 350 ℃ at the heating rate of 5 ℃/min in a tubular furnace, roasting for 30min, and taking out the sample after roasting, thus obtaining the target air electrode.

The reason for adopting the carbonized wood material to be placed on the surface of the PTFE liquid film in a single side is to consider that the carbonized wood material has a vertical hole structure, and capillary tension is generated when the carbonized wood material is immersed in the single side, so that gradient distribution of the PTFE on one side of the carbonized wood material to the other side is promoted.

Example 2

This example 2 provides a specific method for preparing a gradient wettability gas diffusion electrode based on wood, which comprises the following steps:

a: a300 μm thick cherry cross-cut sheet material was assembled with nickel foam into a sandwich and secured. Carbonizing under the conditions that the argon flow rate is 50mL/min, the heating rate is 5 ℃/min, the temperature is increased to 800 ℃, and the heat preservation time is 2h, and then naturally cooling. The resulting samples were cut into 2 x 2cm pieces²And (5) sizing to obtain the carbonized wood material.

b: mixing 20ml of methanol solution dissolved with 0.29g of cobalt nitrate hexahydrate and 20ml of methanol solution dissolved with 0.6g of urea, transferring the mixture to a reaction kettle containing the carbonized wood material obtained in the step a after ultrasonic treatment, and sealing the reaction kettle. After the reaction is carried out for 12 hours in an oven at the temperature of 120 ℃, the reaction kettle is naturally cooled to the room temperature, and the carbonized wood material loaded with pink substances is taken out.

c: weighing 2g of melamine, placing the melamine at the bottom of a porcelain boat, wrapping the mouth of the porcelain boat with foamed nickel, placing the dried precursor on the foamed nickel, covering the foamed nickel with another porcelain boat, raising the temperature to 600 ℃ in a tube furnace at a heating rate of 5 ℃/min under the protection of argon, roasting for 60min, and naturally cooling. Thus obtaining the carbonized wood material loaded with the fluffy substance.

d: the carbonized wood material loaded with plush substances is placed on a 5 wt% PTFE (polytetrafluoroethylene) solution film for 5min at one side, and the polytetrafluoroethylene solution is sucked upwards under the action of capillary force. After blowing the excess PTFE solution from the dry side (i.e., the side not immersed in the PTFE solution) to the wet side (i.e., the side immersed in the PTFE solution) with a blower, the sample was heated to 350 ℃ at a heating rate of 5 ℃/min in a tube furnace, baked for 30min, and after baking, it was taken out to obtain a wood-based gradient-wetting gas diffusion electrode.

As can be seen from fig. 2 to 5, in the samples prepared in this example 2, the vertical pore structure and pore size distribution of the original wood were largely maintained after carbonization. Wherein the diameter of the larger vertical holes is distributed within the range of 40-60 microns, and the diameter of the smaller vertical holes is distributed within the range of 5-10 microns. And the surface hole clogging phenomenon caused by machining is relieved after carbonization. The carbonized wood material substrate is a vertical hole substrate consisting of small-size holes (5-10 microns), and large vertical holes (40-60 microns) are distributed on the substrate in a dispersing mode. These vertical holes present the advantage of low tortuosity. Vertical holes or low tortuosity holes are more conducive to gas transport.

And it is found from fig. 4 and 5 that the catalyst is uniformly dispersed, and the uniformly dispersed fluffy cobalt-nitrogen co-doped carbon nanotube catalyst appears on the outer surface and the inner part of the electrode pore structure.

FIG. 6 is the contact angle of the wood-based gradient wetting gas diffusion electrode prepared in example 2. The test result shows that: the contact angle of the gas diffusion electrode exhibited 83 ° on one side (the side not immersed in the PTFE solution, the hydrophilic side, denoted as side a) and 122 ° on the other side (the side immersed in the PTFE solution, the hydrophobic side, denoted as side B). Both sides had significant wettability differences.

The contact angles described herein are all droplet contact angles.

Comparative example 1

In addition, as a comparison, the present comparative example 1 provides a specific preparation method of a conventional air electrode based on carbon fiber paper: the difference from example 2 is that in step b, the carbonized wood material is replaced by carbon fiber paper; in the step d, the carbon fiber paper loaded with the fluffy substances is completely immersed on the PTFE solution film with the concentration of 0.1 wt% for 5 min.

As can be seen from fig. 7 and 8, in the sample prepared in comparative example 1, the electrode is formed by pressing fiber filaments with diameters of about 7 micrometers, the pore structure is random and variable, and the pore diameter is tortuous and variable, and the pore diameter is not selectable. The tortuous pores in this comparative example 1 are not conducive to gas transport.

