Composite electrode and its preparation method and application

Abstract

The present invention relates to the field of liquid flow batteries in chemical energy storage technology, and specifically to a composite electrode, its preparation method, and application. The composite electrode comprises: a stacked catalytic section and a diffusion section, the catalytic section comprising at least one stacked catalytic layer, the diffusion section comprising at least one stacked diffusion layer, the catalytic layer being a heteroatom-co-doped carbon nanotube film, and the diffusion layer being a carbon-based electrode; wherein the heteroatom comprises a non-metal atom I and a non-metal atom II, wherein the non-metal atom I is nitrogen, and the non-metal atom II is selected from at least one of P, B, and S. Using the heteroatom-co-doped carbon nanotube film with a high specific surface area and high porosity as the catalytic layer significantly reduces resistivity and increases the effective utilization area and active sites of the composite electrode. Furthermore, using the composite electrode in a liquid flow battery can improve the battery's electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the field of liquid flow batteries in chemical energy storage technology, and in particular to a composite electrode and a preparation method and application thereof. Background Art

[0002] Liquid flow batteries are a large-scale electrochemical energy storage technology. Compared to other energy storage technologies, they offer advantages such as high energy conversion efficiency, flexible system design, large storage capacity, site selection flexibility, deep discharge capability, safety, environmental friendliness, and low maintenance costs. They are widely used in renewable energy generation and storage, such as wind and solar power, emergency power systems, backup power stations, and peak load shifting for power systems. Currently, the most mature liquid flow battery system is the all-vanadium liquid flow battery, but its cost is relatively high. The cost of the vanadium electrolyte, in particular, fluctuates significantly with the market, sometimes accounting for up to 50% of the material cost of the flow battery. Zinc-iron liquid flow batteries, a new type of hybrid flow battery, utilize the abundant raw materials of zinc and iron, offering low cost, high safety, excellent stability, and a simple structure and manufacturing process. However, due to the alkaline or weak acid supporting electrolyte used in the electrolyte system, the conductivity of zinc-iron liquid flow batteries is significantly lower than that of the sulfuric acid solution used for all-vanadium. Furthermore, the zinc negative electrode suffers from dendrites, resulting in high ohmic internal resistance and polarization, resulting in low operating current density and energy efficiency.

[0003] As a key component of flow batteries, electrode materials' conductivity, porosity, pore structure, and electrochemical catalytic activity influence the battery's ohmic polarization, concentration polarization, and electrochemical polarization, thereby affecting the battery's operating current density and energy efficiency. Currently, carbon paper or carbon felt, the electrode materials commonly used in zinc-iron flow batteries, suffer from low conductivity, poor hydrophilicity, a small effective surface area, and low operating current density.

[0004] CN110316720A discloses a method for preparing a sulfur- and nitrogen-doped carbon nanotube film, comprising: 1) adding a carbon source, a catalyst, a sulfur source, and a nitrogen source to a beaker with mixing and stirring, and stirring until completely dissolved to obtain a mixed solution; 2) heating and venting, heating a high-temperature furnace while simultaneously introducing an inert gas into the high-temperature furnace and a collection box, and then introducing hydrogen after the high-temperature furnace reaches the target temperature; 3) forming a tube, loading the mixed solution into a propeller and pushing the solution into the high-temperature furnace at a constant rate to obtain fibrous sulfur- and nitrogen-doped carbon nanotubes; and 4) placing the fibrous sulfur- and nitrogen-doped carbon nanotubes into a nanotube film apparatus to obtain a fibrous sulfur- and nitrogen-doped carbon nanotube film with a thickness of 20-80 μm. However, this method is cumbersome to prepare, requires high-temperature treatment (which reduces material stability and lifespan), and easily destroys the original structure of the carbon nanotubes. It does not address or disclose the properties of the doped carbon nanotube film, the content and distribution of heteroatoms, or its application areas.

[0005] CN104319406A discloses a method for preparing high-performance composite carbon felt for all-vanadium liquid flow batteries. Commercial carbon felt is used as raw material and a bonding method of an adhesive is used to prepare functionalized carbon tube composite carbon felt. Functional group carriers such as p-aminobenzenesulfonic acid, p-aminobenzoic acid, p-phenylenediamine, tetrabromoaniline, p-aminophenylboronic acid, and p-aminophenylphosphonic acid are used for treatment. However, the previous methods for preparing composite electrodes using carbon nanotubes and carbon felt all used carbon nanotube powder, and the powder was unevenly distributed or not tightly bonded to the carbon felt matrix, causing the powder to fall off after long-term operation. In addition, chemical methods such as strong acid were used for functionalization, and high-temperature treatment (>500°C) would affect the original structure of the carbon nanotubes, and it was easy to cause agglomeration between the carbon nanotubes during the treatment process.

[0006] CN106558704A discloses a gradient electrode for a flow battery. The electrode is composed of at least two layers of graphite fibers or carbon fiber felts with different bulk densities, stacked in ascending order of bulk density, and integrated by longitudinal needling perpendicular to the electrode surface. This electrode can effectively reduce the electrical resistance of the electrode itself, reduce the flow resistance of the electrolyte, and provide more reaction sites, ultimately reducing the ohmic polarization, electrochemical polarization, and concentration polarization of the flow battery. This improves the energy efficiency and voltage efficiency of the all-vanadium flow battery, thereby increasing its operating current density. However, this method still uses graphite or carbon fiber as the electrode material, which is relatively coarse and has a low effective area.

