Diaphragm Cloth For Water Electrolyzer And Manufacturing Method Therefor

Abstract

A diaphragm cloth for a water electrolyzer includes a woven fabric, non-woven cloth or knitted fabric composed of alkali-resistant fiber at a common use temperature of no less than 150.degree. C., an average pore size of the diaphragm cloth is less than 10 .mu.m and, under conditions of pressure of 3 KPa, venting quality of the diaphragm cloth is 2 L/cm.sup.2/min or less.

Description

TECHNICAL FIELD

[0001] This disclosure relates to a kind of diaphragm cloth for a water electrolyzer and a manufacturing method therefor.

BACKGROUND

[0002] As the key material of a water electrolyzer, diaphragm cloth is disposed between an anode and a cathode of the water electrolyzer to prevent gas on the anode side from mixing with gas on the cathode side and thus to ensure the purity of gas. Diaphragm cloth has the following requirements on its properties: full wettability by the electrolyte; small average pore size and high gas-tightness; large porosity; certain mechanical strength and stiffness; corrosion resistance to alkaline electrolyte, high-temperature resistance, strong chemical stability and ease of production.

[0003] At present, major factories of equipment that produces hydrogen by alkaline water electrolysis in China still use asbestos cloth as a diaphragm cloth. However, with the advance of industrialization and the technical progress, during the production practice, it is gradually recognized that the asbestos diaphragms have some problems. First, due to the swelling property and chemical instability of asbestos diaphragms, pure asbestos diaphragms experience serious swelling in a specific operating environment, particularly under a high current load so that the mechanical strength of the diaphragms is reduced and the service life thereof is shortened. Moreover, limited by the asbestos material, the temperature of the electrolyte has to be controlled below 90.degree. C. When the temperature of the electrolyte exceeds 90.degree. C., the corrosion to the asbestos diaphragms will be aggravated so that the electrolyte is polluted and the service life of the asbestos diaphragms is influenced. As a result, it is very difficult to improve the efficiency of an electrolyzer by increasing the temperature of the solution. In addition, the asbestos material also has the problems of source reduction, high price, and unstable quality. Comprehensively considering the above reasons, the development and application of novel diaphragm material which can replace the asbestos diaphragms has become a very important issue in the industry. The manufacturers of equipment for producing hydrogen by water electrolysis also successively and actively explore high-performance novel diaphragm material which is energy-saving, environmentally friendly and easy to produce. However, due to the following problems, the so-called novel diaphragm material still can not completely replace current asbestos diaphragms.

[0004] CN101372752A discloses non-woven cloth made of common polyphenylene sulfide fiber, where the non-woven cloth is sulfonated with 90%-98% H.sub.2SO.sub.4 at 70-130.degree. C. for 20-40 min and then treated with 30% potassium hydroxide to finally obtain a high-temperature-resistant diaphragm for an alkaline water electrolyzer. As the non-woven cloth has a relatively high liquid absorption rate, the non-woven cloth, after being treated by strong acid, needs to consume a large amount of valuable water resource and chemicals during a cleaning process and takes a long time to clean, and the technological operation is complicated and easily to pollute the environment. Meanwhile, such non-woven cloth is low in safety and not suitable for industrial production.

[0005] In addition, CN101195944A discloses asbestos-free, environmental and energy-saving diaphragm cloth which is woven fabric made of one or more of poly(ether-ether-ketone) fiber, polyphenylene sulfide fiber and polypropylene fiber. Although the gas-tightness of this diaphragm cloth fulfills the standard requirements of an asbestos diaphragm, the hydrophilicity of the obtained diaphragm cloth is poor because the chemical fiber has poor water absorption, and thus is unable to actually fulfill the use requirements.

[0006] It could therefore be helpful to provide a diaphragm cloth for a water electrolyzer with high gas-tightness and excellent ion permeability and a manufacturing method of a diaphragm cloth for a water electrolyzer with a simple process, lower energy use and decreased environmental pollution.

SUMMARY

[0007] We provide a diaphragm cloth for a water electrolyzer including a woven fabric, non-woven cloth or knitted fabric composed of alkali-resistant fiber at a common use temperature of no less than 150.degree. C.; an average pore size of the diaphragm cloth is less than 10 .mu.m and, under conditions of pressure of 3 KPa, venting quality of the diaphragm cloth is 2 L/cm.sup.2/min or less.

[0008] We also provide a method of manufacturing the diaphragm cloth for a water electro-lyzer including a woven fabric, non-woven cloth or knitted fabric composed of alkali-resistant fiber at a common use temperature of no less than 150.degree. C.; an average pore size of the diaphragm cloth is less than 10 .mu.m and, under conditions of pressure of 3 KPa, venting quality of the diaphragm cloth is 2 L/cm.sup.2/min or less, including weaving, non-weaving or knitting with alkali-resistant fiber at a common use temperature of no less than 150.degree. C. to obtain high-temperature-resistant and alkali-resistant woven fabric, non-woven cloth or knitted fabric, refining and drying the woven fabric or knitted fabric after weaving, and subjecting a surface of the obtained woven fabric, non-woven cloth or knitted fabric to discharge modification to obtain the diaphragm cloth.

DETAILED DESCRIPTION

[0009] We provide a diaphragm cloth for a water electrolyzer, wherein the diaphragm cloth is woven fabric, non-woven cloth or knitted fabric composed of alkali-resistant fiber at a common use temperature of no less than 150.degree. C.; the average pore size of the diaphragm cloth is smaller than 10 .mu.m; and under the condition of a pressure at 3 KPa, the venting quality of the diaphragm cloth is 2 L/cm.sup.2/min or less.

[0010] If the average pore size and the venting quality of the diaphragm cloth are controlled within the above ranges, high gas-tightness of the diaphragm for a water electrolyzer can be ensured. In this way, gas molecules and bubbles are difficult to pass through. As a result, gas on the anode side can be prevented from mixing with gas on the cathode side, the purity of gas and good safety are ensured. From the perspective of ensuring the separator fabric to stably have high gas-tightness for a long term, preferably, the average pore size of the diaphragm cloth is less than 5 .mu.m and the venting quality is 1.5 L/cm.sup.2/min or less.

