JP2016023371A - Proton exchange membrane for electrochemical cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a proton exchange membrane capable of preventing pumping cost or the like caused by a large amount of flows for exporting oxygen from rising higher.SOLUTION: There is provided a proton exchange membrane 1 having a first layer and a second layer consisting of a first material, further having a third layer arranged between the first layer and the second layer and consisting of a second material. The first material has a hydrogen permeation degree of 9 10m/ms at maximum under hydrogen differential pressure of 3 MPa and conductivity of at least 0.5 S/m, and has moisture absorption of at least 15 wt.% compared to the material under a dry condition, and the second material is a material having open pores. The first layer contacts with a catalyst layer of a first electrode 2, the second layer contacts with a catalyst layer of a second electrode 3 in a first part of the proton exchange membrane 1 and a third layer projects in a medium supply part in a second part of the proton exchange membrane 1, in an electrochemical cell having the proton exchange membrane 1.SELECTED DRAWING: Figure 3

Description

  The present application relates to a proton exchange membrane. The present application further relates to an electrochemical cell, in particular an electrolysis cell, comprising a proton exchange membrane as described herein.

Water electrolysis, PEM (proton exchange membrane: P roton E xchange M embrane) present in the form of a so-called stack performed in the electrolyzer. A PEM electrolyzer generally comprises a plurality of stacked electrochemical cells that are bipolar. Each electrochemical cell has one anode and one cathode separated by a membrane through which ions pass. This membrane passes protons in the case of PEM electrolysers.

  In general, electrolyzed water is supplied to the anode side and flows over the electrode surface. This flow is distributed by a plurality of water channels arranged in parallel or meandered or through any porous structure. A flow distribution structure is disposed between the flow distribution structure and the catalyst layer. This flow distribution structure transports water for reaction from the flow distribution structure to the catalyst layer, and oxygen generated at the anode during water electrolysis to the flow distribution structure from the catalyst layer and releases during water electrolysis. Transported electrons. In order to carry out the generated gaseous oxygen without increasing the cell voltage due to the overvoltage due to the transport, and thus without reducing the efficiency of the electrolyzer, the flow distribution structure must have a stoichiometric amount. A large quantity of running water beyond (λ) must be supplied. Here, a value of λ = 100 is typical. As a result, a high pumping cost is generated on the system side, and a high cost is also generated during water preparation and treatment.

A proton permeable membrane is in direct contact with the catalyst layer of the anode. This proton permeable membrane ensures that protons generated during water electrolysis are transported to the cathode. Here water electrolysis, if the pressure and temperature is a standard condition, the standard hydrogen electrode (N ormal H ydrogen E lektrode;
Occurs at voltages above 1.23V relative to (NHE). As the membrane material, perfluorosulfonic acid (PFSA) based polymers are mainly used.

  On the cathode side is another catalyst layer that promotes the hydrogen evolution reaction. The flow distribution layer is also in contact with this catalyst layer. The flow distribution layer guides the generated hydrogen gas from the catalyst layer and supplies electrons necessary for the hydrogen generation reaction. The cathode flow distribution layer conducts hydrogen into the flow distribution structure. The flow distribution structure can be formed as a water channel structure or as a porous structure, as in the case of the anode. The flow distribution structure carries hydrogen out of the cell and supplies it to the media path. This media path collects hydrogen from all the cells and finally out of the stack. Since gaseous hydrogen is mainly carried under high pressure in the cathode flow distribution structure, the cathode flow distribution structure can be made much thinner than the anode-side flow distribution structure. As a result, the construction space and cost can be reduced.

  Usually, electrolyzed water is used to cool the stack. This water flows through the anode flow distribution structure. Alternatively, an additional flow distribution plate through which the refrigerant flows can be arranged between the anode of a cell and the cathode of a cell adjacent to this cell. The refrigerant is, for example, water or a mixture of water and glycol.

