1. An Introduction to Sediment Microbial Fuel Cells

2. What is a Fuel Cell? A fuel cell is a device that generates
electricity through a chemical reaction.
It is similar to a battery, but unlike a battery
the chemicals can be continuously supplied

3. What is electricity?
Electricity is energy made available through the flow of electrons.
So, we have to have a transfer of electrons. This occurs when one substance wants to lose electrons and another substance wants to gain electrons. When these two substances come in contact with one another, electrons are transferred.
Loses electrons
Gains
electrons

4. If both substances are in the same solution, then the electrons transfer directly and the energy is dispersed as heat.

5. How does it work?
If the two substances are separated, and the electrons are transferred through a wire then the energy is transformed into electricity.
Tube filled with electrolyte solution e-
The electrodes are necessary because the electrons cannot go directly from the solution to the wire, they need a solid surface to serve as an intermediate. The electrodes are usually made of metal but can be made of any substance that will conduct electricity. The tube of electrolyte solution (commonly referred to as a salt bridge) completes the circuit. Without the salt bridge, the solution on the left would develop a net positive charge and the solution on the right would develop a net negative charge. The cell will not operate this way. The salt bridge allows ions to flow between the two solutions so that the solutions remain neutral and the cell will operate.
Gains
electrons
Loses electrons
Electrodes

6. Vocab
Electrode:
The site at which electrons are either released or collected.
Two types of electrodes:
Anode (-): The site at which electrons are collected.
Cathode (+): The site at which electrons are released.

7. Vocab Electrolyte solution:
A solution that can carry ions between the anodic and cathodic chambers.

8. How do we apply this to a sediment microbial fuel cell?
Cathode
Water
The mud serves to separate the anode chamber from the cathode chamber. The water is the electrolyte solution that allows the completion of the circuit.
Anode
Fish Tank

9. So, where are the chemicals?
The chemicals come from decaying plant and animal matter in the river itself and as a result of runoff. They are mostly organic chemicals which consist mainly of carbon, hydrogen, and oxygen.

10. What is the reaction? Two parts to the reaction:
Reaction in the anodic chamber
+ H2O  CO2 + H+ + electrons
Reaction in the cathodic chamber
Oxygen + H+ + electrons  H2O
Organic compound

11. For example:
Anodic chamber C2H4O2 + 2H2O  2CO2 + 4H+ + 4e- OR C6H12O6 + 6H2O  6CO2 + 24H+ + 24e- Cathodic chamber 4O2 + 4H+ + 4e- 4H2O 6O2 + 24H+ + 24e-  12H2O

12. Why do we need the microbes?
The microbes are what make the reaction “go”. They are the catalyst.
A catalyst initiates or accelerates a chemical reaction but remains unchanged.
Example: enzymes

13. Kinda like this…