[0011] To ensure the diaphragm cloth has high gas-tightness and to improve generation efficiency of gas and purity of the generated gas, the average pore size is kept within a certain range and the weaving conditions are controlled to improve the uniformity of the pore size. In other words, preferably, the average pore size is less than 10 .mu.m, and pores with a pore size of 0.2-10 .mu.m in the diaphragm cloth take up no less than 60% of all pores; more preferably, pores with a pore size of 0.2-10 .mu.m in the diaphragm cloth take up no less than 80% of all pores; and particularly preferably, the average pore size is less than 5 .mu.m, and pores with a pore size of 0.2-5 .mu.m in the diaphragm cloth take up above 60% of all pores.

[0012] The diaphragm cloth for a water electrolyzer is formed from high-temperature-resistant and alkali-resistant fiber at a common use temperature of no less than 150.degree. C., such fiber is usually at least one of polyphenylene sulfide (PPS) fiber, polytetrafluoroethylene (PTFE) fiber, poly(p-phenylene benzobisoxazole) (PBO) fiber and poly(ether-ether-ketone) (PEEK) fiber. Considering the requirement of use performance, cost and hydrophilic processability, the polyphenylene sulfide (PPS) fiber is preferred.

[0013] In addition, the cover factor of the fabric is a parameter which characterizes the tightness of the fabric. The higher the cover factor is, the tighter the fabric is, and the smaller the venting quality and pore size are. The weave of the woven fabric is plain weave, twill weave, satin weave, derivative weave and multiple weave thereof, where the plain cloth has the most weaving points and the largest tightness. From the perspective of better fulfilling the gas-tightness requirement of the diaphragm cloth, the plain cloth is preferred of the above mentioned woven fabric plain cloth. When the diaphragm cloth is plain cloth, the cover factor ranges from 2300 to 3000, preferably 2500 to 2900. If the cover factor of the plain cloth is less than 2300, the gas-tightness of the fabric is low due to insufficient tightness of the fabric, thus the diaphragm cloth is difficult to prevent gas on the cathode side and gas on the anode side from passing through, and both the purity of gas and the safety thus can not be ensured. On the other hand, if the cover factor of the plain cloth is more than 3000, the higher requirements are proposed for a weaving machine and the weaving is difficult. When the diaphragm cloth is of multiple weave, for example, weft-backed, weft-tripled or multi-layer fabric, the density of warps or wefts can be further improved under limited conditions of weaving tightness, thereby reducing the venting quality of the fabric and improving the gas-tightness. When the diaphragm cloth is knitted fabric, the cover factor of the knitted fabric is 0.7 to 1.5.

[0014] When in practical operation, if the diaphragm cloth for a water electrolyzer can remain airtight for 2 min at a pressure of no less than 200 mm H.sub.2O (2 KPa), the use requirement of gas-tightness of the diaphragm cloth for a water electrolyzer can be basically fulfilled. From the perspective of ensuring the diaphragm cloth to have excellent gas-tightness, ion permeability and diaphragm cloth processability, the diaphragm cloth for a water electrolyzer preferably has gas-tightness remaining for 2 min at a pressure of 250-450 mm H.sub.2O (2.5-4.5 KPa). If the gas-tightness is less than 250 mm H.sub.2O (2.5 KPa), the basic requirement on the diaphragm can not be fulfilled, and the purity of the generated gas will be influenced. On the other hand, if the gas-tightness is more than 450 mm H.sub.2O (4.5 KPa), it is likely to result in difficult weaving and high cost; furthermore, the resistance of the separator will be increased and the energy consumption for a unit of gas generation is thus increased.

[0015] The diaphragm cloth for a water electrolyzer has high stiffness. During mounting of the diaphragm, the high stiffness can make the separator difficultly wrinkled during the cutting and mounting process, so it is easier, more convenient and more efficient to mount. Meanwhile, a size deviation caused in the cutting process and a thickness deviation caused by wrinkling in the mounting process of the diaphragm can be reduced. Thus, the uniformity of the diaphragm in use is improved. In addition, during operation of an electrolyzer, electrolyte flows in a space between a polar plate and a diaphragm, and the high stiffness of the diaphragm can make the diaphragm cloth generate a smaller deformation when the diaphragm cloth suffering from pressure or other external acting force so that the diaphragm cloth has a smaller influence on the gas-tightness of the diaphragm, electrolysis and voltage, and the stability of the system operation can be thus ensured. The stiffness of the diaphragm cloth in both warp and weft directions is no less than 3 N, preferably no less than 5N.

[0016] To improve both ion permeability and working efficiency of the diaphragm and achieve the goal of saving energy and reducing consumption, we conducted studies from the perspective of improving the hydrophilicity of the diaphragm. Specifically, in the diaphragm cloth for a water electrolyzer, the high-temperature-resistant and alkali-resistant fiber at a common use temperature of no less than 150.degree. C. contains hydrophilic groups on its surface, and the content of oxygen element on the fiber surface is 12 wt % or more. If the content of oxygen element on the fiber surface is less than 12 wt %, improvement in hydrophilicity of the diaphragm cloth is low, and the diaphragm cloth cannot be completely wetted by the electrolyte, resulting in poor ion permeability, large resistance of the diaphragm cloth, low electrolysis efficiency and large energy loss. Considering the balance between the hydrophilicity of the diaphragm cloth and the processing cost, the content of oxygen element on the fiber surface is preferably with 15-40 wt %, more preferably within 15-30 wt %.

[0017] The type of hydrophilic groups and chemical bonds contained on the surface of the high-temperature-resistant and alkali-resistant fiber at a common use temperature of no less than 150.degree. C. is related to a processing method and the type of processing gas. The hydrophilic groups are at least one of carboxyl groups (COOH), carbonyl groups (C.dbd.O), hydroxyl groups (--OH), formyl groups (CHO) or --SO.sub.x. Preferably, the hydrophilic groups are at least one of carboxyl groups (COOH), carbonyl groups (C.dbd.O), hydroxyl groups (--OH) or formyl groups (CHO), and the total content of the hydrophilic groups takes up 10-60% of the total content (mol number) of the groups on the fabric surface. Considering the balance between the hydrophilicity of the diaphragm and the processing cost, more preferably, the total content of the hydrophilic groups takes up 20-50% of the total content (mol number) of the groups on the fabric surface.

