Download Microbial Fuel Cells2012

Environmental Chemistry - Electricity from Jello
Microbial Fuel Cells (adapted from indestructables.com)
Alternative Energy and Microbial Fuel Cells
Recent rising energy costs, rapidly dwindling crude oil supplies and concern over the negative
effects of carbon emissions have reignited both public and private interest in finding cheap
alternative renewable energy sources. Many “green” energy generating process rely on the
metabolic activity of microbes to turn human waste products into useable energy. For example,
you have probably heard of “bio-ethanol” as an alternative or additive to gasoline. Ethanol is a
normal by-product of the metabolism of many microbes (e.g. in wine or beer) and can be
generated in large amounts by growing ethanol producing microorganisms on “fermentable”
carbon sources like corn or grass.
Microbes can also be used to generate electricity. As we learned in class, when cells break
down food to produce ATP, they use enzymes that pull electrons off of energy rich molecules
such as glucose, capture the energy stored in the electrons using the electron transport chain
and then deposit the spent electrons onto terminal acceptors like oxygen. Electricity is really
just a stream of electrons, so if we can find a way to “steal” the electrons that microbes pull off
of glucose before they get to oxygen and put them through a wire instead, we can generate an
electric current that can be used to power electronic devices! Microbial fuel cells don’t have to
be complicated; Any kind chamber, big or small, that provides food for microbes and a way to
steal electrons from their microbial metabolism to generate a current is called a microbial fuel
cell or MFC.
Enzymes in glycolysis, fermentation and the citric acid cycle remove electrons from food, pass them
to electron carriers like NAD+ and FAD, and these electron carriers shuttle the electrons to the
electron transport system where they will be passed down and given to a terminal electron
acceptor such as oxygen. Making a microbial fuel cell can be as easy as putting microbes in an
anode chamber with food, letting them harvest the electrons from it for you, stealing the
electrons with an anode and then sending the electrons to a cathode to generate a current.
Materials
- 100ml beaker
- 250ml beaker
- 1 wooden splint
- 1 packet Knox gelatin
- ¼ teaspoon baker’s yeast
- 1 plastic droppers
- graphite electrodes (pencils)
- 1 digital multi-meter
Procedure :
1. Mix gelatin with 80ml of boiling water in 100ml beaker. Stir for 2 minutes.
2. Prepare 2.5ml of yeast in 5ml of water. (Add water to white capped tube.)
3. Add 80ml of cold water to the hot gelatin in the 250ml beaker.
4. Stir in the yeast.
5. Stir in 2ml of plant food.
6. Place 250ml beaker in refrigerator for 30 minutes
7. Insert Pencil electrodes into Jello.
8. Set voltmeter to DC 2000mV
9. Connect meter to pencil leads
10. Record highest voltage.
Environmental Chemistry - Electricity from Sunscreen and Blackberries.
Nanocrystalline Solar Cells (adapted from NINN materials)
Goals and objectives: Students will understand photovoltaic technology by studying the Gratzel
Solar Cell and building their own solar cells.
Nanomaterials have a potentially huge role to play in solving some of the world’s most critical
problems, including energy and the environment. Photovoltaics is a technology with many
interesting materials challenges. “Conventional” solar cells are made of single crystal or
amorphous silicon, but still lack in efficiency and cost competitiveness. Certain new thin film
materials, such as CdS/CdTe heterojunctions, have shown some promise in terms of increased
efficiencies and lower material usage, but improvements are only incremental. The full benefit
of solar energy perhaps may only be realized when a very different type of technology is
developed. Gratzel solar cells were developed in the early twenty-first century. The process
used is very similar to photosynthesis.
The Gratzel Solar Cell is made up of four critical parts: a transparent conducting ceramic film
electrode on glass, a nanocrystalline, porous TiO2 layer, a photon-absorbing dye, and an
iodine/iodide electrolyte. Electron transfer from the absorbing dye to the semi conducting
titanium to the cathode is the basis for the energetic characteristics of the system.
Nanocrystalline titanium is required in order to maximize the surface area of the ceramic, which
in turn maximizes the interaction with the dye, which maximizes the electrical output. The
device is a wonderful example of the all-important electron-transfer process as well as the use
of nano-engineered materials.
Gratzel Cell Diagram:
Methods and Materials
1. Conductive SnO2 coated transparent glass from a supplier such as Hartford Glass Co.,
Hartford City, IN 47348
2. Colloidal titanium dioxide (TiO2 ) powder
3. Iodine
4. Potassium Iodide
5. Ethylene Glycol
6. Blackberries or raspberries (fresh or frozen)
7. De-ionized water
8. Heat Source (oven, hot plate, hot-air gun)
9. Light source (overhead projector)
10. 2 multi-meters
11. Mortars and Pestle
12. 2 binder clips
13. Glass Stirring Rod
14. Tissue Paper (Kimwipes)
15. Filter Paper
16. Scotch Tape
17. Ethanol (ETOH)
Student activities
A. Solar Cell Components
1. Obtain a 1in. x 1 in. size conducting glass with tweezers (Do Not Touch the Face of the
Glass) and carefully clean it with deionized water and dry with a soft tissue. Identify the
conductive side using an ohmmeter (10-30 Ω). (Do Not Touch the face with the
electrodes.)
2. Obtain TiO2 suspension and grind with a pestle until it has formed a lump-free paste.
3. Obtain 2 blackberries. Place in 150ml beaker. Add 2ml of water and crush with plastic
bottle. (Starbucks Passion Tea can be used in place of berry juice). Filter with Buchner
funnel with no filter paper. and pestle. Filter.
B. Solar Cell Assembly
1. Using four pieces of scotch tape, mask a 2 mm wide strip on 3 of the 4 sides of the
conducting glass. On the 4th side, mask a 4 mm wide strip. This should form a “well”
with the tape acting as the walls. Secure the glass slide to the table with the tape.
Distribute 3 drops of the aqueous TiO2 solution uniformly in the shallow cavity on the
exposed conducting glass by carefully sliding a glass rod over the well. Allow the film to
air dry for one minute. Carefully remove the tape, and sinter the film on a hot plate set
to 450oC. Allow to slowly cool to room temperature.
2. Place the cell in a small weighing boat and completely cover the TiO2 coated glass plate
for 10 minutes in the dye-solution from the black berries. If the white TiO2 can be seen
from either side of the glass, the film should be placed back into the dye for 5 more
minutes. Wash the film with water and then with ethanol. Gently blot with soft tissue.
3. During the staining of the TiO2 prepare the counter electrode from another 1in. x1in.
piece of conducting glass. Apply a light carbon “film” to the conductive surface by
gently coloring the glass with a pencil “lead”. Anneal the electrode at 450 oC for a few
minutes. Wash with ethanol and gently blot dry with a tissue.
4. Place the dyed electrode face up on the table. Place the counter electrode on top, such
that the carbon is in contact with the TiO2 . The two plates should offset such that the
masked 4 mm strip is exposed and the alligator clips can be connected to this and the
opposite side. Use the binder clip to hold the plates together.
5. Place one or two drops of the iodine electrolyte solution at the edges of the plates and
manipulate the clips until the solution is drawn under the glass.
C. Testing the Solar Cell
1. Measure the dimensions of the active (stained area) of the solar cell with a ruler.
2. Take the solar cell outside to measure the output under illumination from the sun.
Protect the cell from excessive UV light with a plastic filter. Light should enter the glass
sandwich through the TiO2 coated plate (anode). As an alternative light source, use an
overhead projector, noting the distance between the bulb and the cell.
3. Connect the anode to the black wire (-) of the multi-meter using an alligator clip.
Connect the cathode to the red wire (+).
4. Measure the maximum voltage output (open circuit voltage) using the “voltage” mode
of the meter. Measure the maximum current output (short circuit current) using the
“amps” mode.
5. Divide the output current by the active area to obtain a current density rating.
6. Compare the various solar cells made by other participants.
7. Connect several cells together in a series and measure the voltage output.
D. Watts (Optional)
1. Use a 1000-Ω potentiometer as a variable load to obtain the complete current voltage
curve for your cell. Slowly increase the resistance of the variable resistor incrementally,
and record the voltage and current values. Plot your results.
2. Obtain the maximum product of (current x voltage) from your curve near the “knee”.
Divide this by the power of the incoming solar radiation (800-1000W/m2 ) to obtain the
conversion efficiency of your cell. If you are using an artificial light source, calibrate it to
the sunlight by matching the short circuit current as you vary the bulb-to-cell distance.
Questions for review
1. When the cells were connected together in series, was the increase linear?
2. In your own words describe how a nanocrystalline solar cell works.