Additives to the gas supply of fuel cells with circulating electrolytes and means to regenerate used stacks
In a gas diffusion electrode the electrolyte must penetrate the pares of the electrode structure to a certain extent to establish the optimum interface between gas and liquid electrolyte, but it should not reach the gas-side of the electrodes. The best equilibrium of the so-called three phase zone (porous current collector-reaction gas-liquid electrolyte) is achieved by adequate wetproofing the porous structure with a polymeric substance as repellency agent. The polymeric substance serves also as a binder. During operation of the electrodes, the wetproofing material may lose its hydrophobicity for various reasons and the result is a penetration into the pores structures, reducing the interface between liquid and gas, notice by a loss of performance. By adding small amounts of wetproofing agents to the gases supplied to the electrodes, the original three-phase condition is maintained, or, if it is already partially degenerated, means and methods for its re-establishment are described. The invention claims substances and techniques for such maintenance and regeneration processes.
1. A method of regenerating a porous fuel cell electrode of a fuel cell having degraded performance due to loss of hydrophobic repellency of electrode materials, the method comprising adding to an anode or cathode gas supply an electrode regenerating substance selected from the group consisting of a least one hydrophobic organic substance in liquid or gaseous form and at least one hydrophobic organic substance diluted in an organic solvent, wherein the addition of the hydrophobic organic substance occurs during operation of the porous fuel cell with circulating liquid electrolyte or while the fuel cell is not in operation, and hydrophobically repelling said electrolyte in said porous fuel cell electrode with said electrode regenerating substance.
2. The method of regenerating a porous fuel cell electrode according to claim 1 , wherein the at least one hydrophobic organic substance is diluted in a 0.3 to 4.0 mass % solution of crystalline paraffin in an organic solvent having less than 10 carbon atoms.
3. The method of regenerating a porous fuel cell electrode according to claim 2 , wherein the solution of crystalline paraffin is a 1 to 2 mass % solution.
4. The method of regenerating a porous fuel cell electrode according to claim 2 , wherein the organic solvent has a boiling point less than 80° C.
5. The method of regenerating a porous fuel cell electrode according to claim 4 , wherein the organic solvent is ether.
6. The method of regenerating a porous fuel cell electrode according to claim 3 , wherein the at least one hydrophobic organic substance is a pure or diluted organic alcohol, ketone or a mixture thereof.
7. The method of regenerating a porous fuel cell electrode according to claim 3 , wherein the crystalline paraffin is of linear molecular shape.
8. The method of regenerating a porous fuel cell electrode according to claim 7 , wherein the at least one the hydrophobic organic substance is selected from the group consisting of isopropanol, isobutanol, acetone and octylalcohol.
9. The method of regenerating a porous fuel cell electrode according to claim 8 , further comprising contacting the at least one hydrophobic organic substance with an alkaline air cathode of the fuel cell electrode, thereby regenerating the fuel cell electrode by removing carbonate residues from the alkaline air cathode.
10. The method of regenerating a porous fuel cell electrode according to claim 1 , wherein the at least one hydrophobic organic substance is present at a concentration of 10 to 40 mass % in a either a hydrophilic or hydrophobic solvent.
11. The method of regenerating a porous fuel cell electrode according to claim 10 , wherein the solvent is water.
12. The method of regenerating a porous fuel cell electrode according to claim 1 , wherein the electrode regenerating substance is added within an anode gas supply using at least one member selected from the group consisting of a bubbler, a gas jet and a vaporizer.
13. The method of regenerating a porous fuel cell electrode according to claim 12 , wherein the anode gas supply comprises hydrogen from a tank, a reformer or an ammonia cracker.
14. The method of regenerating a porous fuel cell electrode according to claim 1 , wherein the electrode regenerating substance is added within a cathode gas supply using at least one member selected from the group consisting of a bubbler, a gas jet and a vaporizer.
15. The method of regenerating a porous fuel cell electrode according to claim 1 , wherein, when the addition of the hydrophobic organic substance occurs while the fuel cell is not in operation, the method further comprises, prior to said adding:
shutting down the fuel cell,
removing the circulating liquid electrolyte,
washing the fuel cell with an aqueous washing solution comprising at least one hydrophobic organic substance at a concentration of 10 to 40 mass % in water, and
removing the washing solution by evaporation.
16. The method of regenerating a porous fuel cell electrode according to claim 15 , further comprising restoring repellency of the electrode by treating the electrode with at least one hydrophobic organic substance diluted in a 0.3 to 4.0 mass % solution of crystalline paraffin in an organic solvent having less than 10 carbon atoms.
17. The method of regenerating a porous fuel cell electrode according to claim 1 , wherein said electrode regenerating substance is configured to limit reduction of a liquid/gas interface in said porous fuel cell electrode.