Patent Application
20050064266
This invention relates to fuel cells stacks, and in particular to unitized electrochemical fuel cell stacks with mono-polar fuel cell cartridges.
Fuel cell technology, used for clean and efficient power generation, has made tremendous technical progress over the years. Most advances have been in the solid-oxide fuel cell (SOFC) and proton-exchange-membrane fuel cell (PEMFC). The growing acceptance of fuel cells for power generation is due to a number of benefits including low operating temperatures, non-corrosive and stable electrolyte, and broader market applications.
One of the major challenges facing fuel cell technology is whether the electrochemical fuel cell stacks can be designed and mass-produced cost-effectively. To reduce the cost of fuel cell stacks, it is necessary to develop low cost materials and develop new stack designs that allow for simple mass production at low cost.
Bipolar flow field plates are formed between the anode of one fuel cell and the cathode of a second fuel cell. This provides a flow field for both the oxidant and the fuel and also allows the electrons generated at the anode of one fuel cell to be conducted to the cathode of an adjacent cell.
Bipolar flow field plates are typically machined from graphite blocks/plates with strong corrosion resistance, no gas permeability and good electrical conductivity. The flow field channels are machined into the surfaces on both sides of the bipolar plate. The layout of these channels in the bipolar plate determines the uniformity of distribution of the reactants onto the electrode surface, thus the plates can be very complex. Therefore, manufacture of bipolar plates is difficult and expensive.
In addition, when a bipolar flow field plate is made of metal or graphite, a leak current sometimes runs in the bipolar plate across the fluids and electrodes, causing corrosion to occur in the bipolar plate. It has been difficult to manufacture a bipolar plate for polymer electrolyte fuel cells from a single material that exhibits a high degree of resistance to the corrosive fluids, has good current collection properties and a high degree of structural integrity.
In order to form a bipolar fuel cell stack, a group of bipolar plate assemblies are connected in series where each plate supports two gas electrodes, an anode on one side and a cathode on the opposite side. Such a fuel cell stack (maybe comprising 50 or more plates) becomes functional only after introducing reactants to the whole stack. That is, the fuel cell stack is capable of generating electric current only when an appropriate fuel such as H2 and O2 is passed through the stack interior.
While the bipolar fuel cell stack assembly procedure appears uncomplicated, there are many practical manufacturing and assembly problems associated with this conventional fuel cell bipolar design. The major problem is that the fuel cell stack can only be tested after it has been completely assembled. In a large stack, the likelihood that each individual fuel cell performs within specification is very poor. Accordingly, in the case of a failure, for example poor operating cell voltage, the entire stack must be dismantled and the faulty cell removed and replaced. Identifying the faulty cell is a cumbersome procedure because the stack normally contains dozens of fuel cells. In addition, the re-assembly of the stack is as difficult and presents no guarantee that all cells will be functioning after re-assembly. Accordingly, a second or third iteration may be required before the stack performs as specified. Moreover, other problems can develop once the stack is in operation. For example, seals separating the fuel from the oxygen can develop leaks. If this occurs, dismantling and re-assembly of the entire stack is again required.
In summary, bipolar fuel cell stacks are expensive to assemble, the assembly process is slow and very labor intensive, and control of product quality is difficult to achieve. The cost of manufacture of individual fuel cell and stack components is further increased by the relatively inefficient way in which cell components must currently be assembled into the full stack.
It is therefore apparent that there is a need for a fuel cell design that can achieve enhanced energy and power densities while satisfactorily addressing the diverse problems in assembly and design identified above. More particularly, there exists a substantial need for a fuel cell design composed of modular components that can be assembled in an automated, reliable fashion, and independently removed when required and that achieve a well-functioning cell in a cost-effective manner.
In addition, there is a need for fuel cells that can be pre-tested prior to assembly into full fuel cell stacks. This pre-testing would identify and eliminate malfunctioning cells prior to final assembly of the stack.
Accordingly, in one aspect of the present invention, there is provided a modular, unitized electrochemical fuel cell cartridge, comprising:
In a further aspect, the present invention also provides an electrochemical fuel cell module comprising
In a further aspect, the present invention also provides an electrochemical fuel cell stack comprising
The preferred embodiments of the present invention will be described with reference to the accompanying drawings in which like numerals refer to the same parts in the several views and in which:
The present invention provides a new design for a modular unitized electrochemical fuel cell cartridge and electrochemical fuel cell stack, and will now be described with reference to
In one aspect the present invention provides a modular unitized electrochemical fuel cell cartridge designated generally at 20 comprising a monopolar anode plate 22, a monopolar cathode plate 24 and a solid polymer membrane electrode assembly 26 operably interposed between the anode plate 22 and the cathode plate 24. The monopolar anode plate 22 has a first flow field 36 formed in an inwardly facing surface 23 for distributing fuel. A fuel opening 28 (more may be provided) is located at the periphery of the flow field 36 in communication with the flow field 36 via port means known in the art. The monopolar anode plate 22 also comprises a fuel outlet 30 (more may be provided) in communication with the flow field 36, via known port means, and located at the opposite end of the flow field 36 (at its periphery) from the fuel opening 28. The anode plate 22 also has an air opening 32 and an air outlet 34.
