CN1699629A - Process for hydroxide combined production by water electrolysis hydrogen making with low power consumption - Google Patents

Abstract

The present invention discloses a new hydrogen production method of low power consumption. The third main group elements and transition elements are used as anode. The basic electrolyte is alkaline solution, and auxiliary electrolyte is water soluble alkali metal chloride, alkali earth metal chloride, nitrate and sulfate. While electrolyzing by applied directed current, hydroxide is precipitated in anode area and hydrogen is generated on cathode. As compared with traditional hydrogen production of water electrolysis, the invention has the advantages of low power consumption, simple equipment, less environment pollution. Moreover, hydroxide is produced simultaneously.

Description

Method for hydrogen production and co-production of hydroxide by electrolysis of water with low power consumption

technical field

The invention relates to a method for hydrogen production and co-production of hydroxide. Specifically, the Group III metal or transition metal is used as the anode of the electrolysis reaction. In the presence of a certain electrolytic system, a direct current is applied for electrolysis, so that the anode is dissolved to produce hydroxide precipitation, and hydrogen is reduced and precipitated on the cathode. Methods.

technical background

Hydrogen is not only an ideal clean energy, but also an important chemical raw material. Hydrogen is also an excellent energy carrier, which can be stored and transported. At present, the widespread use of fossil fuels has threatened the global environment. Therefore, the development and application of clean energy is the general trend. As a clean energy, hydrogen has attracted widespread attention.

Hydrogen is a secondary energy source. Although hydrogen is one of the most abundant elements on the earth, it exists in a free state (hydrogen gas) very rarely. The most abundant hydrogen-containing substance is water (H ₂ O), followed by various fossil fuels (coal, oil, natural gas) and various biomasses. Therefore, in order to develop and utilize this ideal clean energy, it is necessary to develop hydrogen sources first, that is, to research and develop various hydrogen production methods. At present, hydrogen production methods mainly include: fossil fuel hydrogen production, water hydrogen production, biochemical hydrogen production, nuclear energy hydrogen production and so on. In the long run, using water as raw material to produce hydrogen is the most promising method. The raw material is inexhaustible, and the product water is produced after hydrogen combustion releases energy, which will not cause environmental pollution.

The process of hydrogen production from water as raw material is the reverse process of the reaction of hydrogen and oxygen to generate water, so as long as a certain form of energy is provided, water can be decomposed. The main chemical parameters of the water electrolysis hydrogen production device (electrolysis cell) are the electrolysis voltage (the main indicator that determines the energy consumption of electrolysis) and the current density (determines the amount of hydrogen produced per unit area of the electrolysis cell). At 100kPa and 25°C, the theoretical voltage required for water electrolysis to produce hydrogen is 1.23V. However, due to the loss caused by factors such as resistance, air bubbles, overpotential, and concentration reduction near the electrodes in the electrolytic cell, the actual operating voltage of the industrial electrolytic cell is between 1.65 and 2.2V, and 1m3 of hydrogen is produced under standard conditions. The energy consumption of hydrogen is 4.2-5.5kWh. Although the process is simple and non-polluting, the industrialized electrolytic hydrogen production consumes a lot of electricity and costs a lot, so its application is limited.

CN2127714 discloses an electrode for producing hydrogen and oxygen by electrolysis of water, which consists of an electrode substrate and a porous coating. The electrode can satisfy the low-potential precipitation of hydrogen and oxygen at the same time, so that the utilization rate of electric energy is improved. However, it cannot fundamentally reduce the tank voltage for hydrogen production, so it can only reduce power consumption within a limited range.

CN2181512 discloses a small high-efficiency electrolytic cell specially provided for various electrolytic hydrogen production devices. Its purpose is to solve the problems of large volume, low efficiency, and large consumption of raw materials in the prior art. Its main technical characteristics are The cathode and anode of the electrolytic cell are cylindrical or elliptical cylinders of different sizes, and the anode and the cathode are concentrically set, which is small in size, light in weight, good in heat dissipation, and simple in processing. However, this electrolyzer is suitable for small-scale hydrogen production, and a diaphragm needs to be placed between the two electrodes to avoid gas mixing and explosion, so the process is still relatively complicated.

After experimental research, it is found that the method of using water electrolysis to produce hydrogen and co-produce hydroxide has significant advantages compared with the traditional water electrolysis to produce hydrogen and co-produce oxygen:

1. At 100kPa and 25°C, the theoretical voltage of hydrogen production by this method is between 0-0.2V, which is much lower than the theoretical voltage of 1.23V for traditional water electrolysis hydrogen production.

2. This method of electrolytic hydrogen production can co-produce hydroxides, such as: nickel hydroxide, aluminum hydroxide, cobalt hydroxide, etc. These hydroxides have a wide range of application prospects. If they are dehydrated into oxides, more The scope of its application can be broadened. Therefore, this method can achieve the purpose of killing two birds with one stone.

3. The hydrogen production process of this method is relatively simple. Compared with the traditional electrolysis of water to produce hydrogen, because almost no oxygen is released during the reaction, there is no need to set a diaphragm between the two electrodes to prevent explosions.

