CN112366324A

CN112366324A - Electrically chargeable air electrode with multi-layer functional structure and durable and stable structure and manufacturing method thereof

Info

Publication number: CN112366324A
Application number: CN202110049325.9A
Authority: CN
Inventors: 胡伟康; 钟依均; 刘强; 吕天喜
Original assignee: Zhejiang Normal University CJNU
Current assignee: Zhejiang Normal University CJNU
Priority date: 2021-01-14
Filing date: 2021-01-14
Publication date: 2021-02-12
Anticipated expiration: 2041-01-14
Also published as: CN112366324B

Abstract

The invention discloses an electric chargeable air electrode with a multilayer functional structure and durability and stability, which comprises the following components in sequence: the OER composite catalyst layer, the ORR catalyst layer, the current collector layer and the waterproof gas diffusion layer; the OER catalyst is arranged in a two-phase hydrophilic reaction catalytic area where the electrode is in contact with the electrolyte, and a large amount of oxygen and water vapor generated by charging can directly escape from the electrolyte, so that the OER catalyst is prevented from diffusing and accumulating into the electrode; the ORR catalyst layer is arranged in the electrode and between the waterproof gas diffusion layer and the OER composite catalyst layer, which not only can shorten the air diffusion distance, but also is beneficial to leading the hydrophilic OH generated by the oxygen reduction reaction^‑And the gas/solid/liquid three-phase interface inside the electrode is ensured to be stable in structure by diffusing to the OER hydrophilic layer. The electrode of the invention can reduce the polarization potential of OER reaction and eliminate carbon carrierElectrochemical oxidation corrosion and prevention of ORR catalyst oxidation dissolution or phase change at higher current density (not less than 20 mA/cm)²) The air electrode can be effectively and stably charged and discharged for a long time.

Description

Electrically chargeable air electrode with multi-layer functional structure and durable and stable structure and manufacturing method thereof

Technical Field

The invention belongs to the technical field of new energy materials, relates to an electrically chargeable air electrode and a manufacturing method thereof, and particularly relates to an electrically chargeable air electrode with a multi-layer functional structure and durability and stability and a manufacturing method thereof.

Background

The development of the metal-air battery with high specific energy density is matched with the national requirements for actively promoting the fields of metal-air battery research, engineering development and the like. The metal air battery mainly comprises zinc air, aluminum air, magnesium air and lithium air batteries, which have the advantages of high specific energy density, rich resources (except metal lithium resources), low price, no toxicity, no pollution, and the like, and exert the advantages of hydrogen fuel batteries, and the like, and are hot spots for researching novel energy batteries at home and abroad currently, wherein the design and manufacture of an air electrode structure, the selection of a catalyst and the like are still key problems in research.

The air electrode is a core component of the metal-air battery, the structural characteristics of the air electrode play an important and critical role in the performance of the metal-air battery, and the characteristics of the air electrode not only determine the dynamic performance of the metal-air battery, but also determine the charge-discharge efficiency of the metal-air battery and the service life of the metal-air battery. The main bottleneck of the current metal-air battery is the electricity chargeable and stable circulation, and the key for overcoming the bottleneck is to develop an efficient and durable electricity chargeable air electrode. Therefore, designing and manufacturing durable electrically chargeable air electrodes has great social and economic significance for developing practical applications of high-performance metal-air batteries and hydrogen fuel cells.

CN106784896A discloses a transition metal oxide high-dispersion doped porous carbon catalyst for zinc-air batteries, which adopts transition metal oxide (FexCoyNizO nanoparticles) as a bifunctional catalytic active component, and utilizes low-valent saccharides as a source of catalyst substrate carbon. In the preparation process of the catalyst, transition metal ions are uniformly dispersed in a viscous saccharide solution, then excessive alkaline hydroxide is added, and the mixture is subjected to vacuum or inert gas protectionCarbonizing at high temperature, and finally uniformly dispersing the transition metal oxide FexCoyNizO nano particles in the porous carbon carrier with high specific surface area. Compared with other metal oxide bifunctional catalysts (such as CN109802150A, ACS Energy Lett.2018,3,1183-1191 and the like), the technology avoids using expensive carbon nanotubes, graphene or carbon fibers as catalyst carriers, solves the problem of reducing the cost of raw materials of the catalyst carriers, and is beneficial to large-scale production. But at a current density of 10mA/cm²In the meantime, it was found that the overpotential of the Oxygen Evolution Reaction (OER) was 338mV, the overpotential was high, and the activity was not significantly improved. In addition, the catalyst carrier adopts a porous carbon material, so that the carbon material is easily oxidized and corroded in an alkaline medium in the reaction process of the high-overpotential OER, and the activity and the stability of the catalyst are degraded.

CN110247073A discloses an electrically chargeable zinc-air battery anode catalyst and a preparation method thereof. In order to improve the catalytic activity of the metal oxide, the scheme is that FeNi is adopted₃Adding a small amount of noble metal Pd element on Cx group to obtain FeNi₃C_x7% Pd composite catalyst, reported to have an Oxygen Reduction Reaction (ORR) Tafel slope of 56mV/dec vs. FeNi without palladium₃C_xThe Tafel slope of the catalyst is much smaller, indicating that the introduction of Pd greatly improves the ORR reaction kinetics performance of the catalyst. FeNi determination in Oxygen Evolution Reaction (OER)₃C_xTafel slope of 7% Pd composite catalyst electrode of 53mV/dec, less than commercial RuO₂The Tafel slope of the catalyst was 197mV/dec, indicating FeNi₃C_xThe 7% Pd composite catalyst has good dual-function catalytic activity in the process of OER/ORR bidirectional reaction. However, in the technology, noble metal Pd needs to be added into the catalyst, so that the cost of the composite catalyst is obviously increased; in addition, the bifunctional catalyst carrier is still a carbon-based material, and the carbon-based material has obvious oxidation corrosion phenomenon in the long-term OER reaction process of an alkaline medium, so that the cycle life of the electrode is influenced.