[0018] When the diaphragm cloth for a water electrolyzer is composed of polyphenylene sulfide fiber, no less than 20 wt % of the polyphenylene sulfide fiber is modified cross-section polyphenylene sulfide fiber. As its specific surface area larger than that of a circular cross-section, the modified cross-section polyphenylene sulfide fiber may improve water absorption and water conductivity of the fabric by wicking If the content of the modified cross-section polyphenylene sulfide fiber is less than 20 wt %, the specific surface area of fiber in yarns will be reduced so that improvement in water absorption and water conductivity of the prepared diaphragm cloth is not significant, hydrophilicity of the diaphragm cloth is poor, ion permeability and the effect of energy saving are influenced.

[0019] The modified cross-section polyphenylene sulfide fiber may be crossed, latticed, polygonal, leaf-shaped, elliptic or flat cross-section polyphenylene sulfide fiber. From the perspective of preparing diaphragm cloth with excellent hydrophilicity, the modified cross-section polyphenylene sulfide fiber is preferably crossed or polygonal cross-section polyphenylene sulfide fiber. Among the polygonal cross-section polyphenylene sulfide fiber, hexagonal cross-section polyphenylene sulfide fiber is preferred.

[0020] The knitted fabric may be warp-knitted fabric. The warp-knitted fabric is obtained from weaving polyphenylene sulfide yarns or filaments by warp knitting equipment via warp knitting processes. The number of yarns forming the warp-knitted fabric is brought to be lower than that of yarns forming the woven fabric, and the yarns are arranged in a same direction so that the water absorption and water conductivity of the diaphragm cloth may be improved. In addition, the warp-knitted fabric itself has a feature of shrinkage, and due to the shrinkage of the warp-knitted fabric, the diaphragm cloth may be allowed to have high density and high gas-tightness.

[0021] The fabric for the diaphragm cloth for a water electrolyzer is subjected to hydrophilic treatment so that the water absorption of the diaphragm cloth for a water electrolyzer may be improved by no less than 15%, compared with the fabric before treatment. If the improvement rate of the water absorption is less than 15%, the improvement effect of the hydrophilicity is poor. Considering the balance between the hydrophilicity and the processability of the diaphragm cloth, the improvement rate of the water absorption is preferably 15-200%, more preferably 20-100%.

[0022] We further include a manufacturing method of the diaphragm cloth for a water electrolyzer. In the manufacturing method, high-temperature-resistant and alkali-resistant fiber at a common use temperature of no less than 150.degree. C. are woven, non-woven or knitted to obtain high-temperature-resistant and alkali-resistant woven fabric, non-woven cloth or knitted fabric, the woven fabric or knitted fabric are refined and dried after weaving, and then the surface of the obtained woven fabric, non-woven cloth or knitted fabric is subjected to discharge modification to obtain the finished product.

[0023] The raw material of the non-woven cloth is preferably polyphenylene sulfide fiber. The manufacturing method of non-woven cloth made of polyphenylene sulfide fiber is as fol-lows: stretched polyphenylene sulfide fiber is mixed with non-stretched polyphenylene sulfide fiber in water at a certain proportion by weight to form papermaking dispersion, then the wet-laid non-woven cloth of polyphenylene sulfide fiber wet-laid obtained by a wet-laid non-weaving process, then dried and calendered by a roll calendar consisting of a steel roll and a paper roll, and the surface (front side) of the non-woven cloth of polyphenylene sulfide fiber is brought into contact with the steel roll and then heated and pressurized to obtain single-side pressed non-woven cloth; then, the inner side of non-woven cloth is brought into contact with the steel roll and then heated and pressurized to obtain double-side pressed non-woven cloth; and finally, the surface of the double-side pressed non-woven cloth is subjected to discharge modification.

[0024] The discharge modification increases the number of hydrophilic groups on the surface of fabric by a physical processing method and thus to further improve hydrophilicity of the diaphragm cloth. Compared to a method of subjecting fabric to hydrophilic treatment with a hydrophilic chemical reagent, this method will not bring any burden to the environment and can generate durability which ordinarily will not be generated by the hydrophilic chemical reagent in the alkaline environment, and the hydrophilicity may be remained after long-term use in the alkaline environment.

[0025] The discharge modification is plasma treatment or electric ironing treatment, preferably plasma treatment. After the fabric is subjected to plasma treatment, the fiber surface of the fabric is etched so that the surface area is increased. On the other hand, active groups are generated on the fiber surface so that graft copolymerization of hydrophilic monomers on the material surface is caused. Accordingly, when applied in a water electrolyzer, the fabric is easily wet by the electrolyte so that the hydrophilicity of the diaphragm cloth is improved.

[0026] The plasma treatment is preferably vacuum plasma surface treatment or atmospheric pressure plasma surface treatment. When the vacuum plasma surface treatment is employed, a gas (process gas) that forms plasma may be oxygen or argon, or a gas mixture of oxygen and argon, or may be carbon dioxide or air. Generally, the pressure of the used vacuum chamber is 5-100 Pa, and the treatment intensity is 50-500 KWs/m.sup.2. When the treatment gas is oxygen, after plasma surface treatment, oxygen-containing polar groups can be formed on the fiber surface. Thus, the diaphragm cloth has excellent hydrophilicity. When the process gas is argon, as argon is an inert gas with high molecular energy and is easy to be ionized, the fiber on the surface of the fabric is easily activated to fully form polar groups. When the process gas is a gas mixture of oxygen and argon, under the combined action of oxygen and argon, the fiber on the surface of the plasma-ionized fabric is activated first, to be grafted more easily when meeting the oxygen component. To increase the number of formed hydrophilic groups and prolong duration of their effects, the process gas is preferably a gas mixture of oxygen and argon. In addition, as air contains oxygen, nitrogen and carbon dioxide, when air is used as the process gas, the plasma-treated fabric can also achieve excellent hydrophilicity.

[0027] When the vacuum plasma surface treatment is employed, the pressure in the used vacuum chamber is generally 5-100 Pa. Considering treatment effect and energy consumption, the pressure is preferably 30-70 Pa. The treatment intensity is 50-500 KWs/m.sup.2, preferably 80-300 KWs/m.sup.2. The treatment intensity is calculated by the following formula:

treatment intensity=discharge power (KW).times.treatment duration (s)/treatment area (m.sup.2), or

treatment intensity=discharge power (KW)/treatment rate (m/s)/treatment breadth (m).

