BACKGROUND ART In the pursuit of environmentally enhanced power sources, for by way of example propulsion of a vehicle, fuel cells is an alternative which is subject to extensive research. There are many types of fuel cells that uses different types of fuel for different purposes. However, all fuel cells have the production of electricity in common.

All fuel cells are constructed in a layer structure comprising a fuel side, an oxygen side, a membrane and two electrically conducting plates in the form of an anode and a cathode. The membrane is an electrical insulator at the same time as it works as an electrolyte that admits ionic conduction between the anode and the cathode, which are placed on each side of the membrane.

The fuel side is normally placed at the anode side and the oxygen side is normally placed at the cathode side. For most fuel cells, the anode and the cathode, the electrodes, consist of a porous carbon material which is coated with a catalyst material such as platinum (Pt). The catalyst material catalyses a reduction of the fuel at the anode side by means of a reduction of electrons and catalyses an oxidation of the oxygen at the cathode side by means of a supply of electrons. These two reactions causes an electron migration, i. e. an

electrical current, from the anode side to the cathode side via an electrode connection. The ionised particles from either the anode side or the cathode side diffuses through the membrane and reacts on the opposing side by forming some kind of compound, for example water. If there is hydrogen on the fuel side and the membrane allows ionised hydrogen to diffuse, one speaks about"Protone Exchange Membranes" (PEM), and if the membrane allows ionised oxygen to diffuse from the cathode side, one speaks about "Oxide Fuel Cells" (OFC).

In a structure of the type"Solid Oxide Fuel Cell" (SOFC), a ceramic solid phase membrane (electrolyte) is used. A suitable material that is used is "dense yttrium stabilised zirconium dioxide", which is an excellent conductor for negatively charged oxygen ions at high temperatures around 1830° F (1000° C). At such a temperature it is possible with an inner reforming of carboniferous fuels.

When using a fuel cell, it is necessary to consider a number of parameters such as weight, volume, degree of efficiency, working temperature, material, fuel, exhausts etc., depending on within which field of usage the fuel cell shall be used.

I order to satisfy the power need of a larger unit, e. g. a vehicle, more fuel cells are needed. A way to solve the problem with the mounting of the many fuel cells is to extrude a fuel cell unit in the form of a monolith with a honeycomb structure comprising a number of fuel cells, which thus forms a larger, more compact fuel cell. A single monolith with a honeycomb structure may not be made large enough to supply a larger device, such as a car or similar, with electricity due to manufacturing reasons, which means that a mounting of several fuel cell units in the form of monoliths with a honeycomb structure is necessary.

It is previously known to extrude an SFOC fuel cell unit in the form of a monolith with a honeycomb structure in a material of yttrium stabilised zirconium dioxide which constitutes a membrane that conduct ions but is not electrically conductive. The fuel cell unit then consists of square/rectangular channels defined by extruded walls of yttrium stabilised zirconium dioxide, which form rows of fuel conduit channels with a square/rectangular cross- section with a pole of a conducting catalysing material on the inside of the channel, and rows of oxygen conduit channels with a square/rectangular cross-section with a pole of a conducting catalysing material on the inside of the channel. The rows of channels are placed in such a way that every second row is a fuel conduit channel and every other second row is an oxygen conduit channel. The fuel conduit channels and the oxygen conduit channels are of equal lengths and sizes, why every short side of the monolithic fuel cell unit is covered by a covering plate with a system of channels that is designed to conduct the fuel and the oxygen, respectively, to the correct row, i. e. to the correct channel. The monolithic fuel cell unit may be connected to other similar fuel cell units, thus acquiring a compact system of fuel cell units with desired power, by designing a larger covering plate to cover the short side of the system of monolithic fuel cell units that have been connected and where the covering plate has been equipped with a system of channels which supplies the fuel channels and the oxygen channels with the correct fluid, respectively, i. e. fuel and oxygen, respectively.

Even if previously known systems function well, enhancements may be made concerning acquiring a more compact system of fuel cell units (fuel cell device). According to previously known technology, the covering lid that covers the short side of the fuel cell device is designed with specially adapted channels which shall fit the fuel, oxygen and exhaust channels. For the fuel cell device to function properly, high demands are made upon the fitting and tightness between the covering plate with its channels and the shaped rows of channels in the fuel cell units. The manufacture of such a plate may be expensive, and the special demands make the device quite inflexible. Even if

separate bottom plates were used for the separate extruded fuel cell units, an adaptation should be necessary for the connections that are needed between the different bottom plates, if several such fuel cell units are connected to a fuel cell device.

