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 hydrogen gas anode, in an anode compartment;

a reversible cathode in a cathode compartment;

a membrane separating the anode compartment from the cathode compartment, which membrane is capable of selectively passing protons;

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

wherein the redox reaction at the anode is:

2H − +2e − H 2 (gas)

and the redox reaction at the cathode is selected from:

V 5+ +e − V 4+ ,  (i)

Ce 4+ +e − Ce 3+ , and  (ii)

Mn 3− +e − Mn 2+   (iii).

2. The regenerative fuel cell of claim 1 , wherein the redox reaction at the cathode is:

V 5+ +e − V 4+ .

3. The regenerative fuel cell of claim 1 , which includes at least one vessel configured to contain the liquid catholyte containing the cathodic electrochemically active species, which first vessel is connected, in the power delivery mode, to the catholyte compartment for delivering liquid catholyte containing the electrochemically active species to the catholyte compartment.

4. The regenerative fuel cell claim 3 , wherein the at least one vessel is connected, in the energy storage mode, to the catholyte compartment for receiving catholyte containing generated electrochemically active species from the catholyte compartment.

5. The regenerative fuel cell of claim 1 , which includes at least one vessel configured to contain the liquid catholyte containing spent electrochemically active species, which second vessel is connected, in the power delivery mode, to a conduit for receiving the catholyte containing spent electrochemically active species from the catholyte compartment.

6. The regenerative fuel cell of claim 5 , wherein said at least one vessel is connected, in the energy storage mode, to a conduit for supplying the catholyte containing spent electrochemically active species to the catholyte compartment.

7. The regenerative fuel cell of claim 1 , which includes a pressurised gas source vessel configured to contain hydrogen, which gas source is connectable, in the power delivery mode, to the anode.

8. The regenerative fuel cell of claim 7 , wherein the pressurised gas source vessel is connectable, in the energy storage mode, to the anode to receive hydrogen generated in the energy storage mode.

9. The regenerative fuel cell of claim 8 , which includes at least one compressor configured to pressurise hydrogen generated at the anode in the energy storage mode for storage in the pressurised gas source vessel, and optionally also a hydrogen expander-generator to deliver electricity as a result of expansion of the compressed gas.

10. The regenerative fuel cell of claim 1 , wherein the membrane is a proton exchange membrane.

11. The regenerative fuel cell of claim 1 , wherein the membrane is porous to hydrogen ions and solvated hydrogen ions.

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

a reversible hydrogen gas anode, in an anode compartment;

a reversible cathode in a cathode compartment;

a membrane separating the anode compartment from the cathode compartment, which membrane is capable of selectively passing protons;

and wherein the method comprises, in said power delivery mode, carrying electrochemically active species to the anode and to the cathode and, in an energy storage mode, carrying generated electrochemically active species away from the anode and away from the cathode

wherein the redox reaction at the anode is:

2H − +2e − H 2 (gas)

and the redox reaction at the cathode is selected from:

V 5+ +e − V 4+ ,  (i)

Ce 4+ +e − Ce 3+ , and  (ii)

Mn 3− +e − Mn 2+   (iii).

13. The method according to claim 12 , wherein the redox reaction at the cathode is:

V 5+ +e − V 4+.

14. The method according to claim 12 , wherein the regenerative fuel cell is as claimed in claim 1 .