The present application relates to a proton exchange membrane, and the proton exchange membrane has a first layer, a second layer, and a third layer, and the first layer and the second layer are made of a first material. And the third layer is disposed between the first layer and the second layer and is made of a second material. The first material has a maximum hydrogen permeability of 9 · 10 ⁻⁵ m ³ / m ² s and a conductivity of at least 0.5 S / m under a hydrogen differential pressure of 3 MPa. The second material is a material having open pores, and has a moisture absorption of at least 15 weight percent as compared to the material that has a rate and is dry.

  The present application relates to an electrochemical cell, and the electrochemical cell includes the proton exchange membrane, and in the first portion of the proton exchange membrane, the first layer is in contact with the catalyst layer of the first electrode. The second layer is in contact with the catalyst layer of the second electrode, and in the second part of the proton exchange membrane, the third layer protrudes into the medium supply unit.

Schematic sectional view of a proton exchange membrane according to the first embodiment of the present application FIG. 1 is a schematic cross-sectional view of the proton exchange membrane device shown in FIG. 1 between the anode and cathode of an electrochemical cell according to the first embodiment of the present application. 2 is a schematic cross-sectional view showing how the components in the electrochemical cell according to the embodiment of the present application shown in FIG. 2 are connected to the medium supply unit. Sectional view of a proton exchange membrane according to another embodiment of the present application

DISCLOSURE OF THE INVENTION The proton exchange membrane of the present application has a first layer and a second layer. Each of these layers consists of a first material. Furthermore, the proton exchange membrane of the present application has a third layer disposed between the first layer and the second layer. This third layer is made of the second material. The first material has a hydrogen permeability of up to 6 · 10 ⁻⁹ m ³ / m ² s. This is measured under a differential pressure of 200 Pa in accordance with the standard ISO9237. This hydrogen permeability corresponds to a hydrogen permeability of 9 · 10 ⁻⁵ m ³ / m ² s at maximum under a hydrogen differential pressure of 3 MPa. Furthermore, the first material has a proton conductivity of at least 0.5 S / m at a temperature of 323K. This proton conductivity is determined by measuring the AC resistance in a small signal range (ΔU = 20 mV) at a frequency of 1 kHz in a measuring cell consisting of two platinum electrodes in 1 M sulfuric acid. The measuring cell is moved once without a layer made of the first material as a separator and once with a layer made of the first material. The difference between the resistance with a layer and the resistance without a layer represents the resistance of the layer. If the thickness of the membrane is known, then the proton conductivity is calculated. Eventually, the first material has a moisture absorption (mass absorbed water / first material dry matter) of at least 15 weight percent. This moisture absorption is determined by measuring the increase in mass of the first material layer after soaking in water for 10 hours at atmospheric pressure and at a temperature of 298K. Here, weighing is carried out before and immediately after soaking in water. The second material is a material having open pores.

  The membrane structure of the present application makes it possible to provide an amount of water necessary for the electrolysis reaction without using a pump. Water transport occurs spontaneously through capillary forces and diffusion within the membrane structure. This allows the pump for the electrolyzed water required in the electrolyzer to be about 1/100 the size of conventional electrolyzers. Here the pump must be designed for deionized water having a conductivity below 5 μS / cm, rather than 0.5 μS / cm. The pump can be omitted completely if the equipment is relatively small and medium. In particular, the pump can be omitted if the line pressure in the water connection of the medium supply connected to the proton exchange membrane of the present application is sufficient to provide the required volume of water flow. Since the water permeability of the first layer and the hydrogen permeability of the second layer are low, the proton exchange membrane of the present application is highly airtight.

  The thickness of the first layer and the thickness of the second layer are each preferably in the range from 5 μm to 50 μm, particularly preferably in the range from 10 μm to 18 μm, very particularly preferably in the range from 8 μm to 18 μm. . This thickness, coupled with the hydrogen permeability of the first material of the present application, is sufficient to impart high hermeticity to the proton exchange membrane of the present application.

