WO2015097337A1

WO2015097337A1 - Flow method and arrangement for fuel cell or electrolyzer cell stack

Info

Publication number: WO2015097337A1
Application number: PCT/FI2013/051208
Authority: WO
Inventors: Matti Noponen; Olli HIMANEN; Jari PENNANEN
Original assignee: Elcogen Oy
Priority date: 2013-12-27
Filing date: 2013-12-27
Publication date: 2015-07-02

Abstract

An object of the invention is a fuel flow stack arrangement for solid oxide fuel cells, each cell comprising a fuel side (100), an oxygen rich side (102), and an electrolyte element (104) between the fuel side and the oxygen rich side, the cells being arranged to a formation of a stack, and the arrangement comprises in repetitious structures (138) a flow field plate (121) for each cell to arrange flows in the cell, a flow distribution area (120) on the flow field plate (121), a flow outlet area (131) on the flow field plate (121), and means (123) for guiding fuel feed flow to the flow distribution area (120). The fuel flow stack arrangement comprises flow restriction orifices (126, 136) opened to the flow distribution area (120) and to the flow outlet area (131), and a gasket structure (128) over the flow restriction orifices (126, 136), and height of the flow restriction orifices (126, 136) is determined by a distance from at least one of a bottom (132) of the flow distribution area (120) and of the flow outlet area (131) to a bottom (133) of the gasket structure (128) to stabilize flow distribution in the repetitious structures (138) of the stack having tolerance variations in electrolyte element structure thickness.

Description

Flow method and arrangement for fuel cell or electrolyzer cell stack

The field of the invention

Most of the energy of the world is produced by means of oil, coal, natural gas or nuclear power. All these production methods have their specific problems as far as, for example, availability and friendliness to environment are concerned. As far as the environment is concerned, especially oil and coal cause pollution when they are combusted. The problem with nuclear power is, at least, storage of used fuel.

Especially because of the environmental problems, new energy sources, more environmentally friendly and, for example, having a better efficiency than the above-mentioned energy sources, have been developed. Fuel cell's, by means of which energy of fuel, for example biogas, is directly converted to electricity via a chemical reaction in an environmentally friendly process and electrolysers, in which electricity is converted to a fuel, are promising future energy conversion devices.

Renewable energy production methods such as photovoltaic and wind power faces problems in seasonal production variations as their electricity production is limited by environmental effects. In the case of over production, hydrogen production through water electrolysis is suggested to be one of the future energy storing options. Furthermore, an electrolysis cell can also be utilized to produce high quality methane gas from renewably biogas stores.

The present invention relates to arranging input reactant distribution in a Solid Oxide Fuel Cell (SOFC) stack or in a Solid Oxide Electrolyzer Cell (SOEC) stack. A fuel cell causes input reactant fuel gas on an anode electrode and gaseous oxidizer (oxygen) on a cathode electrode to react in order to produce electricity. Electrolyzer reactions are reverse to fuel cell, i.e. electricity is used to produce fuel and oxygen. SOFC and SOEC stacks comprise stacked cell elements and separators in a sandwiched manner wherein each cell element is constituted by sandwiching an electrolyte, the anode side and the cathode side. The reactants are guided by flow field plates to the porous electrodes.

State of the art Fuel cell, as presented in fig 1, comprises an anode side 100 and a cathode side 102 and an electrolyte material 104 between them. In solid oxide fuel cells (SOFCs) oxygen 106 is fed to the cathode side 102 and it is reduced to a negative oxygen ion by receiving electrons from the cathode. The negative oxygen ion goes through the electrolyte material 104 to the anode side 100 where it reacts with fuel 108 producing electrons, water and also typically carbon dioxide (C02). Anode 100 and cathode 102 are connected through an external electric circuit 111 comprising a load 110 for the fuel cell withdrawing electrical energy alongside heat out of the system. The fuel cell reactions in the case of methane, carbon monoxide and hydrogen fuel are shown below:

