Preparation method of bifunctional catalyst for zinc-methanol air battery

Abstract

The invention belongs to the technical field of electrochemical energy storage, and discloses a bifunctional catalyst capable of efficiently catalyzing methanol oxidation reaction and oxygen reduction reaction at the same time, and application of the bifunctional catalyst to a novel zinc-methanol air battery. The specific preparation process of the catalyst comprises the following steps: dissolving nickel chloride, cobalt chloride, manganese chloride and urea in a mixed solution of deionized water and methanol to form a solution A, then adding a Ti3C2Ox suspension, carrying out a hydrothermal reaction at 120 DEG C for 12 hours, and carrying out centrifugal cleaning and freeze drying to obtain the composite catalyst. The catalyst shows excellent bifunctional activity in an alkaline electrolyte, and a zinc-methanol air battery based on the catalyst shows cycling stability of nearly 20 days. The invention provides a new thought for preparation of the zinc-methanol air battery bifunctional catalyst.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical energy storage, and more specifically, relates to a method for preparing a bifunctional catalyst for a zinc-methanol air battery. Background Art

[0002] With the continuous advancement of economy and technology, humanity's demand for energy is growing rapidly, but this is also accompanied by the rapid consumption of non-renewable resources. Renewable energy sources such as hydropower, solar energy, and wind energy are considered the best alternatives to conventional fossil energy. However, due to geographical location, sunshine, seasons, and weather restrictions, the production and supply of renewable energy are random and discontinuous. Therefore, in order to effectively utilize renewable energy, it is necessary to develop low-cost, sustainable, and efficient energy conversion and storage technologies. Rechargeable metal-air batteries are devices that can efficiently convert chemical energy into electrical energy. They have the advantages of low cost, high theoretical energy density, good safety, and environmental friendliness, making them a highly promising energy storage system.

[0003] Among various metal-air systems, zinc-air batteries (ZABs) are currently the energy storage devices closest to practical application. However, the slow kinetics of the oxygen evolution reaction (OER) and the side reactions it triggers have long severely limited the development of rechargeable Zn-air batteries. During the OER process, the air electrode is susceptible to corrosion at high potentials, resulting in a significant decrease in energy efficiency and power density, as well as a reduction in battery cycle life.

[0004] To overcome these challenges, a series of thermodynamically and economically favorable oxidation reactions have been extensively studied as alternatives to the slow OER. During the charging process of zinc-air batteries, replacing the OER with the OOR can also reduce the charge voltage, alleviate air electrode corrosion, and avoid structural damage to the oxygen electrode, thereby improving the energy efficiency and cycle life of the zinc-air battery. The selective electrooxidation products of methanol, such as formic acid and formate, can be used as general value-added chemicals in the chemical industry. Therefore, using the methanol electrooxidation reaction (MOR) to replace the OER process and coupling it with the oxygen reduction reaction (ORR) as the charge and discharge reaction of zinc-methanol-air batteries can not only significantly reduce the charge voltage and improve the charge and discharge cycle efficiency, but also generate high-value-added products, making it a very promising new type of efficient electrochemical energy storage system. For zinc-methanol-air batteries, bifunctional catalysts that can simultaneously and efficiently catalyze both MOR and ORR are key factors in determining the performance of this type of battery. Summary of the Invention

[0005] The present invention aims to prepare a highly conductive and active bifunctional catalyst by in-situ anchoring a double hydroxide (LDH) on the surface of a MXene by constructing a heterostructure. The method provided by the invention is a simple, green, and economical method for synthesizing the material. The catalyst can also be used in zinc-methanol-air batteries to reduce the battery's overpotential and improve its cycle life.

[0006] The purpose of the present invention is to achieve the following technical solutions: first, a Ti3C2T3O ...4O3O3O4O3O3O3O3O4O3O3O4 x (Ti3C2O x ), and then reacted it with manganese-doped nickel cobalt double hydroxide (Ni1Co2Mn 0.2 -LDH) composite as a bifunctional catalyst for zinc-methanol air batteries.

[0007] A method for preparing a bifunctional electrocatalyst for a zinc-methanol air battery comprises the following steps:

[0008] (1) An appropriate amount of lithium fluoride was dissolved in a mixed solution of deionized water and hydrogen chloride, and then magnetically stirred at room temperature. Subsequently, MXene powder was gradually added to the above solution and stirred for 48 hours. The formed acidic suspension was separated by centrifugation and repeatedly washed with deionized water until the pH value reached 6. After that, the obtained Ti3C2T x The precipitate was subjected to ultrasonic exfoliation for 2 h under argon atmosphere. Then the supernatant was separated and collected after centrifugation for 5 min. Finally, Ti3C2T x The suspension was freeze-dried to obtain Ti3C2T with a few-layer structure. x Product. Ti3C2T x Annealing treatment is further performed under an argon atmosphere to obtain a surface rich in oxygen terminal groups.