  The thickness of the third layer is preferably in the range from 250 μm to 2000 μm, particularly preferably in the range from 500 μm to 1000 μm. As a result, the proton exchange membrane of the present application has a high water conveyance capability, and the pump for guiding water to the vicinity of the proton exchange membrane can be made much smaller than the case of the conventional electrolyzer as described above. Yes, rather this pump can be omitted entirely. At the same time, the proton exchange membrane is sufficiently thin to be constructed with normal elasticity in a proton exchange membrane as described at the beginning.

  The first material is preferably a perfluorosulfonic acid (PFSA) based polymer, in particular sulfonated polytetrafluoroethylene (PTFE). This is selectively conductive to protons and at the same time has a blocking action on anions.

The conductivity of the second material is advantageously below 10 ⁻⁸ S / m. This therefore functions as an electrical insulator. Therefore, when the first layer or the second layer has small pores, the third layer can prevent short circuit when using the proton exchange membrane of the present application in an electrochemical cell.

  The contact angle between water and the second material is preferably less than 5 °, particularly preferably less than 1 °. As a result, the inner surface of the third layer gets wet well by the aqueous solution. The contact angle is determined according to the droplet method. For this purpose, a predetermined volume of water droplets (from the pipette) is dispensed onto the flat layer of the second material. Assuming that the spread drop has the shape of a spherical cap, and using a known liquid volume, calculating the contact angle from a simple geometrical observation by measuring the diameter of the spread drop at rest Can do.

The pore size of the second material is arithmetically averaged, preferably in the range from 1 μm to 100 μm, particularly preferably in the range from 10 μm to 50 μm. In the size range of such holes, 500mA / cm ² to 3000 mA / cm ^2, in particular of 1000 mA / cm ² to 2000 mA / cm ^2, at a current density which is sought in the electrolytic cell, water Or the maximum capillary rise of the aqueous solution is reached. This is in particular in the range from 200 mm to 500 mm.

  The porosity of the second material is advantageously greater than 50%. This is particularly preferably in the region of more than 50% and up to 80%.

  In order to easily realize the advantageous physical properties of the second material described herein, the second material is advantageously a polymer foam, a foam metal, a sintered porous material and mixtures thereof. Selected from the group consisting of Suitable polymeric foams are advantageously polyethylene (PE), polypropylene (PP), polycarbonate (PC), styrene-acrylonitrile (SAN), ethylene-chlorotrifluoroethylene (ECTFE), ethylene-tetrafluoroethylene (ETFE). ), Tetrafluoroethylene-hexafluoropropylene (FEP), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PFDV) and fluoride-polymer-rubber (FKM) Composed of a combination of materials. These polymer foams can be cured, in particular using ceramic particles. Sintered porous materials are in particular particle sinters or sintered fibers or chips.

  Advantageously, a fourth layer is arranged between the first layer and the third layer, and a fifth layer is arranged between the second layer and the third layer. . Each of the fourth layer and the fifth layer is made of a third material. The third material is an arithmetic average material having open pores whose pore size is smaller than that of the second material. The fine pores and the resulting strong capillary forces provide particularly uniform wetting between the third and fourth layers or between the third and fifth layers, As a result, a particularly uniform distribution of the electrolyzed water absorbed by the third layer is obtained on the first and second layers. If there is a pressure difference between the electrode spaces of the electrochemical cell in which the proton exchange membrane of the present application is built, the proton exchange membrane is more reinforced by the additional fourth and fifth layers. Good mechanical support. This is because in the third material, the length of the self-supporting region between the bridges of adjacent holes is shorter than that in the second material.

  The thickness of the fourth layer and the thickness of the fifth layer are particularly preferably in the range from 10 μm to 200 μm, very preferably in the range from 50 μm to 100 μm. At the same time, the sum of the thickness of the third layer, the thickness of the fourth layer and the thickness of the fifth layer is particularly preferably in the range from 250 μm to 2000 μm, very particularly preferably in the range from 500 μm to 1000 μm. It is in. This balances the thickness between the third layer with large pores and the fourth and fifth layers with small pores, from the third layer through the fourth layer. A particularly good water transfer to the first layer and a particularly good water transfer from the third layer through the fifth layer to the second layer are possible.

