RU2198452C1 - Method for assembling diaphragm-electrode unit - Google Patents

Abstract

FIELD: electrical engineering; fuel cells with proton-conducting polymeric diaphragms. SUBSTANCE: novelty is that diaphragm- electrode unit is assembled by electrochemical method , that is, in pulsed mode of operation of fuel cell while reducing them with aid of plane- parallel gas-distributing plates provided with channels on their surfaces, 0.5 to 5.0 sq. mm deep, for feeding chemical agents and with insulating gaskets on their perimeter forming spaces separated relative to electrodes for feeding hydrogen and oxygen; total sectional area of all channels is 1 to 10% of electrode surface. Assembly is conducted at draft pressure of 2 to 150 kg/sq. cm and working gas pressure of 1 to 6 atm. abs. until temperature of 80 to 120 C is attained due to connection of electric load to auxiliary plates in pulsed mode with current density being from 100 mA/sq. cm to short-circuit currents. By the end of assembly diaphragm- electrode unit is checked for its current-voltage characteristics. Diaphragm-electrode unit is also proposed to be subjected to pre- assembly thermal reduction at draft pressure of 2 to 150 kg/sq. cm and at temperature of 90 to 220 C in aqueous dielectric environment or in air. In the latter case diaphragm is pre-dehydrated at 60 to 98 C. EFFECT: enhanced efficiency of using active surfaces of unit. 4 cl, 2 dwg

Description

 The invention relates to the field of electrical engineering, namely to fuel cells with proton-conducting polymer membranes and other chemical current sources in which membrane-electrode blocks (assemblies) are used. Such fuel cells can be used in power plants for sea and land transport, as well as in stationary autonomous power plants.

 A known method of assembling batteries of fuel cells with proton-conducting polymer membranes, which consists in the fact that the battery is assembled by stacking sequentially on each other and subsequent compression in a packet of electrodes, proton-conducting polymer membranes, gas distribution and current-collecting cooling plates (application 19542475, Germany, IPC 6 H 01 M 8/02, H 01 M 2/08, claimed 15.11.95 g, publ. 05.22.97).

 In such assemblies, the membrane is coupled to the electrodes, and therefore the current is transmitted, due to mechanical clamping (longitudinal or axial compression of the electrode stack, proton-conducting polymer membranes, gas distribution and current-collecting cooling plates). In such designs, the membrane-electrode unit does not work uniformly, the electrochemical reaction and current generation occurs mainly in the zone of compression of the membrane-electrode unit by ribs or corrugations of gas distribution (separation) plates. Thus, that part of the active surface of the membrane-electrode block that is in the compressed state as part of the package works most effectively, and the rest of the surface is in the uncompressed state and practically does not work.

 There is also a known method of manufacturing membranes with electrodes fixed on them (see application DE19705468 A1, Germany, IPC 6 V 23 K 20/10, decl. 13.02.97, publ. 27.08.98), which consists in the fact that membranes and porous electrodes are connected by ultrasonic welding. Such a connection provides a mechanical connection of the membranes with the electrodes and more efficient use of the active surface at the membrane-electrode interface. In this case, the membranes are coupled with the electrodes at the points of direct contact of the relief surfaces of these elements without taking into account the electrophysical and electrochemical processes that take place in the fuel cells during their operation in the electric power generation mode. In view of this, it is not possible to use the entire active surface of the membrane-electrode assembly, as well as to ensure uniformity of its operation.

 The aim of the present invention is to increase the efficiency of use of the active surfaces of membrane-electrode blocks (assemblies) and the uniformity of the active surface.

This goal is achieved by the fact that the assembly of the membrane with the electrodes is carried out electrochemically, namely in the pulsed mode of operation of the fuel cell during compression by technological plane-parallel gas distribution plates having channels on their surface with a cross section from 0.5 to 5.0 mm ² for supplying hydrogen and oxygen . In this case, the total cross section of all channels is from 1 to 10% of the electrode surface. The membrane with electrodes is assembled at a compression pressure of 2 to 150 kg / cm ² and working gas pressures of 2 to 6 abs. atm during the time of reaching a temperature of 80 to 120 ^o C, which is provided when connecting an external electrical load to the process plates in a pulsed mode and at current densities of 100 mA / cm ² to short circuit currents.

 It is preferable in the process of such assembly to simultaneously monitor the current-voltage characteristics of the membrane-electrode block (before installing it in the battery of fuel cells).

It is also proposed to perform preliminary thermocompression conjugation of the membrane-electrode block at a compression pressure of 2 to 150 kg / cm ² and at a temperature of 90 to 220 ^o C in an aqueous dielectric medium or in air. In the latter embodiment, the membrane is pre-dehydrated at a temperature of from 60 to 98 ^o C.

