BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a cross sectional, schematic view of the fuel cell having two said single layer plates 1, with plurality of channels on both sides for reactant gas flows and cooling liquid flows, to sandwich water damming layers 6 (WDL) and a membrane electrode assembly (MEA) in between. A schematic view of the MEA is given with a membrane layer 4, two catalyst layers 3 and two gas diffusion layers (GDL) 2 with locally impregnated regions 5 corresponding to the liquid flow channels.
FIG. 2
a shows an enlarged cross-sectional, schematic view of one cooling liquid channel on the plate 1 in connection with WDL 6 and region 5 of GDL 2 of the MEA, both of which are treated with water transferring materials.
FIG. 2
b is mostly the same as FIG. 2a, except the shape of the region 5 which goes deeper down in touch with catalyst layer 3.
FIG. 3 depicts a cross-sectional, schematic view of a single layer plate 1, a half MEA having catalyst layer 3, membrane 4 and gas diffusion layers (GDL) 2 with locally impregnated regions 5 to illustrate three different humidifying paths of the cooling liquid. One of them (Green) is to pass water into reactant flow channels; the second (Yellow) is to humidify reactant right in GDL; the third (Blue) is to deliver water into catalyst and membrane layers.
FIG. 4 illustrates a cross-sectional, schematic view of a single layer plate 1, a half MEA having catalyst layer 3 and gas diffusion layers (GDL) 2 with locally impregnated regions 5 to illustrate water removal principles. There are three paths to remove water generated in fuel cell. One of them (Red) is the traditional way to let the water go into reactant flow channels; the second (Magenta) is to let water move from GDL under reactant gas flow channels into WDL via the impregnated region of the GDL and then cooling liquid flow channels; the third is to let water move from catalyst layer into GDL under landing then directly into WDL and the impregnated regions of the GDL and then further into cooling liquid flow channels (Cyan).
DISCLOSURE OF THE INVENTION
In accordance with the present invention, there is provided a novel design of a fuel cell constructed with single layer bipolar plates, membrane electrode assembly (MEA) with gas diffusion layers (GDL) locally impregnated with water transferring materials (e.g. nafion, etc.), and/or water damming layers (WDL) also treated with water transferring materials. While the fuel cell integrates reactant gas flow fields on both sides of the plates, upon different needs, humidifying, hydrating and cooling water (HHCW) flow fields can be placed on one side or both sides of the single layer plates to achieve functions of gas humidification, membrane hydration, water removal and cell cooling. One of embodiments features the fuel cell constructed with the WDL and locally impregnated GDL stacked together directly in contact with the HHCW flow channels of the plates on one side (WDL side) and catalyst/membrane layers on the other (GDL side), another embodiment has the locally impregnated GDL, without WDL, directly placed underneath the HHCW flow channels of the plates, and another embodiment has WDL placed between the HHCW flow channels and MEA with regular GDL without local treatment for water transport.
In reference to FIG. 1, there is shown a cross sectional, schematic view of the fuel cell having single layer plates 1 fabricated with plurality of reactant (air) flow channels, and HHCW flow channels on one side, and reactant (fuel) flow channels and HHCW flow channels on the other side, and between two plates sandwiched a membrane electrode assembly (MEA) which has catalyst layers 3, membrane 4 and GDL 2 fabricated with local regions 5 impregnated with hydrophilic and water transferring materials, and between regions 5 of GDL 2 and the HHCW flow channels placed with WDL 6 that are also porous medium treated with hydrophilic and water transferring materials, as shown in FIGS. 2a and 2b, so water permeability of the WDL 6 and region 5 is well designed along with certain controlled contact gaps between plates 1, WDL 6 and region 5 to allow required liquid (water) to pass through both ways in or out the HHCW flow channels under adjustable and given pressure difference between HHCW flow channels and reactant flow channels, as shown in FIG. 3 and FIG. 4, to achieve functions of humidifying reactant gases, hydrating membrane, removing excessive water.
FIGS. 2
a and 2b give a closer and enlarged cross-sectional, schematic view of one HHCW flow channel on plate 1 and the porous WDL 6 and the impregnated region 5 of GDL 2 of MEA. Plate 1, WDL 6 and MEA with region 5 on GDL 2 are assembled together to achieve and integrate functions of humidifying gases, hydrating membrane, cooling cells and removing water generated in the fuel cell.
As indicated in FIG. 3, not only do liquid flows in the HHCW flow channels act as a cell cooling means, but also provide humidifying water, a part of which flows through WDL 6 into reactant flow channels, as shown by green arrows, where the water becomes a local source for reactant gas humidification in the reactant gas flow channels, a part of which goes through WDL 6 and region 5 of GDL 2, also into other parts of GDL 2, as shown by yellow arrows, where the water is to humidify reactant flow right in the GDL 2 porous medium, and a part of which penetrates WDL 6 and region 5 of GDL 2 into catalyst layer 3 and membrane layer 4 as a source to hydrate membrane, as shown by blue arrows.
As indicated in FIG. 4, in additional to a traditional way to have excessive water generated in electrochemical reaction removed through the reactant flow channels on plate 1, as shown by red arrows, this invention provides a novel means of water removal that by taking advantage of capillary force formed in the porous media WDL 6, region 5 and GDL 2, and by adjusting pressure difference between the HHCW flow channels and reactant gas flow channels, a portion of the excessive water accumulated in region 5 of GDL 2 and WDL 6, due to hydrophilic and water transferring nature of the materials used in region 5 and WDL 6, can be driven into the HHCW flow channels for removal, as shown by magenta and cyan arrows.
Additional explanations to water management principles, illustrated in FIG. 3 and FIG. 4, are that the pressure difference adjusting process can be a pulsed or continuous process used in either water supplying direction, as shown in FIG. 3, or water removing direction, as shown in FIG. 4, upon different needs in fuel cell operations.
Patent Application
20080020252