[0007] Therefore, there is an urgent need for a composite electrode for liquid flow batteries, which has strong hydrophilicity, low resistivity, and high specific surface area, thereby increasing the effective utilization area of ​​the electrode and catalytic activity. Summary of the Invention

[0008] The purpose of the present invention is to overcome the problems of low conductivity, poor hydrophilicity, small effective utilization area, etc. of carbon electrodes used in liquid flow batteries, as well as the problems of uneven distribution, loose adhesion, easy falling off, and easy agglomeration of carbon nanotubes in composite electrodes containing carbon nanotubes and carbon electrodes. A composite electrode and its preparation method and application are provided. On the basis of maintaining the original structure of the carbon nanotubes, the composite electrode makes the carbon nanotube film evenly distributed on the carbon electrode, thereby improving the conductivity and electrochemical activity of the composite electrode; at the same time, the method is simple, easy to implement, environmentally friendly and pollution-free.

[0009] To achieve the above objectives, the present invention provides a composite electrode in a first aspect, comprising: a stacked catalytic section and a diffusion section, wherein the catalytic section comprises at least one stacked catalytic layer, the diffusion section comprises at least one stacked diffusion layer, the catalytic layer is a heteroatom co-doped carbon nanotube film, and the diffusion layer is a carbon-based electrode;

[0010] The heteroatoms are non-metal atom I and non-metal atom II, the non-metal atom I is N, and the non-metal atom II is selected from at least one of P, B and S.

[0011] A second aspect of the present invention provides a method for preparing a composite electrode, the method comprising the following steps:

[0012] (1) subjecting a carbon nanotube film and a mixed gas to plasma treatment to obtain a heteroatom co-doped carbon nanotube film;

[0013] (2) compounding at least one layer of the heteroatom co-doped carbon nanotube film, optionally at least one layer of carbon nanotube film, and at least one layer of carbon-based electrode to obtain a composite electrode;

[0014] The mixed gas contains heteroatom-containing gas and inert gas, the heteroatom-containing gas is a gas containing non-metallic atom I and a gas containing non-metallic atom II, the non-metallic atom I is N, and the non-metallic atom II is selected from at least one of P, B and S.

[0015] A third aspect of the present invention provides use of the composite electrode provided in the first aspect and / or the composite electrode produced by the method provided in the second aspect in a liquid flow battery.

[0016] Compared with the prior art, the present invention has the following technical effects:

[0017] (1) Compared with a single electrode, the composite electrode provided by the present invention contains a catalytic section, and the catalytic section is defined as comprising at least one catalytic layer arranged in a stacked manner, and the catalytic layer is a heteroatom co-doped carbon nanotube film. That is, the heteroatom co-doped carbon nanotube film having a high specific surface area and high porosity is used as the catalytic layer, which significantly reduces the resistivity and increases the effective utilization area and active sites of the composite electrode;

[0018] (2) The carbon nanotubes in the composite electrode provided by the present invention exist in the form of a thin film, have good structure and stability, and do not fall off as the operating time increases;

[0019] (3) The preparation method of the composite electrode provided by the present invention adopts plasma treatment, so that the original specific surface area, pore structure and morphology of the carbon nanotube film are not destroyed, the surface defects are increased, the conductivity and electrochemical activity of the composite electrode are improved, the polarization of the battery is reduced, and the operating current density and energy efficiency of the battery are improved; at the same time, this method can achieve heteroatom co-doping under low temperature conditions, is mild and controllable, simple to operate, environmentally friendly and pollution-free, and can easily realize large-scale sample processing;

[0020] (4) The composite electrode provided by the present invention is used in a liquid flow battery, which increases the catalytic property of the electrode, promotes the diffusion of the electrolyte, and improves the battery performance; specifically, at least one layer of heteroatom co-doped carbon nanotube film serves as a catalytic segment to catalyze the electrolyte reaction, and at least one layer of carbon-based electrode serves as a diffusion segment to facilitate the diffusion of the electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the cross-sectional structure of the composite electrode provided by the present invention;

[0022] Figure 2 is a SEM image of the nitrogen-sulfur co-doped carbon nanotube S1 in Example 1;

[0023] Figure 3 is a SEM image of carbon paper P1 after pretreatment in Example 1. DETAILED DESCRIPTION

[0024] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0025] A first aspect of the present invention provides a composite electrode comprising: a stacked catalytic section and a diffusion section, wherein the catalytic section comprises at least one stacked catalytic layer, the diffusion section comprises at least one stacked diffusion layer, the catalytic layer is a heteroatom co-doped carbon nanotube film, and the diffusion layer is a carbon-based electrode;

[0026] The heteroatoms are non-metal atom I and non-metal atom II, the non-metal atom I is N, and the non-metal atom II is selected from at least one of P, B and S.

[0027] The inventors of the present invention have discovered that existing carbon nanotubes typically exist in powder form, making them difficult to shape, unstable when composited onto carbon electrodes, and unevenly distributed. However, the use of electrodes such as carbon nanotube films composited with carbon felt, which have excellent film strength and hydrophilicity, solves the problems of poor distribution uniformity, strength, and toughness associated with carbon nanotube powder. Furthermore, the carbon nanotube film is surface-treated with plasma and co-doped with nitrogen, phosphorus, boron, and sulfur, particularly nitrogen and sulfur. A composite electrode is then constructed using a certain number of catalytic layers (heteroatom co-doped carbon nanotube films) and a certain number of diffusion layers (carbon electrodes). This significantly reduces the resistivity of a single electrode. Furthermore, the use of a high-surface-area carbon nanotube film as a catalytic layer increases the effective utilization area of ​​the composite electrode, resulting in higher catalytic performance and improved battery performance.

