Sustainable Electrochemical Energy
If the goal is sustainable energy, where might we find it?
We all know about the possibilities and realities of solar, wind, and to a lesser extent tidal and geothermal power, but I thought there might be another untapped and under-researched area: junk yards.
Note: all images have been lost in the ether
Millions of tons of purified metals are discarded each year* in landfills, in the form of construction refuse and personal and industrial appliances.
These metals were expensive to mine and purify, and represent wealth to some degree, except for the fact that they are scattered about.
But in some developing countries, where scavenging objects is part of daily life for some people, and electrical energy is often in short supply, electrochemical energy from recycled materials might have promise.
EXPERIMENT I - Sandwiches
My first experimenting involved replicating Volta's pile - the first source of electrical energy, predating the mechanical generator by 20 years**.
I didn't actually realize Volta had done essentially the exact same experiment as I did, over 200 years ago, but I find myself often in that situation.
The experiment is simply to use two dissimilar metals, preferably as far apart as possible on the electropotential spectrum*** and separate them with an electrolyte - any water solution of salt, acid, or base****.
I used a copper penny and some aluminum foil as those are cheap and available and well-spaced electropotentially.
For the electrolyte I used a combination of cider vinegar, household bleach, and kosher salt in water.
A piece of paper towel is dampened with the solution and placed between the penny and foil, the electrodes in our simple pile.
The paper is necessary to separate the electrodes to prevent them from shorting out.
Right away, there is some potential and some current:
0.49mA
0.64v
Not enough to do much with, so the next step is to explore some more.
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* fabricated statistic
** http://www.schoolscience.co.uk/content/3/physics/electric/
*** http://www.hilaroad.com/camp/projects/lemon/electric_potential.html
**** Almost any liquid will work, but the more 'stuff' in it, the better. Even saliva will work
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EXPERIMENT II - Containers
I was looking for sources of good electrodes (aluminum, zinc, copper, nickel) and experiemnted with aluminum beverage cans, and zinc-coated steel cans*.
The test involved suspending a penny in an aluminum beer can and an emptied can of pineapple, both of which had been rinsed and filled with salt water.
In both cases, the results were about the same as Experiment I.
The zinc coating in the second can rapidly dissolved in the solution, and I chose not to pursue that.
The aluminum can also wasn't worth pursuing. I don't know if the can is glazed in any way at the factory, but even if not, having the container also be one of the electrodes isn't a good idea, as eventually a hole could appear, spilling acid.
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Also at this time I began looking for a test application of the electrochemical energy source I hoped to build.
Lighting an LED is sort of the "Hello, World" of physical computing projects, and that would be a reasonable start.
Ultimately I hoped to perform electrolysis of water into hydrogen and oxygen**.
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* Certain acidic foods, such as tomatoes and pineapple, are packaged in cans that are either lined with plastic, or galvanized with zinc.
** Another example of me being 20 decades too late. Davy used a voltaic pile to discover this phenomenon. I was barely able to reproduce it.
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Experiment III - Series
Next I tried stacking the mini-piles.
The term 'battery' refers to having a bunch of piles, where a 'pile' is the literal pile of metal disks like those in experiment I.
A true pile would essentially be several of the penny-foil sandwiches arranged in series, one on top of the other.
2 sandwiches in series:
0.486mA
0.75v
2 sandwiches in parallel:
0.89mA
0.53v
Neither the voltage nor current doubled as I expected, though there was significant gain in the two positions.
I suspect that there was too much electrolyte and ions were flowing around all sides of the metals, not just where they met the membrane.
I tried several kinds of membrane, bits of cloth, paper, cardboard, etc. The best seemed to be thin paperboard (unpainted).
If some is good, more is better, so I stacked a bunch more, to the point where the pile began tipping, and I had to build some stands
Here are the results:
One Pile of about 20 pennies and bits of foil:
0.55mA
4.26v
Two piles in series:
0.46mA
7.9v
Two piles in parallel:
0.91mA
4.6v
Again, the expected doubling didn't quite happen, but it was close.
I was surprised that I was able to get nearly 8 volts from literally what was lying around the apartment.
However, voltage doesn't mean anything without current, and I had yet to generate even one milliamp.
At least 100mA is needed to do anything interesting, so I needed to either:
- use circuitry like those used in 'solar engines' to store and release energy from low-current sources such as solar panels
- make a bunch more piles until I had enough
- try something else (see below)
The circuitry was certainly possible, and may have been the right route to pursue.
In fact, I did try it, but I found that the wait time was hours before the LED would light, though it would stay on for about half a minute.
The piles wouldn't work out I realized, because I was two orders of magnitude below where I needed to be in terms of current.
Even if my apparati were completely efficient, I would need 100 piles like the ones I had made to achieve adequate current.
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At this point I was also giving up on the electrolysis of water.
Although I had succeeded at generating lots of little bubbles, I was unable to store the hydrogen gas adequately.
So, in the spirit of of the rest of the project I decided that my ultimate draw on the power I generated would be a small electric motor I built a few years ago.
I tried running the motor with various batteries to see what the power consumption was.
The following 4 batteries all ran the motor, though the 9-volt battery was extremely fast and the AAA battery was just barely able to move it.