Anode: CH₄ + H₂0 = CO + 3H₂

CO + H₂O = CO₂ + H₂

H₂ + O^2" = H₂O + 2e Cathode: O₂ + 4e = 2O^2~

Net reactions: CH₄ + 2O₂ = CO₂ + 2H₂O

CO + l/2O₂ = CO₂

H₂ + l/2O₂ = H₂O

In electrolysis operating mode (solid oxide electrolysis cells (SOEC)) the reaction is reversed, i.e. heat, as well as electrical energy from a source 110, are supplied to the cell where water and often also carbon dioxide are reduced in the anode side forming oxygen ions, which move through the electrolyte material to the cathode side where de-ionization to oxygen takes place. It is possible to use the same solid electrolyte cell in both SOFC and SOEC modes. In such a case and in the context of this description the electrodes are typically named anode and cathode based on the fuel cell operating mode, whereas in purely SOEC applications the oxygen electrode may be named the anode, and the reactant electrode as the cathode.

Solid oxide electrolyser cells operate at temperatures which allow high temperature electrolysis reaction to take place, said temperatures being typically between 500 - 1000 °C, but even over 1000 °C temperatures may be useful. These operating temperatures are similar to those conditions of the SOFCs. The net cell reaction produces hydrogen and oxygen gases. The reactions for one mole of water are shown below, with reduction of water occurring at the anode:

Anode: H₂O + 2e— > 2 H₂ + O^2"

Cathode: O^2" -- > l/2O₂ + 2e Net Reaction: H₂O -- > H₂ + l/2O₂ .

In Solid Oxide Fuel Cell (SOFC) and Solid Oxide Electrolyzer (SOE) stacks where the flow direction of the cathode gas relative to the anode gas internally in each cell as well as the flow directions of the gases between adjacent cells, are combined through different cell layers of the stack. Further, the cathode gas or the anode gas or both can pass through more than one cell before it is exhausted and a plurality of gas streams can be split or merged after passing a primary cell and before passing a secondary cell. These combinations serve to increase the current density and minimize the thermal gradients across the cells and the whole stack.

A SOFC delivers in normal operation a voltage of approximately 0.8V. To increase the total voltage output, the fuel cells are usually assembled in stacks in which the fuel cells are electrically connected via flow field plates (also:

interconnector plates, bipolar plates). The desired level of voltage determines the number of cells needed. Bipolar plates separate the anode and cathode sides of adjacent cell units and at the same time enable electron conduction between anode and cathode. Interconnects, or bipolar plates are normally provided with a plurality of channels for the passage of fuel gas on one side of an interconnect plate and oxidant gas on the other side. The flow direction of the fuel gas is defined as the substantial direction from the fuel inlet portion to the fuel outlet portion of a cell unit. Likewise, the flow direction of the oxidant gas, the cathode gas, is defined as the substantial direction from the cathode inlet portion to the cathode outlet portion of a cell unit. Conventionally, the cells are stacked one on top of each other with a complete overlap resulting in a stack with for instance co-flow having all fuel and oxidant inlets on one side of the stack and all fuel and oxidant outlets on the opposite side. One feature affecting the temperatures of the structure in operation is steam reformation of the fuel that is fed into the cell. Steam reformation is endothermic reaction and cools the fuel inlet edge of the cell.

Due to the exothermicity of the electrochemical process, the outlet gases leave at higher temperature than the inlet temperature. When endothermic and exothermic reactions are combined in an SOFC stack a significant temperature gradient across the stack is generated. Large thermal gradients induce thermal stresses in the stack which are highly undesirable and they entail difference in current density and electrical resistance. Therefore the problem of thermal management of an SOFC stack exists: to reduce thermal gradients enough to avoid unacceptable stresses and to maximize electric efficiency through homogenous current density profile.

Prior art fuel cell stacks or electrolyzer cell stacks have tolerance variations in electrolyte element structure thickness between the cell structures in the stacks. For example in a cell stack structure, in which ceramic materials are used, only thickness variations in the measure of only micrometers would be convenient in the prior art embodiments. This results on differential flowing conditions between the cells causing varying cell voltage profile in the stack structure resulting in thermal gradients between the cells and decreased power density of the stack. Thus both the duty ratio of the stacks is decreased, and lifetime of the stacks is shortened, the first increasing the capital cost of the stack per produced electrical power output and the later increasing the operational cost of the stack structure as e.g. the stack replacement time is shortened in a fuel cell system and cost of electricity is increased in the electrolyzer stack. Brief description of the invention

The object of the invention is to improve the operational performance and lifetime of the fuel cell or electrolyzer cell stack by accomplishing substantially even fuel or input reactant flow conditions between the cells in the stack.