4. Compared with the traditional water electrolysis hydrogen production, because there is no oxygen precipitation at the anode, the overpotential during the electrolysis process is smaller, and the cell pressure is further reduced.

Contents of the invention

The purpose of the present invention is to develop a method with low power consumption, simple process, no pollution, safe and reliable operation, and co-production of hydroxide while producing hydrogen.

The innovation of the present invention is:

1. Use Group III and transition metals as anodes, especially: Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Ga, etc., to co-produce hydroxides while producing hydrogen. The overall electrochemical reaction equation is: , wherein n=2,3; M is the above-mentioned III main group and transition metal.

2. The electrolytic system suitable for the electrochemical reaction was screened and prepared.

The method for electrolytic production of hydrogen and co-production of hydroxide described here is to select a suitable anode metal to be suitable for the electrolytic system of the reaction. Root ions combine to form hydroxide precipitates, and hydrogen ions are reduced at the cathode to form hydrogen gas.

The electrolytes mentioned here include basic electrolytes and auxiliary electrolytes. The basic electrolyte is common alkali, and the auxiliary electrolyte is chloride, nitrate and sulfate of alkali metal and alkaline earth metal, and these salts are all soluble in water.

Detailed ways

1. Selection and activation of anode metal

a. Choice of anode metal

The choice of anode metal must abide by certain principles. First, these metals should not be too reactive, and the hydroxides formed by the metal ions are insoluble in water. Therefore, the elements of the main group I, IV, V, VI, and VII can be excluded, and among the elements of the main group II, Mg and Ca are acceptable, but because they are too active, they are not easy to be used as anodes. Secondly, the hydroxides formed by these metals need to have certain application value, so these metals are concentrated in the third main group and subgroup, we have chosen Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Metals such as Ga are used as anodes.

b. Activation of the anode

Put the anode plate into a 5%-25% (wt) NaOH solution to remove the oil on the surface, then wash it with distilled water, then put it into a 5%-25% (wt) HCl solution to activate the electrode surface, and then Wash several times with distilled water.

2. Preparation of electrolytic system

The electrolytic system here is an alkaline system.

The alkaline system consists of electrolytes such as LiOH, KOH, NaOH, and Ba(OH) ₂ as basic components, and auxiliary electrolytes such as LiCl, Mg(NO ₃ ) ₂ , Na ₂ SO ₄ , etc. are added as auxiliary components. After it is dissolved in water, the concentration of hydroxide ion is 0.1-7.0 mol·L ^-1 , and the total concentration of auxiliary electrolyte is 0.5-7.0 mol·L ^-1 .

3. Electrolysis reaction

The conditions for electrolytic hydrogen production and co-production of hydroxide are:

Voltage: 0.1-2.0V;

Electrolytic system: the concentration of hydroxide ions is 0.1-7.0 mol·L ^-1 , the total concentration of auxiliary electrolyte is 0.5-7.0 mol·L ^-1 .

Anode: Group III and transition metals.

The anode adopts the main group III and transition metals, and electrolysis is carried out in the above electrolysis system. The electrolysis voltage is controlled at 0.1-2.0V. The anode is consumed to produce hydroxide precipitation, and hydrogen is precipitated on the cathode. Every ^1m3 of hydrogen produced under standard conditions , The power consumption of hydrogen production by this method is 0.5-2.5kWh.

Embodiments of the present invention are as follows

Example 1

In a closed self-made electrolytic cell, add auxiliary electrolyte LiCl and strong alkali NaOH to make an aqueous solution of 1.0-3.2L, the concentration of LiCl in the solution is 1.0mol·L ^-1 , the concentration of NaOH is 1.0mol·L ^-1 , and the anode nickel After the plate and cathode copper plate are activated, place them in the electrolytic cell, pass direct current, the cathode current density is constant, the reaction temperature is room temperature, and the electrolytic cell adopts strong stirring to carry out electrolysis. The changes of cell voltage and current efficiency with the production of hydrogen and hydroxide during the electrolysis process are shown in Table 1 below.

Table 1 Variation of cell voltage and current efficiency with hydrogen production and nickel hydroxide production Hydrogen production (L) 10 20 30 40 50 60 Nickel hydroxide output (mol) 0.43 0.87 1.30 1.74 2.17 2.61 Cell pressure (V) 0.70 0.80 1.00 1.10 1.30 2.00 current efficiency 0.95 0.92 0.90 0.85 0.80 0.75

Note: The anode is metal nickel, the electrolyte is composed of LiCl and NaOH, and the concentration is 1mol L ^-1

Example 2

In a closed self-made electrolytic cell, add auxiliary electrolyte LiCl and strong alkali NaOH to make an aqueous solution of 1.0-3.2L. The concentration of LiCl in the solution is 1.0mol·L ^-1 , and the concentration of NaOH is 1.0mol·L ^-1 . After activation, place the cathode copper plate in the electrolytic cell, pass direct current, the cathode current density is constant, the reaction temperature is room temperature, and the electrolytic cell adopts strong stirring to carry out electrolysis. The changes of cell voltage and current efficiency with the production of hydrogen and hydroxide during the electrolysis process are shown in Table 2 below.