[0009] (2) Dissolve appropriate amounts of nickel salt, cobalt salt, manganese salt and urea in a mixed solution of deionized water and methanol in turn, and form a uniform solution (called solution A) under stirring. x The particles were dispersed in 10 mL of deionized water and sonicated to form a suspension (referred to as B). Subsequently, B was slowly added to A under continuous stirring until the solution was mixed uniformly.

[0010] (3) The solution obtained in step (1) is transferred to a hydrothermal reactor and placed in an oven for hydrothermal reaction at a heating temperature of 120-200° C. for 12 hours.

[0011] (4) The catalyst powder was synthesized by a solvothermal method. After cooling to room temperature, the solid product was collected by centrifugation, washed three times with ultrapure water and once with ethanol, and then freeze-dried for 12 h.

[0012] In the step (1), the MXene powder is Ti3C2T x , the annealing temperature is 400℃.

[0013] In step (2), the nickel salt is nickel chloride, the cobalt salt is cobalt chloride, and the manganese salt is manganese chloride. The molar ratio of the nickel salt to the cobalt salt is fixed at 1:2, and the content of the manganese salt varies between 0 and 0.3.

[0014] In the step (3), the hydrothermal reaction temperature is 120-200° C., preferably 120° C.; the volume of the reactor is 1-2 times the total volume of the solution, preferably 1.25 times.

[0015] In the step (4), the reactor should be cooled at room temperature for more than 3 hours before opening to prevent the high temperature and high pressure environment inside the reactor from causing explosion; the drying method is preferably freeze drying to avoid damage to the morphology of the catalyst.

[0016] The prepared electrocatalyst was used in a zinc-methanol-air battery. Its MOR / ORR catalytic performance was first evaluated using a three-electrode system. A platinum sheet was used as the counter electrode, a mercury / mercuric oxide electrode was used as the reference electrode, and the heterostructured catalyst was used as the working electrode. The performance of the methanol reaction was evaluated in a mixed solution of 1M KOH and 0.5M methanol, and the performance of the oxygen reduction reaction was evaluated in a 0.1M KOH solution. A zinc-air battery was then prepared using this catalyst as the air electrode, and its battery performance was evaluated.

[0017] Beneficial effects of the present invention:

[0018] (1) Compared with precious metal catalysts such as carbon dioxide and platinum carbon, the raw materials used in the present invention have the advantages of low price, abundant resources and stable catalytic performance.

[0019] (2) The electrocatalyst prepared by the solvent thermal method adopted in the present invention has mild reaction conditions, simple operation, green environmental protection, safety and easy control during the synthesis process, and well replicates the morphology of the precursor.

[0020] (3) The electrocatalyst prepared by the present invention can reach 10 mA / cm2 in 1M KOH and 0.5M MeOH electrolytes at an overpotential of 102 mV. -2 In 0.1 M KOH electrolyte, the ORR half-wave potential can reach 0.692 V. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1is the X-ray diffraction pattern of the obtained sample;

[0022] Figure 2 is a scanning electron microscope image of the obtained sample;

[0023] Figure 3 is the methanol electrooxidation polarization curve of the obtained sample;

[0024] Figure 4 is the polarization curve of the oxygen reduction reaction of the obtained sample;

[0025] Figure 5 This is the cycling stability diagram of the zinc-methanol air battery prepared using the obtained sample as a catalyst. DETAILED DESCRIPTION

[0026] The present invention is further described with reference to the following examples. However, it should be understood that the following examples are only preferred embodiments of the present invention and do not limit the present invention.

[0027] The MOR and ORR catalytic performances of the catalyst prepared in the present invention were measured using the following methods.

[0028] Take a certain amount of alumina polishing powder on a grinding disc (suede), then add deionized water, stir slightly with the insulating part of the glassy carbon electrode, and finally polish the electrode. Next, the electrode is ultrasonically cleaned with deionized water and anhydrous ethanol, and then naturally air-dried at room temperature after cleaning. Weigh 5 mg of catalyst and add it to a mixed solution of 500 μL ethanol, 450 μL deionized water and 50 μL Nafion (5wt%). Then ultrasonically disperse the catalyst ink at room temperature for 30 minutes. Finally, 5 μL of catalyst ink is evenly dropped on the surface of the glassy carbon electrode, dried naturally at room temperature, and after forming a uniform film, electrochemical testing is performed on the CHI 760E electrochemical workstation.

