A separated gas electrode for preparing indium hydroxide by electrolysis and a preparation method thereof

Abstract

The invention discloses a separate gas electrode for preparing indium hydroxide by electrolysis, comprising an electrode gas chamber, wherein the electrode gas chamber is made of an internally hollow gas chamber frame and expanded polytetrafluoroethylene layers sealed on both sides, and an air filling pipe connected to the inside of the electrode gas chamber is arranged on the frame of the gas chamber frame; the electrode gas chamber is located on one side of the expanded polytetrafluoroethylene layer and is sequentially provided with an aeration layer frame filled with sponge material and a porous titanium plate; the porous titanium plate is loaded with a catalyst Pt; and the electrode is used for electrolysis to prepare indium hydroxide, and the invention solves the problems of low efficiency in the conventional electrolysis process for preparing indium hydroxide, inability to reuse ammonium nitrate electrolyte, inability to separate the gas electrode from the electrolytic cell for use, uneven gas permeability of the gas electrode, and excessively large specific surface area of ​​the indium hydroxide precipitation, which affects the sintering density.

Description

Technical Field

[0001] The invention relates to a separate gas electrode for preparing indium hydroxide by electrolysis and a preparation method thereof, belonging to the field of preparation of indium hydroxide. Background Art

[0002] ITO materials are widely used in electrical materials, transparent electrode materials, solar cell materials, and screen display technologies due to their high visible light transmittance, infrared reflectivity, excellent conductivity, and good etching performance. The production methods of indium hydroxide, which is its raw material, mainly include dissolution precipitation method, electrolysis method, and other methods. However, since the dissolution precipitation method consumes a large amount of materials such as nitric acid and ammonia water, and produces pollutants such as ammonium nitrate solution that are not suitable for recycling, it is not conducive to low-carbon environmental protection. Therefore, the electrolysis method is still commonly used.

[0003] In the prior art, indium hydroxide is prepared by electrolysis. In order to avoid the introduction of impurities, ammonium nitrate is usually used as the electrolyte, an indium plate as the anode, and an inert electrode such as a titanium plate as the cathode for electrolysis. The electrolysis reaction that occurs is:

[0004] Anode: In→In 3+ +3e

[0005] In 3+ +3OH - →In(OH)3;

[0006] cathode:

[0007] NO3 - +2H + +e=NO2+H2O

[0008] NO3 - +H2O+2e=NO2 - +2OH - ;

[0009] Electrolysis process in the electrolysis chamber:

[0010] NH4NO3→NH4 + +NO3 - ;

[0011] NH4 + →NH3+H + ;

[0012] However, in the prior art, since the standard electrode position of the reduction reaction of nitrate ions is higher than the standard electrode position of the reduction reaction of water during the electrolysis process, nitrate ions are easily reduced to nitrite ions, which increases the pH value of the electrolyte, making the pH value of the electrolyte unstable, resulting in the electrolyte being unable to be reused; and, since the pH is unstable and high, the specific surface area of ​​the indium hydroxide produced is too large and uneven, and small agglomerates will be easily formed in the subsequent sintering process, directly affecting the density of the ITO target.

[0013] In the prior art, in order to reduce the phenomenon of nitrate being reduced to nitrite, the cathode adopts a traditional gas electrode to allow oxygen to participate in the cathode reaction. Although it can reduce the phenomenon of nitrate being reduced to nitrite to a certain extent, due to the traditional gas electrode, the cathode reaction is the reaction of oxygen and water on the surface of the titanium plate, involving the solid-liquid-gas three-phase interface, there is a problem of low reaction efficiency, and side reactions will still occur to generate nitrite and increase the pH value of the electrolyte.