  More particularly preferably, the pore size of the third material is in the range of 100 nm to 10 μm, very particularly preferably in the range of 1 μm to 5 μm, on the arithmetic average. This balances the size of the holes between the second material and the third material. This is advantageous for obtaining a stronger capillary force.

  The porosity of the third material is particularly preferably in the range 35% to 65%, very particularly preferably in the range 45% to 55%. This porosity of the third material, coupled with the multi-efficiency of the second material, provides optimal stiffness for the proton exchange membrane of the present application.

In order to provide good rigidity and pressure resistance to the proton exchange membrane of the present application, advantageously the material, i.e. the first material, the second material and possibly the third material, is each at least 0.03 kN / having a modulus of elasticity of mm ^2. This elastic modulus is obtained from a tensile test according to the standard DIN 53457. The second material and possibly the third material can in particular be hardened by weaving the fibers. The fibers are advantageously selected from the group consisting of metal fibers, polymer fibers, glass fibers, carbon fibers and combinations thereof.

  The electrochemical cell of the present application, particularly the electrolytic cell, has the proton exchange membrane of the present application. In the first part of the proton exchange membrane, the first layer contacts the catalyst layer of the first electrode, and the second layer contacts the catalyst layer of the second electrode. In the second part of the proton exchange membrane, the third layer protrudes into the medium supply unit. Here, water necessary for water electrolysis using an acid is supplied to the electrochemical cell through the medium supply unit and further through the third layer of the proton exchange membrane. Thus, there is no need for an electrode flow distribution structure as in the prior art. This eliminates the pump required to circulate the water on the anode side, reduces energy consumption and increases the energy efficiency of the entire system. In the electrochemical cell of the present application, only water evaporated from the proton exchange membrane reaches the flow distribution structure of the anode and cathode of the electrochemical cell, as in conventional electrochemical cells. Since the first layer and the second layer of the proton exchange membrane of the present application are highly airtight, only a small amount of hydrogen reaches the oxygen side when this electrochemical cell is used as an electrolysis apparatus. Only oxygen reaches the hydrogen side.

The medium supply advantageously comprises an acid diluted with water having a pK _s value of up to 3.5 and a concentration in the range of 10 to 50 percent by weight. Particularly advantageously, this concentration is in the range of 20 to 40 percent by weight. This acid is particularly preferably selected from the group consisting of sulfuric acid, dilute nitric acid and phosphoric acid. Very advantageous is sulfuric acid. Thereby, water electrolysis using an acid is realized. Here, at the same time as the outstanding wetting of the proton exchange membrane of the present application is realized, the proton exchange membrane is resistant to the acid used.

  Examples of the present application are illustrated and described in detail in the following specification.

In the first embodiment of the present application, the proton exchange membrane 1 shown in FIG. 1 includes a first layer 11, a second layer 12, and a third layer 13. Each of the first layer 11 second layer 12 was based on the PFSA, consisting sulfonated PTFE (e.g., Nafion DuPont de Nemours, Inc. (USA) ^(R)). The first layer and the second layer here have thicknesses d ₁₁ and d ₁₂ which are each 13 μm. A third layer 13 is disposed between the first layer 11 and the second layer 12. The third layer has a thickness _{d 13} of 750 [mu] m. The third layer here consists of a polypropylene foam with open pores. This has a porosity of 65% and a pore size (arithmetic mean) of 30 μm. All layers 11, 12, 13 are electrically insulating. Therefore, even when the outer layers 11 and 12 are damaged, a short circuit of the proton exchange membrane 1 can be avoided.