The cathode plate 24 also comprises a flow field 37 (not shown) which may be of the same or different configuration as the anode flow field 36, formed in the inwardly facing surface for distributing air and an air opening 32 that is in communication with the flow field 37. The cathode plate 24 also has an air outlet 34 in communication with the flow field 37 and located at the opposite end of the flow field 37 (at its periphery) from the air opening 32. The cathode plate 24 also has a fuel opening 28 and a fuel outlet 30. These openings 28, 30, 32 and 34 are located in the plates 22, 24 such that upon alignment of the plates, channels are formed in the cartridge 20.
Both the anode plate 22 and the cathode plate 24 are substantially planar and in the preferred embodiment are square shaped, however the plates 22, 24 can be any other suitable configuration or size. The plates 22, 24 of the present invention may be integrally formed from a base substrate that is electrically conductive or they may be formed so that the periphery of the flow-field is formed separately and may comprise an electrically insulating thermally conductive polymeric frame. The presence of such a frame may prevent possible short circuiting of adjacent fuel cells and reduce or eliminate parasitic current flow between adjacent fuel cells.
The frame may also improve the heat management of the fuel cell cartridge. Additionally the incorporation of the frame provides a built in safety feature for protecting persons from possible contact with electrically live parts of the fuel cell cartridge 20.
The plates 22, 24 of the present invention may be manufactured from any material that is suitable for an electrochemical fuel cell plate, as is known in the art.
The anode plate 22 and the cathode plate 24 of the present invention are relatively thin and typically of a thickness between 0.015 to 0.12 inches (0.038 to 0.30 cm), however variations on this thickness may occur depending on the requirements of the plates 22, 24 and their use.
As previously mentioned each of the plates 22, 24 contain a flow field 36, 37 on their inwardly facing surfaces. In a preferred embodiment of the present invention the flow field 36 is located in the central portion of the plates 22, 24. The flow field 36 has a network of reactant flow channels (not clearly discernable in the Figures) that distribute reactants over the surface of the plates 22, 24.
Fuel openings 28 are in fluid communication with the flow fields 36, 37. As shown in
As can be seen from
Each of the plates 22, 24 also comprise alignment means 46 to ensure correct alignment of the plates 22, 24 when forming a fuel cell cartridge 20. The alignment means 46 of the present invention preferably comprises a pin integrally formed within each plate 22, 24. The pin aligns with a recess located on the adjacent plate with which a cartridge 20 is formed. Other alignment means may also be used, an example of an alternative alignment means is a series of recesses located through the plates and a series of pins not integrally formed with the plate that can be slotted through the openings when the plates are aligned, other alignment means known in the art may also be used. The pins are made from non-conductive material.
The incorporation of the alignment means 46 on the plates 22, 24 not only ensures correct alignment of the plates 22, 24 but also improves the plate to plate sealing and therefore inhibits intra-cell leaking. As previously discussed, the preferred embodiment of the present invention utilizes integrated pins within the plate design as the alignment means 46. By integrally forming the alignment means 46 within the plate the cost of the plate and the manufacturing time is significantly reduced. The plate, and subsequently when in use, the cartridge has less components which reduces the complexity of the plate and cartridge. The incorporation of the ridges 42 and corresponding mating grooves 44 on the external surfaces of the plates 22, 24 also ensure the alignment of adjacent plates 22, 24 and consequently fuel cell cartridges 20 and also assists in inhibiting inter-cell leaking.
The fuel cell cartridge 20 of the present invention may further comprise one or more adhesive film gaskets (not shown). Each plate 22, 24 may be bonded to a film gasket, and the solid polymer membrane electrode assembly 26 subsequently sandwiched between the plates 22, 24 and bonded to them by such gaskets.
Alternatively, a sealant or bondweld may be used to connect the plates and membrane electrode assembly and form inter-cell seal. Sealant may be applied using fluid dispensing systems. This process reduces or eliminates the laborious assembly and alignment issues encountered with bipolar plate designs. This design also enables a simple and fast quality control and maintenance of the fuel cell units.
As can be seen in
Referring now to
These cartridges 20 allow easy assembly and maintenance, flexible arrangement and use, and can be used in a wide range of applications.
A further aspect of the present invention, shown in
As can be seen in
The assembly of the fuel cell cartridge will now be discussed. The fuel cell cartridge 20 resembles a sandwich structure comprising a mono-polar flow field anode plate 22, a solid polymer membrane electrode assembly 26 and a mono-polar flow field cathode plate 24.