Table 2 Changes of cell voltage and current efficiency with hydrogen production and aluminum hydroxide production Hydrogen production (L) 10 20 30 40 50 60 Aluminum hydroxide output (mol) 0.29 0.58 0.87 1.16 1.45 1.74 Cell pressure (V) 0.70 0.80 0.80 0.70 0.80 1.20 current efficiency 0.98 0.98 0.95 0.92 0.90 0.85

Note: The anode is metal aluminum, the electrolyte is composed of LiCl and NaOH, and the concentration is 1mol L ^-1

Example 3

Add auxiliary electrolyte NaNO ₃ and strong base NaOH in a closed self-made electrolytic cell to form an aqueous solution of 1.0-3.2L. The concentration of NaNO ₃ in the solution is 1.0mol·L ^-1 , and the concentration of NaOH is 1.0mol·L ^-1 . After the anode nickel plate and the cathode copper plate are activated, they are placed in the electrolytic cell, the direct current is applied, the cathode current density is constant, the reaction temperature is room temperature, and the electrolytic cell adopts strong stirring for electrolysis. The changes of cell voltage and current efficiency with the production of hydrogen and hydroxide during the electrolysis process are shown in Table 3 below.

Table 3 Changes of cell voltage and current efficiency with hydrogen production and nickel hydroxide production Hydrogen production (L) 10 20 30 40 50 60 Nickel hydroxide output (mol) 0.43 0.87 1.30 1.74 2.17 2.61 Cell pressure (V) 0.80 0.85 1.05 1.15 1.35 2.05 current efficiency 0.90 0.90 0.88 0.80 0.75 0.70

Note: The anode is metal nickel, the electrolyte is composed of NaNO ₃ and NaOH, and the concentration is 1mol L ^-1

Example 4

In a closed self-made electrolytic cell, add auxiliary electrolyte LiCl and strong alkali KOH to make an aqueous solution of 1.0-3.2L. The concentration of LiCl in the solution is 1.0mol·L ^-1 , and the concentration of KOH is 1.0mol·L ^-1 . After the plate and cathode copper plate are activated, place them in the electrolytic cell, pass direct current, the cathode current density is constant, the reaction temperature is room temperature, and the electrolytic cell adopts strong stirring to carry out electrolysis. The changes of cell voltage and current efficiency with hydrogen production and hydroxide production during electrolysis are shown in Table 5 below.

Table 4 Changes of cell voltage and current efficiency with hydrogen production and nickel hydroxide production Hydrogen production (L) 10 20 30 40 50 60 Nickel hydroxide output (mol) 0.43 0.87 1.30 1.74 2.17 2.61 Cell pressure (V) 0.65 0.80 1.05 1.15 1.35 2.05 current efficiency 0.95 0.91 0.90 0.85 0.75 0.75

Note: The anode is metal nickel, the auxiliary electrolyte is LiCl and KOH, and the concentration is 1mol L ^-1

Claims (8)

1. A method for preparing hydrogen by water electrolysis with low power consumption is characterized in that hydroxide is produced simultaneously during hydrogen preparation, namely, main group III and transition metal are used as anodes, the basic component of an electrolysis system is alkaline solution, water-soluble chlorides, nitrates and sulfates of alkali metal and alkaline earth metal are used as auxiliary electrolytes, direct current is added for electrolysis reaction, during the reaction process, hydroxide precipitates are formed by anodic oxidation, and hydrogen is reduced at a cathode to form hydrogen gas for separation.

2. The method for producing hydrogen by electrolyzing water as claimed in claim 1, wherein the method for producing hydrogen by electrolyzing water is a method of co-producing hydroxide.

3. A method for producing hydroxide according to claim 1 or 2, wherein the anode metal used in the method for producing hydrogen hydroxide by electrolyzing water is a group III and transition metal.

4. Group III and transition metals according to claim 3, characterized in that the hydroxides formed by oxidation of these metals are water-insoluble precipitates.

5. According to claims 1, 3 and 4, the group III and transition metals are characterized in that the metals are in particular Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Ga.

6. Electrolytic system according to claim 1, characterized in that its basic composition is a strong or medium-strong base, these bases comprising NaOH, KOH, LiOH, Ba (OH)₂Etc. dissolved in water to give a solution having a hydroxide ion concentration of 0.1 to 7.0 mol.L^-1。

7. The electrolytic system according to claim 1 wherein the auxiliary electrolyte is a chloride, nitrate or sulphate of an alkali metal or alkaline earth metal, and wherein the salts are soluble in water. The total concentration of the auxiliary electrolyte in the solution formed after the auxiliary electrolyte is dissolved in water is 0.5-7.0 mol.L^-1。

8. An impressed direct current according to claim 1, characterized in that its electrolytic voltage is 0.1-2.0V; 1m per production³Under the standard condition, the power consumption of hydrogen and hydrogen production by water electrolysis and hydroxide coproduction is 0.5-2.5 kWh.