Example 3

The pore size distribution, air permeability, F element distribution, gradient wettability, and electrochemical properties of the electrodes respectively prepared in example 2 and comparative example 1 were respectively tested and compared.

1. Pore size distribution:

fig. 9 is an N2 adsorption-desorption isotherm for testing of the electrodes prepared in example 2 and comparative example 1, respectively, with the inset being the pore size distribution (calculated from the N2 isotherm adsorption branch using the BJH method). Wherein, fig. 9a test sample is a carbon fiber paper based gas diffusion electrode prepared in comparative example 1; figure 9b test sample is a wood-based gradient wettability gas diffusion electrode prepared in example 2.

For the carbonized wood material, in addition to the micron-sized pores with regular surface can be seen through electron microscope images 2-3, in fig. 9b, the existence of a large number of mesopores (6-10 nm) and micropores (1-5 nm) can be seen from the pore size distribution data, and the mesopores and the micropores are caused by volatilization of substances in the carbonization stage, so that the substrate material with the hierarchical pore structure is finally formed. In contrast, in FIG. 9a, the carbon paper material only found pore structures centered around 15nm in the BET test.

2. And (3) analysis of air permeability:

Analysis of the permeability test we can demonstrate that the permeability of the wood-based gradient-wetting gas diffusion electrode is superior to that of the conventional carbon fiber paper-based air electrode under different pressures in the samples prepared in example 2 and this comparative example 1. The gas diffusion electrode of example 2 had a gas permeability of about 13mL/s at 80KPa, which was greater than that of the conventional air electrode of comparative example 1 (gas permeability of about 10 mL/s). This is due to the large number of micron-scale vertical pore structures of the wood substrate that are more conducive to gas conduction than the tortuous pore structure of carbon paper. And the existence of mesopores and micropores in the carbonized wood accelerates the gas conduction process.

3. F element distribution analysis:

FIG. 11 is a graph of a linear scan of the F element of the electrode prepared in example 2.

It can be proved by the analysis of the F element linear scan chart that in the electrode prepared in this example 2, the fluorine element is in gradient distribution from the B side to the a side of the electrode, and the content of the F element is in a gradient decreasing trend as a whole, that is, the polytetrafluoroethylene is in gradient distribution in the thickness direction of the electrode. The polytetrafluoroethylene with the gradient distribution and the low surface energy and the carbon material substrate with the high surface energy act together to ensure that the wettability behavior of the material is in a gradient distribution state. This property of the material is advantageous for the ability to capture gas in air, allowing gas to be transported from the gas-philic side to the gas-phobic side when the gas-philic side of the material is in contact with the gas.

4. Visual analysis of gradient wettability:

the electrode prepared in example 2 was subjected to immersion staining using a pirocin solution, and then placed under a fluorescence confocal microscope to observe a sample to obtain a fluorescence state. And (5) carrying out water distribution observation and analysis.

FIG. 12 is a fluorescent confocal microscope comparison of the electrode made in example 2 with the electrode made in comparative example 1. In the electrode of example 2, the fluorescence exhibited a hill-like protrusion from the electrode a side to the inside of the electrode, and the fluorescence disappeared near the electrode B side. This demonstrates that during immersion of the electrode, water also appears as a hill-like protrusion inside the electrode, exhibiting a gradient profile with a decreasing content from side a to side B. The existence of the gradient wetting property improves the contact area of the solution and the electrode.

Fig. 13 is a digital image of an electrode prepared in example 2 taken by a physical object in a liquid immersion test.

Fig. 14 is an electronic digital image of a real object in a liquid immersion test of the electrode prepared in comparative example 1.

As can be seen from fig. 13 and 14, in the electrodes prepared in example 2 and this comparative example 1, the electrode of example 2 was found to exhibit asymmetric properties by physically taking an electronic digital image in an immersion test, i.e., the a side was submerged in water as in fig. 13a, and the B side was covered with a gas film as in fig. 13B.

In contrast, the electrode of comparative example 1 was covered on both surfaces with a gas film.

This indicates that the both sides of the electrode of example 2 have different gas capturing capacities, and the a side can be sufficiently contacted with the electrolyte solution, while the B side cannot. Comparative example 1 the electrode had strong hydrophobic properties on both sides, making it difficult for the solution to make full contact with the carbon fiber paper.

Thus, the electrode of the present invention has a gradient wettability.

