JPS62227098A - Gas and liquid permeable carbon electrode for electrolysis of aqueous solution - Google Patents

Abstract

PURPOSE:To improve the gas and liq. permeability and to provide high mechanical strength and cushioning action by specifying the amount of expanded graphite in an electrode forming base material and the diameter of the pores in a molded body. CONSTITUTION:A carbonaceous material other than graphite is added to 20-95% expanded graphite and they are kneaded, molded, dried and hardened. The resulting molded body is baked to form a carbon electrode for the electrolysis of an aqueous soln. The electrode has pores of 0.05-10mum diameter. When the electrode is used after it is brought into press contact with an electrode- membrane joined body, the electrode can be well adhered without damaging the membrane because of the proper cushioning action. Since the electrode has satisfactory gas and liq. permeability, the increase of cell resistance due to defective gas/liq. distribution is prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a carbon electrode used in an aqueous electrolysis cell, and in particular has good gas and liquid permeability, high mechanical strength, and cushioning properties. The present invention relates to a carbon electrode having a carbon electrode.

[Prior Art] Solid polymer electrolytic cells have been known for a long time, and their use in cells for electrolyzing water to produce hydrogen and oxygen, etc., has been proposed.

Electrodes bonded to cation exchange membranes that act as solid polymer electrolytes are widely used with conductive and non-passive materials such as platinum group metals, and with binders such as polytetrafluoroethylene (hereinafter referred to as PTFE). Generally, the catalyst particles are bonded to the surface of the ion exchange membrane via a method such as hot pressing the catalyst particles and the binder. For example, JP-A No. 54-93690 discloses that when electrolyzing saline water, the anode is composed of mixed oxide particles of ruthenium and titanium, preferably one that further contains iridium, and the one-sided force sword is mixed with graphite particles. Alternatively, examples of structures composed of supported platinum particles have been reported.

In addition to the above method, it is also known to chemically deposit a porous layer made of an electrocatalytic material (Japanese Patent Publication No. 1983-1999).
36873, Special Publication No. 58-47471, etc.).

When the electrode-membrane assembly (hereinafter referred to as assembly) prepared by the above method is actually incorporated into a cell and operated, the cell is held from both sides by a power supply or current collector and energized.

Such power feeders or current collectors include conventional expanded metals, meshes of metal or carbon, porous bodies, sintered bodies, and carbon or carbon films molded with resins such as PTFE. has been used.

[Problems to be Solved by the Invention] However, the power feeder or current collector electrodes that have been proposed hitherto have the following problems.

That is, electrodes made of the above-mentioned materials with rigidity (for example, metal expanded plates, mesh).

Porous molded bodies, sintered bodies, porous sintered bodies of carbon, etc.) do not have cushioning properties when pressed against a bonded body and are therefore often damaged.

Composite materials with PTFE are flexible and have cushioning properties, which eliminates these drawbacks, but since hydrophobic PTFE is used as a binder, the water permeability of the electrode part decreases, making it difficult to use as a power feeder or current collector. The gas-liquid distribution function is poor, and the electrolytic performance of the cell is reduced.

The present invention has been made focusing on these circumstances,
It is an object of the present invention to provide a carbon electrode for aqueous solution electrolysis that has good gas and liquid permeability, high mechanical strength, and cushioning properties, and does not damage the membrane even when pressed against a bonded body. This is the purpose.

[Means for Solving the Problems] The aqueous electrolysis solution of the present invention achieves the above object.
The liquid permeable electrode is characterized in that it contains 20 to 95% expanded graphite and has a pore diameter of O,OS to 10 μm.

[Function] The carbon electrode according to the present invention uses expanded graphite exhibiting a honeycomb structure and having a large number of continuous pores inside as the electrode forming material (substrate) that dominates the basic structure. Since expanded graphite has such a structure, it has good gas and liquid permeability even after being formed into a molded product, and also exhibits satisfactory cushioning properties even after firing. However, expanded graphite has problems in terms of strength, and has the disadvantage that it often breaks during the firing process after being molded into a desired shape, resulting in a low product yield. Furthermore, the mechanical strength after firing is insufficient, and the electrolytic cell is broken during the assembly stage. In other words, if the drawback of insufficient strength can be overcome, is expanded graphite fired material an excellent water? It is expected that it can be used as a carbon electrode for 8-liquid electrolysis. As a result of various studies on ways to improve the strength, the inventors of the present invention found that if other carbon-based materials are added to the base material of expanded graphite and fired, the excessive continuity contained in the expanded graphite By filling the pores with other carbon-based materials, the continuous pore diameter is adjusted to an appropriate size, and strength can be improved without adversely affecting other required properties (air/liquid permeability and cushioning properties). This discovery led to the completion of the present invention.

That is, the carbon electrode according to the present invention contains expanded graphite in an amount of 20 to 95% as a constituent, and has a continuous pore diameter (i.e., pore diameter) of 0.05 to 10 μm. The content of expanded graphite mentioned above refers to the content in the carbon electrode as a product, and therefore refers to the value after firing the carbon material molded product. Further, the pore size means a pore size range in which both gas/liquid permeability and mechanical strength are good.