[0028] In the present invention, the composite electrode is composed of a catalytic section and a diffusion section arranged in a stacked manner, and the catalytic section contains at least one catalytic layer arranged in a stacked manner, and the diffusion section contains at least one diffusion layer arranged in a stacked manner, wherein the catalytic layer is a carbon nanotube film co-doped with heteroatoms, and the diffusion layer is a carbon electrode.

[0029] In the present invention, unless otherwise specified, the heteroatom includes at least one selected from P, B and S and N.

[0030] In some embodiments of the present invention, the heteroatoms are preferably selected from N and P, N and S, N and B, preferably selected from N and P, N and S, and more preferably N and P. The preferred conditions are used to increase the surface defects of the carbon nanotube film, thereby increasing the effective utilization area and active sites of the catalytic layer.

[0031] In the present invention, the composite electrode contains oxygen atoms in addition to heteroatoms and carbon atoms; wherein the content of oxygen atoms in the composite electrode is 0.5-2 wt %.

[0032] In some embodiments of the present invention, preferably, based on the total mass of the heteroatom co-doped carbon nanotube film, the content of the heteroatom is 1-30 wt %, preferably 5-20 wt %.

[0033] In some embodiments of the present invention, preferably, the molar ratio of the non-metal atom I to the non-metal atom II is 1:0.01-1, preferably 1:0.1-0.5. The preferred molar ratio is more conducive to improving the overall performance of the composite electrode, that is, hydrophilicity and electrochemical performance.

[0034] In some embodiments of the present invention, preferably, the thickness of the catalytic segment accounts for 0.5-30%, preferably 2-15% of the thickness of the composite electrode. In the present invention, the thickness of the catalytic segment is related to the ohmic polarization of the composite electrode.

[0035] To improve the catalytic efficiency and diffusion efficiency of the electrolyte, the composite electrode provided by the present invention has different bulk densities and porosities for the catalytic layer and the diffusion layer. Specifically, the bulk density of the catalytic layer is greater than that of the diffusion layer, and the porosity of the catalytic layer is less than that of the diffusion layer.

[0036] In the present invention, compared with the carbon nanotube film, the catalytic layer provided by the present invention, ie, the heteroatom co-doped carbon nanotube film, can significantly increase the specific surface area and hydrophilicity of the carbon nanotube film.

[0037] In some embodiments of the present invention, preferably, the bulk density of the catalytic layer is 0.6-0.75 g / cm 3 , preferably 0.6-0.7g / cm 3 ; Porosity is 30-55%, preferably 45-55%; Specific surface area is 10-100g / cm 3 , preferably 60-100g / cm 3 ; The contact angle is 0-100°, preferably 0-20°.

[0038] In the present invention, the bulk density parameters of the catalytic layer, transition layer and diffusion layer are all measured by a density tester; the porosity parameters of the catalytic layer, transition layer and diffusion layer are all measured by a porosimeter; the specific surface area parameters of the catalytic layer are measured by nitrogen adsorption; and the contact angle parameters of the catalytic layer are measured by a contact angle tester.

[0039] In some embodiments of the present invention, preferably, the bulk density of the diffusion layer is 0.1-0.45 g / cm 3 , preferably 0.2-0.45g / cm 3 ; The porosity is 75-95%, preferably 75-90%.

[0040] In some embodiments of the present invention, preferably, the composite electrode further comprises a transition section. Further preferably, the transition section is disposed between the catalytic section and the diffusion section, and the transition section comprises at least one stacked transition layer.

[0041] In some embodiments of the present invention, preferably, the transition layer is a carbon nanotube film. It is worth noting that the transition layer is an unmodified carbon nanotube film, and the catalytic layer is a heteroatom-doped carbon nanotube film.

[0042] In the present invention, the bulk density of the transition layer is between that of the catalytic layer and the diffusion layer, and the porosity of the transition layer is between that of the catalytic layer and the diffusion layer. In the present invention, the transition layer is designed to maintain a certain level of electrocatalytic activity while effectively transferring the reactants and products from the catalytic layer to the diffusion layer.

[0043] In some embodiments of the present invention, preferably, the bulk densities of the catalytic layer, the transition layer, and the diffusion layer decrease in sequence, and the porosities of the catalytic layer, the transition layer, and the diffusion layer increase in sequence.

[0044] In some embodiments of the present invention, preferably, the bulk density of the transition layer is 0.45-0.6 g / cm 3 , preferably 0.45-0.55g / cm 3 ; The porosity is 55-75%, preferably 55-70%.

[0045] In the present invention, the transition layer is an unmodified carbon nanotube film. The source of the carbon nanotube film can be selected from a wide range of sources, as long as it meets the above-defined property parameters. The carbon nanotube film can be purchased or prepared, which is not detailed in the present invention.

[0046] In some embodiments of the present invention, there is no particular limitation on the carbon-based electrode. Preferably, the carbon-based electrode is selected from at least one of carbon felt, graphite felt, carbon cloth, and carbon paper.

[0047] In some embodiments of the present invention, preferably, the composite electrode further comprises a proton exchange membrane, and the composite electrode comprises: a catalytic section, a transition section, a diffusion section and a proton exchange membrane stacked in sequence. Figure 1 As shown, the cross-sectional view of the composite electrode provided by the present invention includes: a catalytic section, a transition section, a diffusion section and a proton exchange membrane stacked in sequence; wherein, the catalytic section includes a stacked catalytic section, the transition section includes a stacked transition layer, and the diffusion section includes a stacked diffusion layer.

[0048] In some embodiments of the present invention, preferably, the resistivity of the composite electrode is less than 50 mΩ / cm 2 , preferably ≤5mΩ / cm 2 ; Contact angle ≤ 20°, preferably 0-20°.