[0028] If the treatment intensity is less than 50 KWs/m.sup.2, the energy of the charged particles of the plasma is low, thereby leading to a weak cross-linking action on the fiber surface and very few of hydrophilic groups generated on the fiber surface so the finally formed diaphragm cloth is difficult to be fully wetted by the electrolyte. If the treatment intensity is more than 500 KWs/m.sup.2, the treatment effect becomes stable when the treatment intensity reaches about 500 KWs/m.sup.2 so that further increasing the treatment intensity will increase the energy consumption rather than improving the treatment effect. From the perspective of allowing the number of hydrophilic groups on the fiber surface to be saturated and avoiding waste of energy, the treatment intensity is preferably 80-300 KWs/m.sup.2. In this case, the energy of the charged particles is increased, and the cross-linking action can play a full role.

[0029] When the atmospheric pressure plasma surface treatment is employed and air is used as the process gas, the treatment intensity is generally set as 50-500 KWs/m.sup.2. The treatment intensity is calculated by the following formula:

treatment intensity=discharge power (KW)/treatment rate (m/s)/treatment breadth (m).

[0030] If the treatment intensity is less than 50 KWs/m.sup.2,the energy of the charged particles of the plasma is low, thereby leading to a weak cross-linking action on the fiber surface and very few of hydrophilic groups generated on the fiber surface so the finally formed diaphragm cloth is difficult to be fully wetted by electrolyte. If the treatment intensity is more than 500 KWs/m.sup.2, the treatment effect becomes stable when the treatment intensity reaches about 500 KWs/m.sup.2 so that further increasing the treatment intensity will increase the energy consumption rather than improving the treatment effect. From the perspective of allowing the number of hydrophilic groups on the fiber surface to be saturated and avoiding waste of energy, the treatment intensity is preferably 80-300 KWs/m.sup.2. In this case, the energy of the charged particles is increased, and the cross-linking action can play a full role.

[0031] In addition, during or after the plasma treatment, the fabric surface can be subjected to graft modification with a graft modification chemical reagent. For example, the fabric surface can be grafted with carboxyl groups, acrylic groups, sulfonic groups or the like.

[0032] The diaphragm cloth for a water electrolyzer has the features of high gas-tightness and excellent ion permeability, also has low cost, safety, environmental friendliness and light weight; and the manufacturing method is rapid, high efficiency, no pollution, simple operation and energy saving.

[0033] Alkali resistance, the common use temperature, the hydrophilic groups and the total content (mol number) of the hydrophilic groups are defined as follows: [0034] Alkali resistance: the strength of fiber is still kept no less than 95% of the original strength after the fiber is treated in 10% NaOH at 93.degree. C. for 7 days. [0035] Common use temperature: a temperature at which the strength is to be reduced by half after exposure for one hundred thousand hours. The common use temperature is calculated by the Arrhenius equation. [0036] Hydrophilic groups: atomic groups which are weakly bonded with water molecules by bonding with hydrogen atoms.

[0037] The percentage of the total content of hydrophilic groups in the total content (mol number) of groups on the fabric surface: chemical components on the fiber surface are analyzed qualitatively and quantitatively by an X-ray photoelectron spectroscopy (XPS), then peak separation analysis is performed to Peak C, and the type and mol concentration content of groups are judged according to the result of peak separation, where oxygen-containing polar groups are hydrophilic groups, and the sum of mol concentration percentages of the hydrophilic groups is the percentage of the total content of hydrophilic groups in the total content of groups on the fabric surface.

EXAMPLES

[0038] Our cloth and methods will be further described by the following examples. However, the scope of protection afforded by this disclosure is not limited thereto.

[0039] In the examples, the physical properties of the fiber are measured by the following methods or calculated by the following formulae.

Cover Factor

[0040] (1) The cover factor of woven fabric is calculated by the following formula:

[0040] CF=N.sub.W.times. {square root over (D.sub.W)}+N.sub.f.times. {square root over (D.sub.f)},

[0041] wherein, N.sub.W denotes the warp density of the fabric (yarns/inch);

[0042] D.sub.Wdenotes the fineness of warp filaments in the fabric (dtex);

[0043] N.sub.f denotes the weft density of the fabric (yarns/inch);

[0044] D.sub.f denotes the fineness of weft filaments in the fabric (dtex). [0045] (2) The cover factor of knitted fabric is calculated by the following formula: [0046] the cover factor of knitted fabric is also referred to as a tightness factor, which is a ratio of the square root of a TEX of yarns and a stitch length (L), i.e., a K value, where the K value= {square root over (Tex)}/L .

Average Pore Size

[0047] According to the ASTMF316-03 standard, the pore size of fabric is measured by a capillary flowing porosimeter (a product from PMI; Model: CFP-1100-AE), and the working mode is set as a wet-up/dry-down mode. The test environment is 20.+-.2.degree. C. and 65.+-.4% RH. A fabric sample is placed into a sample chamber and then wetted with silwick silicone fluid with a surface tension of 19.1 dynes/cm. The bottom clamp of the sample chamber has a porous metal disc insert with a diameter of 2.54 cm and a thickness of 3.175 mm, while the top clamp of the sample chamber has a hole with a diameter of 3.175 mm, thus the value of the average pore size of the fabric can be directly read. An average value of two times of measurement is used as the final average pore size value.

[0048] The distribution condition of pore size and the ratio of each pore size range can be directly read from the specific measurement results, and the pore size ratio within a certain range can be obtained by adding the measured values shown in the measurement results.

Venting Quality

[0049] The venting quality is measured by a high-pressure air permeability tester (a product from Technoworld; Model: WI70848) at 23.degree. C. and 50% RH. The specific measurement methods are as follows: 17 circular samples each with a diameter of 10 cm are stretched in a breadth direction of the fabric, the venting quality of each sample is measured at 3 KPa, and an average value of 13 intermediate data is used as a final test result.

Gas-Tightness

[0050] The gas-tightness is measured in accordance with the Term 4.5.2 "Gas-tightness Measurement" of "Asbestos Diaphragm Cloth" of the Chinese building material industry standard JC/T211-2009.

Water Absorption

[0051] The water absorption of diaphragm cloth before or after hydrophilic treatment is measured in accordance with GB/T21655.1-2008.

Water Absorption Rate

[0052] The water absorption rate is measured in accordance with the Term 7.1.1 "Falling-drop Method" of JIS L1907-2010 "Water Absorption Test Method of a Fiber Product."

