Electrocatalytic membrane reactor and method for preparing high-purity hydrogen based on hydrazine hydrate oxidation

Abstract

The invention discloses an electrocatalytic membrane reactor and a method for preparing high-purity hydrogen based on hydrazine hydrate oxidation, which belongs to the field of new energy, and specifically realizes the preparation of high-purity hydrogen by utilizing the potential difference of the electrocatalytic reaction of the cathode and the anode without the need for an external voltage. The electrocatalytic membrane reactor adopts a structure similar to that of a flat membrane electrocatalytic membrane reactor, wherein the cathode chamber and the anode chamber are separated by a diaphragm that can conduct electricity and ions at the same time, and the electrocatalysts required for the anode and the cathode are pressed on both sides of the diaphragm, and the cathode chamber uses a potassium hydroxide aqueous solution, and the anode chamber uses an aqueous solution containing hydrazine hydrate and potassium hydroxide. The reduction potential of the hydrogen evolution reaction at the cathode is higher than the oxidation potential of the hydrazine hydrate oxidation at the anode, and this potential difference drives the electrocatalytic reaction of the anode and the cathode. The hydrogen evolution reaction in the cathode chamber produces high-purity hydrogen, thereby realizing the preparation of high-purity hydrogen without the use of an external voltage. This membrane reactor can greatly reduce the energy consumption of hydrogen production and the cost of hydrogen.

Description

Technical Field

[0001] The present invention belongs to the field of new energy, and relates to an electrocatalytic membrane reactor and a high-purity hydrogen preparation technology, in particular to an electrocatalytic membrane reactor and a method for preparing high-purity hydrogen based on hydrazine hydrate oxidation. Background Art

[0002] As a secondary energy carrier with high calorific value, zero pollution and renewable, hydrogen is expected to become a substitute for fossil fuels. Compared with hydrogen production by reforming fossil fuels, hydrogen production by electrolysis of water has the advantages of high hydrogen purity, wide source of raw materials, low carbon emissions, environmental friendliness and recyclability, and is considered to be the only way to the hydrogen economy.

[0003] During the water electrolysis process, the oxygen evolution reaction (OER) occurs at the anode of the alkaline electrolyzer, but the slow kinetics of the oxygen evolution reaction seriously restricts the energy conversion efficiency of water electrolysis. Therefore, in recent years, people have begun to pay attention to the use of substances that are more easily electrochemically oxidized at the anode, such as methanol, ethanol, ethylene glycol, ammonia, hydrazine, and urea. Among them, the electrochemical oxidation potential of hydrazine is very low (-0.33V vs. RHE). Therefore, using the electrochemical oxidation of hydrazine hydrate to replace the oxygen evolution reaction to promote water decomposition is a feasible path.

[0004] The traditional H-type electrolyzer uses an anion / cation exchange membrane to separate the anode and cathode, uses an electrode clip / platinum carbon electrode to connect the catalyst, and uses an electrochemical workstation to apply a potential to the catalyst for electrocatalytic reaction. The distance between the anode and cathode catalysts of such an H-type electrolyzer is far, and the impedance is large, which further increases the energy consumption, so the energy utilization efficiency is not high enough. The proton exchange membrane reactor electrolysis hydrogen production technology has a fast response speed, high operating current density, low energy consumption, high hydrogen production pressure, and high purity of hydrogen production, so the proton exchange membrane water electrolysis hydrogen production has developed rapidly in recent years. However, these reactors must use pure water as the water source, and the anode reaction can only be an oxygen evolution reaction, which has problems such as high overpotential and high energy consumption. Therefore, reducing the energy consumption of the hydrogen production reaction is still the focus of the future development of the hydrogen economy. Summary of the invention

[0005] The object of the present invention is to provide an electrocatalytic membrane reactor and a method thereof for preparing high-purity hydrogen based on hydrazine hydrate oxidation in view of the problems existing in the prior art. The novel electrocatalytic membrane reactor of the present invention uses a conductive and ion-conducting diaphragm to separate the cathode from the anode without the need for an external voltage, and utilizes the potential difference between the cathode and cathode reactions to drive the electrocatalytic reaction, wherein the anode replaces the oxygen evolution reaction with the hydrazine oxidation reaction, and the cathode prepares high-purity hydrogen through the hydrogen evolution reaction.