[0049] In the present invention, the resistivity of the composite electrode is measured using a resistance meter; and the contact angle of the composite electrode is measured using a contact angle tester.

[0050] A second aspect of the present invention provides a method for preparing a composite electrode, the method comprising the following steps:

[0051] (1) subjecting a carbon nanotube film and a mixed gas to plasma treatment to obtain a heteroatom co-doped carbon nanotube film;

[0052] (2) compounding at least one layer of the heteroatom co-doped carbon nanotube film, optionally at least one layer of carbon nanotube film, and at least one layer of carbon-based electrode to obtain a composite electrode;

[0053] The mixed gas contains heteroatom-containing gas and inert gas, the heteroatom-containing gas is a gas containing non-metallic atom I and a gas containing non-metallic atom II, the non-metallic atom I is N, and the non-metallic atom II is selected from at least one of P, B and S.

[0054] In the present invention, compared with the existing chemical treatment and vapor deposition methods of heteroatoms, plasma doping treatment is adopted, which not only maintains the original structure of carbon nanotubes, but also overcomes the shortcomings of strong acid and high temperature treatment that easily lead to overoxidation of the material, resulting in decreased material stability and reduced battery life; and simplifies the process flow, is low-cost, and is suitable for large-scale sample processing.

[0055] In the present invention, the carbon nanotube film and the carbon electrode in step (1) are in accordance with the above-mentioned definitions, and the present invention will not elaborate on them.

[0056] In some embodiments of the present invention, preferably, the heteroatom gas is selected from ammonia and phosphine, ammonia and boron hydride, ammonia and hydrogen sulfide, preferably ammonia and phosphine, ammonia and hydrogen sulfide, more preferably ammonia and phosphine.

[0057] In some embodiments of the present invention, preferably, the volume ratio of the gas containing non-metal atoms I to the gas containing non-metal atoms II is 1:0.1-4, preferably 1:0.5-1. The volume ratio of the gas containing non-metal atoms I is calculated based on the mole of non-metal atoms I, and the volume ratio of the gas containing non-metal atoms II is calculated based on the mole ratio of non-metal atoms II.

[0058] In some embodiments of the present invention, preferably, in the mixed gas, the volume ratio of the heteroatom-containing gas to the inert gas is 5-90:10-95, preferably 10-40:60-90. The doping amount of the heteroatom can be controlled by the volume ratio.

[0059] In some embodiments of the present invention, preferably, the gas flow rate of the mixed gas is 0.1-50 mL / (min·cm 2 ), preferably 0.5-20 mL / (min·cm 2 ). Using the optimal conditions is more conducive to controlling the doping amount and doping effect of heteroatoms. The unit of the air flow rate is mL / (min·cm 2 ), that is, relative to 1cm 2The carbon nanotube film has a flow rate of the mixed gas of 0.1-50 mL / min, preferably 0.5-20 mL / min.

[0060] In some embodiments of the present invention, the plasma treatment conditions can be selected over a wide range, as long as the heteroatom co-doping of the carbon nanotube film is achieved. Preferably, the plasma treatment conditions include: a pressure of 50-500 Pa, preferably 100-400 Pa; a voltage of 4-18 kV, preferably 10-14 kV; and a duration of 0.1-2 hours, preferably 0.2-1 hour. These optimal conditions are more conducive to improving the efficiency of heteroatom co-doping and increasing the number of active sites in the heteroatom co-doped carbon nanotube film.

[0061] In the present invention, unless otherwise specified, the plasma treatment is performed in a plasma device.

[0062] In some embodiments of the present invention, the carbon nanotube film is preferably subjected to a surface treatment before the plasma treatment. The surface treatment is intended to remove impurities on the surface of the carbon nanotube film. Preferably, the carbon nanotube film is immersed in a solvent and dried before the plasma treatment.

[0063] According to a preferred embodiment of the present invention, the surface-treated carbon nanotube film is placed in a plasma device, and then a mixed gas containing hydrogen sulfide, ammonia and nitrogen is introduced into the plasma device to obtain a sulfur-nitrogen co-doped carbon nanotube film.

[0064] In the present invention, the compounding in step (2) refers to bonding or fixing at least one layer of the heteroatom co-doped carbon nanotube film, optionally at least one layer of the carbon nanotube film, and at least one layer of the carbon-based electrode. Compounding can be performed by bonding with an adhesive or by mechanical fixing, such as lamination.

[0065] According to the present invention, preferably, in step (2), the compounding process includes:

[0066] a. pressing at least one layer of the heteroatom co-doped carbon nanotube film to obtain a catalytic segment;

[0067] b. Pressing at least one optional layer of the carbon nanotube film to obtain a transition section;

[0068] c. Pressing at least one layer of the carbon-based electrode to obtain a diffusion section;

[0069] d. Compounding the catalytic section, the optional transition section and the diffusion section to obtain a composite electrode.

[0070] In some embodiments of the present invention, in step (2)-a, the method of pressing at least one layer of the heteroatom co-doped carbon nanotube film is not particularly limited, as long as at least one layer of the heteroatom co-doped carbon nanotube film is bonded or fixed by an adhesive or pressing.

[0071] In the present invention, the catalytic section preferably contains a plurality of stacked catalytic layers, and the active sites and catalytic activity of the catalytic section are improved by pressing the plurality of heteroatom-co-doped carbon nanotube films, that is, the electrolysis reaction of the electrolyte in the catalytic section is improved.

[0072] In some embodiments of the present invention, in step (2)-b, the method of pressing the optional at least one layer of the carbon nanotube film is not particularly limited, as long as the optional at least one layer of the carbon nanotube film is bonded or fixed by an adhesive or pressing.