Stiffness

[0053] The stiffness is measured by a fabric stiffness tester (SASD-672-1) (J.A. KING & COMPANY) in accordance with the ASTM D4032 stiffness test standard. The specific method is as follows: warp and weft samples are prepared, and then tested on a stiffness tester after the pressure is regulated to 324 KPa. The test environment is 20.+-.2.degree. C. and 65.+-.4% RH, and the humidification to the samples is performed for above 24 hours.

Requirements on sampling:

[0054] Warp: length*width=8 inch (204 mm)*4 inch (102 mm)

[0055] Weft: length*width=4 inch (102 mm)*8 inch (204 mm)

Hydrophilic group components and content of oxygen element therein

[0056] Chemical components on the fiber surface are analyzed qualitatively and quantitatively by an X-ray photoelectron spectroscopy ("KRATOS" that is produced by SHIMAZU Co. Ltd.,; Model: AXIS ULTRA HAS). The content of oxygen element on the fiber surface is calculated according to the X-ray photoelectron energy spectrum. The bonding capacity of each carbon/oxygen peak can be apparently recognized according to the X-ray photoelectron energy spectrum, thus the hydrophilic group components are determined.

Example 1

[0057] Warps and wefts are both woven with 20 s/6 polyphenylene sulfide yarns to obtain plain cloth with a warp density of 39 yarns/inch and a weft density of 27 yarns/inch. After weaving, the plain cloth is refined and dried, and then the surface of the polyphenylene sulfide plain cloth is subjected to vacuum plasma treatment, where the pressure in a vacuum chamber is 50 Pa, the process gas is a gas mixture of oxygen and argon, and the treatment intensity is 150 KWs/m.sup.2. Finally, diaphragm cloth for a water electrolyzer with a cover factor of 2777.89 and an average pore size of 3 .mu.m is obtained, wherein pores with a pore size of 0.2-10 .mu.m take up 90% of all pores, and the breaking strength of the diaphragm cloth is 4008 N/5 cm and 3218 N/5 cm in warp and weft directions, respectively.

[0058] The prepared diaphragm cloth is tested by an X-ray photoelectron spectroscopy. It is measured that the polyphenylene sulfide fiber surface of the diaphragm cloth contains oxygen-containing hydrophilic groups, and the content of oxygen element is 25 wt %. The oxygen-containing hydrophilic groups include carbonyl groups (C.dbd.O) and hydroxyl groups (--OH), and the total content of the oxygen-containing hydrophilic groups takes up 48% of the total content of groups on the fabric surface. The physical properties of the separator diaphragm cloth for a water electrolyzer in Example 1 are shown in Table 1.

Example 2

[0059] Warps and wefts are both woven with 20 s/4 polyphenylene sulfide yarns to obtain plain cloth with a warp density of 47 yarns/inch and a weft density of 32 yarns/inch. After weaving, the plain cloth is refined and dried, and then the surface of the polyphenylene sulfide plain cloth is subjected to atmospheric pressure plasma surface treatment, where the process gas is air, and the treatment intensity is 150 KWs/m.sup.2. Finally, diaphragm cloth for a water electrolyzer with a cover factor of 2705.82 and an average pore size of 4 .mu.m is obtained, and wherein pores with a pore size of 0.2-10 .mu.m take up 85% of all pores, and the breaking strength of the diaphragm cloth is 2247 N/5 cm and 2110 N/5 cm in warp and weft directions, respectively.

[0060] The prepared diaphragm cloth is tested by an X-ray photoelectron spectroscopy. It is measured that the polyphenylene sulfide fiber surface of the diaphragm cloth contains oxygen-containing hydrophilic groups, and the content of oxygen element is 30 wt %. The oxygen-containing hydrophilic groups include carbonyl groups (C.dbd.O), hydroxyl groups (--OH) and formyl groups (CHO), and the total content of the oxygen-containing hydrophilic groups takes up 45% of the total content of surface groups of the fabric. The physical properties of the diaphragm cloth for a water electrolyzer in Example 2 are shown in Table 1.

Example 3

[0061] Crossed cross-section polyphenylene sulfide fiber is mixed with circular cross-section polyphenylene sulfide fiber at a proportion by weight of 20:80, and then 15 s/4 polyphenylene sulfide yarns are obtained by a spinning process. Then, the obtained polyphenylene sulfide yarns are used as warps and wefts for weaving to form plain cloth with a warp density of 39 yarns/inch and a weft density of 28 yarns/inch. After weaving, the polyphenylene sulfide plain cloth is refined and dried, and then the surface of the plain cloth is subjected to atmospheric pressure plasma surface treatment, where the process gas is air, and the treatment intensity is 130 KWs/m.sup.2. Finally, diaphragm cloth for a water electrolyzer with a cover factor of 2658.70 and an average pore size of 5 .mu.m is obtained, wherein pores with a pore size of 0.2-10 .mu.m take up 80% of all pores, and the breaking strength of the diaphragm cloth is 2600 N/5 cm and 2216 N/5 cm in warp and weft directions, respectively.

[0062] The prepared diaphragm cloth is tested by an X-ray photoelectron spectroscopy. It is measured that the polyphenylene sulfide fiber surface of the diaphragm cloth contains oxygen-containing hydrophilic groups, and the content of oxygen element is 20 wt %. The oxygen-containing hydrophilic groups include carbonyl groups (C.dbd.O), hydroxyl groups (--OH) and formyl groups (CHO), and the total content of the oxygen-containing hydrophilic groups takes up 43% of the total content of groups on the fabric surface. The physical properties of the diaphragm cloth for a water electrolyzer in Example 3 are shown in Table 1.

Example 4

[0063] Hexagonal cross-section polyphenylene sulfide fiber is mixed with circular cross-section polyphenylene sulfide fiber at a proportion by weight of 50:50, to obtain 220 dtex polyphenylene sulfide fiber-mixed filaments. The obtained filaments are warp-knitted to form knitted fabric with a longitudinal density of 89 rows/inch and a transverse density of 63 columns/inch. After weaving, the polyphenylene sulfide knitted fabric is refined and dried, and then the surface of the fabric is subjected to vacuum plasma treatment, where the pressure in a vacuum chamber is 50 Pa, the process gas is a gas mixture of oxygen and argon, and the treatment intensity is 150 KWs/m.sup.2. Finally, diaphragm cloth for a water electrolyzer with a cover factor of 1.3 and an average pore size of 7 .mu.m is obtained, wherein pores with a pore size of 0.2-10 .mu.m take up 60% of all pores, and the breaking strength of the diaphragm cloth is 2347 N/5 cm and 1540 N/5 cm in warp and weft directions, respectively.