[0006] The specific technical solutions adopted by the present invention are as follows:

[0007] In the first aspect, the present invention provides an electrocatalytic membrane reactor for preparing high-purity hydrogen based on hydrazine hydrate oxidation, comprising an electrocatalytic membrane reactor body, wherein the inner cavity of the electrocatalytic membrane reactor body is divided into relatively independent cathode chamber and anode chamber by a diaphragm; the diaphragm can conduct electricity and ions at the same time, and is respectively loaded with a cathode catalyst located in the cathode chamber and an anode catalyst located in the anode chamber on both sides; the cathode chamber contains a first electrolyte solution, and the anode chamber contains a second electrolyte solution containing hydrazine hydrate, and a first gas outlet and a second gas outlet that can be connected to the outside are respectively provided on the electrocatalytic membrane reactor body located at the top of the cathode chamber and the top of the anode chamber.

[0008] Preferably, the diaphragm can conduct electricity and ions at the same time, wherein the ions that can be conducted are hydrogen ions or hydroxide ions.

[0009] Preferably, the cathode catalyst and the anode catalyst are tightly connected to both sides of the diaphragm respectively.

[0010] Preferably, the cathode catalyst is one of a platinum-based catalyst, a ruthenium-based catalyst, a nickel-based catalyst or a molybdenum disulfide catalyst.

[0011] Preferably, the anode catalyst is a nickel-based catalyst or a cobalt-based catalyst.

[0012] Preferably, the first electrolyte solution is a potassium hydroxide aqueous solution; and the second electrolyte solution is a mixture of a hydrazine hydrate solution and a potassium hydroxide aqueous solution having the same concentration as the first electrolyte solution.

[0013] Preferably, the diaphragm is nickel foam filled with polyvinyl alcohol gel.

[0014] In a second aspect, the present invention provides a method for preparing high-purity hydrogen based on any one of the electrocatalytic membrane reactors described in the first aspect, as follows:

[0015] The diaphragm, cathode catalyst and anode catalyst together constitute the membrane electrode. Since the diaphragm can conduct both electricity and ions, the cathode and the anode are always at the same potential. High-purity hydrogen is prepared by hydrogen evolution reaction in the cathode chamber, and electrochemical oxidation reaction of hydrazine hydrate is carried out in the anode chamber. Since the reduction potential of the hydrogen evolution reaction at the cathode is higher than the oxidation potential of the hydrazine hydrate oxidation at the anode, the cathode and the anode are driven to produce hydrogen by the potential difference between the two without the need for an external voltage. At the same time, by utilizing the separation characteristics of the diaphragm, high-purity hydrogen can be directly obtained at the cathode.

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

[0017] 1) The present invention operates at room temperature and pressure, and the membrane electrode acts as a cathode and an anode to realize the dual functions of electrocatalysis and membrane separation.

[0018] 2) The diaphragm also has the characteristics of conducting electricity and ions. Since the potential of the hydrazine oxidation reaction at the anode (-0.33V vs. RHE) is lower than the potential of the hydrogen evolution reaction at the cathode (0V vs. RHE), and the diaphragm makes the cathode and anode at the same potential, which is between -0.33V and 0V, it can drive the occurrence of electrocatalytic oxidation and reduction reactions without the need for additional voltage application, reducing costs and energy consumption.

[0019] 3) The separation characteristics of the diaphragm can be used to directly obtain high-purity hydrogen at the cathode, greatly improving the efficiency of the reactor. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of the membrane reactor of the present invention;

[0021] Figure 2 It is a schematic diagram of the working process of the membrane reactor of the present invention;

[0022] Figure 3 is a graph showing the relationship between hydrogen production volume and time in the embodiment;

[0023] In the figure: 1 diaphragm, 2 cathode catalyst, 3 anode catalyst, 4 cathode chamber, 5 anode chamber, 6 first gas outlet, 7 second gas outlet. DETAILED DESCRIPTION

[0024] The present invention is further described and illustrated below in conjunction with the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0025] The present invention provides an electrocatalytic membrane reactor for preparing high-purity hydrogen based on hydrazine hydrate oxidation. The electrocatalytic membrane reactor does not require an external voltage and can drive electrolysis to prepare high-purity hydrogen through the potential difference between the anode and cathode. The structure of the reactor is as follows:

[0026] like Figure 1 As shown, the electrocatalytic membrane reactor of the present invention mainly includes an electrocatalytic membrane reactor body, which adopts a structure similar to that of a flat membrane electrocatalytic membrane reactor, and the inner cavity of the reactor body is divided into a relatively independent cathode chamber 4 and anode chamber 5 by a diaphragm 1. The diaphragm 1 can conduct electricity and ions at the same time, and a cathode catalyst 2 and an anode catalyst 3 are respectively loaded on both sides, wherein the cathode catalyst 2 is located in the cathode chamber 4, and the anode catalyst 3 is located in the anode chamber 5. The cathode chamber 4 contains a first electrolyte solution, and the anode chamber 5 contains a second electrolyte solution containing hydrazine hydrate, and the electrocatalytic membrane reactor body located at the top of the cathode chamber 4 and the anode chamber 5 is respectively provided with a first gas outlet 6 and a second gas outlet 7 that can communicate with the outside world.

