Regenerative fuel cells

1. A regenerative fuel cell capable of operating in a power delivery mode in which it generates electrical power by the reaction of electrochemically active species at an anode and a cathode, and in an energy storage mode in which it consumes electrical power to generate said electrochemically active species, the cell comprising:

a reversible anode in an anode compartment containing an anolyte;

a reversible cathode in a cathode compartment containing a catholyte;

an anionic membrane separating the anode compartment from the cathode compartment, which membrane is capable of selectively passing anions; and

conduits configured, in said power delivery mode, for carrying electrochemically active species to the anode and to the cathode and, in an energy storage mode, for carrying generated electrochemically active species away from the anode and away from the cathode;

wherein the pH of the anolyte and/or the catholyte is at least 10.

2. The regenerative fuel cell of claim 1 , wherein the conduits are configured:

to carry a liquid anolyte and a liquid catholyte containing respective electrochemically active species to the anode compartment and to the cathode compartment in the power delivery mode; and

to carry a liquid anolyte and a liquid catholyte containing respective regenerated electrochemically active species away from the anode compartment and the cathode compartment in the energy storage mode.

3. The regenerative fuel cell of claim 1 , wherein one of the anode or the cathode is a porous gas electrode and wherein one of said conduit is configured to supply a gaseous electrochemically active species to that electrode; and

one of said conduit is configured to carry a liquid anolyte or a liquid catholyte containing electrochemically active species to the other of the anode or the cathode in said power delivery mode, and to carry a liquid anolyte or a liquid catholyte containing regenerated electrochemically active species away from the other of the anode or the cathode in said energy storage mode.

4. The regenerative fuel cell of claim 3 , further comprising a pressurized gas source configured to contain the gaseous electrochemically active species, which gas source is connected, in the power delivery mode, to a conduit for supplying the gaseous electrochemically active species to the porous gas electrode.

5. The regenerative fuel cell of claim 1 , further comprising:

at least one first vessel configured to contain a liquid electrolyte containing electrochemically active species, which first vessel is connected, in the power delivery mode, to a conduit for supplying the electrolyte to the appropriate electrode compartment, and

at least one second vessel configured to receive a liquid electrolyte, which second vessel is connected, in the energy storage mode, to a conduit for receiving the electrolyte containing regenerated electrochemically active species from the appropriate electrode compartment.

6. The regenerative fuel cell of claim 1 , wherein a redox couple present in the anolyte is selected from:

2H 2 O+2 e − H 2 +2OH − ,

S (sol) +2 e − S 2− ,

Se (sol) +2 e − Se 2− ,

2Te (sol) +2 e − Te 2 2− ,

Sb V O 3 +2 e − Sb III O 2 +2OH − ,

Fe III -triethanolamine+ e − Fe II -triethanolamine,

[Cr(NH 3 ) 6 ] 3+ +e − [Cr(NH 3 ) 6 ] 2+ ,

[Cr III -(picolinate) 3 ] 3+ +e − [Cr II -(picolinate) 3 ] 2+ , and

[Cr III -(picolinate) 2 (OH)] 2 4+ +e − [Cr II -(picolinate) 2 (OH)] 2 2+ .

7. The regenerative fuel cell of claim 1 , wherein a redox couple present in the catholyte is selected from:

O 2 +4 e − +2H 2 O 4OH − ,

[Fe III (CN) 6 ] 4− +e − [Fe II (CN) 6 ] 3− ,

Te VI O 4 2− +H 2 O+2 e − Te IV O 3 2− +2OH − ,

I VII O 3 − +6H + +6 e − I − +3H 2 O,

Pb IV O 3 2− +3H + +2 e − HPb II O 2 − +H 2 O,

dehydroascorbate+2H 2 O+2 e − ascorbate+2OH − ,

ethanal+2H 2 O+2 e − ethanol+2OH − ,

propanal+2H 2 O+2 e − propanol+2OH − ,

glyoxal+2H 2 O+2 e − glycoaldehyde+2OH − , and

pyruvate+2H 2 O+2 e − lactate+2OH − .

8. The regenerative fuel cell of claim 1 , wherein a pair of redox couples present in the anolyte and catholyte is selected from the following combinations:

2S (sol) +4 e − 2S 2−

O 2 +4 e − +2H 2 O 4OH − ,

2Se (sol) +4 e − 2Se 2−

O 2 +2H 2 O+4 e − 4OH − ,

4Te (sol) +4 e − 2Te 2 2−

O 2 +2H 2 O+4 e − 4OH − ,

2Sb V O 3 +2H 2 O+4 e − 2Sb III O 2 +4OH −

O 2 +2H 2 O+4 e − 4OH − ,

[Fe III (CN) 6 ] 4− +e − [Fe II (CN) 6 ] 3−

Fe III -triethanolamine+ e − Fe II -triethanolamine,

Pb IV O 2 − +3H 2 O+2 e − HPb II O 2 − +3OH −

2H 2 O+2 e − H 2 +2OH − ,

2[Fe III (CN) 6 ] 4− +2 e − 2[Fe II (CN) 6 ] 3−

2H 2 O+2 e − H 2 +2OH − ,

Te VI O 4 2− +H 2 O+2 e − Te IV O 3 2− +2OH −

2H 2 O+2 e − H 2 +2OH − , and

I VII O 3 − +3H 2 O+6 e − I − +6OH −

6H 2 O+6 e − 3H 2 +6OH − .

9. The regenerative fuel cell claim 1 , wherein the pH of the anolyte ranges from 12 to 15 throughout said energy storage mode and throughout said power delivery mode.

10. The regenerative fuel cell claim 1 , wherein a redox couple present in the anolyte or catholyte comprises a gaseous species.

11. The regenerative fuel cell of claim 1 , wherein a redox couple present in the catholyte is:

O 2 +2H 2 O+4 e − 4OH − .