CN107768688A discloses a gas diffusion catalytic electrode, a preparation method thereof and application thereof in a rechargeable zinc-air battery. The technology is that the natural crystalline flake graphite, adhesive and solvent mixed slurry is spread on a porous metal matrix and dried to obtain the graphite composite electrode. The composite electrode is subjected to electrochemical oxidation to peel off natural flakes to obtain a graphite microchip, a metal manganese oxide catalyst is electrodeposited on the graphite microchip, and the waterproof and breathable film of the gas diffusion electrode is adhered to the other side of the porous metal substrate. The gas diffusion electrode has low cost, uses non-noble metal manganese oxide materials and has simple preparation process. However, the experimental result of the technology does not well solve the charge-discharge catalytic activity and long-term cycling stability of the metal zinc-air battery.

CN108630947A discloses a preparation method of cobalt sulfide/carbon nano-catalyst for rechargeable zinc-air battery. The technology reports that the cobalt sulfide/carbon nano composite material has a nano-size effect and high porosity, and the cobalt sulfide and the carbon material are tightly combined and can be cooperatively catalyzed. The composite material shows good catalytic property and reversibility in the charge and discharge processes of a battery. However, the catalytic properties and good reversibility are described only at a low current density of 10mA/cm²And test results of charge and discharge cycles in a very short time of 10 minutes. Not seen in the condition of higher current density ≧ 20mA/cm²And longer charging and discharging times of 1 hour cycle each. In addition, the catalyst support in this technique still employs a carbon-based material, and if there is also a high risk of oxidative corrosion of the carbon-based material at higher current and longer time of charging.

The OER reaction generates higher overpotential to initiate electrochemical oxidation corrosion (C +6 OH) of the carbon-based material of the catalyst carrier^-=CO₃ ^2-+3H₂O+4e^-) And may cause the catalyst to undergo oxidative dissolution or phase change to undergo a large volume change. In addition, the air electrode generates a large amount of oxygen and water vapor when the OER reaction is performed at a higher current density; with the increase of the number of charge-discharge cycles, oxygen and water vapor are accumulated inside the porous air electrode, and as a result, not only gas and ion diffusion channels inside the electrode are damaged, but also the gas/solid/liquid three-phase interface structure of the ORR liquid film layer is damaged, and finally the degradation of the ORR catalytic activity and the failure of the bidirectional function of the air electrode are caused.

CN105098292A discloses a horizontal three-electrode electrochemically chargeable zinc-air battery. AdoptThe oxygen precipitation reaction electrode and the oxygen reduction reaction electrode, namely two anodes, and a zinc-air battery system with three electrodes are formed by the oxygen precipitation reaction electrode and the oxygen reduction reaction electrode and the metal zinc cathode. The method can avoid the accumulation of oxygen and water vapor generated by the oxygen precipitation reaction electrode in the oxygen reduction reaction electrode during charging, prevent the damage to the physical structure of the oxygen and water vapor, and prolong the cycle life of the air electrode. Also, there are references to improving the cycling stability of batteries by using two positive electrodes (e.g., by using two positive electrodes)Nature Nanotechnology2015,10, 444-452), but because a three electrode cell system adds one electrode more than a two electrode cell system, the weight of the cell increases and the energy density of the cell decreases. Furthermore, the introduction of a third electrode also increases the cost of the battery and leads to a complexity of the battery structure.

In addition, there are many related studies, but in summary, the following defects basically exist in the prior art:

(1) the existing electrically inflatable air electrode often has the defects of an electrode structure, usually, oxygen is separated out and oxygen reduction reaction is carried out in the same catalytic area, a gas diffusion channel in the electrode is easily submerged during charging, the hydrophobic/hydrophilic ratio balance of a gas/solid/liquid three-phase interface in the electrode and a porous structure are damaged, and the degradation of the catalytic performance of oxygen reduction (ORR) is fast.

(2) The Oxygen Evolution Reaction (OER) produces a relatively high overpotential, especially at slightly high current densities (≧ 20mA/cm²) And the high reaction potential causes the oxidative dissolution or phase change of the catalyst and the electrochemical oxidation corrosion of the catalyst carrier carbon material, and finally leads the bidirectional functional electric chargeable performance of the air electrode to lose efficacy.

(3) The prior art of the electric chargeable air electrode only has the current density (5-10 mA/cm)²) And a charge-discharge cycle is performed for a short time (less than 1 hour per cycle) as shown in fig. 1 a. If the current density is higher (≧ 20 mA/cm)²) And its catalytic activity and stability are rapidly degraded under charge-discharge cycling conditions for a long time (20 hours per cycle), as shown in fig. 1 b.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide an electrically chargeable air electrode with a multi-layer functional structure and durability and stability and a manufacturing method thereof so as to solve the problems of repeated charge-discharge cycling stability and the like of the conventional air electrode under high current density.

The invention is realized by the following technical scheme:

an electrically inflatable air electrode of multilayer functional structure and durable stability, comprising, stacked in sequence: the device comprises a hydrophilic OER composite catalyst layer, a hydrophilic/hydrophobic ORR catalyst layer, a current collector layer and a waterproof gas diffusion layer;

the OER composite catalyst layer is a composite material layer of an OER catalyst and a first current collector and does not contain any carbon material; the OER catalyst is based on non-noble metal transition metals: mixtures of one or more of oxides, hydroxides, or other compounds;

the ORR catalyst layer comprises an ORR catalyst, activated carbon and a high polymer adhesive; the ORR catalyst is based on non-noble metal transition metals: mixtures of one or more of oxides, hydroxides, or other compounds;

the waterproof gas diffusion layer is made of hydrophobic high polymer materials or is formed by compounding organic adhesives and hydrophobic carbon.

