Alex’s Guide to DIY Carbon Paper Electrodes
Introduction
Carbon paper electrodes are a good starting point for many electrochemical experiments. While there are many styles, these ones lend themselves to DIY production.
In these examples, we will be creating two types of electrodes. One made with bismuth powder, and the other with silver chloride powder. These happen to be the same types needed for Synthwave.
Note that I’m just a hobbyist, not a professional electrochemist. It is likely that there are better techniques than this one-- However, this is the one I’ve found that works best for my particular setup and workflow.
Materials Needed
I’ve provided links below, but they’re likely to fall victim to link rot over time. If a link isn’t working, just do your best to find a suitable replacement.
I also included amounts, but keep in mind that this will buy you much more than you need for a single set of electrodes. The intention here is that you’ll have enough material to make as many as you want.
- 50g Carbon Black (Carbon Powder)
- 50g Polyvinylidene Floride, a binding agent
- Metal powders, in this example both bismuth and silver chloride
- 500mL of NMP solvent
- At least a square foot of .005" thickness Carbon Paper (AKA Graphite Paper)
- A razor scraper. I like this one, personally, but anything will work
- Ink casting guides (see below)
- A digital scale that works in the thousandth range
- A plastic spoon
- Latex gloves
Ink casting guides
The key to carbon paper electrodes is achieving a very thin and very even spread of “ink” onto a the sheet of carbon paper. The high-end way to do this is with a CNC-assisted spray nozzle. The low-end way is to do something called the “doctor blade” method, which involves laying down several layers of scotch tape in lines to a desired thickness, then using a razor blade to smoothly cast the ink between the lines.
I use a modified doctor blade method, where I 3D print stencils rather than using up a whole roll of tape. The electrodes I’m aiming for are 2cm x 10cm rectangles, cast a depth of 200 μm (0.2mm). The files I use are included in the Synthwave repo, but are easy to create on your own using the CAD tool of your choice.
3d printers are excellent when it comes to making accurately-sized things. Do keep in mind that the first layer of any 3d print is mildly “squished”, and may not end up exactly the thickness you anticipate. Always good to verify with calipers.
If you don’t have a 3d printer, you may use the scotch tape method.
Safety Precautions
While these ingredients aren’t particularly toxic, please make sure to take proper safety precautions when handling powders, solvents, and/or razor blades.
Carbon black is especially powdery, and is not very good for your when inhaled. Wear a mask!
This process can also be a little messy, so I like to wear latex gloves.
Creating The Ink
Begin by weighing your ingredients. The paper that I’m working from only states ratios, which is not particularly useful for knowing how much to make. For your convenience, I’ve included exact weights for each ingredient, which will make enough ink to cover about 200 cm² of surface area (so, 8 electrodes with a little bit of excess).
Tare your mortar and pestle on your scale, then carefully add:
- 0.4g carbon black
- 0.4g PVDF
- 3.2g bismuth powder (or silver chloride, depending on which you’re making)
- 10.0g NMP solvent
Use your mortar and pestle to mix thoroughly. You’re aiming for a perfectly smooth ink with no lumps.
When you’ve achieved this, set up your casting station. My approach here is to tape the 3D printed stencil to both the carbon paper and the workbench, then drop a spoonful of ink into each lane.
Now use your razor scraper to spread the ink as evenly as you can. Apply even pressure as you drag the razor scraper across the stencil. You’ll notice that the guide is designed to give you enough room to scrape two lanes at once. You may then remove the stencil and admire your handywork.
Cleanup
The bad news is that this ink material is not water-soluable. The good news is that it tends to gel together and come off in long sheets. The best way I’ve found to clean my implements is to splash them with very cold water, dry with a paper towel, and repeat.
Drying the electrodes
If you’re in a hurry, you can dry them in an 180F oven for 3 hours (I personally use the back of a cookie sheet). Otherwise, you can leave them at room temperature for 24 hours.
Once they’re dry, carefully cut them into their desired shapes using scissors or a paper cutter.
Congratulations! You have now completed your first set of electrodes.