WO2005056880A1

WO2005056880A1 - Bipolar plate and production method thereof

Info

Publication number: WO2005056880A1
Application number: PCT/ES2003/000629
Authority: WO
Inventors: Mikhail Alexandrovich Tsypkin; Ricardo Blach Vizoso; Vladimir-Nikolaevich Fateev; Vladimir Igorevich Porembskiy; Eugeniy Akimovich Bogatchev
Original assignee: David Systems & Technology, S.L.
Priority date: 2003-12-12
Filing date: 2003-12-12
Publication date: 2005-06-23
Also published as: AU2003288279A1

Abstract

The invention relates to a bipolar plate and to the production method thereof. The inventive bipolar plate comprises a central part (1) and peripheral parts (2), said central part being equipped with current conducting projections (3) having upper ends which are located in the same plane as the peripheral parts (2). According to the invention, the height of the projections is between 0.3 and 2 mm and the distance between the farthest points at the base thereof is between 0.5 and 3 mm. Moreover, the projections (3) are spaced apart such that the distance between the centres of each projection is between 1 and 4 mm. The inventive production method essentially consists in, between drying and pressing, annealing a mixture formed by thermosetting resin, carbon dust and volatile solvent to a temperature of between 50 and 60 °C lower than that of the thermosetting temperature of the mixture, the aforementioned pressing being performed at a pressure of between 15 and 20 mPa at the same time as the heating.

Description

BIPOLAR PLATE AND ITS METHOD OF OBTAINING

D E S C R I P C I Ó N

OBJECT OF THE INVENTION

The present invention relates to a bipolar plate for application in the automotive, naval, energy, chemical and electrochemical industries, in particular it is useful in electrolysis to obtain chlorine, and may have application in the manufacture of fuel elements with membrane-electrode set.

BACKGROUND OF THE INVENTION

Bipolar plates composed of a central part and peripheral parts located in opposite arrangement with respect to the central part are known. In the central part, on one or both sides there are parallel longitudinal channels for the distribution of the flow of gaseous reagents that are limited by conductive projections of the current whose ends connect the peripheral parts. In the peripheral parts of the plates there are through holes that, once assembled the set of adjacent plates, form longitudinal channels for the improvement of the circulation and distribution of the electrolyte flows

(see RU 2187578). The problem of these bipolar plates is in the uniform non-distribution of the flow, and in the limited space for the distribution of the gaseous reagent flows, determined by the large number of parallel longitudinal channels. The method for obtaining bipolar plates is known, which includes the mixing of powdered graphite carbon components and a corrosion-resistant cohesion thermoplastic material, cold pressing of the powder mixture into a mold at 14500 Pa, the heating at 150 ° C, the pressure drop to 2000 kPa, the temperature rise to 205 ° C, and the pressure rise again to 14500 kPa, with a final phase of gradual pressure decrease and temperature (see description of patent RU 2187578). In this way a corrosion resistant plate is obtained by the periphery, which forms a unit with the central conductive part of electricity. The problem of the known method for obtaining bipolar plates is the need to prepare and join mixtures of components of different composition. This complicates the method and inevitably leads to the accumulation of thermal stresses during the cooling of the pieces. The use of the hot pressing method, that is, under conditions of complete understanding, also entails additional costs. The use of a thermoplastic material of cohesion during pressing in the mold (under conditions of pressure in one direction) does not allow to effectively form conductive projections of the current on the surface of the plates, since the thermoplastic polymer, when forming projections complexly, it has the tendency to ooze and not compress under pressure.