When the content of expanded graphite is less than 20%, the proportion of other carbon-based materials blended into expanded graphite becomes relatively large, and the continuous pores of expanded graphite are absorbed by other carbon materials more than necessary. The pores are filled with other materials, and the pore diameter becomes too small. That is 0
．． Fewer pores in the range of 0.05 to 10 μm, 0.05 μm
The number of pores smaller than μm increases and gas and liquid permeability deteriorates. As a result, when the carbon electrode is used, hydrogen and oxygen bubbles generated by electrolysis accumulate in the cell, the bubble diameter increases, the electrical resistance of the carbon electrode increases, and the ohmic loss increases. On the other hand, if the content of expanded graphite exceeds 95%, the amount of other carbon-based materials will be relatively small, so that the continuous pores of expanded graphite will not be sufficiently filled, and pores larger than 10 μm will remain. As a result, the disadvantage that expanded graphite has poor mechanical strength remains unresolved, and problems such as a decrease in yield in the manufacturing process and electrode breakage during the cell assembly stage remain unsolved. On the other hand, when the content of expanded graphite is 20 to 95%, the diameter is 0.05 to 10 μm.
It is possible to obtain a carbon electrode for aqueous solution electrolysis that has high mechanical strength while maintaining sufficient gas/liquid permeability, and also has cushioning properties.

Other carbon-based materials to be mixed with expanded graphite in the present invention are not particularly limited, but include, for example, granular carbon, carbon fiber, glassy carbon, and the like.

That is, examples of the powdery carbon include particles with a developed graphite structure such as natural graphite, quiche graphite, and artificial graphite, and artificial carbon powders such as carbon black and coke powder, and those having a particle size of 100 μm or less are suitable. Incidentally, when the particle size of the granular carbon exceeds ioo μm, the mechanical strength of the carbon electrode decreases. Carbon fibers include those prepared by melt-spinning petroleum or coal pitch and organic resins such as polyacrylonitrile and polyvinyl chloride after appropriate pretreatment, and those obtained by firing the same. The carbon fibers are preferably chopped fibers having a diameter of 3 to 301.1 m and a length of 2 to 30 μm, or those formed into paper or felt shapes. Further, examples of raw materials for glassy carbon include thermosetting resins and cellulose which become glassy when carbonized and fired, and examples of the thermosetting resins include frucrylic alcohol resins and phenol formaldehyde resins.

Next, a typical manufacturing method of the carbon electrode for aqueous electrolysis according to the present invention will be explained. Expanded graphite (20-95%)
The above-mentioned other carbon-based materials and, if necessary, a thickener and a foaming agent are added to the mixture, and after thorough mixing, a phenol resin is added thereto, kneaded, and molded into a desired shape. After molding, drying and curing are performed at a temperature of about 100°C, and then firing at a temperature of about 1000°C in an inert gas stream or in a vacuum to obtain the desired gas/liquid permeable carbon electrode for aqueous solution electrolysis. I can do it. The thickeners used above include known organic thickeners such as methylcellulose, carboxymethyl starch, hydroxyethylcellulose, hydroxypropylcellulose, sodium ligninsulfonate, calcium ligninsulfonate, calcium sulfonate, guar gum, alginate, etc. Examples of the blowing agent used above include polyethylene,
Examples include organic substances with low carbonization yields such as polystyrene, polyvinyl chloride, and polyvinyl alcohol.

[Example] Example 1 An electrode-membrane species combination for water electrolysis was prepared by the following method (Japanese Patent Publication No. 1983-
No. 162780).

DuPont Nafion 1II (No. 117: Thickness 7
The surface of the circular part of about 8 cm in diameter at the center of the diameter of about 12 cm was roughened by sandblasting, and then 4N-HC was applied.
After boiling with IL, it was washed with hot water. The pretreated membrane was sandwiched between acrylic resin Metxcells, and the inside of the cell was divided into two compartments.Tetraamine platinum (!■) solution (P) was added to both compartments of the membrane.
t: 50 mg/100 ml) and left for 3 hours to be adsorbed. After washing with water, add an ammoniacal NaBH40.05% aqueous solution to both compartments at 40-60°C.
The membrane was reduced for 2 hours to deposit approximately 0.5 mg/cm' of platinum on the membrane surface. Next, a crude iridium plating solution having the following composition was circulated in the plating cell, and plating was carried out for 3 hours at 80°C and pH 8.0±0.1.
A 1r (M is membrane) conjugate was obtained.

In the iridium plating solution composition, Ir CJZ, (Ir content 39.7%) 2
50mgNH2OH,HCjZ (5% aqueous solution)
20mILN2'd4. NxO (20% water mt night)
8+nQ water
Total amount: 200 ml Next, a carbon electrode to be used as a power supply material was produced by the following method.

After mechanically mixing the carbon-based materials of each composition shown in Table 1, they were molded into a plate shape, first dried and hardened at 100°C for 4 hours, and then heated at 100°C/hr in an inert gas stream. Firing was performed at a heating rate of 1000°C, and the composition shown in Table 2 was 0.5 mm thick.