[0014] In addition, the traditional gas electrode manufacturing process is complex and the structural strength is not high, making it difficult to achieve the goals of high quality, high efficiency, environmental protection and low cost in production. In addition, the traditional gas electrode is mostly fixed on the electrolytic cell. When the electrolysis is stopped to clean the electrolytic cell, the gas electrode cannot be installed on the spare electrolytic cell, which reduces the efficiency of the gas electrode. Summary of the invention

[0015] In order to solve the above technical problems, the present invention provides a separable gas electrode, and adopts the electrode as the cathode for electrolytic preparation of indium hydroxide, thereby solving the problems of low efficiency in the conventional electrolytic preparation of indium hydroxide, inability to reuse ammonium nitrate electrolyte, inability to separate the gas electrode from the electrolytic cell, uneven gas permeability of the gas electrode, and excessive specific surface area of ​​the indium hydroxide precipitate, which affects the sintering density.

[0016] In order to solve the above technical problems, the first technical solution adopted by the present invention is:

[0017] A separate gas electrode for preparing indium hydroxide by electrolysis comprises an electrode gas chamber, wherein the electrode gas chamber is made of an internally hollow gas chamber frame and expanded polytetrafluoroethylene layers sealed on both sides, and an inflation tube connected to the inside of the electrode gas chamber is arranged on the frame of the gas chamber frame; the electrode gas chamber is located on one side of the expanded polytetrafluoroethylene layer and is sequentially provided with an aeration layer frame filled with sponge material and a porous titanium plate; the porous titanium plate is loaded with a catalyst Pt.

[0018] The porous titanium plate serves as the conductive part of the electrode, that is, the part where the electrolytic reaction occurs, so that oxygen and water can fully contact to receive electrons and generate hydroxide ions; the expanded polytetrafluoroethylene layer and the air chamber frame are sealed to form an electrode air chamber, which can isolate the electrolyte outside the electrode air chamber. The sponge material is installed between the electrode air chamber and the porous titanium plate, so that the oxygen is aerated in the electrolyte before reaching the porous titanium plate, which can increase the oxygen's travel in the electrolyte, increase the oxygen's residence time in the aeration layer, and ultimately increase the amount of oxygen dissolved in the electrolyte, convert part of the heterogeneous reaction into a homogeneous reaction to increase the amount of dissolved oxygen in the electrolyte, and make the oxygen dissolved in the electrolyte more likely to undergo an electrolytic reaction with water, thereby improving the reaction efficiency of oxygen; the separate gas electrode can be taken out of the electrolytic cell at any time and installed in other electrolytic cells, thereby increasing the utilization rate of the separate gas electrode.

[0019] A further improvement of the technical solution of the present invention is that the porous titanium plate is loaded with catalyst Pt by an impregnation method before installation, and the specific operation is as follows:

[0020] A solution with chloroplatinic acid as the solute and ethylene glycol as the solvent is prepared with a mass fraction of 5%. The titanium plate is dried and then soaked at 40°C for 2 hours. After being taken out and drained, it is dried at 100-140°C for 2 hours. During this process, chloroplatinic acid decomposes platinum particles. Ethylene glycol will protect the platinum particles to prevent the formation of large particles. At the same time, ethylene glycol also participates in the decomposition reaction of chloroplatinic acid as a reducing agent. Then the temperature is quickly raised to 500-600°C for calcination to obtain a stable porous titanium plate loaded with a highly dispersed Pt catalyst. Pt is used as a catalyst for the cathode reaction to further improve the reaction rate of the raw material.

[0021] The further improvement of the technical solution of the present invention is that the catalytic active component content of the porous titanium plate is 0.6%, and ethylene glycol is used as the solvent of chloroplatinic acid, which improves the dispersibility and specific surface area of ​​Pt, reduces the usage of Pt, and saves the usage of precious metals.

[0022] A further improvement of the technical solution of the present invention is that the porosity of the porous titanium plate is 35% to 50%, which ensures the strength and large porosity of the electrode structure and increases the adsorption area and reaction area of ​​the catalyst.

[0023] A further improvement of the technical solution of the present invention is that the sponge material is made of polyurethane with a specification of 40 to 60 PPI and a thickness of 1 to 2 cm.