In the above technical solution, further, the OER composite catalytic layer is in a porous distribution structure (i.e. artificial pores are formed on the catalytic layer), the ratio of the area of the pores to the geometric area of the catalytic layer is 1:30-1:85, and the pore structure is favorable for oxygen escape and mass transfer between liquid and solid generated at the interface between the OER catalytic layer and the ORR catalytic layer during charging; the thickness of the OER composite catalytic layer is 0.25-0.60 mm; the thickness of the ORR catalytic layer is 0.8-1.2 mm, and 40-60% of the ORR catalytic layer is of a hydrophilic structure and 60-40% of the ORR catalytic layer is of a hydrophobic structure according to the volume ratio so as to achieve gas-solid-liquid three-phase balance and stable distribution.

Furthermore, the load amount of the OER catalyst in the OER composite catalyst layer is 4-80mg/cm²(ii) a Preferably 10-50mg/cm²。

Further, the OER composite catalyst layer may be prepared by a sintering method, wherein the sintering method comprises:

dissolving an OER catalyst precursor material to form a solution, wherein the concentration of non-noble metal transition metal ions is 0.5-3.0M, cleaning a first current collector to remove grease, soaking the first current collector in the solution, sintering the solution at the temperature of 200-400 ℃ for 30-180 minutes, and repeating the soaking and sintering processes for 1-2 times; an OER composite catalytic layer was obtained.

Further, the OER composite catalytic layer can also be prepared by a paste coating method, which comprises:

dissolving an OER catalyst precursor material to form a solution, wherein the concentration of non-noble metal transition metal ions is 0.1-0.5M, adjusting the pH value to 8-11, cleaning and drying the precipitate, mixing the precipitate with an adhesive and ethanol, and stirring the mixture into a paste; and uniformly coating the obtained paste on the first current collector after cleaning and removing grease, and drying to obtain the OER composite catalyst layer.

Further, the loading amount of the ORR catalyst in the ORR catalyst layer is not more than 20.0mg/cm²(ii) a Preferably 8 to 15.0mg/cm²。

Further, the ORR catalytic layer has the following composition in percentage by mass:

not more than 20wt% ORR catalyst, 60-80wt% active carbon, 0-10wt% conductive additive, 10-30wt% high molecular adhesive; the active carbon can be selected from one or a mixture of more of carbot-XC-72R carbon black, carbot-XC-72 carbon black, BP2000 carbon black and acetylene black, the conductive additive can be selected from a mixture of more of conductive graphite powder, carbon nano tubes and graphene, preferably conductive graphite powder with low price, the polymer adhesive can be one or a mixture of more of polytetrafluoroethylene, polyvinylidene fluoride, styrene butadiene rubber and fluorinated ethylene propylene, preferably polytetrafluoroethylene.

Further, the preparation of the ORR catalytic layer includes the following steps:

(1) dissolving an ORR catalyst precursor material to form a solution, adding activated carbon, uniformly mixing, adjusting the pH value of the solution until metal ions precipitate, or transferring the adjusted solution to a hydrothermal reaction kettle for reaction after the pH value of the adjusted solution is adjusted, filtering to obtain a product, washing and drying to obtain a carbon composite catalyst; or, after obtaining the product, sintering the product at the temperature of 280-350 ℃ to obtain the carbon composite catalyst;

(2) adding distilled water into the carbon composite catalyst, wherein the weight ratio of the distilled water to the carbon composite catalyst is 80-160:12, and stirring to uniformly disperse;

(3) adding distilled water into the high molecular adhesive, wherein the weight ratio of the distilled water to the high molecular adhesive is 80-120:6, and stirring to form an aqueous solution;

(4) mixing the samples obtained in the step (2) and the step (3), magnetically stirring for 30-40 minutes, and then performing ultrasonic treatment for 30-40 minutes to uniformly disperse to obtain a mixed solution;

(5) placing the mixed solution in an oven, evaporating and drying at the constant temperature of 250-330 ℃ for 1-3 hours, naturally cooling to room temperature, and taking out; crushing the mixture to 30-100 microns by using a high-speed crusher, adding conductive carbon powder and a pore-forming agent, and uniformly mixing the mixture by using the high-speed crusher;

(6) adding an organic solvent into the mixed powder obtained in the step (5), and stirring until a paste mud mass is formed; the organic solvent is selected from one or more of kerosene, butanol, isopropanol, propanol and ethanol;

(7) and (3) rolling the paste mud pie in the step (6) for multiple times to be flaky by adopting a hot rolling process technology, wherein the temperature is 25-60 ℃ during hot rolling, and preparing sheets to obtain the ORR catalyst layer.

Further, the material selected for the current collector layer and the first current collector may be the same or different, and are selected from nickel foam, nickel mesh, stainless steel mesh and nickel-plated stainless steel mesh, and the thickness is 0.1-1.0mm, preferably 0.3-0.5 mm.

Further, the waterproof gas diffusion layer is composed of 45-60 wt% of acetylene black and 40-55 wt% of a high polymer adhesive. The polymer adhesive is one or more selected from polytetrafluoroethylene, polyvinylidene fluoride, styrene butadiene rubber and fluorinated ethylene propylene, preferably polytetrafluoroethylene.

