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Researchers and scientists are constantly working to develop solutions that can save our future world, from solving problems like increasing pollution and climate change to producing clean energy. A group of researchers from the University of Naples Parthenope recently published a paper, titled “Development and Performance analysis of Biowaste based Microbial Fuel Cells fabricated employing Additive Manufacturing technologies,” about their efforts to test two different configurations of microbial fuel cells (MFCs): bio-electrochemical devices which can directly produce power by converting stored energy into a substrate. MFCs have this unique capability thanks to electrogenic bacteria that can produce and transfer electrons to an electrode with which they are already in contact.

The abstract reads, “In this work two different configurations of MFCs are tested, evaluating the importance of the operative conditions on power production. All the MFCs were fabricated employing 3D printing technologies and, by using biocompatible materials as for the body as for the electrodes, are analyzed the point of strength and development needed at the state of the art for this particular application. Power productions and stability in terms of energy production are deepen investigated for both the systems in order to quantify how much power can be extracted from the bacteria when a load is fixed for long time.”

Reactor Design.

The three main transfer mechanisms are electron shuttles, conductive nanowires, and redox reactions between bacteria and the electrode. Scaling up for real MFC applications would be expensive, as the needed materials, like NafionR and platinum, are costly. But 3D printing can be used to help lower costs, as well as offer more stable energy production.

“Due to that a more sustainable and less wasteful production can be applied to MFCs bioreactors. In addition, materials suitable for 3D printing are moving to bio-based solutions completely recyclable that would strength the sustainability by closing the loop also for the materials,” the researchers wrote.

For their study, the team investigated and tested two kinds of reactors: single chamber and double chamber. The biggest difference between them regards the use, or lack thereof, of a chamber for locating the cathode electrode.

Exploded and Compact view of (A) Single Chamber MFC, (B) Double Chamber MFC.

“In the reactors design the distances between cathodes and anodes in both layouts is fixed to 2 cm,” the researchers explained.

“In the single chamber configuration, activated carbon coated with PTFE and a nickel mesh as current collector are used as cathode (7 cm2 as active surface area) and a PLA based material is used for realizing the anode (9.7 cm2 active surface area).

“In the double chamber reactor, both electrodes (cathode and anode) are realized by using the PLA based material like that used for the anode of the single chamber reactor. These electrodes have also the same shape (9.7 cm2 active surface area). Moreover, a cation exchange membrane (CEM) is used as medium between the two chambers.”

Open source Free CAD was used to design the cube-shaped reactors, which included an internal circular hole for extra volume, and a Delta Wasp 20 40 3D printer fabricated the reactors out of non-toxic, conductive PLA from Proto-pasta.

The researchers noted, “This material is suitable for the application in MFC, but improvements are needed in order to obtain better power production.”

The team used bacteria from a mixture of compost taken from an Italian waste treatment facility and household vegetable waste for their experiments, and left the 3D printed reactors in a temperature-controlled environment of 20°C for 48 hours before beginning acquisitions.

“An experimental data acquisition system, is used to record the performances of the MFCs, consisting of an embedded system controlled by an Arduino board connected to sensors that recorded voltage and current at each operative condition set. The DAQ, with a sample frequency of 0.1 Hz (10 s), is able to switch automatically the resistance applied at the ends of the electrodes in order to easily obtain polarization curves. In particular, polarization procedure consists in the application of four different resistance (36000-27000-12000-8000 W) for 5 minutes each,” the researchers wrote.

“The procedure is continuous, so the total time needed is 20 minutes. Finally, the value of resistance that gives the maximum power is applied for four hours in order to test how the response of the same to an extended load.”

Conductive PLA Electrode Design.

The researchers continuously recorded the MFCs’ Open Circuit Voltage (OCV), and the double chamber system showed a higher starting potential of 0.95 V compared to the 0.59 V of the single chamber system. They noted a “great stability” during their experimental tests, and determined that 3D printing is “a suitable technology for the fabrication of the MFC in terms of precision and costs.”

“Results of the experiment show that both configurations are affected by a high internal resistance and, as a consequence, a limited power production has been achieved. As expected, better results are registered for the double chamber, mainly due to the use of CEM and the presence of potassium permanganate at the cathode that, probably, better balanced the redox reactions that occurred,” the team concluded. “However, this difference is very low (+11%) and the reason can be found in the materials used for the electrodes. AC coated with PTFE electrode (1 W resistance), used as cathode in the first configuration, allows better performance than the conductive PLA (400 W resistance approximately).”

Co-authors of the paper are Elio Jannelli, Pasquale Di Trolio, Fabio Flagiello, and Mariagiovanna Minutillo.

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