This is achieved by a fuel flow stack arrangement for solid oxide fuel cells, each cell comprising a fuel side, an oxygen rich side, and an electrolyte element between the fuel side and the oxygen rich side, the cells being arranged to a formation of a stack, and the arrangement comprises in repetitious structures a flow field plate for each cell to arrange flows in the cell, a flow distribution area on the flow field plate, a flow outlet area on the flow field plate, and means for guiding fuel feed flow to the flow distribution area. The fuel flow stack arrangement comprises flow restriction orifices opened to the flow distribution area and to the flow outlet area, and a gasket structure over the flow restriction orifices, and height of the flow restriction orifices is determined by a distance from at least one of a bottom of the flow distribution area and of the flow outlet area to a bottom of the gasket structure to stabilize flow distribution in the repetitious structures of the stack having tolerance variations in electrolyte element structure thickness.

The object of the invention is also achieved by an input reactant flow stack arrangement for solid oxide electrolyzer cells, each cell comprising an input reactant side, an oxygen rich side, and an electrolyte element between the input reactant side and the oxygen rich side, the cells being arranged to a formation of a stack, and the arrangement comprises in repetitious structures a flow field plate for each cell to arrange flows in the cell, a flow distribution area on the flow field plate, a flow outlet area on the flow field plate, and means for guiding input reactant feed flow to the flow distribution area. The input reactant flow stack arrangement comprises flow restriction orifices opened to the flow distribution area and to the flow outlet area, and a gasket structure over the flow restriction orifices, and height of the flow restriction orifices is determined by a distance from at least one of a bottom of the flow distribution area and of the flow outlet area to a bottom of the gasket structure to stabilize flow distribution in the repetitious structures of the stack having tolerance variations in electrolyte element structure thickness. The focus of the invention is also a fuel flow method of stack arrangement for solid oxide fuel cells, in which method the cells are arranged to a formation of a stack, and is guided fuel feed flow to a flow distribution area. In the method is restricted fuel flow through flow restriction orifices opened to the flow

distribution area and to a flow outlet area, and is restricted fuel flow by a gasket structure over the flow restriction orifices, and is determined height of the flow restriction orifices by a distance from at least one of a bottom of the flow distribution area and of the flow outlet area to a bottom of the gasket structure to stabilize flow distribution in the repetitious structures of the stack having tolerance variations in electrolyte element structure thickness. The focus of the invention is further an input reactant flow method of stack arrangement for solid oxide electrolyzer cells, in which method the cells are arranged to a formation of a stack, and is guided input reactant feed flow to a flow distribution area. In the method is restricted input reactant flow through flow restriction orifices opened to the flow distribution area and to a flow outlet area, and is restricted input reactant flow by a gasket structure over the flow restriction orifices, and is determined height of the flow restriction orifices by a distance from at least one of a bottom of the flow distribution area and of the flow outlet area to a bottom of the gasket structure to stabilize flow distribution in the repetitious structures of the stack having tolerance variations in electrolyte element structure thickness.

The invention is based on restricting input reactant flow through flow restriction orifices opened to the flow distribution area and to a flow outlet area, and on restricting input reactant flow by a gasket structure over the flow restriction orifices. The invention is further based on provided height of the flow restriction orifices by a distance between from at least one of a bottom of the flow distribution area and the flow outlet area to a bottom of the gasket structure to stabilize flow distribution in the repetitious structures of the stack having tolerance variations in electrolyte element structure thickness.

The well-defined height of the restriction orifices structures together with the well-defined flow distribution area on the electrolyte element defines the pronounced pressure drop characteristics of a unit cell structure in a stack. The amount of pressure drop in the restriction orifices can be freely adjusted in the structure by e.g. adjusting its height, orifices geometrical shape and length of the orifices. Thus the electrolyte element structure thickness possibly having tolerance variations and defining the height of the gas distribution area results on less pronounced effect to the pressure drop characteristics of a unit cell structure. The resulting effect is that the flow distribution to each unit cell structure is essentially more homogenous compared to the prior art stack structures that are lacking the restriction orifices structures.