Further, the preparation method of the air electrode comprises the following steps:

sequentially overlapping and assembling the OER composite catalyst layer, the ORR catalyst layer, the current collector layer and the waterproof gas diffusion layer, and holding the pressure for 2-20 minutes at 60-100 ℃ and 60-120 atmospheric pressure to form a primary air electrode; then annealing treatment is carried out at the temperature of 280 plus 330 ℃ in the nitrogen atmosphere, the porous structure is sintered, and a gas dispersion layer is superposed on the side, which is not covered by the waterproof gas diffusion layer, so as to obtain the electric chargeable air electrode with the bidirectional reaction function, the multi-layer function structure and the durability and stability.

Further, the gas dispersion layer may be a teflon film or a teflon cloth or a hydrophobic carbon cloth, and is preferably a teflon film.

The invention has the beneficial effects that:

(1) through the structural design, an Oxygen Evolution Reaction (OER) layer is arranged in a two-phase hydrophilic reaction catalytic region where an electrode is in contact with an electrolyte, and the current density is higher (not less than 20 mA/cm)²) Under the condition of charging for a long time, a large amount of generated oxygen and water vapor can directly escape from the electrolyte, so that the diffusion and accumulation to the inside of the electrode are prevented; and the ORR catalyst layer is arranged in the electrode, one side of the ORR catalyst layer is connected with the gas diffusion layer to shorten the air diffusion distance, and the other side of the ORR catalyst layer is connected with the OER composite catalyst layer to ensure that hydrophilic OH generated by the oxygen reduction reaction^-The diffusion to the OER hydrophilic layer is facilitated, and the stability of the gas/solid/liquid three-phase interface structure in the electrode is ensured.

(2) According to the invention, by synthesizing the OER composite catalyst layer and compounding the low-overpotential OER catalyst on the porous metal substrate, the electronic conductivity can be effectively increased, the polarization potential of OER reaction is reduced, the electrochemical oxidation corrosion of the carbon carrier is eliminated, and the oxidation dissolution or phase change of the ORR catalyst is prevented.

(3) The composite catalyst (OER catalyst layer and ORR catalyst layer) and the novel-structure electrically-chargeable air electrode designed by the invention can be used for realizing higher current density (≧ 20 mA/cm)²) The air electrode can be effectively and stably charged and discharged for a long time.

Drawings

FIG. 1a is a diagram of a rechargeable Zn-air cell using a CoO/N-CNT ORR and FeNi-LDH/CNT OER mixed catalyst as cathode catalyst at a current density of 5mA/cm²And 10mA/cm²Short cycle (200 seconds per cycle) cycle performance; FIG. 1b shows the use of a mixture of CoO/N-CNT ORR and FeNi-LDH/CNT OERRechargeable Zn-air battery with synthesized catalyst as cathode catalyst and with current density of 20mA/cm²Long cycle (20 hours per cycle) cycling performance: (Nature Communications, 2013, 4: 1805；Advanced Science (Weinh), 2018, 5(4): 1700691.）。

Fig. 2 is a schematic diagram of the multi-layer functional structure and durable and stable electrically chargeable air electrode structure of the present invention.

FIG. 3 is an XRD diffraction pattern of Co-deposited binary Ni-Co and ternary Ni-Co-Fe-LDHs OER catalysts.

FIGS. 4a and 4b illustrate co-deposited NiCo₂SEM images of the LDHs OER catalyst at different magnifications, wherein it can be seen that the catalyst nanosheets are about 2-3 nanometers thick and about 50 to 100 nanometers long.

FIG. 5 is a schematic representation of a binary NiCo formed by sintering₂O₄And ternary NiCo_1.8Fe_0.2O₄Catalyst XRD diffractogram. The crystal face indexes of the strongest peak, the second strongest peak and other diffraction peaks are all equal to those of the spinel structure NiCo₂O₄The peaks corresponding to the standard diffraction pattern are consistent.

FIG. 6 is an OER linear scan curve (LSV) of a 1N potassium hydroxide solution at room temperature (scan rate of 2mV/s, geometric reaction area of electrode exposed to electrolyte of 1cm²)。

FIG. 7 is an OER stable polarization curve (uncorrected iR voltage drop) for 6N potassium hydroxide solution at room temperature.

FIG. 8 is a graph of the ORR overpotential of an air electrode with a 12 cm square area exposed to an electrolyte in a 6NKOH solution with oxygen in air as a reactant at room temperature as a function of discharge current density.

The upper black curve in FIG. 9 is the air electrode discharge and charge potential versus cycle at a current density of 30 milliamps per square centimeter at 6NKOH solution at room temperature, with 1 hour each of discharge and charge, and oxygen in air as the reactant. The lower red line is the discharge and charge current versus cycle curve. The area of the electrode exposed to the electrolyte was 12 cm square.

The upper black curve in fig. 10 is the air electrode discharge and charge potential versus cycle at a current density of 20 milliamps per square centimeter at 6NKOH solution at room temperature, with 5 hours each of discharge and charge, with oxygen in air as the reactant. The lower red line is the discharge and charge current versus cycle curve. The area of the electrode exposed to the electrolyte was 12 cm square.

The upper black curve in fig. 11 is the air electrode discharge and charge potential versus cycle at a current density of 20 milliamps per square centimeter at 6NKOH solution at room temperature, with 10 hours each for discharge and charge, with oxygen in air as the reactant. The lower red line is the discharge and charge current versus cycle curve. The area of the electrode exposed to the electrolyte was 12 cm square.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and specific examples.

