Aluminum battery question

[Justonium]

Wow I have a lot of questions... OK, I just made an aluminum battery using a piece of aluminum foil for the negative terminal, and steel wool for the positive terminal. I put both pieces of metal in a container of NaOH solution. (The NaOH catalyzes aluminum's reaction with water.) Before I connected the aluminum to the steel wool, lots of bubbles of hydrogen formed on the aluminum as the aluminum ions displaced hydrogen ions in the water. But when I connected them in a circuit, though some bubbles started forming on the steel wool (giving me a current), most of them still formed on the aluminum. Steel is a resistor, which may contribute to this inefficiency, but I tried copper too, and though it worked better than steel, I can't get very much surface area with pennies, and most of the bubbles still formed on the aluminum, forming waste heat. Does anybody know a good material I can use for my positive terminal to efficiently redirect all of the electrons exchanged between the aluminum and the water?

 

Here are the equations:

Al --> Al3+ + 3e-

3e- + 3H+ --> 1.5H2

 

The second reaction is supposed to move from the aluminum to the steel wool terminal, but it hardly does. I only got my cell to produce 150mA (1V), but I know it could produce waaay more if I had a better material for my positive terminal. This battery is using the same technology as the zinc-carbon battery. Hey! Maybe I should use carbon, huh? But where the heck can I get a piece of high surface area graphite?

Any ideas for what to use?

[UC]

What you're doing is making aluminum react with water by using sodium hydroxide solution. You're making a lot of hydrogen gas, and cells that use hydrogen tend to be awful at generating useable voltage. The best you'd be able to do would be a high surface area platinum electrode, I believe

 

Voltage generated is characteristic of a set of materials. You won't improve it within the system, except by decreasing internal resistance. The iron probably becomes passivated by iron oxide and hydroxide in the solution, which would be a significant source of resistance.

 

"Zinc-carbon" batteries use MnO2 and zinc with a potassium hydroxide electrolyte. The carbon is only for it's conductive properties and does not take part in the reaction. These rely on the reduction of MnO2 to MnO and the oxidation of zinc to zinc oxide/hydroxide.

 

Aluminum generally makes poor batteries because of the passivating oxide layer. Perhaps you should try something like copper and zinc in copper sulfate first.

[Justonium]

I don't have any zinc or copper sulfate, and I definitely don't have any high-surface area platinum. The zinc-carbon battery I was talking about must not be the standard battery referred to by that term, but there is a type of battery in which the electrodes are zinc and graphite, and they are both in sulfuric acid. The hydrogen bubbles form completely on the carbon when the circuit has sufficiently low resistance. Do you know why they use carbon instead of platinum? Do you think my aluminum battery would work like this if I used carbon? By the way, zinc-carbon-sulfuric acid batteries aren't even used any more, they have been replaced by many better types of batteries. You seam to be very active on this site, thanks for replying to my posts.

[UC]

I don't have any zinc or copper sulfate, and I definitely don't have any high-surface area platinum. The zinc-carbon battery I was talking about must not be the standard battery referred to by that term, but there is a type of battery in which the electrodes are zinc and graphite, and they are both in sulfuric acid. The hydrogen bubbles form completely on the carbon when the circuit has sufficiently low resistance. Do you know why they use carbon instead of platinum? Do you think my aluminum battery would work like this if I used carbon? By the way, zinc-carbon-sulfuric acid batteries aren't even used any more, they have been replaced by many better types of batteries. You seam to be very active on this site, thanks for replying to my posts.

 

Probably because carbon is cheap as dirt and platinum is $38/gram

 

I would try using something other than aluminum. No approach to making a battery with it is not problematic in some way.

[Justonium]

Do you know where I can get some high surface area carbon that will work for my purpose? Activated carbon will not work because it quickly fills with hydrogen and loses its surface area (not to mention its higher resistivity than graphite). A big flat piece of graphite might work, but the only place I know of to get graphite is from pencils.

[Theophrastus]

If you're getting your graphite from pencils, I recommend that you be warry that pencill grapphite, is actually coated in a layer of resin, so it adheres to the wood, however the heat of candle, is hot enough to remove this coating. If you try burning pencils (I've done it on occation, for lack of anything better to do!) You'll eventually notice the wood begin to curve, and split in two as a prominent line forms down the middle of the wood (the wooden portion, actually consists of two separate pieces), and anyhow, the process of burning is probably the simplest.

 

As UC said, aluminum is a horrible conductor for a cell electrode. Copper, nickel, platinum and the like all work quite well, though it's true that the platinum is quite costly. I once bought some platinum coated nickel wire for electrochemical experiments, and even that didn't come cheap.

 

Anyhow, most metals are actually quite available, if you know where to look. Most of my copper i attain, by displacing it from compounds, with iron (however, for obvious reasons, this isn't used as an electrode). Hobby shops, are generally a good source for electrodes at low prices. If you're not serious, and can deal with impurities, you can by means of electroplating remove the upper layers of coins and harvest metals like that. For example, nickels made before 1967 are made with 99.9% pure nickel.

Pennies made between 1997 and 9 are actually made of zinc with a copper coating.

 

To conclude, a little resourcefulness, can bring one a long way. If you're more serious about this however, there are tones of internet sites that supply these materials in better quality, purity and form. Some specialist hardware stores, can also be useful, in that regard.

 

The hydrogen production on the part of the electrolyte can be problematic, and if you have some money, investing in some copper sulfate, to build something along the lines of a daniell cell, which is a simple intro to electrochemical cells, is recommended.

 

Anyhow, happy experimenting, and best of luck!

Edited May 22, 2009 by Theophrastus
Consecutive posts merged.

[Justonium]

The reason I'm using aluminum is because it is very reactive with water when sodium hydroxide is used as a catalyst. It produces hydrogen as a byproduct, which can farther be used in a secondary fuel cell. Some people have been using aluminum and water to make hydrogen to power their cars, and I am looking into this method because it has the potential to produce a lot more electricity than just the hydrogen can. Just for anybody who was wondering why I chose aluminum, which has the horrible tendency to develop an insulating coating of aluminum oxide.

[Theophrastus]

If your main aim is the generation of hydrogen, this can actually be done in various far simpler fashions. Rather than building a fuel cell, simply reacting sodium hydroxide, with aluminum, will yield adequate quantities of hydrogen, just be warned that the reaction is rather violent, so you should exercise caution.

 

You could also produce hydrogen, by heating magnesium to a relatively high temperature, though be warned that it is natural for it to shed white sparks at this point, and then drop it in water. This shall produce hydrogen gas, and white, insoluble magnesium hydroxide, which once filtered out of the surrounding solution, you can use in further chemical exploits.

 

Magnesium, for the amateur chamist, can easily be found in pencil sharpeners, as you can easily tell based on the weight whether its magnesium or steel. I recommend removing the screw and blade, as these are always made of steel.

 

If you are unsure about the content of your sharpener, simply fill a measuring cup with an appropriate amount of water, then add the pencil sharpener. The increase in volume is the volume of the pencil sharpener, and then by finding out the weight you can find its density. You can then easily google the density of magnesium, and if your results seem to match, taking experimental uncertainty into account, you've found your metal. Best wishes, again- I hope this helps!

Edited May 22, 2009 by Theophrastus
Mild modification of content

[Justonium]

You don't understand, the hydrogen is being made for the purpose of powering a fuel cell to make electricity, but I am trying to make the process more efficient by making even more electricity by harnessing the aluminum's strong affinity for the oxygen in the water. I think when I said fuel cell you were thinking of electrolysis, which is the reverse. What I am doing is making a battery that runs on aluminum and water, and makes hydrogen as a waste product, which then goes to a fuel cell to make more electricity.

 

By the way, doing what you said with magnesium and water is very bright, and can cause eye damage.

 

Oh, I've made hydrogen with aluminum before, it sure beats buying helium at the party store! The balloons lose it in a few hours though cuz its soluble in the latex.

 

PS: You don't need to tell me basic stuff like how to find density, or about what coins are made of, I know about basic stuff like that. Not to be ungrateful or anything, I really appreciate that you spent the time to try to help me with my experiments.

Edited May 23, 2009 by Justonium
adding more info

[YT2095]

Do you know where I can get some high surface area carbon that will work for my purpose?

 

Gouging rods from a welding shop will suffice for your purposes, you`ll need to peel the copper plated layer off them but it`s very easy to do.

[Justonium]

Wow how would I remove the copper? Actually, the rod wouldn't be very high surface area anyway, I was thinking more like a plate or something. Yea. I have no idea where to get a flattened plate of graphite. Even if anybody knows where I can buy copper plate, though copper isn't very efficient, I'd still like to know where I can get some. Any information y'all throw out will be useful to me.

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I just tried a carbon electrode, and it wasn't any better than copper was. Maybe the technology for an efficient aluminum battery just doesn't exist. I don't know why it doesn't work like that zinc carbon sulfuric acid battery I saw, all I'm doing is replacing zinc with aluminum, and replacing sulfuric acid with sodium hydroxide dissolved in water. Could anybody give a suggestion as to why with aluminum, the hydrogen bubbles don't completely move over to the carbon electrode when the circuit is closed? Because it works with zinc, to where the zinc completely stops bubbling. Oh yes, this is similar to the voltaic pile invented by Alessandro Volta, where water reacted with zinc to form zinc hydroxide, but the hydrogen bubbles formed on the copper when they leads were connected. (Well, this cell is different in that the activation energy is too high to be reached without the copper, but that is not true with the sulfuric acid battery, and it still does the same type of thing.)

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I'm not, however, abandoning my battery, as it still produces significant current. If I can not find any better solutions, I will use copper foil.

Edited May 24, 2009 by Justonium
Consecutive posts merged.