Benefit of the invention is that duty ratio of the cell stack is improved

decreasing the capital cost of a SOFC and SOEC systems, and lifetime of the cell stack becomes longer, thus making power operation of the entire cell system better and more economical as compared to the prior art embodiments.

Brief description of the drawings

Figure 1 presents a single fuel cell structure.

Figure 2 presents flow field plates.

Figure 3 presents a preferred fuel cell stack structure. Figure 4 presents a preferred fuel flow guiding arrangement according to the present invention.

Figure 5 presents a preferred gasket structure according to the present invention.

Figure 6 presents another exemplary fuel cell stack structure.

Figure 7 presents another preferred fuel flow guiding arrangement according to the present invention. Detailed description of the invention

According to the present invention, the fuel cell or electrolyzer stack comprises at least two single repetitious structures. A single repetitious structure comprises at least of one electrochemically active electrolyte element structure including fuel side, electrolyte in between, and oxygen rich side, placed between at least two flow field plates the other distributing oxygen rich gas in the oxygen rich side of the electrolyte element structure and the other distributing fuel gas in the fuel side of the electrolyte element, and at least one sealing means sealing the gas atmosphere at its intended enclosure. The flow field plate has at least one inlet openings for fuel gas and/or oxygen rich gas and at least one outlet openings for used fuel gas and/or oxygen rich gas. The flow direction of at least one gas of fuel gas and oxygen rich gas at least in one single repetitious structure is changed compared to at least another single repetitious structure by applying sealing means that enable the utilization of gas from an inlet opening and delivering the reaction product gas to an outlet opening that differs from the inlet opening and outlet opening of at least in another single repetitious structure. The fuel and oxygen rich gas flow directions on the electrolyte element compared to each other can be arranged to so called co-flow arrangement where both gas flows have essentially the same direction or to so-called counter-flow arrangement where the gas flow directions differ from each other essentially by 180°.

In the following, the invention is mainly explained in relation to a solid oxide fuel cell technology. The solid oxide electrolyzer stack only differs from solid oxide fuel cell stack in that manner that electricity is used to produce fuel with reverse reactions to fuel cell reactions as described in the state of the art.

Figure 2 shows flow field plates 121a, 121b, 121c of a fuel cell. A complete fuel cell stack comprises several plates 121 placed on successively each other in a shown manner. The plates in this embodiment are rectangular and symmetrical. An electrolyte element structure 104 comprising an electrolyte layer between an anode electrode and a cathode electrode is placed between the plates 121 generally in the middle of the plate. The electrolyte element structure 104 may be any suitable electrolyte element structure and is not therefore described herein in any further detail. The flow field plates 121 and the electrolyte element structure 104 are sealed with sealing means 3 - 6. The purpose of the sealing means 3 - 6 is to ensure that oxidant and fuel are not directly mixed without the fuel cell reactions inside the electrochemically active area, that the fuel and oxidant are not leaked out from the electrochemical cells, that the adjacent electrochemical cells are not in electronic contact with each other, and that oxidant and fuel are supplied to the desired flow field plate planes 121. Two opposing flow field plates 121a, 121b, 121c and the electrolyte element structure 104 therebetween form a single repetitious structure. A flow field plate 121 is a planar thin plate that is made of metal alloy, ceramic material, cermet material or other material that can withstand chemical, thermal and mechanical stresses that are present in a fuel cell. According to the invention, the flow field plate 121 comprises inflow and outflow orifices placed at the edges of the plate 121. In this example the plate 121 is rectangular and flow orifices are placed on slightly shorter edges 19. Both of the edges 19 have four orifices, one inflow orifice 7, 11 for oxygen rich gas (in following exemplary embodiment: air), one outflow orifice 10, 14 for air, one inflow orifice 8, 12 for fuel, and one outflow orifice 9, 13 for fuel. The oxygen rich gas can be any gas or gas mixture, which comprises a measurable amount of oxygen. On both of the edges 19 the orifices are arranged in a sequence that has first air in 7, 11, then fuel in 8, 12, then fuel out 9, 13, and then air out 10, 14. The surfaces of the first face 20 (in the fig. top surface) and the second face 21 (below surface, not shown) around the edges of the flow field plate are shaped to allow efficient sealing and they limit a contoured surfaces 15 - 18 in the middle of the flow field plate that has a specific contour for guiding fuel gas and air over the surfaces of the electrolyte elements 104. It should be noted, that the reference numerals 15 - 18 that depict arrows related to sealing means 3 - 6 that illustrate gas flow routes in figure 1 are also used to refer to a face and a contoured surface 15 - 18 of a flow field plate 121a, 121b, 121c that is facing towards the sealing means 3 - 6 that faces the sealing element or structure in question.

