Systems and Methods of Securing Immunity to Air CO2 in Alkaline Fuel Cells

• US 20110212370A1
• Filed: 08/24/2010
• Published: 09/01/2011
• Est. Priority Date: 08/24/2009
• Status: Active Grant

• Current Assignee: Hydrolite Limited
• Original Assignee: Elbit Systems Land and C4I - Tadiran Limited (Elbit Systems Limited)
• Inventors: Gottesfeld, Shimshon
• Granted Patent: US 8,895,198 B2
• Time in Patent Office: Days
• US Class Current: 429/410
• CPC Class Codes: H01M 10/46 Accumulators structurally combined with charging apparatus circuits for charging H02J7/00
• CPC Class Codes: H01M 2300/0014 Alkaline electrolytes
• CPC Class Codes: H01M 2300/0082 Organic polymers
• CPC Class Codes: H01M 8/0668 Removal of carbon monoxide or carbon dioxide
• CPC Class Codes: H01M 8/0693 Treatment of the electrolyte residue, e.g. reconcentrating
• CPC Class Codes: H01M 8/083 Alkaline fuel cells
• CPC Class Codes: H01M 8/1007 with both reactants being gaseous or vaporised H01M8/12 takes precedence
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

An air CO₂ filtration assembly or system is provided that includes CO₂ filters or traps designed and configured with a limited, but high capacity, volume to maximize filtration/absorption of CO₂ from an air stream supplied to an alkaline fuel cell to thereby minimize the CO₂ level in the air stream fed into the fuel cell cathode. The CO₂ filters or traps include at least one thermally regenerative CO₂ chemical filter or trap arranged in a tandem configuration with a strongly bonding CO₂ chemical filter or trap. The combination of the two types of filters or traps sequentially filter/absorb CO₂ from the air stream and reduce the level of CO₂ in the air stream fed into the cathode. The air CO₂ filtration assembly or system may be used in conjunction with electrochemical purging of the alkaline fuel cell that enables removal of CO₂ from the fuel cell by anodic decomposition of accumulated carbonate ions in the fuel cell anode and release of CO₂ through the anode exhaust stream.

Claims

1. An alkaline fuel cell comprising:

an air cathode operatively coupled with a two-trap air filter assembly;

the two-trap air filter assembly including a series of a first thermally regenerative chemical CO₂ trap arranged in tandem with a second strongly-bonding CO₂ chemical trap, the first and second CO₂ traps being disposed upstream from an inlet to the air cathode, the second CO₂ trap disposed between the first CO₂ trap and the cathode inlet;

the first and second CO₂ traps being configured to reduce levels of CO₂ in an air stream supplied to the inlet to the air cathode;

wherein the alkaline fuel cell includes an alkaline aqueous electrolyte or an OH⁻

ion conducting polymeric membrane without liquid electrolyte.

2. The alkaline fuel cell of claim 1, wherein the first CO₂ trap includes, as active material, a resin with amine functional groups configured to serve as CO₂ trapping sites via a reaction of the amine with CO₂ and water vapor to form bicarbonate according to a process:

R—

NH₂+CO₂+H₂0=R—

NH₃⁺(HCO₃⁻

)

where R includes a carbonaceous polymer backbone.

3. The alkaline fuel cell of claim 1, wherein the first CO₂ trap includes, as active material, a resin with amine functional groups configured to serve as CO₂ trapping sites via a reaction with CO₂ under dry air conditions to form carbamate according to a process:

2(R—

NH₂)+CO₂=(R—

NHCOO⁻

)(R—

NH₃⁺)

where R includes a carbonaceous polymer backbone.

4. The alkaline fuel cell of claim 1, wherein, per kW of power generated, the first CO₂ trap defines dimensions of about 2 liters and is configured to reduce the level of CO₂ in the air stream by a factor of about 10.

5. The alkaline fuel cell of claim 1, wherein the first CO₂ trap is configured to enable residence time of gas within the first CO₂ trap of up to about 1 second, and is further configured to reduce levels of CO₂ in the air stream by a factor of about 10.

6. The alkaline fuel cell of claim 1, wherein the first CO₂ trap is configured to reduce levels of CO₂ in the air stream on passing the air stream through the first CO₂ trap by a factor of about 10 and wherein the air stream passing through the first CO₂ trap has temperatures of up to about 45 degrees C.

7. The alkaline fuel cell of any of claims 2 and 3, wherein the first CO₂ trap is configured for thermal regeneration whereby the first CO₂ trap releases absorbed CO₂ in response to rejuvenation air passing through the first CO₂ trap at temperatures within a range of between about 80 degrees C. and 120 degrees C., and preferably within a range of between about 100 degrees C. to about 105 degrees C.