Further disadvantages with previously known technology is that the channels which are formed in the covering plate cause a quite high fall off pressure, which reduces the degree of efficiency of the system and makes the distribution of air and fuel more difficult.

If a system of fuel cell units shall be commercially practicable, it is demanded that the system has a small volume in relation to the amount of power that is produced. It is also demanded that the system is simple to manufacture and is cheap to manufacture.

DISCLOSURE OF INVENTION The purpose for the present invention is to eliminate the problems that have been identified for previously known technology and thus satisfy the desires stated for an enhanced system of fuel cell units (fuel cell device).

The purpose stated above is obtained by a fuel cell unit of a kind mentioned in the preamble, which characterizing features are disclosed in the appended claim 1, where a fuel cell unit in the form of an extruded monolith comprises channels, of which every second constitutes a fuel channel and every other second an oxygen channel. The invention is characterized in that the channels are designed in such a manner that the fuel channels are displaced laterally in relation to the oxygen channels, in such a way that all the fuel channels protrude a certain distance from the end points of all the oxygen channels, while all the oxygen channels protrude a certain distance from the end points of all the fuel channels, where said distance is less than the length of respective channels.

The purpose mentioned above is also obtained by means of a device according to claim 5, where several fuel cell units are packed to a fuel cell device where the invention is characterized in that the fuel cell units are mounted in such a way that the fuel channels in a first fuel cell unit are in direct connection with the fuel channels in a second fuel cell unit, and in such a way that the oxygen channels in a first fuel cell unit are in direct connection with the oxygen channels in an adjacent fuel cell unit. The packing may be made in one, two or three dimensions.

With the device described above, a simpler and cheaper fuel cell device that may be made compact and occupies less volume per delivered amount of power than previously known devices is thus attained.

Advantageous embodiments are disclosed in the appended dependent claims.

BRIEF DESCRIPTION OF DRAWINGS The invention will be described in the following text, in connection with preferred embodiments and the enclosed drawings, where Fig. 1 shows an outlined drawing of a cross-section of a fuel cell unit according to a first embodiment of the invention before the edge parts have been cut off, and where one of the open sides has not been plugged, i. e. been made gas-tight; Fig. 2 shows an outlined drawing of a cross-section of a fuel cell unit according to a first embodiment of the invention with the edge parts cut off and where one of the open sides has not been plugged;

Fig. 3 shows an outlined drawing of a cross-section of the channels in a fuel cell unit with a first placement of electrode connection according to a first embodiment of the invention; Fig. 4 shows an outlined drawing of a cross-section of fuel cell unit according to a first embodiment of the invention with the fuel and exhaust connections mounted, and where one of the open sides has not been plugged; and Fig. 5 shows an outlined view from above of a three-dimensional packing of a number of fuel cell units in the form of a fuel cell device, with plugged sides.

MODES FOR CARRYING OUT THE INVENTION In the figures, those features which are recurring in different figures are described with the same reference numbers.

Figure 1,2,3 and 4 show outlined drawings of a cross-section of a fuel cell unit 10 according to a first embodiment of the invention, where the cross- section is put along one of the open, not plugged, sides of the fuel cell unit 10. With plugged, it is meant that the open sides of the fuel channels are sealed with a suitable material in a suitable manner in order to acquire more or less gas-tight sides. The fuel cell unit 10 consists of an extruded monolith designed with a lamella structure where the ion conductive material 12 defines channels 14 with a rectangular cross-section, the inner walls of which are coated with a layer (washcoat) of an electrically conductive material 16, e. g. Peroskviter with a high conductivity. The channels 14 are divided into fuel channels 14a and oxygen channels 14b. The inner walls of the fuel channels 14a are coated with a first electrically conductive material 16a (especially shown in fig. 3) and those of the oxygen channels 14b are coated with a second electrically conductive material 16b (especially shown in fig. 3).

The fuel channels 14a and oxygen channels 14b of the fuel cell unit 10 are designed in such a way that every second channel is a fuel channel 14a and every other second channel is an oxygen channel 14b. Further, the channels 14 are essentially of equal length.