The multi-layer functional structure and the durable and stable electrically-chargeable air electrode structure of the present invention can be seen in fig. 2, which sequentially comprises an OER composite catalyst layer formed by an OER catalyst and a current collector I, an ORR catalyst layer, a current collector II, a moisture-proof Gas Diffusion Layer (GDL) and a gas dispersion layer; the OER composite catalyst layer has the high-efficiency oxygen precipitation reaction catalysis characteristic and generates an oxygen precipitation reaction during charging; the ORR catalyst layer has the catalytic characteristic of oxygen reduction reaction, and the oxygen reduction reaction is generated during discharging; the waterproof gas diffusion layer has the functions of freely diffusing reaction gas and preventing liquid from passing through; the gas dispersion layer has the functions of gas dispersion, controlling the humidity of the diffused gas and preventing liquid permeation; the current collector has excellent electron conductivity.

In the structure of the invention, the OER composite catalyst layer is arranged in a two-phase hydrophilic reaction catalyst area where the electrode is contacted with electrolyte; the ORR catalyst layer is arranged in the electrode, one side of the ORR catalyst layer is connected with the gas diffusion layer, and the other side of the ORR catalyst layer is connected with the OER composite catalyst layer; the current collector II is arranged between the ORR catalyst layer and the waterproof gas diffusion layer; the gas dispersion layer is on the side of the electrode in contact with air, and the moisture diffusion preventing layer is between the ORR catalyst layer and the gas dispersion layer.

The preparation process of the electrically chargeable air electrode can be as follows:

the OER composite catalyst layer can be prepared by adopting a sintering method or a paste coating method:

1.1. sintering process

(1) Weighing non-noble metal transition metal salt compounds, oxides or hydroxides into a reagent flask, adding distilled water or other solvents to form a solution, and controlling the total concentration of non-noble metal transition metal ions to be 0.5-3.0M, preferably 1.0-2.0M.

(2) And (3) ultrasonically cleaning an acetone solution to remove grease, dipping the solution in the current collector I, sintering at the temperature of 200-400 ℃, preferably at the temperature of 250-300 ℃, for 30-180 minutes, preferably for 60-120 minutes, and repeating the sintering process for 1-2 times to form the OER composite catalytic layer with uniform appearance.

1.2. Pasting method

1) Weighing non-noble metal transition metal salt compounds, oxides or hydroxides into a reagent flask, adding distilled water or other solvents to form a solution, and controlling the concentration of non-noble metal transition metal ions to be 0.1-0.5M, preferably 0.1-0.3M. Adjusting the pH value of the solution by using ammonia water under room temperature magnetic stirring, then dropwise adding potassium hydroxide to the pH value of 11, continuously and uniformly mixing by magnetic stirring, filtering the precipitate, washing the precipitate by using distilled water to remove other ions, and drying the precipitate at 80 ℃ to obtain the catalyst. Then the next step can be directly carried out or the next step can be carried out after the heat treatment is carried out at the temperature of 250-400 ℃.

2) Weighing a certain amount of the catalyst, the adhesive and the ethanol, mixing and stirring to form paste.

And (3) taking the current collector I, ultrasonically cleaning the current collector I in an acetone solution to remove grease, uniformly coating the paste on the current collector I, and drying in a vacuum box at 120 ℃ to form the OER composite catalyst layer.

Preparation of ORR catalytic layer:

(1) dissolving an ORR catalyst precursor material to form a solution, adding activated carbon, uniformly mixing, adjusting the pH value of the solution by using ammonia water until metal ions are precipitated, magnetically stirring and uniformly mixing, centrifugally separating and filtering a product, and washing the product by using distilled water to remove other ions; or after adjusting pH with ammonia water, transferring to hydrothermal reaction kettle for reaction, filtering the product, washing with distilled water to remove other ions, and drying to obtain carbon based on transition metal hydroxideComposite catalyst, or the obtained product is further processed by 280-350^oSintering at the temperature of C to obtain the carbon composite catalyst based on the transition metal oxide;

(2) adding distilled water into the prepared carbon composite catalyst, wherein the weight ratio of the distilled water to the carbon composite catalyst is 80-160:12, preferably 120:12, and magnetically stirring for 30-40 minutes to uniformly disperse;

(3) weighing the high molecular adhesive in a beaker, adding distilled water, wherein the weight ratio of the distilled water to the high molecular adhesive is 80-120:6, preferably 100:6, and magnetically stirring for 30-40 minutes to form an aqueous solution;

(4) mixing the samples obtained in the step (2) and the step (3) in a beaker, magnetically stirring for 30-40 minutes, and then performing ultrasonic treatment for 30-40 minutes to uniformly disperse to obtain a mixed solution;

(5) the obtained mixed solution is placed in an oven at 250-330^oC (preferably 280-^oC) Evaporating and drying in a constant temperature box for 1-3 hours, naturally cooling to room temperature, and taking out; crushing with high speed crusher to 30-100 μm, adding conductive additive, and mixing with high speed crusher for uniform dispersion;

(6) putting the mixed powder obtained in the step (5) into a beaker, adding an organic solvent (selected from kerosene, butanol, isopropanol, propanol, ethanol or a mixture of any of the above, preferably isopropanol) and continuously stirring until the mixture forms a paste-like paste mass;

(7) preparing the paste mud pie in the step (6) into an ORR catalyst layer by a hot rolling process technology: at a temperature of 25-60 deg.C^oC (preferably 35-40)^oC) Rolling on hot rolling machine for several times to obtain sheet catalyst layer with thickness of 0.5-1.2 mm, preferably 0.8-1.0 mm.

