Thread: Is it possible to generate electricity from a pH gradient?

Hello!

Is it possible to generate electricity from a pH gradient?

Thanks!

Originally Posted by cyentist

Hello!

Is it possible to generate electricity from a pH gradient?

Thanks!

Depends what you mean by gradient I suppose. The old lead/acid battery relies on acid reaction with lead and lead oxide to produce lead sulphate, consuming sulphuric acid in the process.

You can't just do it in one pot though, you need a barrier or salt bridge.

Originally Posted by PhDemon

You can't just do it in one pot though, you need a barrier or salt bridge.

Do you, though? I thought in a lead/acid battery one just has a lead plate and a lead oxide plate, with acid in between them. Must admit I've never taken one to bits, though.

You're right... I mis-remembered. The hazards of posting from the pub!

Originally Posted by PhDemon

You're right... I mis-remembered. The hazards of posting from the pub!

You mean I need to have a material that will be oxidised and another material that will be reduced?
So in addition to the pH gradient, I need to supply a material that will be destroyed (oxidised) and another material that will be reduced (probably destroyed again)?

Isn't it possible to generate electricity from two solutions of HCl with different concentration just by connecting them with a wire?

Yes, to generate a voltage you need an oxidation reaction coupled to a reduction reaction. It will not work with two HCl solutions joined by a wire.

Originally Posted by PhDemon

Yes, to generate a voltage you need an oxidation reaction coupled to a reduction reaction. It will not work with two HCl solutions joined by a wire.

Thanks but I read here the opposite:
https://www.quora.com/How-can-you-ge...rent-pH-levels

Where will the current flow if you just have two solutions and a wire? How are you going to complete the circuit? The link you provided is assuming you have electrodes in place and a complete circuit. When I said this wouldn't work, what I meant is that any current will be very short lived as eventually the concentrations would quickly balance out and the voltages would be very low.

Not sure I understand the difference, can you elaborate please?

As I said, assume you have two separate glasses with HCl solutions in different concentrations.

How can you generate voltage with that? What do you need to do? Do you need to add more substances in the solutions? Any wires, electrodes, membranes etc?

I would like to know how to generate voltage from only those two glasses, regardless if it is short lived and it will die out soon.

thanks!

You need to set it up as a galvanic cell. (In this case it will be a concentration cell). Have a look on wikipedia for galvanic and concentration cells for ths basic info. (My phone is playing silly buggers and won't post the links).

Is it possible to generate electricity from a pH gradient?

I believe it is possible to generate electricity from a pH difference. One needs a salt bridge between the two cells to enable the flow of counterions between the two cells (to maintain charge neutrality). One also needs a gas bridge between the two electrodes because the generation of electricity from a pH difference involves a redox reaction involving hydrogen gas (which flows from the high concentration electrode to the low concentration electrode). Also, the electrodes probably needs to be coated with something like platinum or palladium to reduce overpotential.

This converts pH to voltage: https://www.traditionaloven.com/conv...h-voltage.html

However, even the maximum pH difference of 14, gives only 400mV.

Can anyone explain please?

To get large voltages you need oxidation and reduction reactions with a large energy change not just a concentration gradient. Look up the Nernst equation, the voltage (or cell emf) is proportional to the free energy change of the coupled redox reactions. Diffusion of ions down a concentration gradient is a much lower energy process and so produces smaller voltages.

Originally Posted by cyentist

This converts pH to voltage: https://www.traditionaloven.com/conv...h-voltage.html

However, even the maximum pH difference of 14, gives only 400mV.

Can anyone explain please?

There is something very odd about that site. The description it gives of pH suggests the writer does not know what it is. pH is the negative of the logarithm of the molar concentration of H+. So in neutral water, in which the molar concentration of H+ is 10⁻⁷ moles/l, log of the concentration is -7 and so the pH is 7. None of this has anything to do with millivolts.

And the description of measuring millivolts makes no sense either. They have to be measuring a potential difference between two things, but they do not say what these are.

I'd forget it if I were you. It looks like rubbish.

I have to admit I didn't look at the link and may be talking ex ano, I've just got home from the pub!

Yup, that particular page is utter drivel: The millivolts to pH formula was first discovered by Dr. Jerry Tennant.
And a further search gives us: Dr. Tennant was named among Top 20 Alternative Doctors in America... and also turns out to be the author of this little gem.

Originally Posted by Dywyddyr

Yup, that particular page is utter drivel: The millivolts to pH formula was first discovered by Dr. Jerry Tennant.
And a further search gives us: Dr. Tennant was named among Top 20 Alternative Doctors in America... and also turns out to be the author of this little gem.

Fascinating! I see Tennant has been interviewed on Youtube about "bioelectricity", by Dr Joseph Mercola, who I seem to recall has actually done time for fraud.