[0029] The electrochemical tests are as follows:

[0030] (1) The MOR and ORR catalytic performances were tested using a three-electrode system. A graphite rod was used as the counter electrode (CE), and a mercury / mercury oxide electrode (Hg / HgO) was used as the reference electrode (RE). The working electrode (WE) was prepared as follows: 5 mg of catalyst powder was dispersed in a mixed solvent consisting of 450 μL of ethanol, 400 μL of deionized water, and 50 μL of a 5 wt% Nafion solution. A uniform catalyst slurry was formed by ultrasonic treatment, and the catalyst loading was maintained at 0.35 mg / cm -2 The MOR performance test was carried out in an O2-saturated 1.0 M KOH solution (with or without 0.5 M methanol), while the ORR test was performed in an O2-saturated 0.1 M KOH solution.

[0031] (2) Oxygen (99.9%) was introduced into the electrolyte for half an hour in advance to saturate the electrolyte solution with oxygen, and oxygen was introduced continuously during the test.

[0032] (3) To evaluate the MOR / ORR activity, linear sweep voltammetry (LSV) tests were performed at a scan rate of 5 mV / s. The MOR test voltage scan range was 0 to 1 V, and the ORR test voltage scan range was -0.8 to 0.1 V.

[0033] Example 1

[0034] 142.6 mg NiCl2·6H□O, 285.5 mg CoCl2·6H□O, 23.8 mg MnCl2·6H□O, 18.5 mg NH□F and 451.8 mg urea were dissolved in a mixture of 5 mL deionized water and 30 mL methanol to form a homogeneous solution (referred to as solution A) under stirring. 25 mg Ti3C2O x The particles were dispersed in 10 mL of deionized water and sonicated for 30 minutes to form a suspension (called B). Subsequently, B was slowly added to A under continuous stirring, and the precursor was transferred to a 50 mL polytetrafluoroethylene-lined reactor and kept at 120 ° C for 12 hours. After cooling to room temperature, the resulting Ni1Co2Mn 0.2 -LDH / Ti3C2O x The materials were washed with deionized water and ethanol solution, respectively, and finally freeze-dried to obtain the product.

[0035] Figure 1 The X-ray diffraction pattern of the product obtained in this example shows that the diffraction peak of the product corresponds to the lattice plane of NiCo-LDH, but the intensity is slightly weaker, indicating that the conductive base Ti3C2O x The introduction of and a small amount of Mn doping does not destroy the structure of NiCo-LDH.

[0036] Figure 2 The scanning electron microscope image of the product obtained in this embodiment shows that Ni1Co2Mn 0.2 -LDH in Ti3C2O x The conductive base surface grows vertically and maintains the original Ni1Co2Mn 0.2 -LDH nanoflower structure. This structure can avoid Ni1Co2Mn 0.2 -LDH's reunion.

[0037] Figure 3 This is the linear sweep voltammetry curve of the product obtained in this example in a mixture of 1M KOH and 0.5M KOH. It can be seen from the figure that the current density reaches 10mA / cm 2When , the overpotential is 102mV.

[0038] Figure 4 This is the linear voltammetric scanning curve of the product obtained in this example in a 0.1M KOH mixed solution. It can be seen from the figure that the ORR half-wave potential is 0.692V.

[0039] Figure 5 The product obtained in this example is the cycle stability diagram of the zinc-methanol air battery prepared as the catalyst. It can be seen from the figure that at a current density of 5mA / cm 2 It can circulate stably and continuously for 450 hours.

[0040] Example 2

[0041] 142.6 mg NiCl2·6H□O, 285.5 mg CoCl2·6H□O, 18.5 mg NH□F and 451.8 mg urea were dissolved in a mixture of 5 mL deionized water and 30 mL methanol in sequence to form a homogeneous solution (referred to as solution A) under stirring. 25 mg Ti3C2T x The particles were dispersed in 10 mL of deionized water and sonicated for 30 minutes to form a suspension (referred to as B). Subsequently, B was slowly added to A under continuous stirring, and the precursor was transferred to a 50 mL polytetrafluoroethylene-lined reactor and kept at 12 ° C for 12 hours. After cooling to room temperature, the resulting Ni1Co2-LDH / Ti3C2O x The material was washed with deionized water and ethanol solution respectively, and finally freeze-dried to obtain the product. Linear sweep voltammetry was performed using a three-electrode system. In a mixed solution of 1M KOH and 0.5M MeOH, the current density reached 10mA / cm 2 When the MOR overpotential is 310mV, the ORR half-wave potential is 0.694mV in 0.1MKOH electrolyte.

