Improving the cathode of a microbial fuel cell for efficient electricity production
The worldwide demand for energy is increasing. At the same time, energy rich wastewaters are currently purified by oxygen supply, which costs a lot of energy. The Microbial Fuel Cell is a new technology that offers advantages in both directions: it produces electricity while purifying wastewaters. This research aimed at increasing the electricity production from wastewaters in the Microbial Fuel Cell. In a Microbial Fuel Cell, microorganisms grow on an electrode, the anode. These microorganisms convert biodegradable organic components in wastewater directly into electrons (electricity). The most important limiting factor is currently the cathode, where the electrons are accepted, normally by oxygen. Oxygen is the most desired electron acceptor because of its unlimited availability and its high potential. To drive the oxygen reduction reaction at the desired rate however, a catalyst is needed. The mostly used catalyst for oxygen reduction is Pt, however, its high cost requires development of other cost-effective and renewable catalysts. We followed three strategies to improve cathode performance: the use of Fe3+/Fe2+ as a mediator at the cathode, a biocathode, in which microorganisms were used to catalyze the oxygen reduction reaction, and the reduction of Cu2+ in the presence and absence of oxygen. This last process resulted not only in higher current production, but also in recovery of pure copper. Finally, we have tested a Microbial Fuel Cell on larger scale, with a surface area of 0.5 m2 and a volume of 5 L. Contrary to other studies, we have shown that a larger-scale Microbial Fuel Cell can produce similar power and current densities compared to small lab scale systems, when the distances between the electrodes are small, the electrodes are well flowed-through, and the reaction rate at the cathode is fast. Finally, we show that there is still a factor 10 improvement in power possible, as the estimated maximum power density that can be achieved in Microbial Fuel Cells is 17.3 W/m2 or 3,460 W/m3. Compared with anaerobic digestion, this is almost 3 times as much power at a similar loading rate of 25 kg COD/m3/d. At this estimated maximum performance, the energy efficiency in a Microbial Fuel Cell will be 63%, whereas the energy efficiency in anaerobic digestion is 30%. For reaching this estimated power density, further studies should focus on the cathode as it is still the main limiting factor, leading to largest part of the energy losses in the MFC.
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| Format: | Doctoral thesis biblioteca |
| Language: | English |
| Subjects: | bioenergy, biomass, electricity generators, microbial fuel cells, bio-energie, biomassa, elektriciteitsgeneratoren, microbiële brandstofcellen, |
| Online Access: | https://research.wur.nl/en/publications/improving-the-cathode-of-a-microbial-fuel-cell-for-efficient-elec |
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| Summary: | The worldwide demand for energy is increasing. At the same time, energy rich wastewaters are currently purified by oxygen supply, which costs a lot of energy. The Microbial Fuel Cell is a new technology that offers advantages in both directions: it produces electricity while purifying wastewaters. This research aimed at increasing the electricity production from wastewaters in the Microbial Fuel Cell. In a Microbial Fuel Cell, microorganisms grow on an electrode, the anode. These microorganisms convert biodegradable organic components in wastewater directly into electrons (electricity). The most important limiting factor is currently the cathode, where the electrons are accepted, normally by oxygen. Oxygen is the most desired electron acceptor because of its unlimited availability and its high potential. To drive the oxygen reduction reaction at the desired rate however, a catalyst is needed. The mostly used catalyst for oxygen reduction is Pt, however, its high cost requires development of other cost-effective and renewable catalysts. We followed three strategies to improve cathode performance: the use of Fe3+/Fe2+ as a mediator at the cathode, a biocathode, in which microorganisms were used to catalyze the oxygen reduction reaction, and the reduction of Cu2+ in the presence and absence of oxygen. This last process resulted not only in higher current production, but also in recovery of pure copper. Finally, we have tested a Microbial Fuel Cell on larger scale, with a surface area of 0.5 m2 and a volume of 5 L. Contrary to other studies, we have shown that a larger-scale Microbial Fuel Cell can produce similar power and current densities compared to small lab scale systems, when the distances between the electrodes are small, the electrodes are well flowed-through, and the reaction rate at the cathode is fast. Finally, we show that there is still a factor 10 improvement in power possible, as the estimated maximum power density that can be achieved in Microbial Fuel Cells is 17.3 W/m2 or 3,460 W/m3. Compared with anaerobic digestion, this is almost 3 times as much power at a similar loading rate of 25 kg COD/m3/d. At this estimated maximum performance, the energy efficiency in a Microbial Fuel Cell will be 63%, whereas the energy efficiency in anaerobic digestion is 30%. For reaching this estimated power density, further studies should focus on the cathode as it is still the main limiting factor, leading to largest part of the energy losses in the MFC. |
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