[Sophia7X]

I'm trying to construct a battery with the highest voltage possible. Since voltage decreases with increasing temperature, could cooling the metal electrodes I am using have any impact on the voltage?

[Vidya]

you have to select the minimum temperature at which reaction is spontaneous.It should not become non- spontaneous at low temp 

[Borek]

voltage decreases with increasing temperature

Voltage, or electromotive force?

According to Nernst equation cell potential is directly proportional to the temperature. However, internal resistance grows with temperature, so ℰ can go down.

[Sophia7X]

I came up with a new idea to create a battery for my chem class. The goal is to get the highest standard cell potential using obtainable supplies (and lithium is not allowed ).

Could someone take a look at my drawing to see if my battery could work before I buy the necessary supplies?

https://docs.google.com/document/d/1t38Kgv1sDcKuVuzbPFpQISSWgE3kM7Ud7A-IKBRpOJw/edit
This battery should theoretically have a standard cell potential of 2.87 V.

If I used magnesium (like a magnesium fire starter) as the anode to get even higher voltage, should I soak both sponges in H2SO4?

for the aluminum anode I want to soak the sponge in NaOH because aluminum has a protective layer of oxide, so the NaOH should dissolve that, right?  

Also, how concentrated NaOH or H2SO4 should I use?

[Borek]

Al will dissolve in the NaOH solution (producing H₂), I am not sure what will happen on the MnO₂ side (depends on the acid concentration and temperature).

Does it have to be a single cell? Google Zamboni pile.

[Sophia7X]

I'm planning on using battery acid which I think is around ~30% sulfuric acid. The MnO2 is supposed reduce in acid solution, and the carbon cathode to collect the current.
I have 100% lye, and I'm going to make a NaOH solution.

All of the aluminum won't dissolve right? Since I'm not submerging the whole thing in NaOH, I'm just putting it on top of a sponge soaked with sodium hydroxide solution.

Should this dissolve the oxide layer to expose the aluminum metal so it can oxidize in water?

Also, we don't need a long-lasting cell.  And yeah, only single cell.

[Borek]

As I told you, I am not convinced Al side will work. Not difficult to check experimentally, but as it contains two half cells already it may not work as expected. Oxide layer should dissolve, but reaction won't stop there.

[Sophia7X]

It worked!!! :DD

I got 2.6 V. The standard cell potential is 2.87. At first, I submerged my sponge into the NaOH solution and I pretty much destroyed the sponge, so then I just poured a bit onto another sponge. Worked pretty nicely considering the fact that I didn't measure anything— I just threw it together, hoping that it would work.

Gonna buy magnesium so I can try to get an even higher voltage.
Where can I find magnesium anyway?

[Borek]

For small piece fire starters that you mentioned can be a good idea - although I am not sure how pure it is. I have seen magnesium rods on eBay (stated to be 99.5%), but they will cost much more.

[billnotgatez]

I thought that High School and College labs had magnesium ribbon for some of the class demonstrations.

[fledarmus]

How pure does it need to be? You can get magnesium welding rods in a wide variety of alloys. For example, http://www.airgas.com/browse/product_list.aspx?catID=130&WT.svl=130

Wikipedia has a page that gives the percentages of other metals in magnesium alloys http://en.wikipedia.org/wiki/Magnesium_alloy. For example, the AZ31 listed in the Airgas stock is 3% aluminum and 1% zinc. The wiki page also mentions a 10% Li in Magnesium alloy designed as an improved anode for batteries.

[Sophia7X]

I thought that High School and College labs had magnesium ribbon for some of the class demonstrations.

They do, but for this project we're not allowed to use materials from the school supply.



I used a magnesium fire starter but I got an even lower voltage?
The magnesium fire starter has a black rod (iron?) on it, could this be the reason?

[fledarmus]

As I understand it, the "Magnesium fire starters" actually have very little magnesium in them. These are actually ferrocerium alloys containing a very small amount of magnesium. See http://en.wikipedia.org/wiki/Ferrocerium

[Borek]

Depends on the type. Ferrocerium is used for ignition, but there are magnesium fire starters that contain a block or rod of magnesium that you can shave with a knife and ignite with sparks from ferrocerium. I guess when Sophia mentions a black rod on the fire starter, she refers to ferrocerium attached to magnesium block.

Although whether the magnesium block is a real magnesium may depend on the source. See

<a href="http://www.youtube.com/v/frDMAOlIGaY?version=3&amp;amp;hl=en_US" target="_blank" rel="noopener noreferrer" class="bbc_link bbc_flash_disabled new_win">http://www.youtube.com/v/frDMAOlIGaY?version=3&amp;amp;hl=en_US</a>