Alkaline membrane fuel cells and apparatus and methods for supplying water thereto
A device to produce electricity by a chemical reaction without the addition of liquid electrolyte comprises an anode electrode, a polymer membrane electrolyte fabricated to conduct hydroxyl (OH—) ions, the membrane being in physical contact with the anode electrode on a first side of the membrane, and a cathode electrode in physical contact with a second side of the membrane. The anode electrode and cathode electrode contain catalysts, and the catalysts are constructed substantially entirely from non-precious metal catalysts. Water may be transferred to the cathode side of the membrane from an external source of water.
1. An alkaline membrane fuel cell, the fuel cell comprising:
an anode electrode;
a polymer membrane electrolyte configured to conduct hydroxyl (OH—) ions, the membrane being in physical contact with the anode electrode on a first side of the membrane; and
a cathode electrode in physical contact with a second opposite side of the membrane;
wherein the fuel cell is configured and disposed with a substantially dead ended anode chamber and is configured to transfer water from the anode electrode through the membrane to the cathode electrode at a rate substantially equivalent to water generation at the anode electrode; and
wherein water transport across the membrane is facilitated by a highly hydrophilic membrane or mesh shaped and placed as a frame around the active area on both the anode and cathode sides.
2. The fuel cell of claim 1 , further comprising a mixed hydrophilic/hydrophobic microporous layer proximate to the anode electrode and a gas diffusion layer proximate to the microporous layer.
3. The fuel cell of claim 1 , further comprising a hydrophobic microporous layer proximate to the cathode electrode and a gas diffusion layer proximate to the microporous layer.
4. The fuel cell of claim 3 , when operating in air breathing mode, further comprising an adjustable shutter proximate to the gas diffusion layer.
5. The fuel cell of claim 3 , when operating in air breathing mode with the cathode GDL thickness and porosity designed for a water vapor rate of release matching a selected cell current, Jcell and inner cell temperature, Tcell according to the equation: P* H20,Tcell =0.4[Jcell/Jlim.cath]atm., where P* H20,Tcell is the water vapor pressure at Tcell and Jlim.cath is the limiting current corresponding to the max transport rate of oxygen from air through the GDL.
6. The fuel cell of claim 1 wherein initial activation of the cell achieved by setting the cell voltage at about or near 50 mV and keeping it at this voltage until the cell current plateaus while the cell temperature reaches a target operation temperature.
7. The fuel cell of claim 6 wherein the current plateaus near 1 A/cm2 and the cell operation temperature is between 60 and 70 degrees Celsius.
8. The fuel cell of claim 1 , wherein the substantially dead-ended anode further includes a one-way valve, the one-way valve opening periodically to the ambient by internal pressure buildup and possible temporary use of high flow of hydrogen to periodically purge water buildup.
9. An alkaline membrane fuel cell, the fuel cell comprising:
an anode electrode;
a polymer membrane electrolyte configured to conduct hydroxyl (OH—) ions, the membrane being in physical contact with the anode electrode on a first side of the membrane; and
a cathode electrode in physical contact with a second opposite side of the membrane;
wherein the fuel cell is configured and disposed with a substantially dead ended anode chamber and is configured to transfer water from the anode electrode through the membrane to the cathode electrode at a rate substantially equivalent to water generation at the anode electrode; and
wherein direct supply of liquid water to the cathode side of the membrane is provided by means of a water channel about 1 millimeter wide surrounding an active area of the fuel cell.
10. The fuel cell of claim 9 wherein water transfer from the water channel to and along the membrane surface is facilitated by a wicking mesh incorporated as part of the membrane on the side adjacent the cathode catalyst.
11. The fuel cell of claim 10 wherein the wicking mesh is incorporated to become an integral part of the membrane by placing it along the major surface of the membrane during membrane casting.
12. The fuel cell of claim 10 wherein the wicking mesh is attached onto the surface of a pre-fabricated membrane by using a solution of an ionomer to fill spaces in the mesh and to provide a bonding function following subsequent ionomer recasting.
13. The fuel cell of claim 9 wherein the liquid water supply to the cathode side of the membrane is provided from a stationary reservoir of liquid water with the water wicked from such reservoir into and along the cathode side of the membrane.