Electrolysis, Hydrogen, and Electrolytes

[eswenson]

My son is trying to do a science experiment involving solar panels, electrolysis, and a hydrogen fuel cell. Basically, he is trying to generate hydrogen during electrolysis by applying solar power to electrodes in a water/electrolyte solution and then disconnect the power source after some hydrogen has been produced and then measure the electrical output of the "fuel cell" as the hydrogen recombines with the water. The variable in the experiment will be the electrolyte used. What relatively safe and easy to come by electrolytes should he choose from? Where would he go about getting those electrolytes? (One not-so-safe electrolyte he's read about is Surfuric Acid, and he may try to get a dilute solution of H2SO4 as one electrolyte). But what other electrolytes should he try to get? (He's thought about the following: KOH, NaOH, NaCl, Epson Salt, Baking Soda, HCl, Citric Acid, Drain Cleaner (H2SO4?), Vinegar).

 

In case it is important, he's using one electrode made of platinum-covered nickel wire (for the hydrogen production) and a copper electrode (for whatever other byproduct). The theory is that the hydrogen produced at the platinum electrode will be sufficient, and when the power source is removed, will recombine with the water and produce some current.

 

Any help would be appreciated as neither he nor I has any real chemistry experience. Thanks.

[YT2095]

if you want to split water then use dil H2SO4 and make the Pt electrode the Oxygen side, not the Hydrogen side, as it the oxidising side that does the damage to the electrodes, the copper will be fine at the H2 side.

 

also, where did you get your fuel cell from?

I have a pair here, and one is a splitter, it`s basically a fuel cell that works under water and in reverse, it also uses plain water.

perhaps the place you bought your fuel cell will also supply a splitter?

[eswenson]

Actually, he doesn't have a fuel cell. He is using the same beaker/electrode combination that is used for electrolysis. The theory is the hydrogen will bubble off the electrode during the electrolysis and then when the power source is removed, the hydrogen will react with the water and generate electricity for a short amount of time until consumed. This is sort of a fuel cell.

 

Thanks for the H2SO4 suggestion. His experiment needs to vary the electrolytes, so do you have any other suggestions for electrolytes (in addition to H2SO4)? Also, what concentration (keep it safe) should he use -- 10%? Or does it have to be greater?

[Flashman]

The hydrogen rises to the surface of the electrolyte, there needs to be some means of reintroducing it at the electrode.

[YT2095]

with Sulphuric acid, you only gain safety with dilution in that it buys you time to wash it off if you notice a spill on you or other things.

unlike a few other of the mineral acids, it doesn`t evaporate along with the water, so it becomes very concentrated over time anyway, that`s usually when you notice mysterious holes in your clothes hours/days afterwards, or a stinging sensation of your hand or whatever, some after you`ve finished with the acid.

10 to 20% should work nicely though.

and both of the hydroxides you listed will work also, the others have unwanted breakdown products that will spoil the cells objective, so it`s best not to use them.

[eswenson]

Hi Flashman. Perhaps my son and I misinterpreted this web site:

http://scitoys.com/scitoys/scitoys/echem/fuel_cell/fuel_cell.html

 

It suggests that you can do what I mentioned above regarding cutting off the power source and measuring the electrical energy produced when the hydrogen recombines with the oxygen. Is it the case that this would only work if no eletrolyte were used (in other words, no H2SO4) and both electrodes were platinum (as in the above cited experiment)? It is the case that if my son does the experiment with various electrolytes and one platinum and one copper electrode that this won't work (perhaps O2 will not bubble at the other electrode)? Forgive me for the lack of chemistry knowledge here.

 

YT2095: Thanks for your comments. We will be sure to use only 10% solution and take care to protect ourselves, clothing and other nearby items.

[Flashman]

Ah, yes that way works temporarily as long as it has hydrogen bubbles still attached to the electrode. If you knock the electrode while reconfiguring the wires or something, or have an electrode shape that the bubbles don't like to cling to, or kick the bench it's on or something, you'll have issues.

[inuhbad]

Aaaah. Yeah, I think Flashman was probably envisioning this experiment a little bit differently as I was...

 

I envisioned the coils being arranged coiled higher up, upward inside inverted test tubes where a more sizable amount of Hydrogen Gas would be trapped... And Likewise another test tube would contain the other gasses produced above the 2nd electrode. You might be able to retain a higher charge voltage, and for a longer period of time as well.