Preparing a waterproof gas diffusion layer:

(1) weighing the surface area to be 80m²Mixing and stirring acetylene black and absolute ethyl alcohol in a beaker according to the weight ratio of 3.0-8:100, preferably 5.5-6.0:100, and ultrasonically stirring in a water bath at 40-60 ℃;

(2) adding 60wt% of polytetrafluoroethylene suspension liquid, adding the polytetrafluoroethylene suspension liquid according to the weight ratio of the polytetrafluoroethylene suspension liquid to the weight ratio of acetylene black and absolute ethyl alcohol to be 7-12:100, preferably 9.0-10:100, and continuously stirring the mixture until the mixture is pasty;

(3) the paste of the step (2) is processed at the temperature of 40-60 DEG C^oC on a heated roller press, preferably at a temperature of from 45 to 50 deg.C^oAnd C, rolling for multiple times to form the sheet, and preparing the gas diffusion layer with the thickness of 0.6-1.4 mm, preferably 0.8-1.0 mm.

Preparing an air electrode:

sequentially overlapping and assembling the OER composite catalyst layer, the ORR catalyst layer, the current collector II and the waterproof gas diffusion layer at 60-100 deg.C^oC (preferably 80-90)^oC) And 60-120 atm (preferably 80-100 atm), and maintaining the pressure for 2-20 min to form a primary air electrode; then at 280-^oC（320-330^oC) Annealing treatment is carried out under nitrogen atmosphere to sinter the porous structure, and then a gas dispersion layer is added on the outer side of the waterproof gas diffusion layer, so as to finally obtain the electric chargeable air electrode with the bidirectional reaction function, the multi-layer functional structure and the durability and stability.

The embodiments and effects of the present invention are described below with reference to specific examples.

Example 1

Preparing an OER composite catalyst layer by an OER catalyst and paste coating method:

weighing nickel nitrate and cobalt nitrate (or ferric nitrate) and dissolving in 25ml of absolute ethyl alcohol to form a solution, magnetically stirring, and controlling the concentration of total metal ions to be 0.6-1.0M, wherein: the concentration ratio of nickel to cobalt ions is 2.5:5.0, or the concentration ratio of nickel, cobalt and iron ions is 2.5:4.5:0.5, 0.6N 60 ml of ammonia water is dripped into the mixed solution to the pH value of 8-9, the mixture is continuously and uniformly mixed by magnetic stirring, the coprecipitate is centrifugally separated, filtered and washed by distilled water to remove other ions, and the multicomponent transition metal hydroxide composite catalyst is obtained after drying at 80 ℃. The X-ray results are shown in fig. 3, and structural analysis indicates that the binary Ni-Co and ternary Ni-Co-Fe hydroxide catalysts have hydrotalcite-like layered hydroxide structures, consisting of layered double hydroxide LDH structures with alpha-phase (003) and (006) and (012) characteristic peaks, with crystal plane (003) d spacing between 7.8-8.05 a. Compared with beta-phase hydroxide, the alpha phase has larger interplanar spacing, and is beneficial to the transfer and diffusion of ions and water molecules during large-current charge and discharge. The scanning electron microscope analysis result shows that the binary hydroxide is composed of nanosheets with the thickness of 3-5 nanometers and the length of 50-100 nanometers, as shown in fig. 4a and 4 b. 0.8g of the above-mentioned fine powder of the polyvalent metal hydroxide catalyst was mixed with ethanol, and 0.75g of a 30wt% polytetrafluoroethylene emulsion was added dropwise and mixed and stirred to form a paste. Taking metal foam nickel with the size of 3.0 x 5.5 x 0.15cm, ultrasonically cleaning in acetone solution to remove grease, uniformly coating the paste on the foam nickel, and performing vacuum drying at 120 ℃ to form the OER composite catalyst layer.

Example 2

Preparing an OER composite catalyst layer by using an OER catalyst and a sintering method:

taking metal foam nickel with a porous three-dimensional structure with the size of 3.0X 5.5X 0.15cm as a current collector, ultrasonically cleaning an acetone solution for 30 minutes, corroding the acetone solution for 1 minute by dilute hydrochloric acid and washing the acetone solution for 3 times by distilled water, and then soaking the acetone solution into a solution containing nickel and cobalt ions, wherein the concentration ratio of nickel to cobalt ions is 1 (2-X) (X is more than or equal to 0 and less than or equal to 2) or soaking the acetone solution into an ethanol mixed solution containing nickel, cobalt and iron ions, wherein the concentration ratio of nickel, cobalt to iron ions is 1 (2-X) to X (X is more than or equal to 0.1 and less than or equal to 2); the concentration of total metal ions in the solution was 2.0M; soaking foamed nickel in the mixed ionic solution, sintering at 300 deg.C for 40 min, repeatedly soaking and sintering for 2 times to obtain OER composite catalyst layer with catalyst loading of 8-12mg/cm². X-ray structural analysis of the OER catalyst, as seen in FIG. 5, a binary NiCo₂O₄And ternary NiCo_1.8Fe_0.2O₄The oxides all form spinel structures after sintering at 300 ℃.

OER catalytic performance test evaluation:

the two OER composite catalyst layers prepared in examples 1 and 2 were each pressed at 10 atmospheres to form electrodes, one side of the electrode without active material (either side of the OER composite catalyst layer prepared by sintering) and the metal nickel lead were sealed with epoxy resin to avoid contact with the electrolyte, and after the electrodes were immersed in 1N potassium hydroxide solution at room temperature for half an hour, the LSV curve was scanned linearly (sweep rate was set to be at the sweep rate of 1N potassium hydroxide solution)2 mV/s) to evaluate the OER catalytic activity of the material. As can be seen in FIG. 6, the pasted (also referred to as co-deposition) process results in a ternary NiCo_1.8Fe_0.2The initial potential of the LDHs catalyst is 0.55V (relative to the HgO electrode) and is lower than that of the sintering method. At a current density of 50mA/cm²The catalyst obtained by the lower codeposition method requires a lower potential than the catalyst obtained by the sintering method, which shows that the catalyst synthesized by the codeposition method has better OER catalytic activity. Ternary NiCo synthesized by codeposition method_1.8Fe_0.2LDHs contains layered double hydroxide structure, has larger interlayer spacing and can expose more active sites, and metallic iron with various oxidation states is doped into binary metallic NiCo₂In the LDH host material, the electronic structure of the LDH host material can be adjusted, a large number of catalytic active sites can be ensured, iron in various valence states strongly interacts with other metals in an LDH matrix, the synergistic effect is enhanced, and the adsorption characteristic of oxygen-containing compounds in the OER process is adjusted, so that the catalytic activity is promoted.

