Heat in Electrolysis

[zking786]

Is a heated container along with hot electrodes and water common in electrolysis? Should the water get really hot (boiling). If so, why does this happen?

[YT2095]

basicly Friction

 

the ions are "wanting" to move from pole A to pole B, and do so at such a rate as to cause frictional heat energy.

[jdurg]

There's also the resistance to the flow of electrons, and any time you have resistance in an electrical system it will generate heat. Water has some resistance to electrical 'flow' so the power wasted when the electrons aren't flowing is translated into heat.

[raivo]

Amount of power is proportional to current and voltage. If you electrolyser uses 5A current ( for example ) then power consumption is 15W if voltage at electrodes is 3V, and 60W if voltage is 12V. In both cases electrolysis goes with same intensity, ( depends only of current ) but power consumption is very different. That excess power goes for heating.

 

Electrolyser has to have very low electrical impedance - otherwise it requires high voltages to get reasonable currents. High voltage & high current means heating problems.

[zking786]

Firstly, I know very little about electricity.

 

So, if I understand you correctly, I need to minimize power to minimize impedance. But minimizing power decreases the amount of hydrogen produced. Is there a way to have low "electrical impedance" while increasing current and maintaining 12V?

[raivo]

You do not need to mantain 12V. If you can lower impedance of your electrolyser you get as much ( or even more current ) using lower voltages. Amount of hydrogen produced is directly proportional to current. Voltage in itself does not count. Voltage is just for increasing or decreasing current.

 

Current can be computed by Ohms law. I = U / R where I is current, U voltage of your power supply and R impedance of electrolyser.

 

Amount of hydrogen produced depends only of current (that Faradys law), no matter what voltage was needed to generate that current. To increase current you need to lower impedance or to rise voltage. By rising voltage you get heating problems so you need to lover impedance of electrolyser. This can be made by using more concentrated electrolyte and/or more electrode surface.

 

Industrial electrolysers work usually with voltages as low as 3...4V. Still they get currents of 1000 -s of ampers because electrodes have great surface area and electrolytes are well chosen.