Water splitter that runs on a single AAA battery

JordanCClark

http://www.gizmag.com/water-splitter-aaa-battery-hydrogen-fuel-cell/33497/

I think the thing to take away from this article shouldn't be "Hey, I already did this in high school"

Tor

But still.. there must be more to it than the article states. Creating hydrogen by putting electrodes into slightly salty water was something even described in my childhood chemistry kit. It seemed to work almost whichever way you set it up. I used a 9V battery though, not 1.5V. The article says it's a first that non-precious metals could be used for a voltage that low.. but how low is 'low'? Because surely no precious metals were used in all those experiments everybody did at some point during childhood.
I assume there must be something missing from the article. Or something I'm missing.

Heater.

From the article I get:

1) They use nickel and iron electrodes. We have to assume these are not just any old lumps of nickel and iron else many a school kid would have discovered this before (Back in school we had the luxury of platinum electrodes). It does go on to say "nickel-based catalyst" and "nickel-metal/nickel-oxide catalyst" so clearly there is something a bit more complex going on here.

2) These electrode split water at a lower voltage than those expensive platinum electrodes.

3) The electrodes decay pretty quickly but they might be able to fix that.

Mark_T

See http://en.wikipedia.org/wiki/Electrolysis_of_water#Thermodynamics

ElectricAye

Mark_T wrote: »

See http://en.wikipedia.org/wiki/Electrolysis_of_water#Thermodynamics

wikipedia wrote:

"...each mole of water requires two moles of electrons... the minimum voltage necessary for electrolysis is about 1.23 V...."

This is how I've always understood this process. The voltage to split the water molecule is not very high. However, your production rate of hydrogen and oxygen is dependent upon how much electrical current you can drive through the water between the electrodes. A weeny battery simply can't provide that much current, so you get what you pay for. I suppose what their catalytic electrodes are doing is allowing the reaction to happen closer to the theoretical minimum voltage required.

Heater.

The electrolysis of water in requires a theoretical minimum of 237 kJ of electrical energy input to dissociate each mole of water ... Since each mole of water requires two moles of electrons and given that the Faraday constant F represents the charge of a mole of electrons (96485 C/mol), it follows that the minimum voltage necessary for electrolysis is about 1.23 V.



Just now I don't get it.

It says we know how much energy is required to disassociate a given about of water.

We also know how many electrons are involved.

And so we know the charge on all those electrons.

How does it follow that we need 1.23 volts?

twm47099

1 v = 1 J / 1 C but need 2 C of electrons.

V = 237,000 / (2 * 96485)

Tom

Beau Schwabe

My understanding on "why" it is important to use inert relatively stable metals, is so that the gas produced is only Hydrogen and Oxygen and not some combination of the Electrode itself as a contaminant or precipitate in the aqueous solution ... i.e. Aluminum-Hydroxide if Aluminum electrodes happened to be used.

Heater.

Yes, I guess we don't want anything out but hydrogen and oxygen.

A big point though is that you want your electrodes to work for a long time. Else your are constantly having to renew them making the process uneconomic.

Then there is the efficiency angle. I don't recall that they mentioned the efficiency of these new catalysts.

JordanCClark

Heater. wrote: »

A big point though is that you want your electrodes to work for a long time. Else your are constantly having to renew them making the process uneconomic.

Ideally, yes, but there are exceptions...
Case in point: In a previous life I worked for a company that brazed tubing for automotive fuel lines. The furnaces used a Type R thermocouple, which is a platinum type. Replacing them with an N-type still kept us within our process range, but at 25% of the cost (This was back in the late 90's. R-TCs are around 10 times the cost today vs. Ns.). Even if we would have had to replace them three times as often (we didn't, this is just an example) , it would still come out as an overall savings in consumables.

Granted, I have no idea how long the electrodes last in current setups. I just don't have that kind of data. But the potential cost savings is certainly there.

davejames

...my water splitter doesn't require any batteries!

http://www.homedepot.com/p/Orbit-Zinc-Faucet-Adapter-27903/100659292?N=5yc1vZbx5n

Mark_T

Heater. wrote: »

The electrolysis of water in requires a theoretical minimum of 237 kJ of electrical energy input to dissociate each mole of water ... Since each mole of water requires two moles of electrons and given that the Faraday constant F represents the charge of a mole of electrons (96485 C/mol), it follows that the minimum voltage necessary for electrolysis is about 1.23 V.

Read the wikipedia link, 1.23V is not obtainable if the gasses are produced at the same temperature as the water. 1.48V is then the limit,
or somewhere near it.

Difference between enthalpy and free-energy I think. Remember there's a very large increase in entropy when converting
a liquid to gasses, which allows the reactants to be produced at a much lower temperature (if they are then not allowed
to equilibrate with the water and cool it). Think of it like evaporation - extra energy is needed to keep a liquid at a constant
temperature when its evaporating.

prof_braino

Tor wrote: »

Creating hydrogen by putting electrodes into slightly salty water was something even described in my childhood chemistry kit. .... Or something I'm missing.

using salty water gives off chlorine gas.