Harness the power of rust! Metal-Air batteries are a way to capture the power of metal oxidation in a salt solution. In this instructable, I'll be building an iron-air battery, turning iron into rust using salt and atmospheric oxygen.
For a quick background, take a look at the energy that can be released from various metals:
While aluminum would release more energy, My goal here is to create a power source that is cheap to refuel (using rebar or scrap as the fuel source), and could be made from easliy obtainable materials in a third world environment. additionally, iron oxide is easily smelted back into raw iron using charcoal, and is non toxic - unlike aluminum, which is nasty stuff.
A metal-air cell is just: ANODE of metal (in this case iron), CATHODE of carbon/air, and a salt electrolyte. So far, my experiments have yielded Epsom Salts are a pretty darn good electrolyte.
What DOESN'T WORK? Seems like urea-based sidewalk salt is a huge failure, avoid everything containing urea.
COVER PICTURE: This is a carbon-block water filter. It was a little difficult to build the cell, as there is no inside liner. The newer filters (in the rest of the instructable, you will notice a white liner).
UPDATED: 3/10/14 - Added tables and additional data on most pages. Added diagram of how it works to main page.
UPDATED: 3/11/14 - added positive/negative to diagram and added Polarity step. Updated Filter page to indicate preferred filter (block) and style.
UPDATED: 3/12/14 - Polyethylene Glycol (PEG)- otherwise known as Miralax (the laxative).. immediate boost in power under load. 10Ohm resistor 0.5v fell under 0.01.. after PEG, jumped to 0.113 and was climbing when I left the basement... will let it run a few hours to see what happens.
UPDATED: 3/14/14 - Updated results with current output from a two cell in the final step, a few other edits in the mix as well.
UPDATED: 3/17/14 - 2 cells running with PEG since 3/12, 0.88v, 10Ohm resistor since 2/12 = 10.560 Ah * 0.88v = 9.2928 Watts expended. I think it's time to scale this up to 12v.
UPDATED: 3/17/14 - removed all iron from the outside of the cells, voltage went from ~0.4 to 0.55 immediately. Added two more cells to scale up to an initial voltage of 2.0v .. once it stabilizes I'll add the 10 Ohm resistor for a 200mA load .. and we'll see how it goes.
UPDATED: 3/18/14 - I attempted a recharged on the 4-cell at 3v for about an hour, which made the cells hold a nice 2.34 volts .. the two fresh cells seem to have a higher internal resistance, and don't show the surface crystals the older ones do. I think building up this lattice of epsom, salt, and PEG has something to do with efficiency... keeps the unit wet (from atmospheric water) without dripping.
UPDATED: 5/6/2014 - realized Maalox is incorrect, the product is Miralax, composed of only Polyethylene glycol.