Bipolar plates composed of a central part and peripheral parts located around the central part are known. Labyrinth grooves are placed on one or two sides of the central part for the distribution of the gaseous reagent flows Longitudinal Y-shaped [, which form functional conductive projections of each other with their extremities located in the same plane, with a central hole and two diagonally arranged for the circulation and distribution of electrolyte flows. In the peripheral parts of the plates, holes are placed for block assembly. The peripheral and central parts are separated by a cohesion element located in the perimeter of the central part. In addition, for the organized distribution of gaseous reagent flows, the ü-shaped longitudinal grooves, and the current conductive functional projections, have a labyrinthine sense from the central orifice to the peripherals or vice versa (as it appears in a advertising catalog of the firm Schunk KOHLENSTOFF GMBH). This design, in comparison with its analogue, makes it possible to lengthen the flow path of gaseous reagents and organize a relatively uniform distribution of said flow through the cell surface of the fuel element, although it has the following drawbacks:

Significant shielding of the surface of the porous collector of the current by the functional conductive projections of the current, which condition the reduction of the effectiveness of the transport of reagents and the deviation of the products of the reaction towards these screened areas and, as a consequence, the reduction of the cell current density of the fuel element with the given voltage;

- Possibility of clogging the channels with drops of condensed water due to fluctuations in the temperature regime of the fuel element and / or in the water balance of the system, which would also lead to reduction of the effectiveness of the transport of reagents and the deviation of the products of the reaction through these channels, and as a consequence to the reduction of the density of the current of the cell of the fuel element with the given tension.

The closest technical solution refers to a method of obtaining bipolar plates, which includes the preparation of a mixture of thermo-rigid resin of a certain composition in a volatile solvent, the mixing of the carbon aggregate with the prepared solution until reaching a homogeneous state , drying, pressing and thermal hardening (US patent application No. US2002 / 0037448.

The problem with this method is that thermal hardening is carried out not simultaneously but after pressing the piece. In addition, drying the mixture at low temperature does not guarantee the removal of a large number of volatile components of the cohesion material, which prevents the pressing of microscopic amounts of the material of the bipolar plates, especially in the areas of the conductive projections. of the current, which serve to allow electrical contact and mechanical attachment of the current collector to the catalytic layer. This can lead to the formation of defective areas at the base of the projections, and to the rupture of these during the operation, assembly and exploitation of the elements of the fuel cell.

DESCRIPTION OF THE INVENTION

The objective of the proposed invention is to obtain bipolar plates with conductive projections of the free form and placement current with a height of between 0.3 to 2.0 mm by the mold pressing method of an electrically conductive composite material on a base of dispersed aggregates of carbon and thermo-rigid resin, as well as in the increase of the effectiveness in the transport of reagents and diversion of the products of the reaction.

The expected thermal result is an improvement in the operating properties of the bipolar plates and the fuel element as a whole.

The objective is achieved because the bipolar plate is composed of peripheral parts and a central part with prismatic conductive projections with a square or rectangular base or with a cylindrical or conical shape with a circular or elliptical base whose diameter or distance between more distant points of the base is between 0.5-3.0 mm, extending a height between 0.3 and 2.0 mm with variable or constant section with its free upper ends located in the same plane as the peripheral parts, and whose Distance between centers of projections is 1.0 to 4.0 mm. In addition, the highlights can be placed freely and neatly on the board, in the form of chess boxes, rhombuses, circles, spirals, or labyrinth.

This allows a uniform distribution of the reagents across the cell surface of the fuel element, and an effective deviation of the reaction products, and as a consequence thereof, allows increasing the density of the current in the cell of the fuel element With the tension given. In the method for obtaining bipolar plates the preparation of a mixture of thermo-rigid resin of a certain composition in a volatile solvent is included, adding the aggregate of carbon powders and mixing them until reaching a homogeneous state, drying, pressing and thermal hardening. The objective pursued is achieved because between drying and pressing the mixture is subjected to an annealing at a temperature between 50 and 60 ° C lower than the thermal hardening temperature of the mixture, and the pressing is carried out with a repeated load up to 15-20 mPa pressure, while heating to the point of thermal hardening of the mixture. The annealing is carried out with a gradual increase in temperature over 10 to 15 hours and the subsequent maintenance of the temperature reached for between 1 and 2 hours, and the pressing is carried out with a temperature of the active element of the Upper press 1.5-2 times at annealing temperature. The proportion s: l ''