[0073] In the present invention, the transition section preferably comprises a plurality of stacked transition layers, which are formed by laminating the plurality of carbon nanotube films. The function of the transition section is to further improve the mass transfer of the electrolyte while maintaining a certain electrochemical activity compared to the catalytic section.

[0074] In some embodiments of the present invention, in step (2)-c, the method of pressing at least one layer of the carbon-based electrode is not particularly limited, as long as at least one layer of the carbon-based electrode is bonded or fixed by an adhesive or pressing.

[0075] In the present invention, the diffusion section preferably comprises a plurality of stacked diffusion layers, and the diffusion rate of the electrolyte in the diffusion section is increased by pressing the multi-layer carbon electrodes.

[0076] In some embodiments of the present invention, in step (2)-d, there is no particular limitation on the manner in which the catalytic section, the optional transition section, and the diffusion section are compounded, as long as the catalytic section, the optional transition section, and the diffusion section are bonded or fixed by an adhesive or pressing.

[0077] In a preferred embodiment of the present invention, preferably, before the composite is performed, the catalytic section is soaked in a solution containing a binder.

[0078] According to the present invention, preferably, the carbon electrode is pretreated before the pressing is performed. Further preferably, the pretreatment includes: soaking the carbon electrode in an acid solution and an alkyl alcohol solution in sequence.

[0079] In some embodiments of the present invention, preferably, the acid in the acid solution is selected from at least one of hydrochloric acid, nitric acid and sulfuric acid; further preferably, the acid content in the acid solution is 0.1-10 mol / L, preferably 0.5-5 mol / L.

[0080] In some embodiments of the present invention, preferably, the alkyl alcohol in the alkyl alcohol solution is selected from at least one of methanol, ethanol, propanol and isopropanol; further preferably, the volume content of the alkyl alcohol in the alkyl alcohol solution is 5-100 vol.%, preferably 50-100 vol.%.

[0081] According to a preferred embodiment of the present invention, the pretreatment of the carbon electrode includes: soaking the carbon electrode in an acid solution for 5-24 hours, and then cleaning it with deionized water; then soaking it in an alkyl alcohol solution for 1-10 hours, and then washing it with deionized water until it is neutral.

[0082] In some embodiments of the present invention, preferably, the method further comprises: hot pressing the composite electrode and a proton exchange membrane to obtain a composite electrode.

[0083] In some embodiments of the present invention, the conditions for the thermal pressing include: a temperature of 80-200° C., a pressure of 0.1-5 MPa, and a time of 30-300 s.

[0084] A third aspect of the present invention provides use of the composite electrode provided in the first aspect and / or the composite electrode produced by the method provided in the second aspect in a liquid flow battery.

[0085] The composite electrode provided by the present invention has low resistivity and high electrochemical activity. When used in a zinc-iron liquid flow battery, the polarization of the battery is reduced and the energy efficiency of the battery is improved.

[0086] The present invention will be described in detail below through examples.

[0087] Carbon nanotube film-I was purchased from BoChuang Energy Technology Co., Ltd., wherein the bulk density of carbon nanotube film-I is 0.65 g / cm 3 , porosity of 55%, thickness of 15 μm, pore diameter of 10 nm, and specific surface area of ​​13.1 m 2 / g, contact angle is 111°;

[0088] Carbon paper was purchased from Toray Industries, Japan. The bulk density of carbon paper was 0.44 g / cm 3 , porosity is 75%, thickness is 190μm, surface fiber thickness is 8μm, channel is 100μm, specific surface area is 0.45m 2 / g; contact angle is 126°.

[0089] The property parameters of the catalytic layer and the composite electrode in Examples 1-10 and Comparative Examples 1-6 are listed in Table 1.

[0090] Example 1

[0091] (1) The surface-treated carbon nanotube film-I was placed in a plasma device and a mixture of ammonia, hydrogen sulfide and nitrogen (the volume ratio of ammonia, hydrogen sulfide and nitrogen was 10:10:80 and the gas flow rate was 1 mL / (min·cm 2 )) performing plasma treatment to obtain a nitrogen-sulfur co-doped carbon nanotube film S1, wherein the plasma treatment conditions include: a gas pressure of 200 Pa, a voltage of 12 kV, and a time of 0.5 h;

[0092] Wherein, in the nitrogen-sulfur co-doped carbon nanotube film S1, the total content of nitrogen and sulfur is 6.2 wt %, and the molar ratio of nitrogen atoms to sulfur atoms is 1:0.4;

[0093] The SEM image of the nitrogen-sulfur co-doped carbon nanotube film S1 is as follows: Figure 2 shown by Figure 2 It can be seen that the morphology and structure of the nitrogen-sulfur co-doped carbon nanotube film S1 have not changed.

[0094] (2) The carbon paper was first soaked in a 1 mol / L nitric acid solution for 12 h, then rinsed with deionized water, and then soaked in a 50 vol.% methanol solution for 2 h. After washing with deionized water until neutral, the pretreated carbon paper P1 was obtained;

[0095] The SEM image of the pre-treated carbon paper P1 is as follows: Figure 3 shown by Figure 3 It can be seen that there are no impurities on the surface of the pre-treated carbon paper P1; and the hydrophilicity test of the pre-treated carbon paper P1 shows that the hydrophilicity is enhanced.

[0096] (3) The nitrogen-sulfur co-doped carbon nanotube film S1 and the pretreated carbon paper P1 are compounded to obtain a composite electrode Q1.

