I saw a Youtube video on how to make a zinc-air battery using a zinc electrode and a piece of steel wool for the other electrode. The zinc reacts with the air and electrolyte (potassium hydroxide or KOH) and the steel wool does not, it serves as the conductor.
I ordered some KOH online from a dealer, it cost a bit more than $6.00 for a two pound bottle but the shipping was nearly as much. It is used to make soap, among other things. Caution! This is caustic and burns skin, eyes and is poison. The flakes get very hot when mixed with water, so you have to be careful and not let it get on you.
The video said to add 50 grams of KOH to 150 grams of water. It did get very hot, and I put the glass jar into a pan of cool water to cool it off. Instead of the steel wool, I used a piece of copper plate small enough to fit into the jar. Instead of a zinc plate, I used a zinc electrical fitting. I drilled a small hole in both of these electrodes so I could put a copper wire through and hang the electrodes in the solution by the copper wires. The zinc electrode was completely submerged in the solution, so I don’t think it could get any air.
I measured the voltage at 1.06 volts. I connected a germanium Joule Thief to the wires and the two yellow LEDs lit up brightly, but after ten or so seconds they began to dim. The copper plate didn’t appear to be changed, but the zinc started bubbling and was coated with bubbles. The LEDs continued to dim, until they went out. The voltage dropped as the LEDs dimmed.
I disconnected he JT and the voltage recovered and climbed back up to 1.06 volts. When I connected the JT, the LEDs flashed on brightly, but dimmed even more rapidly, going out in a few seconds. The buildup of hydrogen bubbles and/or lack of air could be causing the fast drop in the output current.
Update Jan 21 – I thought that the solution to this dropoff in current would be to put a large capacitor across the output to store the charge as it came off the cell. I went to the box of large capacitors and was going to take one of the 10 000 uF electrolytics, but instead I grabbed the 350 farad super capacitor. I connected it up to the cell and of course it acted as a super large current sink. The voltmeter barely moved as it charged. Several hours later I checked the voltage and it had climbed to 300 millivolts. At this rate it is going to take a lot more than a day to fully charge this capacitor.
As of 8 PM Jan 23, the meter reads 645 millivolts. It’s still climbing slowly, a few millivolts per hour. But now that it’s over 0.6 volts, it will run a JT with a silicon transistor for awhile, until the voltage drops down to about 0.45 volts.
As of 10 PM Jan 24, the meter reads 780 millivolts. This is about half way to 1.6 volts.
As of 10 PM Jan 25, the meter reads a bit over 900 millivolts.
As of 10 PM Jan 26, the meter reads 965 millivolts. I noticed that the rate of charging has gone down, probably from a number of factors. I noticed that the zinc electrode has turned black, and the copper electrode has also tarnished. Some of the electrolyte has evaporated. I disconnected the super cap, and the meter read .978 volt, lower than when I started. I took the electrodes out and washed them off and put them back, and added some water. It looks like the current and charging rate have gone up slightly. I’m not sure the voltage will go past 0.978 volts. I’ll see what happens tomorrow evening.
As of 10 PM Jan 27, the meter read 1.077 volts. I got up this morning and checked the voltage and it had passed 1 volt by a few millivolts. The cleaning I did seemed to have sped up the charging quite a bit.
As of 10 PM Jan 30, the meter read 1.132 volts. I have watched it for the last 24 hours, and it has maxed out and does not go any higher. The reading varies a few millivolts between 1127 and 1132 millivolts, so there may be some change due to temperature or the meter. I have added a bit more vinegar to the jar to make up for evaporation, but I don’t think this has affected the readings.
Feb 2 – Sometime today the copper wire holding the zinc electrical fitting gave out and the fitting dropped to the bottom of the glass jar. I’m guessing that the localized interaction between the copper wire and zinc ate both away and the copper wire got so thin it broke. And since the wire and copper plate were connected by the fluid, it discharged the super capacitor. I guess I could say that the test has ended.
Can you report back on something Aluminum instead of Zinc please. Paul
I have a cell that uses magnesium and copper electrodes and a few layers of paper towel wetted with vinegar. It lights up the germanium Joule Thief just fine. But when I replaced the magnesium with aluminum/aluminium, it didn’t light. I saw somewhere that the aluminum forms an oxide layer as soon as it comes in contact with air. This may be the problem. If the electrolyte dissolves this oxide layer, then the cell may work. My guess is that KOH may only add oxide, since it has oxygen. I’ll try it and see what happens.