FIG. 7 is an OER polarization curve measured by the stabilization method at 6N potassium hydroxide solution and high current density, and the results of the test show that the iron-containing ternary hydroxide shows a lower overpotential and that the co-precipitation method yields the iron-containing ternary NiCo_1.8Fe_0.2LDHs at a current density of 100mA/cm²The lower overpotential is 290mV, and the Tafel slope is 10-80mA/cm at the medium current density²The interval is 52mV/dec, and the current density is 100mA/cm²The above Tafel slope was 106 mV/dec.

Example 3

The preparation methods of the OER catalyst and the OER composite catalytic layer were the same as those of example 1.

The preparation process of the ORR catalyst and the ORR catalyst layer is as follows:

weighing 2.19g of nickel nitrate and 4.38g of cobalt nitrate, dissolving the nickel nitrate and the cobalt nitrate in 150mL of absolute ethanol solution, magnetically stirring and mixing the nickel nitrate and the cobalt nitrate uniformly at room temperature, weighing 12g of cabot XC-72 activated carbon, adding the cabot XC-72 activated carbon into the solution, magnetically stirring and mixing the mixture uniformly, adjusting the pH value of the solution to 8 by using 0.6M ammonia water, dropwise adding the solution to the pH value of 12 by using 0.5M KOH solution, after magnetically stirring and mixing the mixture uniformly, separating and filtering a product, washing the product by using distilled water to remove other ions, drying the product at 80 ℃, sintering the product at 300 ℃ for 2 hoursGrinding by a grinder, weighing the mixture and distilled water in a weight ratio of 12:100, weighing 60wt% of polytetrafluoroethylene emulsion and distilled water in a weight ratio of 6:100, respectively magnetically stirring for 30 minutes, then mixing and magnetically stirring for 30 minutes, then ultrasonically mixing for 30 minutes, then drying for 2 hours at 280 ℃ in an oven, crushing to 30-100 micrometers by a high-speed crusher, and then stirring for 2 minutes by a high-speed stirrer. Adding isopropanol solvent into the obtained mixture, making into paste, and heating at 35 deg.C^oAnd C, rolling for many times on a double-shaft rolling machine to form a sheet, and preparing the catalyst layer with the thickness of 1.0mm (wherein the polytetrafluoroethylene accounts for 20.7wt%, the catalyst accounts for 10.3wt%, and the activated carbon accounts for 69 wt%).

Preparation of a waterproof gas diffusion layer:

taking the surface area as 80m²Mixing acetylene black and ethanol at a weight ratio of 12:100, continuously stirring in 45 deg.C water bath under ultrasound, adding 60wt% polytetrafluoroethylene emulsion, wherein the weight ratio of 60wt% polytetrafluoroethylene emulsion to acetylene black is 1.66:1.0, continuously stirring to obtain paste, and heating at 45 deg.C to obtain the final product^oAnd C, rolling for many times on a hot rolling machine to form a sheet, and preparing the gas diffusion layer with the sheet thickness of 1.0 mm.

Preparing an air electrode:

sequentially overlapping the waterproof gas diffusion layer, the current collecting net, the ORR catalyst layer and the OER composite catalyst layer, and then stacking at 80 DEG C^oC, holding and pressing for 15 minutes under the atmospheric pressure of 90 ℃, pressing into a planar air electrode, then treating the air electrode for 2 hours at the high temperature of 320 ℃ in a nitrogen atmosphere, cooling, and then superposing a polytetrafluoroethylene film gas dispersion layer outside the waterproof gas diffusion layer to finally form the electrically-chargeable air electrode with a multi-layer functional structure with a bidirectional reaction function and durability and stability.

And (3) performance testing:

the air electrode uses oxygen in air as reactant, and is prepared by dissolving in 6N potassium hydroxide solution and 5-100mA/cm²The ORR polarization curve at room temperature is shown in FIG. 8 at different current densities of 5-20mA/cm²The ORR tafel slope is measured to be 80mV/dec at 100mA/cm²The ORR overpotential at current density was 355 mV. The air electrode electricity chargeable circulation performance test is carried out when the charging current density is 30mA/cm²And a discharge current density of 30mA/cm²The following was performed for 1 hour each of charge and discharge time, and the charge and discharge cycle was repeated 115 times, and the test results are shown in fig. 9, showing good OER and ORR reaction cycle stability.

Example 4

The preparation methods of the OER catalyst and the OER composite catalytic layer were the same as in example 2.

The preparation processes of the ORR catalyst, the ORR catalyst layer, the moisture-proof gas diffusion layer, and the air electrode were the same as those of example 3.

Testing the air electrode OER and ORR electric chargeable cycle performance: under the conditions of room temperature and 6N potassium hydroxide solution, taking oxygen in the air as an electrode reactant at 20mA/cm²The charge and discharge were carried out at current density for 10 hours per cycle, and the results of the charge and discharge cycle test are shown in FIG. 10. From the test results, it can be seen that the air electrode of the present invention also exhibits good OER and ORR charge-discharge cycle stability at higher current densities and over 300 hours of charge-discharge cycling for 10 hours per cycle.

Example 5

The preparation methods of the OER catalyst and the OER composite catalytic layer were the same as those in example 1.