  When the electrolysis apparatus is incorporated in the electrochemical cell, the proton exchange membrane 1 is disposed between the first electrode 2 and the second electrode 3 as shown in FIG. The first electrode 2 is used as an anode hereinafter, and the second electrode 3 is used as a cathode. The first electrode 2 includes a catalyst layer 21, a flow distribution layer 22, and a flow distribution layer 23 that overlap each other. Similarly, the second electrode 3 has a catalyst layer 31, a flow distribution layer 32, and a flow distribution layer 33 that overlap each other. The catalyst layer 21 of the first electrode 2 is disposed so as to be in contact with the first layer 11 of the proton exchange membrane 1 over a part of the length of the proton exchange membrane 1. The catalyst layer 31 of the second electrode 3 is in contact with the second layer 12 of the proton exchange membrane 1 over the same length of the proton exchange membrane 1. A region of the proton exchange membrane 1 that is not in contact with the first electrode 2 and the second electrode 3 protrudes from the two electrodes 2 and 3.

  As shown in FIG. 3, this apparatus comprising the proton exchange membrane 1 and the two electrodes 2 and 3 is connected as follows to a medium supply unit 4 configured as a wetted part. The That is, the proton exchange membrane 1 is connected so as to protrude into the medium supply unit 4. The sealing between the medium supply unit 4 and the two electrodes 2 and 3 and the sealing of the proton exchange membrane 1 and the two electrodes 2 and 3 with respect to the outside and the sealing with respect to the outside of the medium supply unit 4 are performed by non-conductive plastic. This is done by a sealing frame 5 consisting of When this electrochemical cell is operated as an electrolysis cell for water electrolysis using an acid, the medium supply unit 4 is filled with 30 weight percent sulfuric acid as the acid 6. In FIG. 3, as indicated by the arrow, the acid 6 is guided into this layer by capillary forces in the third layer 13 of the proton exchange membrane 1, and the outer layer of the proton exchange membrane 1. 11 and 12 are also wetted. In the course of electrolysis, water evaporated from the proton exchange membrane 1 reaches the anode 2. In the catalyst layer 21 on the anode side, water is oxidized to oxygen, protons and electrons. Protons are transported through the first layer 11, through the acid 6 in the third layer 13, through the second layer 12, and into the catalyst layer 31 on the cathode side. The protons are then converted to gaseous hydrogen by electrons carried through an external current circuit (not shown).

  A plurality of electrolysis cells according to the first embodiment of the present application are arranged vertically in a stack. Here, all the proton exchange membranes 1 of this stack protrude beyond the active surface of the stack into the region of the medium supply unit 4 below.

In the second embodiment of the proton exchange membrane 1 of the present application shown in FIG. 4, the first layer 11 and the second layer 12 of the proton exchange membrane 1 are respectively the same as in the first embodiment of the present application. It corresponds to the first layer and the second layer. The thickness _{d 13} of the third layer 13 is only 600 .mu.m. A fourth layer 14 is disposed between the first layer 11 and the third layer 13. A fifth layer 15 is disposed between the second layer 12 and the third layer 13. The thickness _{d 14} of the fourth layer 14, the thickness _{d 15} of the fifth layer 15 is 75μm, respectively, the third layer 13 in the second embodiment of the present and the fourth layer 14 fifth thick total of the layer 14 corresponds to the thickness d ₁₃ of the third layer 13 in the first embodiment of the present application. The material porosity and the pore size (arithmetic mean) of the third layer 13 in the second embodiment of the proton exchange membrane 1 of the present application are the material multi-efficiency and pore size (arithmetic mean) in the first example. ). The fourth layer 14 and the fifth layer 15 are made of the same material as that of the third layer 13. However, the porosity of these two layers 14 and 15 is only 50% and the pore size (arithmetic mean) of these layers is only 3 μm. As a result, a strong capillary force is generated between the third layer 13 and the fourth layer 14 and between the third layer 13 and the fifth layer 15, and the first layer 11 and the second layer 15. The layer 12 is particularly well wetted by the water 6 absorbed by the third layer 13 from the medium supply 4 or the acid 6 diluted with water.