[0024] A further improvement of the technical solution of the present invention is that the air permeability parameter of the expanded polytetrafluoroethylene layer is 300-400 ml / min / cm 2 .

[0025] A further improvement of the technical solution of the present invention is that the air chamber frame is made of corrosion-resistant plastic.

[0026] A further improvement of the technical solution of the present invention is that the inflation tube is arranged on the top frame of the air chamber frame.

[0027] In order to solve the above technical problems, the second technical solution adopted by the present invention is:

[0028] Pure indium plate is used as anode, separated gas electrode is used as cathode, ammonium nitrate aqueous solution is used as electrolyte for electrolysis, and adjustable DC power supply is used as electrolysis power supply. During electrolysis, 60ml / dm 2 Oxygen is added at a flow rate of / min to obtain hydroxide ions that combine with indium ions in the electrolyte to form indium hydroxide precipitates; wherein the concentration of the ammonium nitrate aqueous solution is 0.5 mol / L, the initial pH value is 4.5-5.2, and the adjustable DC power supply output current is 4-20A.

[0029] During electrolysis, the separated gas electrode and the pure indium plate are immersed in ammonium nitrate electrolyte, the power anode is connected to the pure indium plate, and the power cathode is connected to the separated gas electrode. During electrolysis, oxygen is continuously introduced into the gas electrode at a certain flow rate. At this time, the indium metal on the anode loses electrons and becomes indium ions that dissolve into the electrolyte (In-3e = In 3+ ), oxygen on the cathode obtains electrons and reacts with water to generate hydroxide ions that dissolve into water (2O2+2H2O+4e=4OH - ), indium ions and hydroxide ions combine in the solution to form indium hydroxide precipitates that precipitate in the electrolyte, and the precipitated indium hydroxide precipitates are washed, dried, and calcined to obtain indium oxide.

[0030] Since oxygen is reduced (2O2+2H2O+4e=4OH - ) has a standard electrode potential of 0.401v, which is greater than the nitrate reduction (NO3 - +H2O+2e=NO2-+2OH - ) has a standard electrode potential of 0.01v, which is also greater than the reduction of water to generate hydrogen (2H2O+2e=2H2+2OH - ) has a standard electrode potential of -0.83v, so it is feasible to use oxygen and water to react to provide the hydroxide ions required to produce indium hydroxide without producing hydrogen and nitrite ions.

[0031] The further improvement of the technical solution of the present invention is that: the pH of the electrolyte is maintained at 5-6; the specific surface area of ​​the obtained indium hydroxide is 9.5-12m 2 / g, the particle size is D50 between 0.5-0.9μm, and D90 between 2.0-2.8μm.

[0032] Due to the adoption of the above technical solution, the technical progress achieved by the present invention is:

[0033] The electrode gas chamber of the present invention adopts a frame-type design, which can realize electrolysis on both sides at the same time, and has the advantages of being light and occupying a small space, and can be taken out from the electrolytic cell at any time, which is convenient for actual production maintenance and expansion needs; sponge material is used as the oxygen aeration layer, which increases the dissolved oxygen content in the electrolyte, makes the oxygen reaction efficiency higher, and inhibits the progress of side reactions; at the same time, a porous titanium plate loaded with a Pt catalyst treated by a special impregnation process is used as the electrode conductive part, which ensures the reaction area of ​​the electrode and the strength of the gas electrode, further accelerates the reaction rate, further reduces the generation of by-products, and the pH of the electrolyte can be maintained at 5-6, so that an indium hydroxide precipitate with a suitable specific surface area and uniform particle size distribution can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the structure of the separated gas electrode of the present invention;

[0035] Among them, 1. air chamber frame, 2. expanded polytetrafluoroethylene layer, 3. aeration layer frame, 4. sponge material, 5. porous titanium plate, 6. inflation tube. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below in conjunction with embodiments:

[0037] A separate gas electrode for electrolytically preparing indium hydroxide, such as Figure 1 As shown, it includes an electrode air chamber, which is made of an internal hollow air chamber frame 1 and expanded polytetrafluoroethylene layers 2 sealed on both sides, wherein the air chamber frame 1 is made of corrosion-resistant plastic, and an inflation pipe 6 connected to the inside of the electrode air chamber is arranged on the frame of the air chamber frame 1. Generally, the inflation pipe 6 is arranged on the top frame of the air chamber frame 1; the electrode air chamber is located on one side of the expanded polytetrafluoroethylene layer 2 and is successively provided with an aeration layer frame 3 filled with sponge material 4 and a porous titanium plate 5; the porous titanium plate 5 is loaded with catalyst Pt.

[0038] The porous titanium plate 5 is loaded with catalyst Pt by impregnation method before installation, and the specific operation is as follows:

[0039] A solution with chloroplatinic acid as the solute and ethylene glycol as the solvent is prepared with a mass fraction of 5%. The titanium plate is dried and then soaked at 40°C for 2h. After being taken out and drained, it is dried at 100-140°C for 2h. During this process, chloroplatinic acid decomposes platinum particles. Ethylene glycol will protect the platinum particles to prevent the formation of large particles. At the same time, ethylene glycol also participates in the decomposition reaction of chloroplatinic acid as a reducing agent. Then the temperature is quickly raised to 500-600°C for calcination to obtain a stable porous titanium plate 5 loaded with a highly dispersed Pt catalyst.

[0040] Furthermore, the catalytically active component content of the porous titanium plate 5 is 0.6%, and the porosity is 35% to 50%.

[0041] Furthermore, the sponge material 4 is made of polyurethane, with a specification of 40-60 PPI and a thickness of 1-2 cm.

[0042] Furthermore, the air permeability parameter of the expanded polytetrafluoroethylene layer 2 is 300-400 ml / min / cm 2 .

[0043] Embodiment 1:

[0044] Place the separated gas electrode in the experimental electrolytic cell, add 0.5 mol / L ammonium nitrate solution as the electrolyte, the initial pH value is 5, put in an indium plate weighing 1330 g, use an adjustable DC power supply as the electrolysis power supply, adjust the current output to 5 A, connect the power supply anode to the indium plate, and the power supply cathode to the gas electrode.

[0045] The electrodes are energized and air is filled into the air filling tube 6 at a flow rate of 60 ml / dm 2 / min, and after continuous electrolysis for 24h, the nitrate content in the electrolyte was tested: a small amount of ammonia water was added to adjust the pH value to 6-7. After the indium hydroxide was completely precipitated, a small amount of clarified liquid was taken and dried at 95℃ using a moisture meter. At this time, the ammonium nitrite had decomposed and the remaining dry matter was ammonium nitrate. The nitrate content in the solution could be obtained by calculation, and the measurement result was 0.496mol / L.

[0046] The generated indium hydroxide was washed with deionized water for multiple times to remove nitrate ions. After washing, the sample was dried and the specific surface area of ​​indium hydroxide was measured using a specific surface area analyzer. The specific surface area was measured to be 9.65 m 2 / g.

[0047] The washed indium hydroxide precipitate was sampled, deionized water was added and the indium hydroxide was treated using an ultrasonic dispersion instrument to fully mix and disperse the indium hydroxide. The particle size of the indium hydroxide was then measured using a laser particle size analyzer, and the results showed that D50 and D90 were (0.76, 2.69).

[0048] The pH value during electrolysis was detected and recorded using a handheld pH meter. The data obtained are shown in Table 1 below:

[0049] Table 1 pH value record table of Example 1

[0050] Duration / h 0.5 1 2 4 7 11 16 24 pH 5.13 5.36 5.45 5.51 5.50 5.52 5.51 5.56

[0051] Comparative Example 1

[0052] Place an ordinary titanium plate electrode in an experimental electrolytic cell, add 0.5 mol / L ammonium nitrate solution as the electrolyte, with an initial pH value of 5, put in an indium plate weighing 1336 g, use an adjustable DC power supply as the electrolysis power supply, adjust the current output to 5 A, connect the power supply anode to the indium plate, and the power supply cathode to the gas electrode.