The invention is based on that the channels 14 are displaced laterally in relation to each other in such a way that all the fuel channels 14a, facing a first side 18, protrude a certain distance from the end points of all the oxygen channels 14b, while all the oxygen channels 14b, facing a second side 20, protrude a certain distance from the end points of all the fuel channels 14b, where said distance is less than the length of the respective channels, and where the sides 18,20 mainly constitute parallel side pieces. On the sides 18,20, a first edge part 22 and a second edge part 24 is formed, respectively, the width of which is determined of how long the channels 14 are, and how large the displacement of the channels 14 is. The channels extend in depth from a third side 26 to a fourth side 28, which has an extension that is mainly perpendicular to the first side 18 and the second side 20. In the figures, a third part 30 is marked, which constitutes a predetermined distance along the first side 18, from the edge between the first side 18 and the third side 26. In the figures, a fourth part 32, a fifth part 34 and a sixth part 36 are also marked, which constitute corresponding distances on respective corner parts.

Figure 1 shows an outlined drawing of a cross-section of a fuel cell unit according to a first embodiment of the invention before the edge parts have been cut off, and where one of the open sides, more precisely the third side 26, has not been plugged.

Figure 2 shows an outlined drawing of a fuel cell unit 10 according to a first embodiment of the invention where the first edge part 22 has been cut off in the level of the end parts 38 of the fuel channels 14a on the first side 18, in such a way that the protruding end parts 38 of all the fuel channels 14a have

been exposed during a distance that consists of the third part 30 and the fourth part 32, respectively. With end part, the part of the channel where the channel ands sideways and the material in the edge parts follows, is meant.

In the same manner, the other edge part 24 has been cut off in the level of the end parts 40 of the oxygen channels 14b at the other side 20, in such a way that the protruding end parts 40 of all the oxygen channels 14b have been exposed during a distance that consists of the fifth part 34 and the sixth part, respectively. The figure shows the third side 26 without a plug.

Figure 3 shows an outlined drawing of a cross-section of the channels in a fuel cell unit with a first placement of electrode connections according to first embodiment of the invention, where a first electrode connection 42 is brought on the outer side of the first electrically conductive material 16a, which also coats the, in the figure, upper outer side of the extruded fuel cell unit 10, while a second electrode connection 48 is brought on the outer side of the second electrically conductive material 16b, which also coats the lower outer side of the extruded fuel cell unit 10. The electrode connections have connection points made in a material with high conductivity, e. g. platinum. In order to locally avoid too high electrical currents in the electrically conductive materials 16a, 16b in the channels 14a, 14b, the washcoat of the electrically conductive material is deliberately made uneven at the manufacture of the fuel cell unit, which results in electrically conductive connection points 44 between the electrically conductive materials 16a, 16b in respective fuel channels 14a and oxygen channels 14b. The electrically conductive connection points 44 thus short-circuits the layers of electrically conductive material and thus distributes the current over the surfaces of the channels walls.

Another possibility (not shown) to apply electrode connections on a fuel cell unit 10 according to a first embodiment of the invention, is that the exposed protruding end parts 38 of fuel channels 14a partly are coated by a first electrode connection which is fastened on the extruded material with an

electrically conductive adhesive, via a layer of a third electrically conductive material which is connected to the first conductive material 16a in the fuel channels 14a. The exposed protruding end parts 40 of the oxygen channels 14b are partly coated by a second electrode connection which is fastened on the extruded material with an electrically conductive adhesive, via a layer of a fourth electrically conductive material Figure 4 shows an outlined drawing of a fuel cell unit 10 according to the invention, where a first connection 52 is connected to the first side 18 in the level of the third side 26, a second connection 54 is connected to the first side 18 in the level of the fourth side 28, a third connection 56 is connected to the second side 20 in the level of the third side 26 and a fourth connection 58 is connected to the second side 20 in the level of the fourth side 28. The figure shows the third side 26 without a plug.

Figure 5 shows an outlined drawing of a view from above of a three- dimensional packing of a fuel cell device which in turn comprises several fuel cell units 10a, 10b, 10c, 10d, 10e, 10f of the kind described above. A three- dimensional packing here refers to that said fuel cell units 10a, 10b, 10c, 10d, 10e, 10f are piled in three dimension. The connections 52,54,56,58 shown in figure 4 are here removed. The indicated fuel cell units 10a, 10b, 10c, 10d, 10e, 10f each one corresponds to the previously mentioned fuel cell unit 10 (see fig. 1-4) and the reference numbers are solely intended to facilitate the understanding of the three-dimensional device and the packing procedure, respectively. The open third 26 and fourth 28 sides of all the fuel cell units shown in figure 1-4 are shown without a plug.