The number of the orifices for arranging the gas flows on a fuel cell stack may vary as well as the way how the gas flows are arranged. The basic idea is that orifices 7 - 14 on superposed flow field plates 121 are arranged so that their positions are matched and the orifices in same line form a gas manifold channel through the stack. Sealing means 3 - 6 are used in order to prevent feeding of the fuel and air to wrong layers between electrolyte elements and the flow field plates. The sealing means are arranged to surround each orifice 7 - 14 on the flow field plate 121. The flow field plate 121 and the sealing elements 3 - 6 are used to form ducts (i.e. channels) that go through whole fuel cell stack. The orifices in the flow field plates are super positioned in order to form such a duct. One possible arrangement for arranging the gas flows is described in the following. In here definitions top and bottom as well as up and down are used in conjunction of the figure 2 only, and have no other structural meaning. First, air is fed over a flow field plate that is first in the stack. This plate 121c is shown in the bottom of the exploded view in fig. 2. Now, an air path is arranged to start from air inflow channel 7 and the exit is arranged at the outflow channel 14. The air flows along the flow media 18 and is divided over the bottom surface of the electrolyte element structure 104. The electronic paths are set against electrolyte element structure and provide for guiding the gas over said surface as well as heat and electron transfer over a significantly large area. The flow medium is preferably straight channel structure but any other form may be used, for example such as sine, parabolic or zigzag curve or net type structures. On the opposite side of the electrolyte element structure 104 is the second flow field plate 121b. Now, fuel is guided over the electrolyte element. This is accomplished by arranging a flow path from fuel inflow channel 8 over the underside of the second flow field plate and over the electrolyte element structure in flow media 17. Fuel is exhausted through the outflow orifice 13. In this embodiment air and fuel gases have same flow directions. On following layer gas flows are arranged as follows: air from orifice 11 to orifice 10 through gas distribution media 16, fuel from orifice 12 to orifice 9 through gas distribution media 15. The flow arrangement with varying inflow and exhaust locations can be continued with as many layers as required for the application. The purpose of varying the inflow and exhaust locations is to provide means for arranging the gas flows so that the temperatures over the fuel cell and fuel cell stack can be kept as constant as possible and the temperature gradients small. As the flow arrangements cannot be changed after the fuel cell is assembled and in operation, the design of the flow characteristics is done by using calculations and simulation models. Further, it must be noted that each gas flow flows into a space between two flow field plates 121a - 121c through inflow channel and exits therefrom via exit channel. Each inflow channel feeds fresh gas to the electrolyte element structure 104 and each outflow channel leads the exhaust gas directly out from the stack.

Thus, gas flows are not redirected to further electrolyte elements. It must further be noticed that the inflow and outflow orifices do not have to be formed on to the flow field plate but they can be arranged in separate means, such as closed gas compartments.

The number of the orifice used for gas feed may vary according to the design of the fuel cell. Minimum number might be one inflow orifice for a gas as well as an outflow orifice. Using more orifices allows for more flow patterns but naturally complicates the design. According to one embodiment, the fuel gas and air flow may be arranged crosswise to each other. This can be done simply by rotating every other flow field plate 90°. The rectangular form described above can be used to simplify manufacturing and assembling processes.

However, any geometric form desired may be used such as polygonal, circular, oval, etc. The preferred manufacturing methods for forming the contoured (as example: corrugated) surface are methods using plastic deformation such as stamping, pressing and like, wherein the shape of the material is changed but no material is added or removed, or methods wherein material is added such as welding or removed such as etching. Other manufacturing methods can be utilized if the flow field material is brittle such as extrusion, casting, printing, molding, and like. The orifices for fuel and air can be usually made in a same manufacturing step.