9-volt battery
~1A
8.78v
C-battery
122.0mA
1.38v
AA-battery
138mA
1.48v
AAA-battery
117.7mA
1.36v
Based on this, I figured I needed at least 1 volt of potential and 100 milliamps of current.
I was easily able to generate more than enough voltage, so current became my goal, and so I 'tried something else;'
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Experiment IV - Parallel
What is a parallel connection but simply a larger one, one that increases the surface area of contact?
I read about how to make home-made capacitors, by simply using two sheets of aluminum foil separated by a piece of paper, which can then be rolled up*.
I thought about pounding pennies into sheets, but since 1982, American pennies have been made of zinc, with only a plating of copper.
Zinc and copper act as opposites in terms of electropotentiality, so any nick in a penny made since 1982 would cause electrons to flow between the zinc inside and the copper outside, rather than between the copper and the other electrode.
And smashing them flat would result in a sheet of zinc with bits of copper showing.
So I cheated and got some copper flashing (used in roofing houses).
The 20' roll has a tar-and-paper back which can only be removed by vigorous scraping**, but that's okay as it meant a built in barrier between the metals so I wouldn't have to add that.
I cut a piece of copper about 4" x 8" and laid on top of it a larger piece of paper towel wet with the same solution used in the piles.
On top of that, I put a piece of aluminum foil***, off-center.
I wrapped it up, with the positive terminal being where I had scraped tar off the copper, and the negative terminal where a bit of foil stuck out
The results pleased me:
0.58v
25.1mA
The same voltage as the previous experiments, but about 50 times the current.
So I made a bigger one, with about 3 feet of copper instead of 4 inches.
The results surprised me:
0.58v
46.2mA
Exactly the same voltage, but less than double the current, even though I had increased the area of contact by 9-fold.
So I tried an even bigger one, with 6 feet of copper, but got no results.
Unwrapping I saw that the paper towel had torn while I was rolling it, shorting out the insides.
So I cut it in half and made two more out of it, which had pretty much identical power readings to the other large one.
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* http://www.scitoys.com/scitoys/scitoys/radio/homemade_radio.html
** I tried burning it off, but there must be some flame-retardant stuff in there - and flame-resistant material is hard to burn off!
*** It seems using the shiny-side of the foil against the paper worked best.
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Experiment V - The Final Test
If my numbers were right, I only needed 4 of these batteries (2 parallel columns of 2 in series) to get the 1 volt/100mA I wanted to power the motor.
2 rolled batteries in parallel:
0.55v
44.1mA
2 in series:
1.1v
54mA
3 in parallel
0.53v
40.4mA
3 in series
1.56v
36.9mA
I wired 4 of them all up and connected them to the motor. I had just under the readings that I wanted, but with a nudge to the motor, it spun on its own for nearly a minute.
I tested the power readings again and found they were already deteriorating.
They seem to have a half-life of about 3 hours
SHELF-LIFE
All the piles degraded quickly after construction.
The penny-piles were completely inert after sitting overnight.
This partly due to the electrolyte evaporating, and re-wetting the membranes brought some back to life.
The penny-piles can be hydrated with a mister like those used to spray household cleansers, and in fact, the cleansers work well as electrolytes.
The flashing piles are more difficult to rehydrate, but drying is likely to be the issue since they dropped from their peak potentials and currents to about half or a third after only three hours.
In this case, I think the problem is small shorts within the rolls, at points where the membrane tore while rolling.
CONCLUSION
It is possible to create electrochemical energy sources using easily-found junk.
However, it is a true micropower source, similar to solar power, and the likely way to use this energy source is by storing the power in capacitors.
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Epilogue - Can't Give up Yet
I unwrapped the first roll, the little one, and saw little cracks in the copper (perpendicular to the line of rolling) through which I saw the back of the tar paper.
Maybe I need an impervious membrane that separates the copper from the aluminum that is better.
So I unrolled it and rerolled it inside a plastic grocery bag (maybe we now have a use for those).
I also started using lemon juice in my electrolyte instead of vinegar because it smells better*.
The new results:
29mA
0.48v
Slightly higher amperage, slightly lower voltage, but it fluctuates so much it's hard to tell - really about the same.
It may be the plastic, or it may be that I rehydrated the paper towel.
Opening one of the big ones revealed foil with lots of pitting in it, and copper that was heavily tarnished (black, cupric oxide? this is a red/ox reaction after all)
Wrapping it up the same way, with plastic (but not rehydrating the paper) gave:
0.54v
wildly fluctuating current but peaking around 40, then settling back down to dead-level values.
The last thing to try is not wrapping it at all, just using a big sheet of copper (12 feet should work) with wet newspaper and a roll of foil over that.
Unrolling another big one and laying it flat brings the numbers back to where they were
The aluminum is significantly pitted - hold it up to the light and it looks like stars.
Both metals were irregularly corroded. In places the copper was turning green where it was exposed to air and electrolyte but no aluminum on the other side.
This tells me that really flat is important, and I wasn't able to keep it flat when rolling it.
It was harder to keep it flat when the rolls were bigger, which may explain why the bigger rolls didn't scale up as I expected.
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* Bleach is stored in opaque containers because it breaks down in the presence of light. The stuff I used started to smell odd, not bad, but more like peroxide than chlorine.