The preparation process of the ORR catalyst and the catalytic layer is as follows:

weighing 1.83g of two crystal water cobalt oxalate and 1.79g of two crystal water ferrous oxalate, dissolving the two crystal water cobalt oxalate and the two crystal water ferrous oxalate in 125mL of distilled water and 30mL of absolute ethyl alcohol, uniformly mixing the two crystal water cobalt oxalate and the two crystal water ferrous oxalate at room temperature by magnetic stirring and ultrasonic waves, weighing 24g of cabot XC-72 activated carbon, adding the mixture into the solution by magnetic stirring and mixing, adjusting the pH value of the solution to 10 by ammonia water, performing magnetic stirring and refluxing at 80 ℃ for 10 hours, transferring the solution to a hydrothermal reaction kettle for reacting at 180 ℃ for 10 hours at constant temperature, performing suction filtration on the product, washing the product by distilled water to remove other ions, drying the product at 80 ℃, sintering the product for 2 hours at 320 ℃, taking out the product, polishing the product by a high-speed crusher, weighing the mixture and the distilled water according to the weight ratio of 12:100, weighing 60% by weight of polytetrafluoroethylene emulsion and the distilled water according to the weight ratio of 6:100, respectively performing magnetic stirring for 30, crushing to 30-100 μm with high-speed pulverizer,then stirred for 2 minutes by a high-speed stirrer. Adding isopropanol solvent into the obtained mixture, making into paste, and heating at 35 deg.C^oAnd C, rolling for many times on a biaxial roller press to form a sheet, and preparing the catalyst layer with the thickness of 1.2 mm (wherein the polytetrafluoroethylene accounts for 21.4wt%, the catalyst accounts for 7.2wt%, and the activated carbon accounts for 71.4 wt%).

The preparation processes of the gas diffusion layer and the air electrode were respectively the same as those of example 3.

Air electrode OER and ORR reaction cycle performance testing: under the conditions of room temperature and 6N potassium hydroxide solution, taking oxygen in the air as an electrode reactant at 20mA/cm²The charge and discharge were carried out at current density for 20 hours per cycle, and the results of the charge and discharge cycle test are shown in FIG. 11. The air electrode is subjected to repeated charge-discharge cycles for 600 hours, and test results show that the electrocatalyst synthesized by the invention and the manufactured electrically chargeable air electrode show very good OER and ORR cycle stability performance.

Claims

1. An electrically inflatable air electrode of multilayer functional structure and durable stability, characterized in that it comprises, in succession superimposed: the device comprises a hydrophilic OER composite catalyst layer, a hydrophilic/hydrophobic ORR catalyst layer, a current collector layer and a waterproof gas diffusion layer;

2. The electrically chargeable air electrode with multi-layer functional structure and durable stability as claimed in claim 1, wherein the OER composite catalyst layer has holes thereon, and is in porous distribution structure, and the ratio of the area of the holes to the geometric area of the catalyst layer is 1:30-1:85, so as to facilitate the oxygen evolution and mass transfer between liquid and solid generated at the interface of the OER and ORR catalyst layers during charging; the thickness of the OER composite catalytic layer is 0.25-0.60 mm; the ORR catalytic layer has a thickness of 0.8-1.2 mm, and 40-60% of the ORR catalytic layer is hydrophilic and 60-40% of the ORR catalytic layer is hydrophobic.

3. The multi-layer functional structure and durable stable electrically chargeable air electrode of claim 1, wherein said OER composite catalyst layer is prepared by a sintering process comprising:

4. The multi-layer functional structure and durable stable electrically chargeable air electrode of claim 1 wherein said OER composite catalytic layer is prepared by a pasting method comprising:

dissolving an OER catalyst precursor material to form a solution, wherein the concentration of non-noble metal transition metal ions is 0.1-0.5M, adjusting the pH value to 8-11, filtering, cleaning and drying the precipitate, mixing with an adhesive and ethanol, and stirring to form a paste; and uniformly coating the obtained paste on the first current collector after cleaning and removing grease, and drying to obtain the OER composite catalyst layer.

5. The electrically chargeable and air-filled electrode with multi-layer functional structure and durable stability according to claim 1, wherein the ORR catalyst layer has an ORR catalyst loading of not more than 20.0mg/cm²。

6. The multi-layer functional structure and durable stable electrically chargeable air electrode of claim 1, characterized in that the composition of the ORR catalytic layer comprises, in mass percent:

contains ORR catalyst, active carbon 60-80wt%, conductive additive 0-10wt% and polymer adhesive 10-30 wt%.

7. The multi-layer functional structure and durable stable electrically chargeable air electrode of claim 6, wherein the preparation of the ORR catalyst layer comprises the following:

(5) placing the mixed solution in an oven, evaporating and drying at the constant temperature of 250-330 ℃ for 1-3 hours, naturally cooling to room temperature, and taking out; crushing the mixture to 30-100 microns by using a high-speed crusher, adding a conductive additive in proportion, and uniformly mixing the mixture by using the high-speed crusher;

8. An electrically chargeable and air-chargeable electrode with multi-layer functional structure and durable stability according to claim 1, characterized in that the material of the current collector layer is the same or different from the first current collector, and is selected from nickel foam, nickel mesh, stainless steel mesh and nickel-plated stainless steel mesh, and the thickness is 0.1-1.0 mm.

9. The electrically chargeable air electrode with multi-layer functional structure and durable stability as claimed in claim 1, wherein the moisture diffusion preventing layer is composed of 45-60 wt% of acetylene black and 40-55 wt% of polymer binder.

10. The multilayered functional structure and durable stable electrically chargeable air electrode according to claim 1, characterized in that the air electrode is prepared by a method comprising: