This sounds crazy I know. I thought it was crazy when I saw it but I have tested it so many times and have shown that it actually works.
I stumbled upon this while working with the light activated protein domain from Oat(Avena sativa) LOV2
You put metal electrodes in ordinary tap water and you see photovoltages. This data is not so precise, I know but I ordered a multimeter I can attach to my computer a few days ago. So once I receive it I can have actual plottable data.
This is very similar to the Original battery except without salt and with light
http://en.wikipedia.org/wiki/Voltaic_pile
Basically what is happening in these electrochemical cells is Atoms are being oxidized in one electrode(anode) and reduced in the other(cathode). So electrons from the oxidized electrode flow to the reduced electrode.
So this is what I tried:
All were measured in 300uL of tap water in a polystyrene plate.
I took two pieces of metals and placed them in the liquid not touching, one higher than the other and connected a multimeter to each electrode.
Steel wire, Steel is an Iron alloy, so it is composed mostly of iron but has ~1.5% Manganese and 0.8% Silicon and other trace elements
(http://www.lincolnelectric.com/en-us/Consumables/Pages/product.aspx?product=Products_Consumable_MIGGMAWWires-SuperArc-SuperArcL-56(LincolnElectric) )
About 10-20mV from one electrode to the other in tap water. This voltage increases over time about 10 mV every 15 minutes. There is a transient photovoltaic action of about 10mV. Repeatable with delay. I think this is the photo-fenton reaction in which the light is photoexciting Fe3+ to Fe2+.
(http://en.wikipedia.org/wiki/Photocatalysis) In the photofenton reaction light produces free radicals producing Fe2+ and OH radical. These radicals should react quickly. But why doesn't continuous light keep a stable voltage? Maybe it is something with my setup.
These transients last for about 1-2 seconds and then the voltage starts to return to the normal value even if there is still light in most cases. I don't quite understand the process.
Copper wire, which is composed from as far as I can tell mostly of copper. Maybe not?
Pretty good acquired the highest voltages from this. >100mV on some occasions.
Stable around 80-100mV.
Electrodes wear out in about 30 minutes
Platinum Electrode
No voltage which was expected as platinum is pretty inert.
Steel and Copper
This is a steel cathode and copper anode.
>400mV and 5uA of current
Light effect transient stays with continuous light. A ~5-10mV decrease is observed after a few seconds of light exposure. However, there is an increase upon long-term light exposure. The voltage was around 500mV after about 5 minutes of light exposure! That's 50-100mV increase from light. crazy! also, upon removal of the light we don't lose much in terms of voltage maybe just a few mV.
~20mV per 10 minutes decrease in voltage that is based solely on the copper. i.e. Switching out the copper brings the voltage back up.
In a solution of table salt(Sodium Chloride, Dextrose, Potassium Iodide, Calcium silicate)
The current increases to between 10-20uA.
I also see transient current increases in response to light.
This solution decreases what I assume is the destruction of one of the electrodes to about 5mV / 20 minutes, which means the electrode has a half-life of about 1 day if the destruction is mostly linear.
Steel and Aluminum Silicon
~40mV
There is a light effect but surprisingly unlike the other light effects this one takes a bit of time before it will work again. Usually when I shine light I see the transient and then it starts to decay and it decays in a few seconds. After it is decayed I shine again and it works to the same magnitude. In this one if I try the same the second time there is much less amplitude in the transient.
Steel and Aluminum foil
~200mV 1uA
I see a nice 10mV change upon light which is alot more stable than in all the other cases. Under continuous light I see a somewhat stable value. However, I think the aluminum is being rapidly oxidized from the increases in Fe2+ so the voltage starts to decay pretty fast. A very small change in the current upon photoillumination.
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Using filters I narrowed down the light wavelength that causes the effect to somewhere between 300 and 450 nm.
It seems like this is some form of the photo Fenton reactionor maybe a Photoelectric effect. I don't know much about this type of photochemistry.
Iron can be photoexcited between those wavelengths.
I know this data is not that exciting at the moment but it was interesting to understand the properties of these metals and see crazy photochemistry. Even in just tap water. Who knew that you could generate voltage and current like this!
I need to scale it up and I want to build a light that works by using rain and the sun! Much cheaper than a solar panel! Can connect in series and it works great but low current. Which means I need a decent electrolyte.
Or what about a piezo-electric light that works by rain?
More studies on electrochemistry coming. I just need to learn more about it.