(solid and liquid phases) during the formation of the mixture of powdered carbon and the solvent of the thermo-rigid resin (acetone) varies within a range of between 1: 3 and 1: 5, and the composition of the final mixture is added 0.1-3.0% (weight) of a pore forming agent. The need to use the thermo-rigid resin is given by the fact, experimentally demonstrated, that when pressing the bipolar plates with carbon content on a thermoplastic cohesive, the proper understanding does not occur in the area of the conductive projections of the current, which produces a weak adhesion of these projections to the body of the plate and its detachment. The presence of a thermo-rigid resin of any composition in the pressing mixture allows conductive projections of the current and bipolar plates to be formed without defects as a whole by the agglutination mechanism with liquid phase, which disappears just after its appearance, despite continuous heating. The sequence of phenomena that take place during the course of the main operations for the manufacture of bipolar plates is as follows:

1. Formation of a thin layer of thermo-rigid cohesive polymer on the surface of the particles of the carbon aggregate during the preparation of the mixture, its drying and subsequent annealing.

2. Condensation of the mixture.

3. Appearance of a liquid phase due to the appearance of a cohesive layer in the aggregate particles.

4. Continuation of the condensation of the piece due to the sedimentation characteristic of the agglutination of the liquid phase.

5. Thermal hardening of the cohesive and the piece as a whole.

Annealing prior to pressing is necessary due to the presence in agglomerated mixtures of a large number of volatile components that hinder effective pressing. A higher temperature during annealing can produce unwanted processes of premature hardening of the cohesive in microscopic amounts of the mixture, and a lower temperature is not effective. An important parameter is the pressure during pressing. For mixtures of dispersed carbon aggregates and thermo-rigid cohesive, the pressing pressure depends on the specific type of aggregate and must not exceed the extraction value of the liquid cohesive mixture: 20 mPa. A low pressing pressure (less than 15 mPa) does not provide an effective understanding of the bipolar plate, especially in the area of the current conductors. In carrying out the pressing while heating the mold with the mixture of thermal curing is performed ^to the four phase sequence indicated above phenomena that occur during the formation of plaques. An important peculiarity of the bipolar plate is in the structure of its surface. In order to obtain better properties of the fuel element, it is necessary that the surface, between whose projections the active gases circulate, has a certain roughness and microporosity. In that case, the water formed as a result of the reaction between the gases, partially accumulates in the subsurface pores, and thus increases the humidity of the gases, which positively influences the specific energy characteristics of the fuel element.

The formation of the due structure of the subsurface layer according to the proposed method takes place by the introduction of a pore forming agent (ammonium carbonate, polyethylene glycol, polyethylene) in the composition of the initial mixture for pressing, in a 0.1 -3.0% (weight) in relation to the solid components of the mixture. The pore forming agent included in the initial mixture does not hinder the hardening of the cohesive, and when decomposing during the process thermal and pressing during hardening, it forms a microporous structure of the plate, and consequently also of the subsurface layer (at a depth of 1-2 microns).

The decrease in the pore-forming agent content by less than 0.1% practically does not influence the microporosity and roughness of the subsurface layer, and the increase in the content of said agent above 3.0% is not convenient because the decrease of the mechanical resistance and the possible appearance of permeability in the plate.

DESCRIPTION OF THE DRAWINGS

To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, according to a preferred example of practical implementation thereof, a set of drawings is attached as an integral part of said description. where, for illustrative and non-limiting purposes, the following has been represented: Figure 1.- Shows a plan view of the bipolar plate.

Figure 2. - Shows a sectional view of the bipolar plate represented in the previous figure according to A-A.