[0064] The prepared diaphragm cloth is tested by an X-ray photoelectron spectroscopy. It is measured that the polyphenylene sulfide fiber surface of the diaphragm cloth contains oxygen-containing hydrophilic groups, and the content of oxygen element is 11 wt %. The oxygen-containing hydrophilic groups include carbonyl groups (C.dbd.O) and hydroxyl groups (--OH), and the total content of the oxygen-containing hydrophilic groups takes up 21% of the total content of groups on the fabric surface. The physical properties of the diaphragm cloth for a water electrolyzer in Example 4 are shown in Table 1.

Example 5

[0065] Hexagonal cross-section polyphenylene sulfide fiber is mixed with circular cross-section polyphenylene sulfide fiber at a proportion by weight of 80:20, and then 20 s/6 polyphenylene sulfide yarns are obtained by a spinning process. Then, the obtained yarns are used as warps and wefts for weaving to form 3/3 twill-woven fabric with a warp density of 56 yarns/inch and a weft density of 40 yarns/inch. After weaving, the 3/3 twill-woven fabric is refined and dried, and then the surface of the fabric is subjected to vacuum plasma treatment, where the pressure in a vacuum chamber is 50 Pa, the process gas is air, and the treatment intensity is 100 KWs/m.sup.2. Finally, diaphragm cloth for a water electrolyzer with an average pore size of 8 .mu.m is obtained, wherein pores with a pore size of 0.2-10 .mu.m take up 70% of all pores, and the breaking strength of the diaphragm cloth is 4980 N/5 cm and 3600 N/5 cm in warp and weft directions, respectively.

[0066] The prepared diaphragm cloth is tested by an X-ray photoelectron spectroscopy. It is measured that the polyphenylene sulfide fiber surface of the diaphragm cloth contains oxygen-containing hydrophilic groups, and the content of oxygen element is 26 wt %. The oxygen-containing hydrophilic groups include carbonyl groups (C.dbd.O) and hydroxyl groups (--OH), and the total content of the oxygen-containing hydrophilic groups takes up 40% of the total content of surface groups of the fabric. The physical properties of the diaphragm cloth for a water electrolyzer in Example 5 are shown in Table 1.

Example 6

[0067] Warps and wefts are both woven with 440 dtex-60 f polytetrafluoroethylene filaments to obtain plain cloth with a warp density of 76 yarns/inch and a weft density of 62 yarns/inch. After weaving, the plain cloth is refined and dried, and then the surface of the plain cloth is subjected to vacuum plasma treatment, where the pressure in a vacuum chamber is 50 Pa, the process gas is a gas mixture of oxygen and argon, and the treatment intensity is 200 KWs/m.sup.2. Finally, diaphragm cloth for a water electrolyzer with a cover factor of 2895 and an average pore size of 5 .mu.m is obtained, wherein pores with a pore size of 0.2-10 .mu.m take up 75% of all pores, and the breaking strength of the diaphragm cloth is 4008 N/5 cm and 3218 N/5 cm in warp and weft directions, respectively.

[0068] The prepared diaphragm cloth is tested by an X-ray photoelectron spectroscopy. It is measured that the polytetrafluoroethylene fiber surface of the diaphragm cloth contains oxygen-containing hydrophilic groups, and the content of oxygen element is 20 wt %. The oxygen-containing hydrophilic groups include carbonyl groups (C.dbd.O) and hydroxyl groups (--OH), and the total content of the oxygen-containing hydrophilic groups takes up 38% of the total content of surface groups of the fabric. The physical properties of the diaphragm cloth for a water electrolyzer in Example 6 are shown in Table 1.

Example 7

[0069] Stretched polyphenylene sulfide fiber ("TORCON .RTM." from TORAY; Specification: S301) with a fineness of 1.0 dtex (10 .mu.m in diameter) and a cutting length of 6 mm and non-stretched polyphenylene sulfide fiber ("TORCON.RTM." from TORAY; Specification: S111) with a fineness of 3.0 dtex (17 .mu.m in diameter) and a cutting length of 6 mm are dispersed in water at a proportion by weight of 60:40 to form papermaking dispersion. A 140-mesh papermaking net for handmade paper is provided on the bottom, and the dispersion is fed at a rate of 80 g/m.sup.2 by a small paper machine (from KUMAGAI RIKI KOGYO Co., Ltd.) with a size of 25 cm.times.25 cm and a height of 40 cm. Then, water is added into the dispersion to make the total amount of the dispersion to be 20 L, and the dispersion is fully stirred by a stirrer. Water in the small paper machine is drained, and the residual wet-laid paper on the papermaking net is transferred to a piece of filter paper. The described wet-laid paper and the filter paper are put into a rotary dryer (ROTARY DRYER DR-200 from KUMAGAI RIKI KOGYO Co., Ltd.) together for drying (a temperature of 100.degree. C., a rate of 0.5 m/min, a length of 1.25 m and a duration of 2.5 min) for one time to obtain wet-laid non-woven cloth of polyphenylene sulfide fiber. At this moment, one side in contact with a roll of the dryer is used as surface (front side), and another side not in contact with the roll of the dryer is used as an inner side. Calendering is performed under a steel roll temperature of 200.degree. C., a line pressure of 490 N/cm and a roller rotation speed of 5 m/min by a hydraulic three-roll calender (from Ligun Company; Model: IH type H3RCM) consisting of a steel roll and a paper roll. The surface (front side) of the wet-laid non-woven cloth of polyphenylene sulfide fiber is brought into contact with the steel roll and then heated and pressurized to obtain single-side pressed non-woven cloth. Then, the inner side of the wet-laid non-woven cloth is brought into contact with the steel roll and then heated and pressurized to obtain double-side pressed non-woven cloth. Then, the surface of the double-side pressed non-woven cloth is subjected to vacuum plasma treatment, where the pressure in a vacuum chamber is 50 Pa, the process gas is a gas mixture of oxygen and argon, and the treatment intensity is 150 KWs/m.sup.2. Finally, diaphragm cloth for a water electrolyzer with a volume density of 0.94 and an average pore size of 8 .mu.m is obtained, wherein pores with a pore size of 0.2-10 .mu.m take up 80% of all pores, and the breaking strength of the diaphragm cloth is 151 N/5 cm and 143 N/5 cm in warp and weft directions, respectively.