[0042] Example 3

[0043] 142.6 mg NiCl2·6H□O, 285.5 mg CoCl2·6H□O, 11.9 mg MnCl2·4H□O, 18.5 mg NH4F and 451.8 mg urea were dissolved in a mixture of 5 mL deionized water and 30 mL methanol to form a homogeneous solution (referred to as solution A) under stirring. 25 mg Ti3C2O x The particles were dispersed in 10 mL of deionized water and sonicated for 30 minutes to form a suspension (called B). Subsequently, B was slowly added to A under continuous stirring, and the precursor was transferred to a 50 mL polytetrafluoroethylene-lined reactor and kept at 120 ° C for 12 hours. After cooling to room temperature, the resulting Ni1Co2Mn0.1 -LDH / Ti3C2O x The material was washed with deionized water and ethanol solution respectively, and finally freeze-dried to obtain the product. Linear sweep voltammetry was performed using a three-electrode system. In a mixed solution of 1M KOH and 0.5M MeOH, the current density reached 10mA / cm 2 The MOR overpotential is 112 mV. In 0.1 M KOH electrolyte, the ORR half-wave potential is 0.674 mV

[0044] Example 4

[0045] 142.6 mg NiCl2·6H□O, 285.5 mg CoCl2·6H□O, 35.7 mg MnCl2·4H□O, 18.5 mg NH□F and 451.8 mg urea were dissolved in a mixture of 5 mL deionized water and 30 mL methanol to form a homogeneous solution (referred to as solution A) under stirring. 25 mg Ti3C2O x The particles were dispersed in 10 mL of deionized water and sonicated for 30 minutes to form a suspension (called B). Subsequently, B was slowly added to A under continuous stirring, and the precursor was transferred to a 50 mL polytetrafluoroethylene-lined reactor and kept at 120 ° C for 12 hours. After cooling to room temperature, the resulting Ni1Co2Mn 0.3 -LDH / Ti3C2O x The material was washed with deionized water and ethanol solution respectively, and finally freeze-dried to obtain the product. Linear sweep voltammetry was performed using a three-electrode system. In a mixed solution of 1M KOH and 0.5M MeOH, the current density reached 10mA / cm 2 The MOR overpotential is 310 mV. In 0.1 M KOH electrolyte, the ORR half-wave potential is 0.698 mV.

Claims

1. A method for preparing a bifunctional electrocatalyst for zinc-methanol air batteries, comprising the following steps: (1) An appropriate amount of lithium fluoride was dissolved in a mixed solution of deionized water and hydrogen chloride, and then magnetically stirred at room temperature. Subsequently, MXene powder was gradually added to the above solution and stirred for 48 hours. The formed acidic suspension was separated by centrifugation and repeatedly washed with deionized water until the pH value reached 6. After that, the obtained Ti3C2T x The precipitate was subjected to ultrasonic exfoliation for 2 h under argon atmosphere. Then the supernatant was separated and collected after centrifugation for 5 min. Finally, Ti3C2T x The suspension was freeze-dried to obtain Ti3C2T with a few-layer structure. x Product. Ti3C2T x The annealing treatment is further performed under an argon atmosphere to obtain a surface having abundant oxygen end groups. (2) Dissolve appropriate amounts of nickel salt, cobalt salt, manganese salt and urea in a mixed solution of deionized water and methanol in turn, and form a uniform solution (called solution A) under stirring. x The particles were dispersed in deionized water and sonicated to form a suspension (referred to as B). Subsequently, B was slowly added to A under continuous stirring until the solution was mixed uniformly. (3) The solution obtained in step (1) is transferred to a hydrothermal reactor and placed in an oven for hydrothermal reaction at a heating temperature of 120-200° C. for 12 hours. (4) The catalyst powder was synthesized by a solvothermal method. After cooling to room temperature, the solid product was collected by centrifugation, washed three times with ultrapure water and once with ethanol, and then freeze-dried for 12 h.

2. The method for preparing a MXene-based layered double hydroxide catalyst for oxygen evolution reaction according to claim 1, wherein: In step (1): The Mxene powder is Ti3C2T x , the annealing temperature is 400℃.

3. The method for preparing a bifunctional electrocatalyst for zinc-methanol air battery according to claim 1, characterized in that: In step (2): The nickel salt is nickel chloride, the cobalt salt is cobalt chloride, and the manganese salt is manganese chloride. The molar ratio of the nickel salt to the cobalt salt is fixed at 1:2, and the content of the manganese salt varies between 0 and 0.

3.

4. The method for preparing a bifunctional electrocatalyst for zinc-methanol air battery according to claim 1, characterized in that: In step (3): The hydrothermal reaction temperature is 120° C.; the volume of the reactor is 1 to 2 times, preferably 1.25 times, the total volume of the solution.

5. The method for preparing a bifunctional electrocatalyst for zinc-methanol air battery according to claim 1, characterized in that: In step (3): Before opening the reactor, it must be cooled at room temperature for more than 3 hours to prevent the high temperature and high pressure environment inside the reactor from causing explosion; the drying method is preferably freeze drying to avoid damage to the morphology of the catalyst.

6. An electric bifunctional catalyst for a zinc-methanol air battery prepared by the preparation method according to any one of claims 1 to 5.

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