An 80 mm $ carbon electrode was manufactured.

According to the arrangement shown in FIG. 1(b), the bonded body 9° and the cathode power supply body (carbon electrode) shown in Table 2 8 (0.5 mm thick 8
0 mmφ) and platinum-plated expanded titanium (0.3 mm thick Ti manufactured by Katsurada Grating Co., Ltd., 8
0mmφ, 0.3-M20F) 11, and then attach a titanium plate (15mm thick) 10 on the anode side and an impermeable graphite plate (20mm thick) 7 on the cathode side to the end plate electrode and tighten to complete the cell. Assembled. Next, this cell was installed in the system shown in FIG. 1(a), and I! was heated at 80°C. Electrolysis was performed while circulating pure water to the south pole side, and the relationship between current density and cell voltage was investigated.

Here, some explanations regarding the above-mentioned cell and cell system will be given. The carbon electrode 8 (1) allows current to flow to the electrode-membrane assembly 9, (2) conducts the Hz'EL generated within the cell and the permeated water in the membrane to the outside. It performs the function of transmitting information to On the other hand, the platinum-plated porous titanium 11 had the function of (1) and (2) generated within the cell. 2 permeates to the outside, and 2) supplies electrolyzed water to the membrane. Also, Figure 1(b)
(7) 3 is a 02-H20 gas-liquid separator and pure water storage tank, and the pump 5 supplies pure water therein to the cell 1.

Reference numeral 6 indicates a heater which normally maintains the water temperature at about 80°C, and 2 indicates an H2-H20 gas-liquid separation unit. Then, H2 or 02 generated in the cell 1 by electrolysis are respectively line j! ! or 12 to the H2-H20 gas-liquid separator 2 or the 02-H,O gas-liquid separator 3, where it is recovered.

FIG. 2 shows the relationship between current density and cell voltage when using the cathode power supply (b) according to the present invention. The figure also includes data investigated for conventionally used porous carbon electrodes for comparison, but as is clear from the figure, the power supply of the present invention has a cell voltage that is approximately 100mv lower under the 200A/dm2 condition. shows.

The power feeder of Example (c) in Table 2 also showed the same tendency as Example (b). Note that (a) and (d) in Table 2 are comparative examples, and (a) has an expanded graphite content of more than 95% and 10
Pores larger than μm were formed and the mechanical strength decreased. On the other hand, regarding (d), since the expanded graphite content is less than 20%, pores smaller than 0.05 μm are generated, resulting in an increase in cell resistance due to poor gas-liquid distribution, resulting in a cell comparable to that of conventional products. Indicated voltage.

Example 2 An Ir-Pt/M/Pt-Ir conjugate was produced in the same manner as in Example 1. The cation exchange membrane is Nafion membrane No.

117 was used.

In the cell configuration shown in Fig. 1, the carbon electrode power supply body (c) of Example 1 is used for the cathode side, and the iridium-plated titanium extracted metal ((1.3m) is used for the anode side power supply body.
m thickness M-20F) was used. It was installed in a system similar to that shown in Figure 1, and chlorine was generated by circulating 20% hydrochloric acid in the anolyte. The relationship between current density and cell voltage at each temperature is
Shown in the figure.

For comparison, when porous carbon cathode power feeder (prefectural chemical laminated paper, 2 mm thickness) was used, under the same conditions, the current density of 100 A/dm2 was approximately 1
00 mv higher cell voltage.

[Effects of the Invention] The present invention is configured as described above, and the following remarkable effects can be obtained.

(1) When the carbon electrode of the present invention is used in pressure contact with an electrode-membrane combination, it has appropriate cushioning properties, so it can be brought into close contact with the membrane without damaging it, and the contact resistance can be lowered. Furthermore, since the contact condition is uniform and reliable, even if electrolysis is performed at a high current density, local heat generation does not occur and the membrane does not deteriorate.

(2) Since the compressive strength is high, the thickness of the carbon electrode can be made thinner, making it possible to apply it to large electrodes.

(3) Good gas/liquid permeability, and no increase in cell resistance due to poor gas/liquid distribution.

(4) Since the electrode plate thickness can be made thinner and can be constructed from a single piece, the cell structure is simplified compared to conventional cells, and the manufacturing process is also simplified, reducing cell costs. be able to.

[Brief explanation of drawings]

Figure 1(a) is a schematic diagram showing the cell system, Figure 1(b)
) is a developed explanatory diagram showing the structure of a cell, and FIG. 2.3 is a graph showing the effects of the present invention. 1...Cell 2...Cathode 8...Carbon electrode 9...Electrode-membrane species combination 1O...Anode 11...Platinum-plated porous titanium Fig. 1(a) Fig. 1(b) \± Fig. 2 Current density (A/dm2) Fig. 3 Current density + A/dm2)

Claims (1)

[Claims] A carbon electrode for aqueous electrolysis produced by molding and firing a carbon-based material, containing 20 to 95% expanded graphite,
A gas/liquid permeable carbon electrode for aqueous electrolysis, characterized in that the pore diameter is 0.05 to 10 μm.