Each flow field plate 121 can be made similar in the stack assembly structure, thus only one type of plate is needed to produce a fuel cell stack having desired amount of repetitious electrolyte element structures 104. This simplifies the structure and eases manufacturing of the fuel cells.

Feeding in air and fuel into a SOFC causes normally an uneven temperature distribution since the inlet air and fuel cool the electrolyte elements from the inlet side. On the other hand, exothermic fuel cell reactions heats up the gases on their way to the exhaust side of the electrolyte elements. The thermal distribution causes thermomechanical stresses to the SOFC structure which may cause breakage of the electrolyte element. The performance of a SOFC improves as the temperature is increased but the increased temperature speeds up aging of the cell. In order to maximize the performance and lifetime of the cell, it is essential to be able to use the cell as accurately as possible on optimum temperature over the whole cell structure. The flow guiding

arrangement structure provided by the present invention diminishes the temperature differences of the cell and thus improves reliability, performance and lifetime. The invention is also economically usable in stack manufacturing. As the structure is simple, benefits can be obtained in design and production.

In figure 3 is presented a preferred fuel cell stack arrangement according to the present invention. The fuel cell stack arrangement comprises flow restriction orifices 126, 136 opened to the flow distribution area 120 and to the flow outlet area 131, and a gasket structure 128 over the flow restriction orifices 126, 136. The gasket structure 128 is preferably made of compressible material, which is e.g. ceramic material. The gasket structures 128 according to the present invention are compressed when the cells are assembled to a stack formation. The gasket structures can also be pre-compressed at least from the flow parts 140. Heights of the flow restriction orifices 126, 136 are determined by a distance from at least one of a bottom 132 of the flow distribution area 120 and of the flow outlet area 131 to a bottom 133 of the gasket structure 128 to stabilize flow distribution in the repetitious structures 138 of the stack having tolerance variations in electrolyte element 104 structure thickness. Similar pressure loss conditions between the cells are accomplished by utilizing the gasket structure 128 which can be compressed and also pre-compressed at least from the flow parts 140 in order to accomplish even thermal distribution, i.e. similar thermal gradients between the cells in the stack. Thus the duty ratio of the fuel cell stack is improved, and lifetime of the fuel cell stack is made longer.

In figure 4 is presented a preferred fuel flow guiding arrangement according to the present invention, in which structure the cell comprises a fuel side 100, an oxygen rich side 102, and an electrolyte element 104 between the fuel side and the oxygen rich side. The electrolyte element comprises preferably a flow channel area 130, but in some embodiments it can be for example a porous flow field area 130. The arrangement comprises means for guiding oxygen rich side gas to and from the electrolyte element 104, and a flow field plate 121 for each cell to arrange flows in the cell. There is a flow distribution area 120 on the flow field plate 121, and a flow outlet area 131 on the flow field plate 121. The fuel flow guiding arrangement comprises means 123 for guiding fuel feed flow to the flow distribution area 120 from sides 127 of the fuel cell. The arrangement further comprises means 125 for turning at least one of the fuel feed flow on the flow distribution area 120 and fuel outlet flow on the flow outlet area 131 in order to equalize flow distribution on the electrolyte element 104. The means 125 are preferably structured by the flow field plate 121 under the electrolyte element 104 and a gasket structure over the electrolyte element 104. The preferred embodiment of figure 4 comprises a fuel flow adjusting structure 122 having at least one geometrical shape 124 for adjusting essentially homogenous at least one of the fuel feed flow and fuel outlet flow over the electrolyte element 104 on the basis of the flow functional effect of said at least one geometrical shape of the fuel flow adjusting structure. The flow adjusting structure 122 of the embodiment presented in figure 2 comprises of the flow restriction areas, e.g. orifices 126, 136 and of a gasket structure 128. Preferably the gasket structure 128 comprises said at least one geometrical shape 124 for adjusting essentially homogenous flow over the electrolyte element. The geometrical shape 124 is for example at least partly elliptic, e.g. Vi elliptic or ¹A elliptic or other geometrical shape 124 than ellipitic. In figure 5 is presented one preferred embodiment of the gasket structure according to the present invention, said gasket structure having the ¹A elliptic geometrical shape 124 which is also shown in the exemplary embodiments of figures 3 and 4. The gasket structure 128 is preferably made of compressible material, which can be pre-compressed at least from the flow parts 140. The gasket structure is made e.g. of ceramic material. On the basis of said compression and/or pre- compression pressure loss characteristics are more controllable, and flowing conditions between different cells in the stack are achieved as substantially equal. The gasket structure on the restriction orifices area 126, 136 can be pre- compressed to a well-defined thickness in order to prevent the gasket material from spreading to the restriction orifices structure and thus in order to prevent the gasket material from changing the height characteristics of the restriction orifices.