[0097] Example 2

[0098] (1) The surface-treated carbon nanotube film-I was placed in a plasma device and a mixture of ammonia, hydrogen sulfide and nitrogen (the volume ratio of ammonia, hydrogen sulfide and nitrogen was 25:10:65, and the gas flow rate was 2 mL / (min·cm 2 )) performing plasma treatment to obtain a nitrogen-sulfur co-doped carbon nanotube film S2, wherein the plasma treatment conditions include: a gas pressure of 200 Pa, a voltage of 12.5 kV, and a time of 1 hour;

[0099] Wherein, in the nitrogen-sulfur co-doped carbon nanotube film S2, the total content of nitrogen and sulfur is 13.5 wt %, and the molar ratio of nitrogen atoms to sulfur atoms is 1:0.4;

[0100] (2) The carbon paper was first soaked in a 1.5 mol / L hydrochloric acid solution for 10 h, then rinsed with deionized water, and then soaked in an 80 vol.% methanol solution for 3 h. After washing with deionized water until neutral, the pretreated carbon paper P2 was obtained;

[0101] (3) First, two nitrogen-sulfur co-doped carbon nanotube films S2 are pressed together, and the obtained catalytic segment is compounded with the pretreated carbon paper P2 to obtain a composite electrode Q2.

[0102] Example 3

[0103] (1) The surface-treated carbon nanotube film-I was placed in a plasma device and a mixture of ammonia, hydrogen sulfide, and nitrogen (the volume ratio of ammonia, hydrogen sulfide, and nitrogen was 20:20:60, and the gas flow rate was 3 mL / (min·cm 2 )) performing plasma treatment to obtain a nitrogen-sulfur co-doped carbon nanotube film S3, wherein the plasma treatment conditions include: a gas pressure of 200 Pa, a voltage of 12.5 kV, and a time of 1 hour;

[0104] Wherein, in the nitrogen-sulfur co-doped carbon nanotube film S3, the total content of nitrogen and sulfur is 15.2 wt %, and the molar ratio of nitrogen atoms to sulfur atoms is 1:0.4;

[0105] (2) The carbon paper was first soaked in a 1 mol / L sulfuric acid solution for 18 h, then rinsed with deionized water, and then soaked in a 70 vol.% ethanol solution for 5 h. After washing with deionized water until neutral, the pretreated carbon paper P3 was obtained.

[0106] (3) First, three pre-treated carbon papers P3 are pressed together, and the obtained diffusion section is compounded with the nitrogen-sulfur co-doped carbon nanotube film S3 to obtain a composite electrode Q3.

[0107] Example 4

[0108] (1) The surface-treated carbon nanotube film was placed in a plasma device and a mixture of ammonia, hydrogen sulfide, and nitrogen (the volume ratio of ammonia, hydrogen sulfide, and nitrogen was 20:18:62, and the gas flow rate was 2 mL / (min·cm 2 )) performing plasma treatment to obtain a nitrogen-sulfur co-doped carbon nanotube film S4, wherein the plasma treatment conditions include: a gas pressure of 200 Pa, a voltage of 15 kV, and a time of 2 h;

[0109] Wherein, in the nitrogen-sulfur co-doped carbon nanotube film S4, the total content of sulfur and nitrogen is 13.6 wt %, and the molar ratio of nitrogen atoms to sulfur atoms is 1:0.8;

[0110] (2) The carbon paper was first soaked in a 2 mol / L nitric acid solution for 12 h, then rinsed with deionized water, and then soaked in a 75 vol.% methanol solution for 2 h. After washing with deionized water until neutral, the pretreated carbon paper P4 was obtained;

[0111] (3) First, two nitrogen-sulfur co-doped carbon nanotube films S4 are pressed together to obtain a catalytic section; then three pretreated carbon papers P4 are pressed together to obtain a diffusion section; finally, the catalytic section and the diffusion section are compounded to obtain a composite electrode Q4.

[0112] Example 5

[0113] The method of Example 3 was followed, except that nitrogen and phosphorus co-doping was performed, that is, the volume ratio of ammonia, phosphine and nitrogen was 20:20:60, and the gas flow rate was 2 mL / (min·cm 2 ) to obtain a nitrogen-phosphorus co-doped carbon nanotube film S5, wherein the total content of nitrogen and phosphorus in the nitrogen-phosphorus co-doped carbon nanotube film S5 is 15.6 wt%, and the molar ratio of nitrogen atoms to phosphorus atoms is 1:0.4; the remaining steps are the same to obtain a composite electrode Q5.

[0114] Example 6

[0115] The method of Example 3 is followed, except that nitrogen and boron co-doping is performed, that is, the volume ratio of ammonia, boron hydride and nitrogen is 20:15:65, to obtain a nitrogen and boron co-doped carbon nanotube film S6, wherein the total content of nitrogen and boron in the nitrogen and boron co-doped carbon nanotube film S6 is 12.3 wt%, and the molar ratio of nitrogen atoms to boron atoms is 1:1. The remaining steps are the same to obtain a composite electrode Q6.

[0116] Example 7

[0117] The method of Example 3 is as follows, except that in step (3), two nitrogen-sulfur co-doped nanotube films S3 are first pressed together to obtain a catalytic section; then two surface-treated carbon nanotube films-II (with a bulk density of 0.2 g / cm 3 , porosity of 75%) were pressed to obtain a transition section; finally, the catalytic section, the transition section and the pretreated carbon paper P3 were compounded to obtain a composite electrode Q7.

[0118] Example 8

[0119] The method of Example 3 is followed, except that in step (3), the composite electrode and the proton exchange membrane are placed on a hydraulic press and hot-pressed at 110° C. for 1 minute to obtain a composite electrode Q8.