[0070] The prepared diaphragm cloth is tested by an X-ray photoelectron spectroscopy. It is measured that the polytetrafluoroethylene fiber surface of the diaphragm cloth contains oxygen-containing hydrophilic groups, and the content of oxygen element is 25 wt %. The oxygen-containing hydrophilic groups include carbonyl groups (C.dbd.O) and hydroxyl groups (--OH), and the total content of the oxygen-containing hydrophilic groups takes up 48% of the total content of surface groups of the fabric. The physical properties of the diaphragm cloth for a water electrolyzer in Example 7 are shown in Table 1.

Example 8

[0071] Stretched polyphenylene sulfide fiber ("TORCON.RTM." from TORAY; Specification: S301) with a fineness of 1.0 dtex (10 .mu.m in diameter) and a cutting length of 6 mm and non-stretched polyphenylene sulfide fiber ("TORCON.RTM." from TORAY; Specification: S111) with a fineness of 3.0 dtex (17 .mu.m in diameter) and a cutting length of 6 mm are dispersed in water at a proportion by weight of 60:40 to form papermaking dispersion. A 140-mesh papermaking net for handmade paper is provided on the bottom, and the dispersion is fed at a rate of 100 g/m.sup.2 by a small paper machine (from KUMAGAI RIKI KOGYO Co., Ltd.) with a size of 25 cm.times.25 cm and a height of 40 cm. The other processing conditions are the same as Example 7. Finally, diaphragm cloth for a water electrolyzer with a volume density of 0.96 and an average pore size of 4 .mu.m is obtained, wherein pores with a pore size of 0.2-10 .mu.m take up 90% of all pores, and the breaking strength of the diaphragm cloth is 204 N/5 cm and 198 N/5 cm in warp and weft directions, respectively.

[0072] The prepared diaphragm cloth is tested by an X-ray photoelectron spectroscopy. It is measured that the polytetrafluoroethylene fiber surface of the diaphragm cloth contains oxygen-containing hydrophilic groups, and the content of oxygen element is 25 wt %. The oxygen-containing hydrophilic groups include carbonyl groups (C.dbd.O) and hydroxyl groups (--OH), and the total content of the oxygen-containing hydrophilic groups takes up 48% of the total content of surface groups of the fabric. The physical properties of the diaphragm cloth for a water electrolyzer in Example 8 are shown in Table 1.

Comparative Example 1

[0073] Warps and wefts are both woven with 20 s/6 polyphenylene sulfide yarns to obtain plain cloth with a warp density of 36 yarns/inch and a weft density of 22 yarns/inch. After weaving, the plain cloth is refined, dried and shaped to finally obtain diaphragm cloth for a water electrolyzer with a cover factor of 2441.17 and an average pore size of 12 .mu.m, wherein the breaking strength of the diaphragm cloth is 3800 N/5 cm and 2120 N/5 cm in warp and weft directions, respectively.

[0074] The prepared diaphragm cloth is tested by an X-ray photoelectron spectroscopy. It is measured that the content of oxygen element on the polyphenylene sulfide fiber surface is 2 wt %. The physical properties of this diaphragm cloth for a water electrolyzer are shown in Table 1.

Comparative Example 2

[0075] Warps and wefts are both woven with 20 s/4 polyphenylene sulfide yarns to obtain plain cloth with a warp density of 42 yarns/inch and a weft density of 24 yarns/inch. After weaving, the plain cloth is refined, dried and shaped to finally obtain diaphragm cloth for a water electrolyzer with a cover factor of 2268.13 and an average pore size of 15 .mu.m, wherein the breaking strength of the diaphragm cloth is 2100 N/5 cm and 1980 N/5 cm in warp and weft directions, respectively.

[0076] The prepared diaphragm cloth is tested by an X-ray photoelectron spectroscopy. It is measured that the content of oxygen element in the polyphenylene sulfide fiber surface is 4 wt %. The physical properties of this diaphragm cloth for a water electrolyzer are shown in Table 1.

Comparative Example 3

[0077] Polyphenylene sulfide fiber with a fineness of 2.2 dtex and a length of 51 mm are successively subjected to opening, mixing, carding, web-forming and needle-punched to form non-woven cloth, and then the non-woven cloth is sulfonated in 98% H.sub.2SO.sub.4 at 80.degree. C. for 30 min and then treated with 30% KOH solution. Finally, diaphragm cloth for a water electrolyzer with an average pore size of 13 .mu.m is obtained, wherein the breaking strength of the diaphragm cloth is 1180 N/5 cm and 1500 N/5 cm in warp and weft directions, respectively.

[0078] The prepared diaphragm cloth is tested by an X-ray photoelectron spectroscopy. It is measured that the polytetrafluoroethylene fiber surface of the diaphragm cloth contains oxygen-containing hydrophilic groups, and the content of oxygen element on the polytetrafluoroethylene fiber surface is 12 wt %. The physical properties of the water electrolyzer are shown in Table 1.