The process for assembling the fuel cell cartridge 20 may be automated using well-known combinations of conveyor, dispenser and pressure seal mechanisms (not shown). The fuel cell 20 assembly conveyor receives all cell components in succession from a component dispenser having a component feeder/loader and conveys the components through adhesive film, or adhesive gasket dispensing station located along the conveyor path. The conveyor operates intermittently to transport the cell components to a station where it is pressure bonded to form the fuel cell cartridge 20, which is then transferred to a single cell dispenser. The single cell dispenser includes a quality control station and a cell dispensing mechanism, which dispenses and counts cells one by one. After this, the individual fuel cell cartridges are stacked in alternating fashion with fuel cells of opposite polarity connected in series until the desired number of fuel cells have been achieved. The fuel cells are then aligned by vibrating the stack. After alignment, the stack is placed into a stack holder.
The manufactured fuel cell cartridges 20 may first be tested at a quality control station along the production line. At this station, a number of test methods and tools may be used to test the quality of the individual fuel cell cartridges. These include electrochemical methods, such as open circuit potential measurements and polarization techniques, and alternating current (AC) resistance methods. An AC milliohmmeter provides a practical tool for testing the quality of each of the individual fuel cells by measuring its internal resistance. Faulty cells will be eliminated prior to assembly in the stack. This pre-testing capability significantly improves stack productivity and reliability.
The assembly of the stack 50 will now be discussed with reference to a fuel stack containing more than one fuel cartridge 20, however the stack can contain only one fuel cell cartridge 20 and would be assembled in a similar manner to that which is described. The fuel cartridges 20 are arranged in series so that the outer surface of the anode plate 22 of one cartridge abuts the outer surface of the cathode plate 24 of an adjacent cartridge 20. The ridges located 42 located on the outer surface of the anode plate 22 are releasably received in the mating grooves 44 located on the outer surface of the cathode plate 24 and provide a sound cartridge-to-cartridge seal. When the cartridges 20 are aligned in series the fuel openings 28 located on the plates 22, 24 are all aligned and form a fuel feed channel 52, likewise the fuel outlets 30 are aligned and form a fuel exhaust channel 56, the air openings 32 are aligned and form an air feed channel 54 and the air outlets 34 are aligned and form an air exhaust channel 58.
Once the cartridges 20 are aligned in series, a current collector 60 is placed at each end of the series of cartridges 20 in parallel with the surface of the cartridges 20. The current collectors 60 of the present invention are preferably made from copper. Gold plating may be used to improve corrosion resistance of the copper current collector. After addition of the current collectors 60, a first end plate 62 is placed at one end of the cartridges 20 and a second end plate 64 is placed at the opposite end.
The first end plate 62 contains an air inlet port 66 and a fuel inlet port 68 and when placed at the end of the stack the air inlet port 66 is aligned with the air feed channel 54 and allows air to flow through the air inlet port 66 and into the air feed channel 54 and through the flow fields 36 that are in fluid communication with the air feed channel 54. Likewise the fuel inlet port 68 is aligned with the fuel feed channel 52 and allows fuel to flow through the fuel inlet port 68 into the fuel feed channel 52 and through the flow fields 36 that are in fluid communication with the fuel feed channel 52.
At the opposing end of the stack, the second end plate 64 contains an air exhaust, not shown, and a fuel exhaust, not shown. In a similar configuration to the first end plate 62, the air exhaust of the second end plate 64 is aligned with the air outlet channel 58 and allows the air that flows through the flow fields 36 and out of the air outlets 34 to pass through the air outlet channel 58 and out of the air exhaust. Similarly the second end plate 64 also has a fuel exhaust, not shown, that is aligned with the fuel outlet channel 56 and allows the fuel that flows through the flow fields 36 and out of the fuel outlets 30 to pass through the fuel outlet channel 56 and out of the fuel exhaust.
Further details of the preferred embodiment of the present invention will now be illustrated in the following example that is understood to be non-limiting with respect to the appended claims.
Modular, unitized electrochemical fuel cell cartridges were designed and constructed for a 500 W fuel cell stack module in general accordance with the embodiment depicted in
A dielectric one-sided adhesive material was placed on the endplate. The bus bar was secured to the endplate using Nylon screws. A seal between the endplate-bus bar subassembly and cell cartridge was established using o-rings. The stack was fabricated using an assembly rig with alignment guides. The first endplate-bus bar subassembly was laid down. The unitized cell cartridges were placed over the subassembly until the desired number of cells is assembled. The ridges and grooves ensure proper cell-to-cell alignment and establish cell-to-cell seal. The stack was clamped to the desired pressure and the resistance of the stack was measured. Pneumatic leak test using air or helium was performed. The current-voltage performance and steady state operation of the stack was evaluated.
Although the present invention has been shown and described with respect to its preferred embodiments, it will be understood by those skilled in the art that other changes, modifications, additions and omissions may be made without departing from the substance and the scope of the present invention as defined by the attached claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CA02/01418 | 9/17/2002 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 60323061 | Sep 2001 | US |