Figure 6 presents another exemplary fuel cell stack structure, which differs from the cell stack structure of figure 3 so that the means 123 guide fuel feed flow to the flow distribution area 120 from end of the fuel cell structure or electrolyzer cell structure, not from sides, and so that the gasket structure 128 comprises rectangular shape as said at least one geometrical shape 124 for adjusting essentially homogenous flow over the electrolyte element 104.

In figure 7 is presented another preferred embodiment of the gasket structure according to the present invention, said gasket structure having the Vi elliptic geometrical shape 124. In a cell stack arrangement using a flow guiding arrangement with said Vi elliptic geometrical shape 124 or with another shapes 124 of the gasket structure 128 feed-in flows and out flows can be differently arranged than presented above related to another embodiments.

In some embodiments of the invention can also be utilized an arrangement in which are arranged larger flow ducts (i.e. flow channels) on the middle area of the electrolyte element and smaller flow ducts on the side areas of the electrolyte element.

The invention also enables the electrolyte element placement to be eased during the assembly process of the fuel cell stack or electrolysis cell stack. The gasket structure is shaped so that the electrolyte element can be placed a hole in the gasket structure which then locks the electrolyte element to its desired position both during the assembly process as well as gives a support for the electrolyte element during the said fuel cell and electrolyzer stack operation. Thus, while there have been shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the invention may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements which perform substantially 5 the same results are within the scope of the invention. Substitutions of the elements from one described embodiment to another are also fully intended and contemplated. It is also to be understood that the drawings are not necessarily drawn to scale but they are merely conceptual in nature. It is the intention, therefore, to be limited only as indicated by the scope of the claims i o appended hereto.

Claims

Claims:

1. Fuel flow stack arrangement for solid oxide fuel cells, each cell comprising a fuel side (100), an oxygen rich side (102), and an electrolyte element (104) between the fuel side and the oxygen rich side, the cells being arranged to a formation of a stack, and the arrangement comprises in repetitious structures (138) a flow field plate (121) for each cell to arrange flows in the cell, a flow distribution area (120) on the flow field plate (121), a flow outlet area (131) on the flow field plate (121), and means (123) for guiding fuel feed flow to the flow distribution area (120), characterized in that the fuel flow stack arrangement comprises flow restriction orifices (126, 136) opened to the flow distribution area (120) and to the flow outlet area (131), and a gasket structure (128) over the flow restriction orifices (126, 136), and height of the flow restriction orifices (126, 136) is determined by a distance from at least one of a bottom (132) of the flow distribution area (120) and of the flow outlet area (131) to a bottom (133) of the gasket structure (128) to stabilize flow distribution in the repetitious structures (138) of the stack having tolerance variations in electrolyte element structure thickness.

2. Input reactant flow stack arrangement for solid oxide electrolyzer cells, each cell comprising an input reactant side (102), an oxygen rich side (100), and an electrolyte element (104) between the input reactant side and the oxygen rich side, the cells being arranged to a formation of a stack, and the arrangement comprises in repetitious structures (138) a flow field plate (121) for each cell to arrange flows in the cell, a flow distribution area (120) on the flow field plate

(121), a flow outlet area (131) on the flow field plate (121), and means (123) for guiding input reactant feed flow to the flow distribution area (120),

characterized in that the input reactant flow stack arrangement comprises flow restriction orifices (126, 136) opened to the flow distribution area (120) and to the flow outlet area (131), and a gasket structure (128) over the flow restriction orifices (126, 136), and height of the flow restriction orifices (126, 136) is determined by a distance from at least one of a bottom (132) of the flow distribution area (120) and of the flow outlet area (131) to a bottom (133) of the gasket structure (128) to stabilize flow distribution in the repetitious structures (138) of the stack having tolerance variations in electrolyte element structure thickness.