TABLE-US-00001 TABLE 1 Item Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Content of modified 0 0 20 50 80 0 cross-section fiber (%) Type of modified -- -- Crossed Hexagonal Hexagonal -- cross-section fiber Form of fabric Woven Woven Woven Knitted Woven Woven Fabric fabric fabric fabric fabric fabric Thickness (mm) 1.0 0.8 0.8 1.2 1.4 0.5 Weight (g/m.sup.2) 568 426 455 400 1130 275 Density Warp 39 47 39 89 56 76 direction (yarns/ inch) Weft 27 32 28 63 40 62 direction (yarns/ inch) Cover factor 2777.89 2705.82 2658.70 1.3 -- 2895 (volume density) (g/cm.sup.3) -- -- -- -- -- -- Average pore sizes (.mu.m) 3 4 5 7 8 5 Gas-tightness (mmH.sub.2O) 300 370 380 240 320 350 Venting quality 0.68 0.79 1.06 1.59 1.89 1.05 (L/cm.sup.2/min) Stiffness Warp 27.3 5.6 5.0 3.3 38.6 2.2 direction (N) Weft 14.3 7.0 5.6 3.0 42.3 1.3 direction (N) Water absorption 101.8 114 91 143.9 152 45 before treatment (%) Water absorption 120.5 132.6 115.1 163.9 186 88 after treatment (%) Water absorption 16 6 42 100 4 300 rate before treatment (%) Water absorption <1 <1 <1 <1 <1 2 rate after treatment (%) Operability of No No No Wrinkling, No Much a diaphragm during wrinkling, wrinkling, wrinkling, no influence wrinkling, wrinkling, mounting convenient convenient convenient on cutting convenient inconvenient for cutting for cutting for cutting and for cutting for cutting and and and mounting and and mounting mounting mounting mounting mounting Stability of Not easy Not easy Not easy Certain Not easy Easy to an electrolyzer to cause to cause to cause deformation, to cause cause during deformation, deformation, deformation, but stable deformation, deformation, operation and stable and stable and stable system and stable and system system system operation system poor long- operation operation operation operation term operation stability Comparative Comparative Comparative Item Example 7 Example 8 Example 1 Example 2 Example 3 Content of modified -- -- 0 0 0 cross-section fiber (%) Type of modified -- -- -- -- -- cross-section fiber Form of fabric Non- Non- Woven Woven Non- woven woven fabric fabric woven cloth cloth cloth Thickness (mm) 0.09 0.11 0.9 0.8 1.5 Weight (g/m.sup.2) 83 106 498 419 500 Density Warp -- -- 36 42 -- direction (yarns/ inch) Weft -- -- 22 24 -- direction (yarns/ inch) Cover factor -- -- 2441.17 2268.13 -- (volume density) (g/cm.sup.3) 0.94 0.96 -- -- 0.33 Average pore sizes (.mu.m) 8 4 12 15 13 Gas-tightness (mmH.sub.2O) 370 480 200 130 180 Venting quality 0.82 0.33 2.68 2.98 2.43 (L/cm.sup.2/min) Stiffness Warp 2.6 3.4 24.5 4.8 21.5 direction (N) Weft 3.2 3.8 11.8 5.3 28.6 direction (N) Water absorption 117 123 101.8 114.8 300 before treatment (%) Water absorption 139 147 -- -- 318 after treatment (%) Water absorption 143 150 17 6 300 rate before treatment (%) Water absorption 4 6 -- -- 5 rate after treatment (%) Operability of Much Wrinkling, No No No a diaphragm during wrinkling, no influence wrinkling, wrinkling, wrinkling, mounting inconvenient on cutting convenient convenient convenient for cutting and for cutting for cutting for cutting and mounting and and and mounting mounting mounting mounting Stability of Easy to Deformed, Unqualified Unqualified Unqualified an electrolyzer cause but stable gas- gas- gas- during deformation, system tightness, tightness, tightness, operation and operation and can and can and can poor long- not be used not be used not be used term operation stability

Claims

1-19. (canceled)

20. A diaphragm cloth for a water electrolyzer comprising a woven fabric, non-woven cloth or knitted fabric composed of alkali-resistant fiber at a common use temperature of no less than 150.degree. C., an average pore size of the diaphragm cloth is less than 10 .mu.m and, under conditions of pressure of 3 KPa, venting quality of the diaphragm cloth is 2 L/cm.sup.2/min or less.

21. The diaphragm cloth according to claim 20, wherein said alkali-resistant fiber at a common use temperature of above 150.degree. C. is at least one selected from the group consisting of polyphenylene sulfide fiber, polytetrafluoroethylene fiber, poly(p-phenylene benzobisoxazole) fiber and poly(ether-ether-ketone) fiber.

22. The diaphragm cloth according to claim 21, wherein said alkali-resistant fiber at a common use temperature of no less than 150.degree. C. is polyphenylene sulfide fiber.

23. The diaphragm cloth according to claim 20, wherein the alkali-resistant fiber at a common use temperature of above 150.degree. C. contains hydrophilic groups on its surface, and the content of oxygen element on a surface of the fiber is 12 wt % or more.

24. The diaphragm cloth according to claim 23, wherein said content of oxygen element on the fiber surface is 15-40 wt %.

25. The diaphragm cloth according to claim 23, wherein said hydrophilic groups are at least one selected from the group consisting of carboxyl groups, carbonyl groups, hydroxyl groups and formyl groups, and total content of the hydrophilic groups is 10-60% of the total content of the groups on the fabric surface.

26. The diaphragm cloth according to claim 20, wherein pores with a pore size of 0.2-10 .mu.m in the diaphragm cloth take up no less than 60% of all pores.

27. The diaphragm cloth according to claim 20, wherein stiffness of the diaphragm cloth in both warp and weft directions is no less than 3 N.

28. The diaphragm cloth according to claim 20, wherein stiffness of the diaphragm cloth in both warp and weft directions is no less than 5 N.

29. The diaphragm cloth according to claim 22, wherein the polyphenylene sulfide fiber contains no less than 20 wt % of modified cross-section polyphenylene sulfide fiber.

30. The diaphragm cloth according to claim 29, wherein said modified cross-section polyphenylene sulfide fiber is crossed, latticed, polygonal, leaf-shaped, elliptic or flat cross-section polyphenylene sulfide fiber.

31. The diaphragm cloth according to claim 20, wherein said woven fabric is plain cloth.

32. The diaphragm cloth according to claim 31, wherein the plain cloth has a cover factor of 2300 to 3000.

33. The diaphragm cloth according to claim 20, wherein said knitted fabric is wrap-knitted fabric.

34. A method of manufacturing the diaphragm cloth according to claim 20, comprising: weaving, non-weaving or knitting with alkali-resistant fiber at a common use temperature of no less than 150.degree. C. to obtain high-temperature-resistant and alkali-resistant woven fabric, non-woven cloth or knitted fabric, refining and drying the woven fabric or knitted fabric after weaving; and subjecting a surface of the obtained woven fabric, non-woven cloth or knitted fabric to discharge modification to obtain the diaphragm cloth.

35. The method according to claim 34, wherein said discharge modification is plasma treatment or electric ironing treatment.

36. The method according to claim 35, wherein said plasma treatment is vacuum plasma surface treatment or atmospheric pressure plasma surface treatment.

37. The method according to claim 36, wherein, during the vacuum plasma surface treatment, the process gas is selected from the group consisting of oxygen, argon, a gas mixture of oxygen and argon, carbon dioxide and air, pressure of a vacuum chamber is 5-100 Pa, and treatment intensity is 50-500 KWs/m.sup.2.

38. The method according to claim 36, wherein, during the atmospheric pressure plasma surface treatment, the process gas is air, and treatment intensity is 50-500 KWs/m.sup.2.