[0120] Example 9

[0121] The method of Example 3 is followed, except that the mixed gas is replaced with ammonia and hydrogen sulfide, and the volume ratio of ammonia to hydrogen sulfide is 90:10, to obtain a nitrogen-sulfur co-doped carbon nanotube film S9, wherein the total content of sulfur and nitrogen in the nitrogen-sulfur co-doped carbon nanotube film S9 is 12.6 wt%, and the molar ratio of nitrogen atoms to sulfur atoms is 4:1; the remaining steps are the same to obtain a composite electrode Q9.

[0122] Example 10

[0123] The method of Example 3 was followed, except that the mixed gas was replaced with nitrogen and hydrogen sulfide, and the volume ratio of nitrogen to hydrogen sulfide was 20:80, to obtain a sulfur-doped carbon nanotube film S10, wherein the sulfur content in the sulfur-doped carbon nanotube film S10 was 5 wt%. The remaining steps were the same to obtain a composite electrode Q10.

[0124] Comparative Example 1

[0125] The two nitrogen-sulfur co-doped carbon nanotube films S1 in Example 1 are pressed together to obtain an electrode DQ1.

[0126] Comparative Example 2

[0127] The pretreated carbon paper P1 in Example 1 is directly used as the electrode DQ2.

[0128] Comparative Example 3

[0129] The two pre-treated carbon papers P1 in Example 1 were pressed together to obtain an electrode DQ3.

[0130] Comparative Example 4

[0131] The three pre-treated carbon papers P1 in Example 1 were pressed together to obtain an electrode DQ4.

[0132] Comparative Example 5

[0133] According to the method disclosed in CN110316720A, a sulfur-nitrogen dual-doped carbon nanotube film DS5 was prepared; the remaining steps were the same to obtain a composite electrode DQ5.

[0134] Comparative Example 6

[0135] The method of Example 3 is followed, except that the carbon nanotube film-I after surface solvent treatment is directly composited with the pretreated carbon paper P1 to obtain a composite electrode DQ6.

[0136] Table 1

[0137]

[0138] Note: 1-the ratio of the thickness of the catalytic section to the thickness of the composite electrode; 2-the ratio of the number of layers of the catalytic section, the number of layers of the transition section and the number of layers of the diffusion section in the composite electrode.

[0139] The results in Table 1 show that the composite electrode provided by the present invention allows the carbon nanotube film to maintain its original structure and property parameters and effectively reduces the resistivity of the composite electrode, thereby improving the conductivity and catalytic activity of the composite electrode. In particular, the resistivity of the composite electrode can be regulated by adjusting the number of layers of the catalytic section and the diffusion section.

[0140] Test Case

[0141] The electrochemical performance of the zinc-iron flow battery assembled with the composite electrodes Q1-Q10 and DQ1-DQ6 prepared in Examples 1-10 and Comparative Examples 1-6 was tested.

[0142] Assembly method of zinc-iron flow battery: the electrodes are composite electrodes, the bipolar plates are graphite plates, and the ion exchange membrane is Nafion-115 membrane produced by DuPont, with an effective area of ​​4cm 2 .

[0143] The test conditions include: the flow rate of the positive and negative electrolytes is 70mL / min, the charging current is 80A / cm 2 , the charge cut-off voltage is 1.8V, and the discharge current is 80mA / cm 2 The discharge cut-off voltage is 0.1V, the charging capacity is 20Ah / L, and the test results after 100 cycles are listed in Table 2.

[0144] Table 2

[0145] Coulombic efficiency, % Energy efficiency, % Voltage efficiency, % Example 1 97.1 87.5 90.1 Example 2 97.4 88.7 91.1 Example 3 98.1 90.6 92.4 Example 4 96.5 86.7 89.8 Example 5 96.3 84.8 88.1 Example 6 96.2 84.5 87.8 Example 7 98.2 90.1 91.8 Example 8 98.2 92.5 94.2 Example 9 96.2 84.1 87.4 Example 10 96.1 83.7 87.1 Comparative Example 1 95.1 78.5 82.5 Comparative Example 2 95.5 80.8 84.6 Comparative Example 3 95.4 80.5 84.4 Comparative Example 4 95.4 80.2 84.2 Comparative Example 5 95.2 82.1 86.2 Comparative Example 6 95.8 81.6 85.2

[0146] As shown in Table 2, the composite electrode provided by the present invention reduces polarization in a zinc-iron flow battery and improves the battery's coulombic efficiency, voltage efficiency, and energy efficiency. In particular, by limiting the volume ratio of the gas containing non-metallic atoms I to the gas containing non-metallic atoms II, the gas flow rate of the mixed gas, and the plasma treatment conditions to within a preferred protection range, the battery's electrochemical performance (coulombic efficiency, voltage efficiency, and energy efficiency) is further improved.

[0147] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A composite electrode for a zinc-iron flow battery, characterized in that: The composite electrode comprises: a stacked catalytic section and a diffusion section, wherein the catalytic section comprises at least one stacked catalytic layer, and the diffusion section comprises at least one stacked diffusion layer, wherein the catalytic layer is a heteroatom co-doped carbon nanotube film, and the diffusion layer is a carbon electrode; the carbon electrode is selected from at least one of carbon felt, graphite felt, carbon cloth, and carbon paper; The heteroatoms are non-metal atom I and non-metal atom II, the non-metal atom I is N, and the non-metal atom II is selected from at least one of P, B, and S; the molar ratio of the non-metal atom I to the non-metal atom II is 1:0.01-1; and the content of the heteroatoms is 1-30 wt% based on the total mass of the carbon nanotube film co-doped with the heteroatoms; The bulk density of the catalytic layer is 0.6-0.75 g / cm 3 ; Porosity is 30-55%; Specific surface area is 60-100m 2 / g; the contact angle is 0-20°; the bulk density of the diffusion layer is 0.1-0.45g / cm 3 , the porosity is 75-95%.