3. Flow stack arrangement according to claim 1 or 2, characterized in that the electrolyte element (124) comprises at least one of a flow channel area (130) and of a porous flow field area (130).

4. Flow stack arrangement according to claim 1 or 2, characterized in that the arrangement comprises means (123) for guiding input reactant flow to the flow distribution area (120) from sides (127) of the electrolyzer cell, and the arrangement comprises means (125) for turning at least one of the input reactant feed flow on the flow distribution area (120) and output reactant outlet flow on the flow outlet area (131).

5. Flow stack arrangement according to claim 1 or 2, characterized in that the arrangement comprises a fuel flow adjusting structure (122) having at least one geometrical shape (124) for adjusting essentially homogenous at least one of the fuel feed flow and fuel outlet flow over the electrolyte element (104) on the basis of the flow functional effect of said at least one geometrical shape of the fuel flow adjusting structure.

6. Flow stack arrangement according to claim 3, characterized in that the gasket structure (128) comprises at least one geometrical shape (124) for adjusting essentially homogenous flow over the electrolyte element (104) on the basis of the flow functional effect of said at least one geometrical shape of the flow adjusting structure.

7. Flow stack arrangement according to claim 6, characterized in that the gasket structure (128) comprises at least partly elliptical shape as said at least one geometrical shape (124).

8. Flow stack arrangement according to claim 1 or 2, characterized in that the gasket structure (128) is pre-compressed at least from the flow areas.

9. Fuel flow method of stack arrangement for solid oxide fuel cells, in which method the cells are arranged to a formation of a stack, and is guided fuel feed flow to a flow distribution area (120), characterized in that in the method is restricted fuel flow through flow restriction orifices (126, 136) opened to the flow distribution area (120) and to a flow outlet area (131), and is restricted fuel flow by a gasket structure (128) over the flow restriction orifices (126, 136), and is determined height of the flow restriction orifices (126, 136) by a distance from at least one of a bottom (132) of the flow distribution area (120) and of the flow outlet area (131) to a bottom (133) of the gasket structure (128) to stabilize flow distribution in the repetitious structures (138) of the stack having tolerance variations in electrolyte element structure thickness.

10. Input reactant flow method of stack arrangement for solid oxide electrolyzer cells, in which method the cells are arranged to a formation of a stack, and is guided input reactant feed flow to a flow distribution area (120),

characterized in that in the method is restricted input reactant flow through flow restriction orifices (126, 136) opened to the flow distribution area (120) and to a flow outlet area (131), and is restricted input reactant flow by a gasket structure (128) over the flow restriction orifices (126, 136), and is determined height of the flow restriction orifices (126, 136) by a distance from at least one of a bottom (132) of the flow distribution area (120) and of the flow outlet area (131) to a bottom (133) of the gasket structure (128) to stabilize flow

distribution in the repetitious structures (138) of the stack having tolerance variations in electrolyte element structure thickness.

11. Flow method of stack arrangement according to claim 9 or 10,

characterized in that the electrolyte element (124) comprises at least one of a flow channel area (130) and of a porous flow field area (130).

12. Flow method of stack arrangement according to claim 9 or 10,

characterized in that in the method is guided input reactant flow to the flow distribution area (120) from sides (127) of the electrolyzer cell, and in the method is turned at least one of the input reactant feed flow on the flow distribution area (120) and output reactant outlet flow on the flow outlet area (131).

13. Flow method of arrangement according to claim 9 or 10, characterized in that in the method is effected to the fuel flow by at least one geometrical shape (124) for adjusting essentially homogenous at least one of the fuel feed flow and fuel outlet flow over the electrolyte element (104), said effecting being made on the basis of the flow functional effect of said at least one geometrical shape.

14. Flow method of stack arrangement according to claim 13, characterized in the method is utilized as said at least one geometrical shape (124) at least one geometrical shape of the gasket structure (128).

15. Flow method of stack arrangement according to claim 13, characterized in that in the method is utilized as said at least one geometrical shape (124) at least partly elliptical shape (124) of the gasket structure (128).

16. Flow method of stack arrangement according to claim 9 or 10,

characterized in that the gasket structure (128) is processed by a pre- compression at least from the flow areas.