Patent Application
20080076005
In situ seals
One example of a process to make the in situ seals is given as representative of a wide range of alternatives. The catalyst coated membrane and the gas diffusion layers can either be pre-assembled by pressing under a specified set of temperature, time and pressure or the catalyst coated membrane and the gas diffusion layers are handled separately. The conduit's geometry, size and spacing are all variables that can be selected. The choice is determined to some degree by the application, the operating parameters and the auxiliary equipments. The gas diffusion layers are then precisely perforated to match the seal's location. The appropriate sealing material is prepared and injected in the openings (perforations in the GDL) and cured. The gasket material is selected for the compatibility with the membrane and the catalysts and to have the required mechanical, thermal, electrical and viscous properties to provide an adequate seal in reference to gas tightness, mechanical strength durability and reliability. The edge seals can also be done by a number of alternatives. Once the integrated gaskets are formed the assembly CCM+GDL+ separator plates are perforated. The individual cells with the plurality of conduits are then ready for assembly. Again numerous alternatives are possible to align and compress the stack of cells. Current collectors are positioned at each extremity and the manifold—end plate combination completes the stack assembly. Pressure is applied and maintained by mechanical means. Two examples are described as illustrative of the many possibilities can be proposed by a person skilled in the art.
Once the membrane and the porous gas diffusion media have been selected, in the present case Nafion™ membrane and GDL from SGL Carbon Group, the catalyst coated membrane (membrane plus platinum) and the porous gas diffusion media are pressed together according to the recommendation of the manufacturers regarding temperature, pressure and time. The geometry, size and number of conduits are selected based on the operating conditions and the required power per cell and total power. The first step is then to prepare the assembly CCM-GDL for the integrated gaskets on the anode and cathode side of the membrane and to mold the gaskets. The final step prior to assembly is to pierce the gaskets and membrane.
The assembled individual cells are then stacked inserting a separator/bipolar plate between each cell. Current collectors (10) complete the stack, the fluid distribution manifold (11) is then added and finally the end plates (12, 13) and tie-rods (missing from the figure) compress the stack. Fittings for oxygen/air, hydrogen, and water are then attached to the manifold and the stack is ready to be put in operation.
FIG. 5—The catalyst coated membrane and the porous gas diffusion media, in the present case Ion-Power CCM with Nafion™ membrane, and SGL 34BC GDL, are pressed together according to the recommendation of the manufacturers regarding temperature, pressure and time. The geometry, size and number of conduits are selected based on the operating conditions and the required power per cell and total power. The assembly CCM-GDL is prepared by mechanically making the openings in the GDL for the integrated gaskets on the anode and cathode side of the membrane. A silicone based product with an inert carbon base additive is injected and the gaskets are cured. The final step prior to assembly is to pierce the gaskets together with the CCM and the GDL on the opposite side.
The assembled individual cells (9) are then stacked. Current collectors (10) complete the stack. In this example the combination fluid distribution manifold and end plates (14) are added and the system is compressed by elastic wrapping around the stack, not shown in the figure. Fittings for oxygen/air, hydrogen and water are then attached to the manifold and the stack is ready to be put in operation.
FIG. 6—An exploded view of the combination end plate (structural function) and manifold (fluid distribution) (14-4). This design and variants on the same idea have several advantages over the basic intuitive concept of Example 1:
FIG. 7—An illustration of the several components for this example. The number of conduits, 48, is totally arbitrary and only illustrative of the concept of plurality of conduits. The illustrated conduits pattern is a rectangular matrix; however one can easily use other geometries. In this example three separate conduits are used for the inlet and two for the outlet, therefore the cooling conduits must be either combined with the air or hydrogen exhaust, in the illustration air and water are combined.
The core of the fuel cell is the catalyst coated electrolyte membrane (6+7+8), sandwiched between the cathode GDL (5) and the anode GDL (5). Each cathode and anode has integrated gaskets; on cathode side (4) and on anode side (4). These integrated gaskets ensure that the anode fuel is prevented from entering the cathode side of the membrane and the air prevented from entering the anode side. The water cooling conduits in this example are combined with the air exhaust conduits which is also the exhaust for the reaction water. The first and the last cell are connected in series with the current collectors (10). The distributor plates (14-1, 14-2, and 14-3) are inserted between the current collector (10) and the fluid manifold (14-4).
