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Topic: Does a higher voltage used in electrolysis increase the rate of electrolysis?  (Read 27426 times)

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Offline Jango

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Hi,

I'm interested in doing various experiments, including electrolysis of various solutions. I'm searching for DC power supplies, and have found some good ones on eBay. I want the electrolysis to be done as fast as possible (i.e: larger amounts of chemical to be formed at each electrode per second).

Should I look for a DC power supply that has a higher voltage and a lower current (e.g: 20V 2A)? Or should I look for one with a lower voltage and a higher current (e.g: 13.8V 15A)?

I can't afford the ones that have a massive voltage and current, and I only want to electrolyse relatively small amounts at once (e.g: 100-200ml of a 1M solution).

Offline Grundalizer

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current is the driving force in electrolysis, because the amount of charge (current) that flows between the electrodes means more electrons are changing places which means more things are being reduced/oxidized.  I'd just get a 9V D cell battery for $5

Offline Jango

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Ok, thanks for your reply. :)

So I should look at getting the 13.8V 15A DC power supply? I can get one from eBay for £35.

I've tried using 9V batteries in the past, but they run out, so I only get an hour or so of full-power electrolysis from that. I've been looking for something that has a constant, reliable supply so that I can leave it running so that the electrolysis finishes relatively quickly (also why I am only electrolysing small quantities).

I don't know exactly what you mean by a '9V D cell battery', or where to get them from.
« Last Edit: November 23, 2010, 01:48:51 PM by Jango »

Offline Jango

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Sorry, accidental double post.
« Last Edit: November 23, 2010, 01:49:26 PM by Jango »

Offline Jango

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Sorry again, not used to this forum layout. I'll get used to it. Won't happen again. :)

Offline Grundalizer

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Yeah, that power supply sounds fine.  Remember that if you look at the redox potentials of whatever metals you are trying to electrolyze...say Copper and Zinc, I think it's a max voltage production of 1.5 V or something.  So you really only need 1.5V battery to run it in reverse, but the more current the better.  I'm not sure if a higher voltage allows it to run faster, or if it's a waste.

Sorry, this is what I meant by D cell.

http://en.wikipedia.org/wiki/Lantern_battery

Offline Grundalizer

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Also, as much as I love chemical forums for general questions, for serious at home chemistry I also check out sciencemadness.org which I know a lot of people on here also use.

http://www.sciencemadness.org/talk/

They are a little more hardcore DIY at home chemists who have some really detailed posts along the lines of what you are asking.  I'd check with them.

Offline FreeTheBee

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Make sure to stir properly and use large surface area electrodes if you want things to go fast. The kinetically limited current increases exponentially with the overpotential, so it is quite easy to run into mass transport limitations.

Offline billnotgatez

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i vaguely remember CRC Handbook of Chemistry & Physics had various measurements involving electrolysis.

Offline Zerm

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Voltage determines which reactions are being driven by redox potential but current determines the rate.  A derivative of Ohm's law holds Voltage = Current * Resistance.  The resistance of your cell depends on electrode surface area, distance between electrodes, electrolyte concentration, temperature, and charge carrier mobility.  The resistance will be whatever it is during the procedure and will likely change dramatically over the course of the reaction.  Considering the resistance as fixed (that is we can do nothing to affect it), a change in voltage will yield a change in current.  It is largely a question of what undesirable side reactions may be driven at higher voltage potentials.

What ever power supply you choose should best have precision tunable voltage regulation and be rated for high power. 

Offline FreeTheBee

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A Faradaic process does not follow Ohm's law. There is an ohmic resistance in the cell of course, due to contacts, concentrations and so on.. but that's only part of the story. The rate of the electrochemical reactions at the surface determines the current and the rate depends exponentially on the potential. You can look up Butler-Volmer to get a description.
However, the reactions can only proceed if there are electroactive species available at the electrode surface. So, if you push the reaction faster than material can be brought to the surface, you will get a mass transport limited current.
Sorry, to go a little of-topic.

Offline Grundalizer

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It's always great to go in depth--thanks for the explenation

Offline Jango

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Thanks for all of your explanations everyone. :)

Voltage determines which reactions are being driven by redox potential but current determines the rate.  A derivative of Ohm's law holds Voltage = Current * Resistance.  The resistance of your cell depends on electrode surface area, distance between electrodes, electrolyte concentration, temperature, and charge carrier mobility.  The resistance will be whatever it is during the procedure and will likely change dramatically over the course of the reaction.  Considering the resistance as fixed (that is we can do nothing to affect it), a change in voltage will yield a change in current.  It is largely a question of what undesirable side reactions may be driven at higher voltage potentials.

What ever power supply you choose should best have precision tunable voltage regulation and be rated for high power. 

So, basically, I need a power supply where I can change the voltage, has a high current (eg: 10-20A), and that also has a high wattage, am I right?

Offline billnotgatez

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an interesting experiment you can post here is

vary the voltage and see the change of output

hypothesis may be

a curve with a peak

Offline Jango

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It would be interesting, yes.

But can you answer my question? :)

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