Jello-Yeast Biobattery

Microbial fuel cells (MFC) generate electric current using the catalytic activity of living microorganisms. Currently, MFCs are generally thought to be difficult to implement for many large-scale applications; their raw material costs are high, and their performance and reliability are low compared to conventional Li-ion batteries. However, there has been considerable research interest in small-scale, single-use bio-batteries for low-power devices. For instance, over a decade ago, Sony presented a bio-battery that generates electricity from breaking down sugar using enzymes. Also, microbial fuel cells have also been used successfully in wastewater treatment, a very particular case in which the wastewater itself serves as the organic feed for the microbes. The development of bio-batteries could open up many potential applications in medicine and consumer electronics, with the added benefit of being more environmentally-friendly than the typical metal-based battery.

Yeast are eukaryotic microorganisms that can function as biocatalysts in MFCs. Fuel cells rely on redox reactions to generate electricity, a process which is driven here by the innate cellular respiration mechanisms of yeast as it metabolizes sugars to produce energy as ATP. Since electrons are being juggled around, fuel cells can harness this to create an electric potential. A bio-battery typically consists of an anode, cathode, separator, and electrolyte. The anode accepts electrons from the yeast and passes them to the cathode. Those electrons that travel through an external wire this way are capable of generating a measurable current. An ion-exchange membrane, which in our case is also the yeast-Jello, allows charge to be balanced in the cell through the movement of positively-charged ions. At the cathode, oxygen, an oxidizing agent, is the final electron acceptor. The cathode should be a material with high redox potential. We chose to use Pt-carbon cloth as our cathode, with the Pt serving as a catalyst for the redox reaction.

The following experiment is a fun and easy way to create your own yeast bio-battery using materials that are safe for home, inspired by an existing Instructables: https://www.instructables.com/Lime-Jello-Yeast-an...

For more information about the characterization of the bio-battery, please refer to this link: https://docs.google.com/document/d/1FAm1PeeREauRa...

Yeast: Fleishman’s Instant Dry Yeast

Membrane: Jello Gelatin Dessert Mix

Anode (top of the bio battery): Toray carbon paper (wet proofed) If unavailable, carbon tracing paper plain white printer paper can be used in place of this.

Cathode (bottom of the bio battery): Carbon cloth with Pt (0.2 mg/cm² 20% Platinum on Vulcan) If unavailable, carbon tracing paper or plain white printer paper can be used in place of this. Try to use a different material than the anode if possible.

Current collector: Two aluminum foil (around 5 cm by 7 cm) rectangles

Mold: Glass tupperware OR 3D-printed mold (highly recommended)

3D-printable mold: https://www.thingiverse.com/thing:4868786

Additional: Plastic wrap; Double-sided tape

Other: Multimeter; Spoon and knife; Hot water; Kitchen scale and/or measuring spoons and/or measuring cups; Food thermometer

Set-up: Cut all electrodes into 2.5 cm by 2.5 cm squares Cut the aluminum foil into rectangles that are slightly larger than the electrodes

Add 21 g of Jello powder (about ¼ of an 85g box) to 235 mL (about ½ cup) of boiling water in glass Tupperware (or other heat-safe container).

After the mixture cools to around 55 °C (130 °F), add 0.8 g (¼ tsp)yeast and stir thoroughly until yeast particles are no longer visible. Go to the appropriate step for the type of mold you have chosen.

If using the 3D-printed mold, cover the bottom lid with plastic wrap and use double-sided tape to affix the carbon cloth with Pt electrode in the center, on top of the plastic wrap. If using this method, the electrode should be water-resistant. Then, snap the walls on. Once the Jello mixture further cools to about 40 °C, pour it into the prepared mold to the brim and place the Toray carbon paper electrode on top of the solution. This electrode should float while the first electrode should stay affixed at the bottom.

After the mixture in the mold cools to about room temperature, carefully place it in the refrigerator for 1-2 hours or until solid.

Use a flat-headed screwdriver or a butter knife to pry the bottom lid off, leaving the plastic wrap attached to the Jello and being careful to not disturb the upper surface. Then, slowly peel off the plastic wrap. The electrode should stay in place. Assemble bio-battery as shown in Figure 1. The Jello does not need to be taken out. The aluminum foil can be sandwiched between the bottom lid and the Jello itself and also placed directly on top of the upper electrode, as shown in the images. Ensure that the foil makes good contact with the electrodes.

If using Tupperware, the cathode should be affixed to the bottom of the mold using double-sided tape in an arrangement such that it will be centered in a piece of cut Jello. Pour the mixture to a height of 2 cm. This step can be skipped if the electrodes of choice are not water resistant. Place the anode on top of the liquid Jello. It should float.

After the mixture in the mold cools to about room temperature, carefully place it in the refrigerator for 1-2 hours or until solid.

Then, carefully scoop out the Jello (with electrodes attached). Cut the Jello such that its base is a 5 cm by 5 cm square. Assemble bio-battery as shown in Figure 1. Ensure that the foil makes good contact with the electrodes.

At this point, construction is complete! Try measuring the voltage, resistance, and/or current across the bio-battery using a multimeter.

Again, to learn more about how we characterized our bio-battery, see:

https://docs.google.com/document/d/1FAm1PeeREauRa7...