by Keith Schubert

The following biological fuel cell was built at the Desert Studies Center at Zzyzx in 2010 as part of NASA Ames' Spaceward Bound.

Making the Fuel Cell

Salt Bridge

This is an economic alternative to a PEM (proton exchange membrane). A PEM costs hundreds of dollars for a small sheet and our salt bridge costs less than a buck and can be made from household products. If you use a PEM you still need the tube to connect the two chambers.

Materials(consumable): Materials(non-consumable): Procedure:
  1. Cut about a 3" portion of the 2" pipe. Clean the cut with sandpaper. We only need a 3" portion, the rest of the pipe is no longer needed. We will refer to the 3" section as the pipe for the rest of this section.
  2. Sand the inside of the pipe so that it is rough, this helps the gelatin to stick.
  3. Wrap one end of the pipe and secure with the rubber band.
  4. Fill the pipe half way with gelatin, then fill the rest with salt. Pour it out into the bowl and then mix thoroughly. Do not add water.
  5. Cut about a foot of the mesh tape and hot glue it inside the tube such that it goes across the center of the inside of the pipe. The mesh is here to support the gelatin, so make sure it crosses enough to provide support.
  6. Pour the gelatin salt powder mixture back into the pipe.
  7. Put the pipe in the bowl (provides support and it is easier to clean), then slowly add hot water. Only add enough water to wet the entire mixture, you are not dissolving the powder you are making a solid block. The result should be thick like cake batter.
  8. Let it harden over a couple days. It will be reasonably dry in a day, but rock hard in two. After it is reasonably dry you can remove the plastic wrap to help it dry faster. Check the resistance when it is done, the less the better. We got around 5 ohms.

Cell Setup

We will be making two cells, one for the aerobic and one for the anaerobic side.

Materials(consumable): Materials(non-consumable): Procedure:
  1. Cut two portion of the 4" pipe around 5" in length. Clean the cut ends with sandpaper. We need this to cap off one end of the tee, and provide a little volume. One piece is for each cell
  2. Apply cement in an even ring around the outside of one end of one of the pipes. It should be roughly the width of the brush in the pipe cement can and within half an inch of the end. Don't put too much on, a thin even coat is all you need. Do the same thing to the inside of an endcap. Insert the cemented pipe end into the cemented endcap. Repeat on the other pipe piece and endcap.
  3. Apply cement as above to the other end of one pipe and to the inside of one of the slip-fit portions of one tee. Insert them together. Repeat for the other pipe and the other tee.
  4. Apply cement to the outside of one of the flush bushings (4" to 2" reducer) and the inside of the remaining slip-fit connection on a tee. Insert the flush bushing into the tee. Repeat for the other flush bushing and tee.
  5. Put the cleanout plugs in the threaded cleanouts on the tees so you don't lose them.
  6. Drill a small hole (to run wires through) on each tee. I suggest putting it near the threaded portion (but not in the cap as removing and reattaching the cap would twist the wires, or in the threaded portion as it would block the cap.) and close to the reducer as the cells will be connected by the reducers and this will put the wires close to each other.
  7. Let dry for a day.

Electrode Construction

Assembling the Fuel Cell

Materials(consumable): Materials(non-consumable):

Results and things to do


I will try to add pictures of each step into the the descriptions above, but for now the pictures are available below.