 The membrane-electrode block is designed to operate as part of hydrogen-oxygen and hydrogen-air batteries of fuel cells. Electrochemical assembly or thermocompression conjugation of membranes with electrodes ensures their "monolithic" connection and allows the efficient use of almost 100% of the active surface. In fact, these processes lead to the formation of three-dimensional structures of the active surface and allow the creation of multilayer fuel cells without mechanical compression over the surface or by an order of magnitude with less effort, which ultimately leads to an improvement in the overall dimensions of the fuel cell batteries.

 The analysis of the prior art showed that the claimed combination of features set forth in the formula is not known. This allows us to conclude that the claimed method meets the criterion of "novelty."

 To verify the conformity of the claimed invention to the criterion of "inventive step", a search was made for technical solutions in order to identify features that match the distinctive features of the prototype of the claimed invention.

 It is established that the claimed invention does not follow for a person skilled in the art explicitly from the prior art. Therefore, the claimed invention meets the criterion of "inventive step".

 Figure 1 shows a cross section of a single fuel cell with a membrane-electrode unit operating during mechanical compression. The membrane 1 is located between the electrodes 2 and 3. The specified assembly is crimped on both sides by gas distribution current collection plates 4 and 5, gaskets made of electrically insulating material 6. The membrane contacts the electrodes in the area of sections 7 when the packet is compressed, and practically occurs in the areas of sections 8 stratification of membranes with electrodes. The effect of uneven operation of such structures is manifested during operation as part of fuel cells, because as the resource is depleted, the membranes partially merge with the electrodes and only in the places of compression. When defining spent fuel cells and separating the electrodes from the membranes, the "pattern" of the gas distribution plates is clearly manifested.

 Figure 2 illustrates the method of electrochemical assembly of the membrane-electrode block.

The membrane 9 is installed between two electrodes 10, 11 in a device consisting of a lower flange 12 and an upper flange 13, between which there are sealing gaskets 14, 15. These gaskets provide sealing of the membrane along the perimeter, as well as sealing spaces 16, 17 between the electrodes and flanges . Channels 18 are made in the flanges 12, 13, connecting the electrodes 10, 11 with the cavities in the flanges 16.17, respectively. Channels 18 are made in the form of holes with a diameter of 1-2 mm. The lower 12 and upper 13 flanges are in direct contact with the electrodes 10, 11 and are compressed by a force P (from 5 to 150 kg / cm ² depending on the thickness of the membrane and the design of the electrodes). After assembly and compression of the flanges in the cavity 16, 17, the working gases (H ₂ , O ₂ ) are supplied. The flanges 12, 13 are electrically connected through a switching device 19 to an external electrical load 20. To control the current-voltage characteristics, a voltmeter 21 and ammeter 22 are installed in the load circuits. A temperature sensor is installed in one of the flanges. Outside the device is thermally insulated. The membrane with electrodes is assembled in the continuous compression mode of the flanges when the working gases are supplied and the electrical load is periodically connected. The control points are the achievement of the operating temperature and the required current-voltage characteristics.

 The claimed method of assembly of the membrane-electrode block was implemented on prototypes with an active surface diameter of 50 mm. At a voltage of 0.8 V, the increment in current density (compared with the purely mechanical clamp in the fuel cell) for the electrochemical method of connection was about 12-16%, and for the thermocompression one about 5-8%.

 Based on the foregoing, we can conclude that the claimed invention can be used in practice to achieve the specified result and, therefore, meets the criterion of "industrial applicability".

Claims (4)

1. The method of assembly of the membrane-electrode block of a fuel cell with a proton-conducting polymer membrane and gas diffusion electrodes, which consists in creating a package of two electrodes and a membrane installed between them, and compressing the specified package, characterized in that the assembly is carried out by electrochemical method, namely in pulsed the operation mode of the fuel cell when the package is compressed by technological plane-parallel plates having channels on their surface with a cross section from 0.5 to 5.0 mm ² for supplying working gases - hydrogen and oxygen, and the total cross-section of all channels is from 1 to 10% of the surface of the electrodes, and equipped with electrically insulating sealing gaskets along the contour, forming spaces separated from the electrodes for supplying working gases, while assembly is performed at a compression pressure of 2 to 150 kg / cm ² and working gas pressures from 2 to 6 abs. during the time of reaching a temperature of 80 to 120 ^o C, which is provided when connecting an external electrical load to the process plates in a pulsed mode and at current densities of 100 mA / cm ² to short circuit currents.  2. The method according to claim 1, characterized in that at the end or after the electrochemical assembly of the membrane-electrode block, its current-voltage characteristics are monitored. 3. The method according to p. 1, characterized in that the membrane is pre-assembled with electrodes by the thermocompression method at a pressure of 2 to 150 kg / cm ² and a temperature of 90 to 220 ^o C in an aqueous dielectric medium. 4. The method according to p. 1, characterized in that the preliminary thermocompression assembly of the membrane with electrodes in air is performed at a pressure of 2 to 150 kg / cm ² and a temperature of 90 to 220 ^o C, while the membrane is transferred to a dehydrated state at a temperature of 60 to 98 ^o C.

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