PREFERRED EMBODIMENT OF THE INVENTION The bipolar plate object of this invention consists of a central part (1) and a peripheral part (2). The central part has projections (3), whose upper free ends are in the same plane as the peripheral part (2), have a height a between 0.3 and 2 mm and a diameter or distance b between more points distant from its base between 0.5 and 3.0 mm. The projections are spaced with a distance between centers c comprised between 1.0 and 4.0 mm and allow, with a large area and volume of passage of the gaseous reagent flows, to distribute the tensions (pressures) in all directions. It is possible to arrange the highlights in the form of a chess board, rhombuses, circles, spirals, or labyrinth. The projections can be shaped like a cylinder, sectioned pyramid, prism, and / or sectioned cone.

Bipolar plates are manufactured as described below: First, dispersed carbon components are combined to form a homogeneous mixture, with a certain amount of thermo-rigid resin solvent. As dispersed carbon components, graphite, soot, chopped fiber, powdered coke, etc. can be used.

The prepared mixture, periodically stirred, is then placed for drying at room temperature, so that the main quantity of volatile components is eliminated. In this way, a semi-finished material can be obtained, for example, from granules for a subsequent manufacturing process of bipolar plates. Subsequently, after performing a visual exam, you cover the dry mixture at a temperature between 50 and 60 ° C lower than the thermal hardening temperature.

The annealed mixture is then pressed at a pressure of 15-20 mPa in a mold, whose punches have channels that will shape the conductive projections of the current during pressing and hardening. At the same time as the pressing is carried out, the heating of the mold with the mixture takes place, from annealing temperature to hardening temperature.

After maintaining the hardening temperature of 0.5-1 hours, the mold is removed from the press and cooled in the air.

Finally it is dismantled by means of a special instrument.

The relevance of this invention is illustrated by the following examples:

EXAMPLE 1. For the manufacture of a bipolar plate (with conductive projections of the cylindrical current of 0.5 mm diameter, a height of 0.5 mm, and a distance between its centers of 1.0 mm) of 100 x 100 mm, a thickness of 7 mm, and a weight of 115 g, a mixture of the following composition was prepared, with a solid-liquid ratio = 1.3376: 1

- graphite brand KS-10 - 98 g.

- PM-100 brand soot - 1 g.

- Baqulita lacquer brand LBS-1 - 34 g.

- Acetone - 380 mi. The quantities were mixed in a measuring glass lacquer and acetone bakelite indicated until a homogeneous color solution is obtained. The graphite and soot suspension was previously combined dry to obtain a homogeneous mixture. The powder mixture and the lacquer bakelite solution were then poured into a container to be mechanically mixed for 5-10 minutes until homogeneity was achieved. The mixture was then placed under the action of an extraction cabinet at room temperature for 12-15 hours until it reached a dry appearance, periodically stirring the mixture and breaking up the larger agglomerates (more than 2-3 mm) by means of a metal grid with 2 mm cells.

The suspension of the dry mixture was introduced into the mold, which was placed in the oven, heating it for 13.5-14 hours until reaching a temperature of 90 ° C, which was then maintained for 2 hours.

It was then removed from the oven and placed in a hydraulic dam heated to 170 ° C. Pulse (load speed) of 1-2 seconds was pressed to a force of 22 Tm after approximately 5 sec. The force was increased again to 22-25 Tm by keeping the mold in the press for 1 hour, and then removed to cool to room temperature.

Once cooled, the mold was released in a manual screw dam with the help of 4 steel pushers.

The visual control of the bipolar plate showed the absence on the surface of the bipolar plate (including the areas of the current conductors) of scratches, defects and fissures, and detachments of the material of the bipolar plate at the boundary between the zones of the conductive projections of the current and the base of the plate.