[0027] In actual use, the diaphragm is a diaphragm that can conduct electricity and ions at the same time, for example: nickel foam filled with polyvinyl alcohol gel is used as a diaphragm. The preparation method of this material is: S1. Add 3g of polyvinyl alcohol to 30mL of water, and heat to 85°C while stirring until the solution is clear. S2. Add 1.5g of potassium hydroxide to 10mL of water, stir and dissolve, and then add it to the solution obtained in S1. S3. Stir the mixed solution of S1 and S2 at 85°C until it is uniform, and the solution is in a gel state. S4. Soak a piece of cut nickel foam in the gel obtained in S3, and take it out after soaking for 5 minutes. S5. Place the mixture of the nickel foam and gel in a dry environment at room temperature for 6 hours to obtain a nickel foam diaphragm filled with polyvinyl alcohol.

[0028] The cathode chamber and the anode chamber are separated by a diaphragm, which can conduct electricity and ions (hydrogen ions or hydroxide ions). The present invention uses a membrane that can conduct electricity and ions as a diaphragm, which can not only separate the cathode and the anode to form two independent reaction chambers, but also separate the gas at the anode from the hydrogen at the cathode to achieve high-purity hydrogen of more than 99%. If the cathode and anode do not use a diaphragm, the reactor is equivalent to an ordinary single cell, and high-purity hydrogen cannot be directly obtained.

[0029] In actual use, the cathode catalyst 2 and the anode catalyst 3 are closely connected to both sides of the diaphragm 1, respectively. Specifically, the cathode and anode catalysts can be catalysts loaded on a substrate and closely attached to the diaphragm by hot pressing or the like, or can be catalysts directly loaded on the membrane electrode. The cathode catalyst uses an electrode loaded with a high-efficiency hydrogen evolution reaction catalyst, such as platinum, ruthenium, nickel and other precious metal-based catalysts or molybdenum disulfide as the cathode electrode. The anode catalyst uses an electrode loaded with a high-efficiency hydrazine hydrate electrocatalytic oxidation reaction, such as nickel, cobalt and other metal-based catalysts as the anode electrode. The first electrolyte solution used in the cathode chamber is a potassium hydroxide aqueous solution; the second electrolyte solution used in the anode chamber is a mixture of a hydrazine hydrate solution and a potassium hydroxide aqueous solution, wherein the potassium hydroxide aqueous solution has the same concentration as the first electrolyte solution.

[0030] In the reactor of the present invention, the membrane and the cathode catalyst and the anode catalyst form a membrane electrode, and the membrane can conduct electricity and ions, so that the cathode and the anode are always at the same potential. Since the potential of the anode hydrazine oxidation reaction (-0.33V vs. RHE) is lower than the potential of the cathode hydrogen evolution reaction (0V vs. RHE), and the membrane makes the cathode and the anode at the same potential, which is between -0.33V and 0V, it can drive the occurrence of electrocatalytic oxidation and reduction reactions. Furthermore, without the need for an external voltage, the novel electrocatalytic membrane reactor of the present invention can realize electrochemical reaction hydrogen production through the potential difference between the cathode and anode reactions.

[0031] like Figure 2 As shown, the present invention also provides a method for preparing high-purity hydrogen based on the above-mentioned electrocatalytic membrane reactor, and the method is specifically as follows:

[0032] The diaphragm 1, the cathode catalyst 2 and the anode catalyst 3 together constitute a membrane electrode. Since the diaphragm 1 can conduct electricity and ions, the cathode and the anode are always at the same potential. High-purity hydrogen is prepared by hydrogen evolution reaction in the cathode chamber 4, and the electrochemical oxidation reaction of hydrazine hydrate is carried out in the anode chamber 5. Since the reduction potential of the hydrogen evolution reaction at the cathode is higher than the oxidation potential of the hydrazine hydrate oxidation at the anode, the cathode and the anode are driven to produce hydrogen by the potential difference between the two without the need for an external voltage. At the same time, by utilizing the separation characteristics of the diaphragm 1, high-purity hydrogen can be obtained directly at the cathode.