8. The alkaline fuel cell of any of claims 2 and 3, wherein the configuration and operation temperatures for the first CO₂ trap ensure that the time for thermal regeneration to recover CO₂ trapping capacity is shorter than the CO₂ saturation time under substantially equal air flow rates during adsorption and desorption half cycles.

9. The alkaline fuel cell any of claims 2 and 3, wherein the first CO₂ trap is configured for thermal regeneration by passing a rejuvenating air stream through the first CO₂ trap, wherein the rejuvenating air stream includes the cathode exhaust air supplied to the first CO₂ trap with or without additional heating.

10. The alkaline fuel cell of claim 9, wherein the additional heating includes heating provided by an electric heater or a catalytic heater operatively coupled with the fuel cell.

11. The alkaline fuel cell of claim 1, wherein the second CO₂ trap includes an active material including soda lime, lithium hydroxide, or sodium hydroxide.

12. The alkaline fuel cell of claim 1, wherein the second CO₂ trap is configured to reduce levels of CO₂ in the air stream exiting from the first CO₂ trap by a factor of about 10.

13. The alkaline fuel cell of claim 1, wherein the first CO₂ trap is configured to reduce levels of CO₂ in the air stream by a factor of about 10, and the second CO₂ trap is configured to reduce levels of CO₂ in the air stream exiting from the first CO₂ trap by a factor of about 10, wherein the level of CO₂ in the air stream supplied to the cathode air inlet is under about 5 ppm, and preferably equal to or less than about 1 ppm.

14. The alkaline fuel cell of claim 1, wherein the second CO₂ trap is disposable and configured for periodic replacement.

15. An alkaline fuel cell comprising:

an air cathode operatively coupled with a two-trap air filter assembly;

the air filter assembly including a first thermally regenerative chemical CO₂ trap and a second thermally regenerative chemical CO₂ trap;

each of the first and second traps being arranged in a tandem configuration with a strongly bonding CO₂ trap, the first and second traps and the strongly bonding CO₂ trap disposed upstream from an inlet to the air cathode and the strongly bonding CO₂ trap disposed between the first and second traps and the cathode inlet;

each of the first and second traps being configured to reduce the level of CO₂ in an air stream passing through the trap by a predetermined amount, and the strongly bonding CO₂ trap being configured to reduce the level of CO₂ in an air stream passing through the strongly bonding CO₂ trap by a second predetermined amount; and

each of the first and second traps being arranged with the fuel cell to permit one trap to actively trap CO₂ in an air stream passing through the one trap while the other trap undergoes thermal regeneration,

wherein the alkaline fuel cell includes an alkaline aqueous electrolyte or an OH⁻

ion conducting polymeric membrane without liquid electrolyte.

16. The alkaline fuel cell of claim 15, wherein each of the first and second thermally regenerative chemical CO₂ traps is configured to switch from a CO₂ trapping mode to a thermal rejuvenation mode and back to a CO₂ trapping mode after each preset period of operation of the fuel cell at a given fuel cell power output.

17. The alkaline fuel cell of claim 16, wherein each of the first and second thermally regenerative chemical CO₂ trap is configured to switch from a CO₂ trapping mode to a thermal rejuvenation mode with appropriate redirection of inlet air and cathode exhaust air streams, wherein cathode exhaust air is redirected to each CO₂ trap for thermal rejuvenation.

18. The alkaline fuel cell of claim 15 being adapted to receive an application of a perturbation current to remove residual carbonate buildup in the electrolyte through anodic electrochemical consumption of carbonates and release of CO₂ through the anode exhaust stream, the perturbation current having a magnitude being just short of an onset of cell reversal in the stack.

19. The alkaline fuel cell of claim 18, wherein duration of the application of the perturbation current is from about 1 second to about 30 seconds.

20. The alkaline fuel cell of claim 19, wherein the perturbation current is triggered in response to a decrease in fuel cell performance over a given operation time.

21. The alkaline fuel cell of claim 18, further comprising an auxiliary power supply operatively coupled with the fuel cell and configured to supplement or supply power to the load and without interruption during the application of the perturbation current.

22. The alkaline fuel cell of claim 21, wherein the auxiliary power includes a battery operatively coupled with the fuel cell for recharging from the fuel cell after completion of the application of the perturbation current.

23. The alkaline fuel cell of claim 15, wherein the predetermined amount includes a factor of 10, and the second predetermined amount includes a reduction by a factor of 10.