[0053] The electrodes were energized, and the electrolysis was continued for 24 hours before the nitrate content in the electrolyte was detected (using the detection method of Example 1). The measurement result was 0.303 mol / L.

[0054] The particle size of the generated indium hydroxide was measured (using the detection method of Example 1), and the results were D50 and D90 of (0.53, 5.89).

[0055] The generated indium hydroxide was sampled and tested for specific surface area (using the detection method of Example 1), and the specific surface area was measured to be 14.83 m 2 / g, and the pH value during electrolysis was detected and recorded. The obtained data are as follows:

[0056] Table 2 pH value record table of comparative example 1

[0057] Duration / h 0.5 1 2 4 7 11 16 24 pH 7.51 8.25 8.93 9.20 9.36 9.42 9.47 9.59

[0058] Comparative Example 2

[0059] Place the gas electrode without Pt catalyst in the experimental electrolytic cell, add 0.5 mol / L ammonium nitrate solution as the electrolyte, the initial pH value is 5, put in an indium plate weighing 1333 g, use an adjustable DC power supply as the electrolysis power supply, adjust the current output to 5 A, connect the power supply anode to the indium plate, and connect the power supply cathode to the gas electrode.

[0060] The electrodes were energized, and after electrolysis was continued for 24 hours, the nitrate content in the electrolyte was detected (using the detection method of Example 1), and the measurement result was 0.351 mol / L.

[0061] The particle size of the generated indium hydroxide was measured (using the detection method of Example 1), and the results were D50 and D90 of (0.55, 4.22).

[0062] The generated indium hydroxide was sampled and tested for specific surface area (using the detection method of Example 1), and the specific surface area was measured to be 12.69 m 2 / g, and the pH value during electrolysis was detected and recorded. The obtained data are as follows:

[0063] Table 3 pH value record table of comparative example 2

[0064] Duration / h 0.5 1 2 4 7 11 16 24 pH 6.44 6.73 7.08 7.49 7.80 8.16 8.55 8.88

[0065] Comparative Example 3:

[0066] A gas electrode loaded with Pt catalyst by ordinary impregnation method was placed in an experimental electrolytic cell, 0.5 mol / L ammonium nitrate solution was added as the electrolyte, the initial pH value was 5, an indium plate weighing 1328 g was placed, an adjustable DC power supply was used as the electrolysis power supply, the current output was adjusted to 5 A, the power supply anode was connected to the indium plate, and the power supply cathode was connected to the gas electrode.

[0067] The electrodes were energized, and the electrolysis was continued for 24 hours before the nitrate content in the electrolyte was detected (using the detection method of Example 1). The measurement result was 0.428 mol / L.

[0068] The particle size of the generated indium hydroxide was measured (using the detection method of Example 1), and the results were D50 and D90 of (0.61, 3.04).

[0069] The generated indium hydroxide was sampled and tested for specific surface area (using the detection method of Example 1), and the specific surface area was measured to be 10.11 m 2 / g, and the pH value during electrolysis was detected and recorded. The obtained data are as follows:

[0070] Table 4 pH value record table of comparative example 3

[0071] Duration / h 0.5 1 2 4 7 11 16 24 pH 5.48 5.70 5.93 6.16 6.30 6.54 6.75 6.86

[0072] In addition, in Comparative Example 3, after a period of electrolysis, it was found that the catalyst was separated from the gas electrode, contaminating the electrolyte.

[0073] By comparing the experimental data of Comparative Examples 1 to 3 with Example 1, it can be seen that:

[0074] After the experiment of electrolysis using the separated gas electrode of the present invention with oxygen filling, the nitrate concentration in the electrolyte did not change much. In comparison, the nitrate concentration in the comparative example was significantly reduced, and it was obvious that reduction reactions occurred to varying degrees. Therefore, the electrolyte in Example 1 can be recycled and reused, while the electrolyte in the comparative example cannot be recycled and reused.

