System and method for initializing and operating metal-air cell
A method and system for creating low corrosion passivation layer on an anode in a metal-air cell comprise asserting high negative potential and low drawn current density on the cell after its operational parameters have stabilized after the cell has been powered-on. As a result the H2 evolution rate momentarily raises and then drops sharply, thereby causing the creation of a passivation layer on the face of the anode.
1. A method of creating a passivation layer on an Anodic Alloy anode in an Al-air cell, the method comprising:
providing to the Al-air cell electrolyte comprising alkali or ammonium oxoanion salt additive at a given concentration;
controlling the operational conditions of the Al-air cell to a specific point, that comprises controlling a specific temperature of the electrolyte and a specific current density drawn from the anode; wherein the specific current density drawn from the anode influences a specific negative potential of the anode with respect to the electrolyte,
when the operational condition parameters stabilize—decreasing the drawn electrical current density from the Al-air cell to a first low current density thereby causing momentary lowering of the anode potential below a first negative potential value and a momentary rise of evolution rate of H 2 from the electrolyte followed, after a first period of time, by sharp drop of the H 2 evolution rate; and
when the level of H 2 evolution stabilizes at low values and no later than a second period of time from the time the level of H 2 evolution rate lowered, drawing from the Al-air cell operational current.
2. The method of claim 1 wherein the concentration of the alkali or ammonium oxoanion salt additive is 0.001-0.1M.
3. The method of claim 2 wherein the alkali or ammonium oxoanion salt additive is at least one of stannate, zincate, indate, gallate, plumbate and mercurate.
4. The method of claim 2 wherein the temperature of the electrolyte at stabilized operational conditions is less than 50° C. and is between 50° C. and 65° C. during the momentary time of rise of the H 2 evolution.
5. The method of claim 1 wherein the first negative potential of the anode is −1.6V or less with respect to the electrolyte.
6. The method of claim 5 , wherein the first low current density is in the range of −50 to 50 mA/cm 2 .
7. The method of claim 1 wherein the first period of time is in the range of 1-120 seconds.
8. The method of claim 1 , wherein the momentary lowering of the anode potential below a first negative voltage is performed using an external electrical power source.
9. The method of claim 1 , wherein the momentary lowering of the anode potential begins within the first 10% of total expected duration of the Al-air battery operation cycle.
10. The method of claim 2 wherein the temperature of the electrolyte during the momentary time of rise of the H 2 evolution is between 50° C. and 65° C.