Many alternative energy projects such as metal oxide batteries and microbial fuel cells call for a carbon electrode. The phrase alone is enough to stop most people dead in their tracks.
This instructable shows how to make a very efficient, production grade carbon electrode for use in a variety of alternative energy applications. The electrode is tested using a simple aluminum air battery.
Many of the internet demonstrations of an aluminum air battery, including my own, try various means to surmount the carbon electrode problem. They mostly involve placing a copper lead in a pile of carbon be it graphite powder, pencil lead or ground up charcoal and hoping for the best. This is okay for novelty demonstrations and classroom work but is hardly adequate for the home experimenter.
One day while lurking in the specialty hardware section of my local Ace One day as I was working on a vertical axis windmill thing (soon to come I hope) I thought I would need brushes so off to Ace I went. There I stood in the novelty hardware section , mumbling to myself and attempting to connects bits of hardware that were never intended for the same device and the next thing you know I'm looking at a couple of drawers filled with lovely replacement brushes for all manner of power tools and appliances.
Before you can say "Bob's your uncle" I snatch up several samples and head off to my secret lair for testing. Read on for detailed information.
Step 1: Bill of Materials
Once you get to Ace you'll see that they have a variety of replacement brushes in various sizes. You can almost certainly find these at TrueValue as well as the big box stores but probably not Walmart or Target.
I am very pleased to update this instructable with the information that a very nice carbon electrode may be ordered online from www.carbonbrush.com. I have no relationship with these folks other than as a satisfied customer. They have a good shopping cart and accept paypal as well as small orders.
To see their selection of carbon brushes with insulated leads and end terminals visit: Flat Top Brushes with Leads
If, for one reason or another, you just can't wait. For instance if you have a burned out vacuum cleaner and have pulled the brush out of the motor. Or you don't use PayPal or you just want to support your local independent hardware store press on...
Mine cost about $4 each.
Copper wire to make the lead
soldering iron and solder - may be optional
hot glue gun or epoxy - seal exposed copper
The novelty hardware section is the part of the store where they rows and rows of shelves container odd looking bits, nuts, bolts and what have you. Tell the clerk you're looking for a Black&Decker replacement brush and he will take you to the right place. Or not...
The replacement brushes are carbon blocks with a copper lead connecting to a terminator ( most often a circular disk ). The copper lead is surrounded by a spring which we will remove.
The picture is from the Ace Hardware site and shows the B&D replacement brushes. The carbon blocks come in a variety of small and a small variation in shapes. It's not clear to me what the relationship is between the size of the carbon electrode and transfer rates. Pick a size that fits your application.
These are extremely well engineered to transfer power through the carbon block and copper lead efficiently. There is no need to concern ourselves with particle size, liquid tape or piles of fine carbon powder. We know that the carbon block will conduct and we know that there is extremely good connectivity between the carbon and the copper lead.
Step 2: Make the Electrode
First we remove the wire spring using a pair of pliers (or wirecutters). This will expose the copper lead with the end piece attached. I left removing the end piece until last, it is also possible to just push the spring down, cut off the head and remove the spring.
Strip one end of your copper wire to a length roughly matches the lead on the brush and twist the two wires together making sure to establish a good connection.
I soldered the connection to reinforce it.
Cover the exposed copper with hot glue or epoxy to seal it to avoid secondary reactions.
Voila at this point you have a production grade carbon electrode. In the next step we will test it using a simple aluminum air battery.
Step 3: Can You Shock Me Now?
In this step we will test the effectiveness of the electrode by creating a simple aluminum air battery with it and ensuring that we get voltage.
Bill of Materials:
Paper plate or other non conductive surface
A small square of aluminum foil large enough to hold a kitchen sponge
A cellulose kitchen sponge
A carbon electrode, perhaps the one we just made...
Some Du...er, um, well, water resistant tape. Scotch tape will do.
A piece of wire
A bowl, warm water and some table salt
Strip a short length from the end of the wire. Attach it firmly to back of the aluminum foil with the water resistant tape. It should NOT normally get wet or come in contact with the saltwater.
Put the aluminum foil on the paper with the wire side down (facing the paper). Mix a small amount of salt and water in the bowl. This should be enough to thoroughly wet the sponge without dripping, puddling or running.
Place the sponge on the aluminum foil, place the carbon electrode on top of the sponge positioned so that the lead does not come in contact at the sponge.
Measure voltage across the two leads to verify operation of the carbon electrode.
I got between 675 and 715 mV sustained output.