[0075] Due to the continuous reduction of nitrate ions, the pH value of the solution cannot remain stable and continues to rise to a higher level. The high and unstable pH value causes the specific surface area of ​​the electrolyzed indium hydroxide to be large and uneven, and the particle size distribution is not as concentrated as the indium hydroxide obtained in Example 1, which will be unfavorable for the subsequent sintering of a higher density ITO target.

[0076] Therefore, the use of the present invention to prepare indium hydroxide can realize the recycling of the electrolyte and can produce indium hydroxide precipitates with a moderate specific surface area.

Claims

1. A separate gas electrode for preparing indium hydroxide by electrolysis, characterized in that: The invention comprises an electrode air chamber, wherein the electrode air chamber is made of an air chamber frame (1) with a hollow interior and expanded polytetrafluoroethylene layers (2) sealed on both sides, and an air filling pipe (6) connected to the interior of the electrode air chamber is arranged on the frame of the air chamber frame (1); an aeration layer frame (3) filled with sponge material (4) and a porous titanium plate (5) are arranged in sequence on one side of the expanded polytetrafluoroethylene layer (2); and a catalyst Pt is loaded on the porous titanium plate (5).

2. The separate gas electrode for preparing indium hydroxide by electrolysis according to claim 1, characterized in that: The porous titanium plate (5) is loaded with catalyst Pt by an impregnation method before installation, and the specific operation is as follows: A solution with chloroplatinic acid as the solute and ethylene glycol as the solvent is prepared with a mass fraction of 5%. The titanium plate is dried and then soaked at 40°C for 2 hours. After being taken out and drained, it is dried at 100-140°C for 2 hours. The temperature is then quickly raised to 500-600°C for calcination to obtain a porous titanium plate (5) stably loaded with a highly dispersed Pt catalyst.

3. The separate gas electrode for preparing indium hydroxide by electrolysis according to claim 2, characterized in that: The catalytically active component content of the porous titanium plate (5) is 0.6%.

4. The separate gas electrode for preparing indium hydroxide by electrolysis according to claim 2, characterized in that: The porosity of the porous titanium plate (5) is 35% to 50%.

5. The split gas electrode for preparing indium hydroxide by electrolysis according to claim 1, characterized in that: The sponge material (4) is made of polyurethane, with a specification of 40-60 PPI and a thickness of 1-2 cm.

6. The split gas electrode for preparing indium hydroxide by electrolysis according to claim 1, characterized in that: The air permeability parameter of the expanded polytetrafluoroethylene layer (2) is 300-400 ml / min / cm 2 .

7. The split gas electrode for preparing indium hydroxide by electrolysis according to claim 1, characterized in that: The air chamber frame (1) is made of corrosion-resistant plastic.

8. The split gas electrode for preparing indium hydroxide by electrolysis according to claim 1, characterized in that: The inflation tube (6) is arranged on the top frame of the air chamber frame (1).

9. A method for preparing indium hydroxide by electrolysis using a separated gas electrode according to any one of claims 1 to 8, characterized in that: Pure indium plate is used as anode, separated gas electrode is used as cathode, ammonium nitrate aqueous solution is used as electrolyte for electrolysis, and adjustable DC power supply is used as electrolysis power supply. During electrolysis, 60ml / dm 2 Oxygen is added at a flow rate of / min to obtain hydroxide ions that combine with indium ions in the electrolyte to form indium hydroxide precipitates; wherein the concentration of the ammonium nitrate aqueous solution is 0.5 mol / L, the initial pH value is 4.5-5.2, and the adjustable DC power supply output current is 4-20A.

10. The method for preparing indium hydroxide by electrolysis according to claim 9, characterized in that: The pH of the electrolyte is maintained at 5-6; the specific surface area of ​​the obtained indium hydroxide is 9.5-12m 2 / g, the particle size is D50 between 0.5-0.9μm, and D90 between 2.0-2.8μm.

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