silverknight
I have been looking in a lot of electroplating books for hydrogen generation info. In plating, they are trying to supress it, but still.
First thing: The minimum voltage you need to generate hydrogen depends on the metal your electrodes are made from. Sounds crazy! The key phrase here is "hydrogen overvoltage"
2: Hydrogen is produced by the flow of current (electrons) thru the solution. So production depends on amps, and it is not tied to volts, or watts, or energy. (someone tell me I'm wrong here if you think so)
3: Now some bad news: The best choice for electrodes is platinum, which has been electroplated with more platinum (with a trace of lead) to make (wait for it
) Platinised Platinum Electrodes. Note the spelling is with an S not a Z.
platinised platinum - Google Search
This is done afaik to make more surface area on the electrodes for hydrogen generation.
4: Good news!
The hydrogen overvoltage of platinum can be as low as .03 Volts according to a electroplating book from 1963. This paper:
http://www.pubmedcentral.nih.gov/pic...9&blobtype=pdf
shows a graph of overvoltage that varies between 1.6 to 1.9 millivolts!!!! (it changes as a H2 bubble gets free)
5: I found (and cannot find again
) a web page that gave data on conductivity of soluitons. It said 2 things: The maximum conductivity depends on WHAT you dissolve in the water. It also depends on HOW STRONG the solutilon is. And again here is a crazy thing: too MUCH or too LITTLE concentration gives a poorer conductivity. There is an ideal sweet spot for best conductivity.
This web page suggests that production of H2 can be enhanced by ultrasonic bombardment to strip the H2 off the electrodes as it is made.
Sonoelectrochemistry : Chlorine, hydrogen and oxygen evolution at platinised platinum
So my conclusions: The most efficient generation of H2 is from a cell with platinised platinum electrodes, with a very large electrode surface area, in a solution that has a material and concentration which gives the best conductivity. The power to the cell should NOT be 12 volts. It should be reduced to much, much lower voltages, and deliver maximum current. Sound like a transformer to me.
To add to what some have said, I have been guilty of mixing up "Browns Gas" generation with adding H2 from a tank. I guess I see them as interchangable (and maybe they are not!)