[0033] Example

[0034] This embodiment uses the electrocatalytic membrane reactor of the present invention to achieve the preparation of high-purity hydrogen without the need for external voltage, as follows:

[0035] The nickel foam loaded with cobalt array catalyst was used as the anode, with a loading of 1 mg cm -2 The nickel foam with Pt / C (20%wt Pt) catalyst is used as cathode, and the nickel foam filled with polyvinyl alcohol is used as separator. The three are combined together by hot pressing to form a membrane electrode. The cathode electrolyte is 1M KOH aqueous solution, and the anode electrolyte is 0.2M N2H4 / 1M KOH aqueous solution.

[0036] Figure 3 is the volume and time of hydrogen recorded in the experiment. It can be obtained that the rate of hydrogen production is 7 mL h -1 The actual area of ​​the catalyst used in the membrane reactor used in this example is 2 cm 2 Therefore, the hydrogen production rate per square centimeter is 3.5 mL h -1 cm -2 (1.56×10 -4 mol h -1 cm -2 ). Accordingly, the conversion frequency of hydrogen per square centimeter per hour is 156 mol (H2) mol -1 (Pt). It can be seen that the present invention realizes the use of an electrocatalytic membrane reactor without an external voltage for the preparation of high-purity hydrogen.

[0037] The present invention couples the electrocatalysis with the separation function of the membrane, couples the conductivity and ion-conducting characteristics of the diaphragm, and couples the electrocatalytic oxidation of hydrazine hydrate with the cathode hydrogen evolution reaction. Based on this electrocatalytic membrane reactor, it not only has the advantage of high purity of hydrogen production of traditional proton exchange membrane electrolysis cells, but more importantly, we use the potential difference between the cathode and the anode to drive the entire reactor. This reactor does not require additional voltage input, which greatly reduces the energy consumption and cost of hydrogen production and improves economic benefits.

[0038] The above-described embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. An electrocatalytic membrane reactor for preparing high-purity hydrogen based on hydrazine hydrate oxidation, characterized in that: The invention comprises an electrocatalytic membrane reactor body, wherein the inner cavity of the electrocatalytic membrane reactor body is divided into a relatively independent cathode chamber (4) and an anode chamber (5) by a diaphragm (1); the diaphragm (1) can conduct electricity and ions at the same time, and the cathode catalyst (2) located in the cathode chamber (4) and the anode catalyst (3) located in the anode chamber (5) are respectively loaded on both sides; the cathode chamber (4) contains a first electrolyte solution, and the anode chamber (5) contains a second electrolyte solution containing hydrazine hydrate, and the electrocatalytic membrane reactor body located at the top of the cathode chamber (4) and the anode chamber (5) are respectively provided with a first gas outlet (6) and a second gas outlet (7) that can communicate with the outside world; The cathode catalyst (2) and the anode catalyst (3) are respectively tightly connected to the two sides of the diaphragm (1); the cathode catalyst (2) is one of a platinum-based catalyst, a ruthenium-based catalyst, a nickel-based catalyst or a molybdenum disulfide catalyst; the anode catalyst (3) is a nickel-based catalyst or a cobalt-based catalyst; and the diaphragm (1) is nickel foam filled with polyvinyl alcohol gel.

2. The electrocatalytic membrane reactor for preparing high-purity hydrogen based on hydrazine hydrate oxidation according to claim 1, characterized in that: The ions that the diaphragm (1) can conduct are hydrogen ions or hydroxide ions.

3. The electrocatalytic membrane reactor for preparing high-purity hydrogen based on hydrazine hydrate oxidation according to claim 1, characterized in that: The first electrolyte solution is a potassium hydroxide aqueous solution; the second electrolyte solution is a mixture of a hydrazine hydrate solution and a potassium hydroxide aqueous solution having the same concentration as the first electrolyte solution.

4. A method for preparing high-purity hydrogen based on the electrocatalytic membrane reactor according to any one of claims 1 to 3, characterized in that: The details are as follows: The diaphragm (1), the cathode catalyst (2) and the anode catalyst (3) together constitute a membrane electrode. Since the diaphragm (1) can conduct electricity and ions, the cathode and the anode are always at the same potential. High-purity hydrogen is prepared by hydrogen evolution reaction in the cathode chamber (4), and electrochemical oxidation reaction of hydrazine hydrate is carried out in the anode chamber (5). Since the reduction potential of the hydrogen evolution reaction at the cathode is higher than the oxidation potential of the hydrazine hydrate oxidation at the anode, the cathode and the anode are driven to produce hydrogen by the potential difference between the two without the need for an external voltage. At the same time, by utilizing the separation characteristics of the diaphragm (1), high-purity hydrogen can be directly obtained at the cathode.

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