5. And (3) analyzing electrochemical properties:

the electrodes prepared in example 1 and comparative example 1 were used for the ORR polarization curve test floating on the electrolyte, respectively. The electrolyte solution was 0.1M KOH, the counter electrode was a platinum electrode, and the reference electrode was a saturated calomel electrode.

Fig. 15 is a graph comparing ORR polarization curves of the carbonized wood-based electrode prepared in example 2 and the carbon paper-based electrode prepared in comparative example 1.

As can be seen from fig. 15, the electrochemical performance of the electrode prepared in example 2 is more excellent, and the open circuit potential is represented by 0.78V. Reaches 27mA cm at the potential of 0V^-2The limiting current density is higher, the slope of the curve is larger, and the gas diffusion mass transfer performance is better. Whereas the electrode prepared in comparative example 1 had the same catalyst material, the open circuit potential still appeared to be 0.78V. But only reaches 23mA cm at the potential of 0V^-2The limiting current density, the curve slope is small, and the gas diffusion mass transfer performance is poor.

Application example 1

The carbonized wood-based electrode prepared in example 2 and the carbon paper-based electrode prepared in comparative example 1 were used for an aluminum-air battery negative electrode, respectively. The distance between the anode and the cathode of the aluminum-air battery is 10mm, 6M KOH solution is introduced between an anode aluminum plate and an air electrode by adopting a peristaltic pump, and the aluminum-air battery is assembled to form an aluminum-air single cell structure.

Fig. 16 is a graph comparing the performance of the carbonized wood-based electrode prepared in example 2 and the carbon paper-based electrode prepared in comparative example 1 in an aluminum-air battery.

As can be seen from fig. 16, the open circuit voltage of the electrodes prepared in example 2 and comparative example 1 was 1.9V in the working environment, but the carbonized wood-based electrode having the structural advantage exhibited a higher power density at 382mA · cm^-2Shows up to 267mW cm at operating current densities of^-2The power density of (a). And the carbon paper-based gas diffusion electrode with the same open-circuit voltage has a current density of 323mA cm^-2The maximum power density reached is only 236mW cm^-2Much lower than the electrochemical performance exhibited by air electrodes with gradient wettability.

Application example 2

Based on application example 1, the aluminum-air battery prepared in application example 1 with the carbonized wood-based electrode cathode prepared in example 2 was connected to a USB interface by using an appropriate circuit to form a quick-connect output of electric current.

Fig. 17 is a practical application test of the aluminum-air battery manufactured in application example 2. Fig. 17a shows a lighting test of the LED lamp, and fig. 17b shows an operation test of the electric fan.

The results show that: under the power of monocell, can successfully light the LED night-light that has the USB interface, also can make electronic little fan normal operating, at long-time working process, no matter be LED night-light or electronic little fan all not appear because of the phenomenon that the power is not enough to cause, equal steady operation.

Example 4

In order to fully show the universality of the scheme. The following experiments were carried out using a cross-cut sheet material of different kinds of wood (which includes pine, white oak) with a thickness of 300 μm as a raw material.

This example 4 provides a general preparation method of a gradient wetting gas diffusion electrode based on wood, which comprises the following steps: the difference from example 2 is that in step a, the cherry wood cross-cut sheet material was replaced with pine wood and white oak wood cross-cut sheets, respectively, and a gas diffusion electrode having a thickness of 300 μm using a pine wood cross-cut sheet as a raw material and a gas diffusion electrode using a white oak wood as a raw material were prepared, respectively.

The above two electrodes were subjected to structural characterization and performance testing, respectively, as in examples 2-3.

FIG. 18 is a SEM top view of a gas diffusion electrode made of transverse pine wood slices as a raw material according to example 4, which has a more dense and regular pore structure and no larger pore structure.

Fig. 19 is an SEM side view of the gas diffusion electrode made of white oak wood as a raw material according to example 4. It also has the structural feature of a large pore (50 μm) interspersed on a porous (≈ 10 μm) substrate, but its pore structure is larger compared to cherry cross-sliced materials.

Fig. 20 shows the contact angle of the gas diffusion electrode made of pine as a starting material in example 4. The electrode A side presents 88 degrees, the electrode B side presents 140 degrees, and the wettability difference is obvious

Figure 21 is the contact angle of the gas diffusion electrode made in example 4 as a white oak raw material. The electrode A side presents 48 degrees, the electrode B side presents 124 degrees, and the wettability difference is obvious

Fig. 22 demonstrates that: pine wood with smaller and dense pore structures has poorer air permeability, while white oak with larger pore structures has better air permeability. The reason is that pine having a more porous structure is less permeable to gas because the fluid flow rate is slower closer to the wall.