2. The composite electrode according to claim 1, wherein The heteroatom is selected from N and P, N and B, N and S; The content of the heteroatom is 5-20 wt % based on the total mass of the heteroatom co-doped carbon nanotube film; The molar ratio of the non-metal atom I to the non-metal atom II is 1:0.1-0.

5.

3. The composite electrode according to claim 2, wherein The heteroatom is selected from N and P, N and S.

4. The composite electrode according to claim 1, wherein The thickness of the catalytic section accounts for 0.5-30% of the total thickness of the composite electrode; The bulk density of the catalytic layer is 0.6-0.7 m 2 / g; porosity is 45-55%; The bulk density of the diffusion layer is 0.2-0.45 g / cm 3 ; Porosity is 75-90%.

5. The composite electrode according to claim 4, wherein The thickness of the catalytic section accounts for 2-15% of the total thickness of the composite electrode.

6. The composite electrode according to any one of claims 1 to 5, wherein: The composite electrode further includes a transition section; The transition section is arranged between the catalytic section and the diffusion section, and the transition section contains at least one transition layer arranged in a stacked manner.

7. The composite electrode according to claim 6, wherein The bulk densities of the catalytic layer, the transition layer, and the diffusion layer decrease in sequence, and the porosities of the catalytic layer, the transition layer, and the diffusion layer increase in sequence.

8. The composite electrode according to claim 6, wherein The bulk density of the transition layer is 0.45-0.6 g / cm 3 ; Porosity is 55-75%.

9. The composite electrode according to claim 8, wherein The bulk density of the transition layer is 0.45-0.55 g / cm 3 ; Porosity is 55-70%.

10. The composite electrode according to claim 6, wherein The composite electrode further comprises a proton exchange membrane, and the composite electrode comprises: a catalytic section, a transition section, a diffusion section and a proton exchange membrane which are stacked in sequence.

11. The composite electrode according to claim 6, wherein The resistivity of the composite electrode is less than 50 mΩ / cm 2 ;Contact angle ≤20°.

12. The composite electrode according to claim 11, wherein The resistivity of the composite electrode is ≤5mΩ / cm 2 ;Contact angle 0-20°.

13. The composite electrode according to claim 11, wherein The thickness ratio of the catalytic section, the transition section and the diffusion section is 0.5-30:0-30:40-90.

5.

14. The composite electrode according to claim 13, wherein The thickness ratio of the catalytic section, the transition section and the diffusion section is 2-20:10-30:50-80.

15. A method for preparing the composite electrode according to claim 1, characterized in that: The method comprises the following steps: (1) subjecting a carbon nanotube film and a mixed gas to plasma treatment to obtain a heteroatom co-doped carbon nanotube film; (2) compounding at least one layer of the heteroatom co-doped carbon nanotube film, optionally at least one layer of carbon nanotube film, and at least one layer of carbon-based electrode to obtain a composite electrode; The mixed gas contains heteroatom-containing gas and inert gas, the heteroatom-containing gas is a gas containing non-metallic atom I and a gas containing non-metallic atom II, the non-metallic atom I is N, and the non-metallic atom II is selected from at least one of P, B and S.

16. The method according to claim 15, wherein The heteroatom-containing gas is selected from ammonia and phosphine, ammonia and boron hydride, ammonia and hydrogen sulfide; The volume ratio of the gas containing non-metal atoms I to the gas containing non-metal atoms II is 1:0.1-4; In the mixed gas, the volume ratio of the heteroatom-containing gas to the inert gas is 5-90:10-95; The gas flow rate of the mixed gas is 0.1-50 mL / (min·cm 2 ); The plasma treatment conditions include: gas pressure of 50-500 Pa; voltage of 4-18 kV; and time of 0.1-2 h.

17. The method according to claim 16, wherein The heteroatom-containing gas is selected from ammonia and phosphine, ammonia and hydrogen sulfide; The volume ratio of the gas containing non-metal atoms I to the gas containing non-metal atoms II is 1:0.5-1; In the mixed gas, the volume ratio of the heteroatom-containing gas to the inert gas is 10-40:60-90; The gas flow rate of the mixed gas is 0.5-20 mL / (min·cm 2 ); The plasma treatment conditions include: gas pressure of 100-400 Pa; voltage of 10-14 kV; and time of 0.2-1 h.

18. The method according to claim 16, wherein Before the plasma treatment, the carbon nanotube film is surface treated.

19. The method according to claim 15, wherein In step (2), the compounding process includes: a. pressing at least one layer of the heteroatom co-doped carbon nanotube film to obtain a catalytic segment; b. Pressing at least one optional layer of the carbon nanotube film to obtain a transition section; c. Pressing at least one layer of the carbon-based electrode to obtain a diffusion section; d. Compounding the catalytic section, the optional transition section and the diffusion section to obtain a composite electrode.

20. The method according to claim 19, wherein Before the composite is performed, the catalytic section is immersed in a solution containing a binder; Before the pressing, the carbon electrode is pretreated; the pretreatment includes: soaking the carbon electrode in an acid solution and an alkyl alcohol solution in sequence; The method further comprises: hot pressing the composite electrode and the proton exchange membrane, so as to stack the proton exchange membrane on the other surface of the diffusion section to obtain a composite electrode.

Images