The fuel cell units 10 are mounted in such a way that that the fuel channels 14a in a first fuel cell unit 10a are in a direct connection with the fuel channels 14a in a second fuel cell unit 10b, and also in such a way that the oxygen channels 14b in a first fuel cell unit 10a are in a direct connection with the oxygen channels 14b in an adjacent fuel cell unit.

An important principle behind the invention is that the fuel cell units 10a, 10b, 10c are mounted in a first row, one dimension, with the first side 18 of a first fuel cell unit 10a placed towards the first side 18 of a second fuel cell unit 10b, in such a way that the exposed end parts 38 of the fuel channels 14a of the different fuel cell units 10a, 10b and the space that is constituted by the removed first edge parts 22 of the fuel channels 14a with the length of the third parts 30 and fourth parts 32, respectively, of the fuel cell units 10a, 10b, forms first fuel conduit channels 60 and second fuel conduit channels 62. In a similar way the second side 20 of the second fuel cell unit 10b is placed towards the second side 20 of a third fuel cell unit 10c, resulting in that the space that is constituted by the removed second edge parts 24 of the oxygen channels 14b with the length of the fifth parts 34 and sixth parts 36, respectively, of the fuel cell units 10a, 10b, forms first oxygen conduit channels 64 and second oxygen conduit channels 66. A packing pattern for one row, one dimension, has thus been formed by always turning the first side 18 of a fuel cell unit 10 towards the first side 18 of another fuel cell unit, and by always turning the second side 20 of. a fuel cell unit 10 towards the second side 20 of a fuel cell unit 10.

The packing pattern formed in the first row is repeated in a second row where the fuel cell units 10d, 10e, 1 Of correspond to the fuel cell units 10a, 10b, 10c mentioned above. The first row is then placed next to the second row, forming a packing pattern in a plane, i. e. two dimensions, in such a way that the third sides 26 and fourth sides 28 of the fuel cell units 10a, 10b, 10c are placed towards the third sides 26 and fourth sides 28 of the fuel cell units 10d, 10e, 10f, and the space that is constituted by the removed first edge parts 22 of the fuel channels 14a with the length of the third parts 30 and fourth parts 32, respectively, of the fuel cell units 10a, 10b, forms first fuel conduit channels 60 and second fuel conduit channels 62, and the space that is constituted by the removed second edge parts 24 of the oxygen channels 14b with the length of the fifth parts 34 and sixth parts 36, respectively, of the

fuel cell units 10a, 10b, forms first oxygen conduit channels 64 and second oxygen conduit channels 66, which results in a possibility for a common air supply for the oxygen conduit channels 64,66, and a common fuel supply for the fuel conduit channels 60,62 for all the fuel cell units 10 in the assembled fuel cell device, after which the packing pattern may be repeated both longitudinally and transversely. In order to pack the fuel cell units 10 vertically, the pattern from a lower layer is repeated in a new layer, where the new layer is put on the lower layer in such a way that the fuel conduit channels 60,62 and the oxygen conduit channels 64,66, respectively, are matched together.

One of the advantages with plugging the third side 26 and the fourth side 28, respectively, is that after that the corners are cut off, it becomes less delicate to adapt the many fuel cell units 10 to create the fuel conduit channels 60,62 and the oxygen conduit channels 64,66, respectively, of a fuel cell device, i. e. the adaptation of the different fuel cell units 10 vertically and laterally in relation to each other becomes less delicate. During the packing according to what has been described above, the sides of the different fuel cell units 10 may also be"glued"together, e. g. using ceramics, and thus create a gas- tight seal that makes the fuel conduit channels 60,62 and the oxygen conduit channels 64,66, respectively, gas-tight, which further reduces the degree of delicacy at the adaptation of the different fuel cell units 10, which may have different symmetries.

Depending on how the fuel conduit channels 60,62 and the oxygen conduit channels 64,66, respectively, are used, either a downstream flow or an upstream flow, flows in relation to each other, may be acquired through the fuel cell units 10 of the fuel cell device. Of course, this also applies when one only has one fuel cell unit with connections according to fig. 4, where the flow is determined in dependence of the choice of connection. In an arrangement with a two-or three-dimensional packing, the fuel conduit channels 60,62 constitute a fuel conduit channel and an exhaust conduit channel,

respectively, and the oxygen conduit channels 64,66 constitute an oxygen conduit channel and an exhaust conduit channel, respectively, depending on the choice of downstream or upstream flow through the fuel cell units 10.