Once the hardness test was carried out (the plate was placed between two pieces of steel and subjected to a force of 5 Tm (5 mPa pressure), equivalent to the operating force of the fuel element, for 1 hour) they were not detected Changes or defects. The volume resistivity value was 0.025

Ω-cm

EXAMPLE 2. The bipolar plate was manufactured with a composition and method analogous to that of Example 1, with the difference that the projections are shaped like a truncated cone of 3.0 mm in diameter at the base, 2.5 mm at the end upper, a height of 2.0 mm, and a distance between its centers of 4.00 mm. Before and after performing the hardness test, no defects were detected on the surface or on the projections.

The volume resistivity value was 0.030 Ω -crn.

EXAMPLE 3. The bipolar plate was manufactured with a configuration and method analogous to that of example 1, with the difference that 31 g of epoxy-phenolic cohesive No. 560 produced by FGUP GNC "VIAM" were used as thermal hardening cohesive.

Before and after performing the hardness test, no defects were detected on the surface and in the Highlights

The volume resistivity value was 0.017 Ω • cm.

EXAMPLE 4. The bipolar plate was manufactured with a configuration and method analogous to that of Example 1, with the difference that 3.5 g (3.0% by weight) of pore-forming agent were added to the initial pressing mixture (high pressure polyethylene).

Before and after performing the hardness test, no defects were detected on the surface and on the projections.

The volume resistivity value was 0.028 Ω • cm.

The porosity of the subsurface layer (depth up to 100 microns), measured by water absorption, was 2.8%.

Claims

1.- Bipolar plate of the type that is constituted by a central part (1) and peripheral parts (2) characterized in that the central part has some current conductive projections (3) whose upper free extremities are located in the same plane than the peripheral parts (2).

2. - Bipolar plate according to claim 1 characterized in that the current conductive projections (3) have a height between 0.3 and 2 mm and a distance between points more distant from its base between 0.5 and 3.0 mm . , as well as the projections (3) are spaced with a distance between centers of projections (3) between 1.0 and 4.0 mm.

3. - Bipolar plate according to previous claims characterized in that the projection (3) shows a configuration selected from the configurations: sectioned pyramidal, prismatic, cylindrical and conical sectioned.

4. Bipolar plate according to previous claims characterized in that the projections are combined in the plate with combined configurations that are selected from pyramidal sectioned, prismatic, cylindrical and conical sectioned.

5. Bipolar plate according to previous claims characterized in that the geometry of the base of the shoulder (3) is selected from among the geometries: circular, elliptical, square and rectangular.

6. - Bipolar plate according to previous claims characterized in that the projections (3) are unevenly distributed randomly located on the plate.

7. - Bipolar plate according to claims 1 to 5 characterized in that the projections (3) are arranged in the plate according to a geometric distribution.

8. - Bipolar plate according to claim 7, because the geometric distribution of the projections (3) is selected from the distributions: rhomboid, circular, spiral, labyrinth and checkered.

9.- Method of obtaining bipolar plates that includes the preparation of a mixture of a thermosetting resin in a volatile solvent, the inclusion of carbon powders and their mixing to a homogeneous state, followed by drying, pressing and thermosetting, characterized in that between Drying and pressing is an annealing at a temperature below 50 to 60 ° C at the temperature of the thermosetting of the mixture, as well as pressing is carried out to a pressure between 15 and 20 mPa at the same time as heating corresponding to the hardening of the mixture.

10. Method of obtaining bipolar plates according to claim 9, characterized in that the annealing is performed with a progressive increase in temperature over 10 to 15 hours, followed by a constant temperature maintenance over 1 to 2 hours. , Y because the pressing is carried out at a temperature of the active element of the press between 1.5 and 2 times higher than the annealing temperature.

11. Method of obtaining bipolar plates according to claim 9, characterized in that the solid: liquid ratio in the formation of the mixture of the carbon powders with the solvent of the thermosetting resin varies within a range with a ratio between 1: 3 and 1: 5.

12. - Method of obtaining bipolar plates according to claim 9, characterized in that prior to pressing, between 0.1 and 3% by weight of porous agents is added in relation to the solid components of the mixture.