[dongfang]

Hi,
I am sort of a novice with this.
Anyway : I am trying to produce a little hydrogen for a balloon experiment. It should be reasonably pure.
I tried water + a little sodium hydroxide + two carbon fiber electrodes + 3VDC, appears to work great.
Then before scaling it up, I tried to replace one electrode by something cheaper than carbon fiber. I had some aluminum around.
Aluminum cathode --> no corrosion, but current draw and H_2 production drops after a little time. I suppose the Al gets an insulating oxide layer.
Aluminum anode --> Very nice low resistance, but there is no gas coming from the anode? Where does the oxygen go?

And is there any possibility that the oxygen, or anything else, gets into the H_2 coming off the cathodes? I don't really care if the aluminum (or other metal) corrodes, as long as the H_2 is clean.

Kind regards, Soren

[Hunter2]

Aluminium ist not the right material, because it will be dissolved in NaOH-solutions. You would also obtain hydrogen, but without using electrical current.

[Enthalpy]

Aluminum anode --> Very nice low resistance, but there is no gas coming from the anode? Where does the oxygen go?

You have conducted an anodization, with a high probability. Oxygen ions (or atoms or molecules, I don't care) go through the existing alumina layer to the aluminium (unless alu goes through to meet the oxygen - I don't remember which one works with aluminium, and it doesn't change the outcome) and they combine to let the oxide layer grow. This goes on until the layer is thick enough to stop the current, and then the game is over.

More generally, aluminium is far too reactive to serve as an electrode. Graphite fibre was a good idea, except that contacts are difficult to make. You find a graphite rod in 1.5V and 4.5V batteries, but please mind the corrosive contents.

Did you check how strong a current it takes over how long to inflate a balloon? Interesting to compute before getting disappointed. You'd get the gas faster with an acid acting on a metal. Or from a hydrogen bottle.

You can also inflate a balloon from a helium bottle. It destroys the rubber less quickly. Or from methane, if you have a natural gas line; it just lifts half as much as hydrogen does, but detonates less brutally.