The indications in fig. 5 and the following example are referred to, in order to shed some light on the opportunities with the fuel cell device mentioned above. The fuel conduit channels 60,62 are aligned in a row one after the other, which also the oxygen conduit channels 64,66 are. If the second fuel conduit channel 62 and the second oxygen conduit channel 66 are chosen to constitute exhaust channels, every second conduit channel of the fuel cell device is an oxygen or a fuel channel, and every other second an exhaust channel. The second fuel conduit channel 62 and the second oxygen conduit channel 66 which constitute exhaust channels may be plugged at e. g. the upper side, which results in that all exhausts have their outlet at one side, here the lower side, which results in the advantage that only one exhaust pipe has to be applied to the fuel cell device. The exhaust pipe may then consist of a standard exhaust pipe made in metal, with or without a manifold.

By means of the arrangement mentioned above, the upper side of the fuel cell device constitutes a fuel/oxygen side and the lower side constitutes an exhaust side. Since the oxygen channels 64 are placed in a row, and the fuel channels 60 are placed in a row, it is easy to arrange supply of the two gases by means of e. g. arranging a channel that runs across all the inputs to the fuel channels and which constitutes a common fuel supply, and by arranging a channel that runs across all the inputs to the oxygen channels and which constitutes a common oxygen supply. Another alternative may be to arrange a specially designed plate which covers all of the upper side, which plate comprises channels which supply fuel and oxygen conduit channels, respectively.

At the extrusion the fuel cell unit 10 is made in the form of a rectangular parallelepiped where the two sides that constitute cross-sections of the channels are open. When using the fuel cell unit 10, these sides are plugged

with a suitable material, after which the edge parts 22,24 of the fuel cell unit are cut off in accordance with the invention. The machined block is thereafter put in a gas-tight reactor.

An approximate measure of the desired power amount required to propel a vehicle is approximately 80 kW. A fuel cell produces approximately 0.9 V, which provides approximate values for the volume, approximately 12.5 L, and the number of cells, 457 pieces, for a system of fuel cell units that shall produce 80 kW. For reasons of strength, a fuel cell unit consists of approximately 98 cells/fuel cell unit, which results in that approximately 5 fuel cell units are needed in order to obtain a power of 80 kW. When making calculations for a fuel cell device producing 80 kW at approximately 800° C, made of extruded yttrium stabilised zirconium dioxide with a wall thickness of approximately 150, um, a desired area of 22.8 m2 is obtained. Then, suitable dimensions for such a fuel cell device with the volume 12.5 L in order to produce 80 kW are approximately 0.005 m X 1 m X 0.25 m. Suitable wall thickness of extruded yttrium stabilised zirconium dioxide in respective fuel cell unit 10 is approximately 50-150 um. The calculations above are based on results obtained experimentally, and shall only be regarded upon as a descriptive example.

The fuel cell unit 10 according to the invention is an (SOFC) which admits fuel types which are oxidised by oxygen at 500-1000° C, e. g. gasoline, diesel, natural gas, hydrogen, biogas, rapeseed oil, ethanol, methanol and others.

Air and chosen fuel are supplied to the fuel cell unit 10, which after reaction forms an exhaust product containing mainly C02 and water, but also smaller amounts of non-combusted fuel and other waste products may be acquired.

One of the advantages with the invention is that one may choose if the flows of air and fuel shall run upstream or downstream. An upstream flow provides

an optimum combustion as there is excess oxygen where the share of fuel in relation to the exhaust products is minimal, which results in that the share of non-combusted and the share of other waste products in the exhaust product is very low. The reactions take place at approximately 800° C and provides an exhaust product at approximately 10000 C.

One of the advantages with the fuel cell unit being able to run at such a high temperature is that the waste heat from the fuel cell unit may be used for heating of the exhausts that run a turbo unit instead of disappearing to the environment, which results in an increased degree of efficiency for the device. The turbo unit may be used as a"Sterling or Ranking cycle". The turbo unit's compressor compresses the air in to the fuel cell to 2-3 bar. At reaction temperatures exceeding 400° C, an amount of power exceeding the amount of power that is needed for compressing the gas is acquired, which excess amount of power may be used to run a conventional generator which increases the degree of efficiency for the device. If the generator is run "backwards"as an engine, it may be used for starting the device.

The invention is not limited to what has been described above, but different embodiments are possible within the scope of the claims. The fuel cell unit and the fuel cell device may also be used for other purposes than for propulsion of vehicles, e. g. they may be used for producing electrical power at stationary establishments.