Fig. 23 is a comparative graph of ORR polarization curve tests for floating on electrolyte using two gas diffusion electrodes made from pine and white oak as raw materials, as made in example 4. The electrolyte solution was 0.1M KOH, the counter electrode was a platinum electrode, and the reference electrode was a saturated calomel electrode. In the test, the electrode A side was contacted with an electrolyte and the electrode B side was contacted with air.

As can be seen from FIG. 23, pine wood obtained in example 4The gas diffusion electrode (pine-based) as a raw material is more excellent in electrochemical performance, and the open circuit potential is represented by 0.78V. Reaches 22mA cm at the potential of 0V^-2The limiting current density is higher, the slope of the curve is larger, and the gas diffusion mass transfer performance is better. The gas diffusion electrode (oak-based) made from oak had the same catalyst material, so the open circuit potential was still represented as 0.78V. But only reaches 16mA cm at the potential of 0V^-2The limiting current density, the curve slope is small, and the gas diffusion mass transfer performance is poor.

Electrochemical performance is limited by two factors, first, good gas diffusion properties, which help to eliminate polarization, but performance degradation occurs at the expense of the reactive active area. In general, the balanced relationship between gas permeability and reactive area results in superior performance of gas diffusion electrodes made from pine wood to gas diffusion electrodes made from white oak wood.

Claims

1. A wood-based gas diffusion layer material, characterized in that the surface of the gas diffusion layer material consists of a number of vertical pores, and the gas diffusion layer material is carbonized wood.

2. The gas diffusion layer material of claim 1, wherein a plurality of large vertical holes and small vertical holes are distributed on the surface of the gas diffusion layer material, the diameter of each large vertical hole is 50-150 micrometers, the diameter of each small vertical hole is 5-30 micrometers, and the number of the small vertical holes is greater than that of the large vertical holes;

or only a plurality of small vertical holes with the diameter of 5-30 microns are distributed on the surface of the gas diffusion layer material.

3. The gradient wettability gas diffusion electrode based on wood is characterized by comprising a gas diffusion layer material and a catalyst loaded on the gas diffusion layer material, wherein the thickness of the gas diffusion layer material is 200-1000 micrometers, a vertical hole structure penetrating through the surface of the gas diffusion layer material is formed in the surface of the gas diffusion layer material, and the contact angle of the gas diffusion layer material is in gradient change in the thickness direction of the gas diffusion layer material.

4. The gas diffusion electrode according to claim 3, wherein the gas diffusion layer material surface of the gas diffusion electrode is distributed with a plurality of large vertical holes and small vertical holes penetrating through the gas diffusion layer material surface, the diameter of the large vertical holes is 50-150 micrometers, the diameter of the small vertical holes is 5-30 micrometers, and the number of the small vertical holes is larger than that of the large vertical holes;

or only a plurality of small vertical holes with the diameter of 5-30 microns are distributed on the surface of the gas diffusion layer material;

the gas diffusion layer is made of carbonized wood.

5. A preparation method of a gradient wettability gas diffusion electrode based on wood is characterized by comprising the following steps:

(3) gradient wettability modification: and (3) placing one side of the carbonized wood cross section loaded with the catalyst obtained in the step (2) on a low-surface-energy substance solution film for a period of time, drying redundant low-surface-energy substance solution from the dry side to the wet side of the carbonized wood cross section, and roasting to obtain the gas diffusion electrode.

6. The preparation method according to claim 5, wherein in the step (1), the thickness of the wood cross-section is 200-1000 microns; in the step (1), a plurality of large vertical holes and small vertical holes are distributed on the surface of the gas diffusion layer material of the wood transverse slice, the diameter of each large vertical hole is 50-150 micrometers, the diameter of each small vertical hole is 5-30 micrometers, and the number of the small vertical holes is larger than that of the large vertical holes.

7. A metal-air battery, characterized in that the negative electrode material of the battery comprises the gas diffusion electrode according to any one of claims 3 to 5.

8. A fuel cell, characterized in that a negative electrode material of the cell comprises the gas diffusion electrode according to any one of claims 3 to 5.

9. A carbon dioxide reduction device, characterized in that the negative electrode material of the device comprises the gas diffusion electrode according to any one of claims 3 to 5.

10. Use of a wood-based gradient-wetting gas diffusion electrode to increase the current density of the electrode and accelerate gas conduction.