Best* Electrolyte for Water Electrolysis

[Macocio]

Hey guys, looking for the best* electrolyte.

* Temperature range of the electrolyte(Water will be pressurized so temperatures may exceed 100°C)

Conductivity
Efficiency (Heat, Mole H₂/Mole Electrolyte)
Stability

I scouted the web, some said KOH, H₂SO₄ others Fe(NO₃)₃. So I'd just want to ask it here.

 

[Macocio]

Noone reacts?
Am I doing something wrong? Should the water be used as a dielectric instead?

Please give me a hint.

 

[chemisttree]

Hey man, you asked about a pressurized aqueous cell that exceeds the boiling point of the solvent at 1 atm. Who is going to know what is best in your situation? How are you sealing your electrodes? What is the material of the vessel? Is safety a consideration? What potential do you intend to use? How will you deal with evolved gases in your closed system if you use an aqueous solvent? What are you trying to accomplish in the cell?

Flesh out what you are doing and you will get responses.

 

[Topher925]

Hey man, you asked about a pressurized aqueous cell that exceeds the boiling point of the solvent at 1 atm. Who is going to know what is best in your situation? How are you sealing your electrodes? What is the material of the vessel? Is safety a consideration? What potential do you intend to use? How will you deal with evolved gases in your closed system if you use an aqueous solvent? What are you trying to accomplish in the cell?

Flesh out what you are doing and you will get responses.

Other things that need consideration:

What is your electrode material? Are you using any type catalyst? Can any amount of your electrolyte be consumed/used/suffer degradation in the reaction? What purities of your products do you desire?


I've used KOH, NaOH, and Nafion as electrolytes for electrolysis cells before. The Nafion was the best to use by far but also the most expensive.

 

[Macocio]

Hey man, you asked about a pressurized aqueous cell that exceeds the boiling point of the solvent at 1 atm. Who is going to know what is best in your situation? How are you sealing your electrodes? What is the material of the vessel? Is safety a consideration? What potential do you intend to use? How will you deal with evolved gases in your closed system if you use an aqueous solvent? What are you trying to accomplish in the cell?

Flesh out what you are doing and you will get responses.

Other things that need consideration:

What is your electrode material? Are you using any type catalyst? Can any amount of your electrolyte be consumed/used/suffer degradation in the reaction? What purities of your products do you desire? I've used KOH, NaOH, and Nafion as electrolytes for electrolysis cells before. The Nafion was the best to use by far but also the most expensive.

Oke guys those stuff i previously mentioned were mostly hypothetical situations. Anyways, I'll answer you.

First I don't really get what you mean with sealing electrodes (Yes my second language is English but I haven't heard about sealed electrodes before in the electrolysis of water).
The material of the vessel will preferably be some kind of (or equal) Plexiglas which would be highly resistant against corrosive elements and also be strong and something that'd be able to withstand some pressure and temperatures. Safety is important. I intend to use it to store energy like a battery. There will be no evolved gases other than Hydrogen and Oxygen (I do not clearly know what you mean with evolved gases though) which will be compressed and separated during electrolysis. I am trying to accomplish successful, effective and safe electrolysis of water.

Next poster:
My electrode material will probably (theoretically)be made out of a noble metal, but I ain't rich so make that something similar to pencil graphite. No catalyst will be used (is it necessary?). No my electrolyte should not suffer from degradation at all. Perhaps distilled water and an electrolyte that won't spout out a bunch of chemicals such as using salt as an electrolyte.

btw, does the Nafion cause any 'pollution' inside the cell? Does it degrade anything at all?

 

[chemisttree]

Oke guys those stuff i previously mentioned were mostly hypothetical situations. Anyways, I'll answer you.

First I don't really get what you mean with sealing electrodes (Yes my second language is English but I haven't heard about sealed electrodes before in the electrolysis of water).

You said that the temperature would be over 100C and that the water was pressurized. To maintain this you need a vessel of some sort with electrodes having electrical connections outside the vessel. There will need to be a hole and a sealant, yes?

The material of the vessel will preferably be some kind of (or equal) Plexiglas which would be highly resistant against corrosive elements and also be strong and something that'd be able to withstand some pressure and temperatures. Safety is important. I intend to use it to store energy like a battery. There will be no evolved gases other than Hydrogen and Oxygen (I do not clearly know what you mean with evolved gases though)...

That's them.

...which will be compressed and separated during electrolysis. I am trying to accomplish successful, effective and safe electrolysis of water.

So you aren't making Brown's Gas and you will keep the oxygen and hydrogen separate. That implies a semipermeable membrane of some kind. Like Nafion, for example. Sulfuric acid would be best with that setup, IMO.

 

[Topher925]

btw, does the Nafion cause any 'pollution' inside the cell? Does it degrade anything at all?

I recommend you look into using a PEM electrolyzer as this will reduce the chances of you hurting yourself. Building a pressure vessel that operates at 100'C made from plexiglass and contains acidic or alkaline solutions is just not a good idea. You would save yourself a lot of time and trouble by sending yourself to the hospital by jumping off a roof. PEM electrolyzers are considered to be the most efficient low temperature method of electrolysis, and are rather safe to build, but also the most expensive.

Nafion will not pollute your cell(s). It does outgas, but it does so slowly, especially at lower temperatures. You will not want to operate a PEM electrolyzer above ~70'C.

You don't have to use Nafion. You can use an anionic membrane instead (Nafion is cationic). What is it that you are after? The O2, the H2, or both?

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

 

[Macocio]

Hey guys thanks for the quick replies.

@Chemisttree, Well a pressurized cell was just an idea, I guess I drop that, and thanks, I guess that I know what you meant with sealing the electrodes.

So you aren't making Brown's Gas and you will keep the oxygen and hydrogen separate. That implies a semipermeable membrane of some kind. Like Nafion, for example. Sulfuric acid would be best with that setup, IMO.

Well my original idea was to create a PEMFC and an electrolysis cell in one so Brown's isn't a good option in this case.

@Topher
I am after H₂ and I'll look into 'PEM electrolyzer' (doesn't PEM mean Proton Exchange Membrane?) anyways thanks for the safety tips.

TL;DR: I've changed my mind a bit, want to make a cell that operates around room temp. I am after H₂ and I want it to be efficient. I'd also like to create a PEMFC inside of the cell but that is not part of the question here. Well, actually having both H and O would be good, yes, it would be a nice asset, but hydrogen is the priority in this case.

Yet again thanks for the quick replies =)

 

[Topher925]

If your looking for a system that just basically a big battery, the PEMFC/PEME is a good combo. And yes, PEM does stand for "Proton Exchange Membrane" or "Polymer Electrolyte Membrane" depending on who you're talking too.

However, you need to be careful of your storage mechanism. If your just throwing H2 in a large low pressure tank you shouldn't have any problems. However, if you're storing it in a metal hydride or high pressure canisters, precautions must be taken.

We are currently designing an electrolyzer here at my uni where the electrolyzer will generate H2 at storage pressure for metal hydride canisters. I can tell you from my experiences so far that doing this is anything but easy and cheap.