  DESCRIPTION OF SYMBOLS 1 Proton exchange membrane, 2 1st electrode, 3 2nd electrode, 4 Medium supply part, 5 Sealing frame, 6 Acid, 11 1st layer, 12 2nd layer, 13 3rd layer, 14 4th 15th layer, 21 catalyst layer, 22 flow distribution layer, 23 flow distribution layer, 31 catalyst layer, 32 flow distribution layer, 33 flow distribution layer

Claims (15)

A proton exchange membrane (1),
The proton exchange membrane (1) has a first layer (11), a second layer (12), and a third layer (13),
The first layer (11) and the second layer (12) are made of a first material,
In the proton exchange membrane, the third layer (13) is disposed between the first layer (11) and the second layer (12) and is made of a second material.
The first material has a maximum hydrogen permeability of 9 · 10 ⁻⁵ m ³ / m ² s and a conductivity of at least 0.5 S / m under a hydrogen differential pressure of 3 MPa. And has a moisture absorption of at least 15 percent by weight relative to the material being dried,
The second material is a material having open pores.
A proton exchange membrane (1). The thickness of the first layer (11) _{(d 11)} and the thickness of the second layer (12) _{(d 12)} is in the range of 5μm to 50μm, respectively, the third layer (13) The proton exchange membrane (1) according to claim 1, wherein the thickness (d ₁₃ ) is in the range of 250 µm to 2000 µm.   The proton exchange membrane (1) according to claim 1 or 2, wherein the first material comprises a polymer based on perfluorosulfonic acid. The proton exchange membrane (1) according to any one of claims 1 to 3, wherein the conductivity of the second material is ^less than ^10-8 S / m.   The proton exchange membrane (1) according to any one of claims 1 to 4, wherein the contact angle between water and the second material is less than 5 °.   The proton exchange membrane (1) according to any one of claims 1 to 5, wherein the pore size of the second material is an arithmetic average in the range of 1 µm to 100 µm.   The proton exchange membrane (1) according to any one of claims 1 to 6, wherein the porosity of the second material is greater than 50%.   The proton exchange membrane according to any one of claims 1 to 7, wherein the second material is selected from the group consisting of a polymer foam, a foam metal, a sintered porous material, and a mixture thereof. 1). A fourth layer (14) is disposed between the first layer (11) and the third layer (13), and the second layer (12) and the third layer (13). ) To the fifth layer (15),
Each of the fourth layer (14) and the fifth layer (15) is made of a third material, and the third material has an arithmetic average pore size larger than that of the second material. The proton exchange membrane (1) according to any one of claims 1 to 8, which is a material having small open pores. The thickness of the fourth layer (14) _{(d 14)} and the thickness of the fifth layer (15) _{(d 15)} is in the range of 10μm to 200μm, respectively, the third layer (13) thickness and _{(d 13),} the thickness of the fourth layer (14) and _{(d 14),} said fifth layer thickness (15) total and _{(d 15)} is of 250μm to 2000μm The proton exchange membrane (1) according to claim 9, which is in range.   The proton exchange membrane (1) according to claim 9 or 10, wherein the pore size of said third material is in the range of 100 nm to 10 µm in arithmetic mean.   The proton exchange membrane (1) according to any one of claims 9 to 11, wherein the porosity of the third material is in the range of 35% to 65%. Each of the plurality of materials, has at least elastic modulus of 0.03kN / mm ^2, a proton exchange membrane according to any one of claims 1 to 12 (1). An electrochemical cell,
The electrochemical cell has a proton exchange membrane (1) according to any one of claims 1 to 13,
In the first part of the proton exchange membrane (1), the first layer (1) is in contact with the catalyst layer (21) of the first electrode (2), and the second layer (12). Is in contact with the catalyst layer (31) of the second electrode (3),
In the second part of the proton exchange membrane (1), the third layer (13) protrudes into the medium supply part (4).
An electrochemical cell characterized by that. The medium supply (4) comprises an acid (6) diluted with water having a pK _s value of up to 3.5 and a concentration in the range of 10 to 50 weight percent. Item 15. The electrochemical cell according to Item 14.

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