Optimisation of Microbial Fuel Cells (MFCs) through bacterial-robot interaction

For over 100 years, Microbial Fuel Cells (MFCs) have been developed as eco-friendly alternatives for generating electricity via the oxidation of organic matter by bacteria. In the early 2000s, collectives of MFCs were proven fea-sible energy providers for low-power robots such as Gastrobot and EcoBots. Even though individual MFC units are low in power, significant progress has been achieved in terms of MFC materials and configurations, enabling them to generate higher output levels. However, up to this date, MFCs are produced and matured using conventional laboratory methods that can take up to three months to bring the MFCs to their maximum power aptitudes. In this work, an approach to use a low-cost (£1.5k) RepRap liquid handling robot called EvoBot was employed with the aim to automate the maturing process of MFCs and allow them to reach their maximum power ability in a shorter time span. Initially, the work focused on establishing an interface and interconnection between the living cells (in the MFC) and the robotic platform, and investigating whether the MFC voltage can trigger a feedback loop feeding mechanism. It was shown that the robot successfully matured the MFCs in just 6 days and, they were also 1.4 times more powerful than conventionally matured MFCs (from 19.1 mW/m2 to 26.5 mW/m2). This work took a rounded approach in improving the overall MFC perfor-mance. 3D-printable materials that can emerge from EvoBot were investi-gated for fabricating MFCs. MFCs employing these materials improved their power output by almost 50% (from 66μW to 130 μW) compared to the ones based on conventional, fluorinated materials. Furthermore, EvoBot was able to improve the fuel supply frequency and composition using evolutionally algorithms. For the first time, this project has demonstrated that the fabrica-tion, maintenance and power generation of MFCs can be optimised via the interaction and support of a dedicated robotic system

Developing 3D-printable cathode electrode for monolithically printed microbial fuel cells (MFCs)

© 2020 by the authors. Microbial Fuel Cells (MFCs) employ microbial electroactive species to convert chemical energy stored in organic matter, into electricity. The properties of MFCs have made the technology attractive for bioenergy production. However, a challenge to the mass production of MFCs is the time-consuming assembly process, which could perhaps be overcome using additive manufacturing (AM) processes. AM or 3D-printing has played an increasingly important role in advancing MFC technology, by substituting essential structural components with 3D-printed parts. This was precisely the line of work in the EVOBLISS project, which investigated materials that can be extruded from the EVOBOT platform for a monolithically printed MFC. The development of such inexpensive, eco-friendly, printable electrode material is described below. The electrode in examination (PTFE-FREE-AC), is a cathode made of alginate and activated carbon, and was tested against an off-the-shelf sintered carbon (AC-BLOCK) and a widely used activated carbon electrode (PTFE-AC). The results showed that the MFCs using PTFE-FREE-AC cathodes performed better compared to the PTFE-AC or AC-BLOCK, producing maximum power levels of 286 μW, 98 μW and 85 μW, respectively. In conclusion, this experiment demonstrated the development of an air-dried, extrudable (3D-printed) electrode material successfully incorporated in an MFC system and acting as a cathode electrode

Gelatin as a promising printable feedstock for microbial fuel cells (MFC)

© 2016 Hydrogen Energy Publications LLC The microbial fuel cell (MFC) is an energy transducer that can directly produce electricity from bacterial oxidation of organic matter. MFCs consist of two reaction chambers (anode and cathode) separated by a semipermeable membrane. This study describes the work carried out towards the optimization of critical MFC components, with 3D fabricated materials. The response of the optimized fuel cells, which were fed with soft materials such as gelatin, alginate and Nafion™, is also reported. The optimised components were the membrane and the cathode electrode. A conventional Nafion membrane was substituted with a custom made terracotta sheet and the electrode used was a single sheet of carbon veil coated with an activated carbon paste. The results showed that among the soft materials tested within the anodic chamber, gelatin performed the best; it also revealed that even after a 10-day starvation period gelatin demonstrated better longevity. These results show that MFCs have the potential to be 3D-printed monolithically using the EVOBOT platform

Urine in bioelectrochemical systems: An overall review

In recent years, human urine has been successfully used as an electrolyte and organic substrate in bioelectrochemical systems (BESs) mainly due of its unique properties. Urine contains organic compounds that can be utilised as a fuel for energy recovery in microbial fuel cells (MFCs) and it has high nutrient concentrations including nitrogen and phosphorous that can be concentrated and recovered in microbial electrosynthesis cells and microbial concentration cells. Moreover, human urine has high solution conductivity, which reduces the ohmic losses of these systems, improving BES output. This review describes the most recent advances in BESs utilising urine. Properties of neat human urine used in state‐of‐the‐art MFCs are described from basic to pilot‐scale and real implementation. Utilisation of urine in other bioelectrochemical systems for nutrient recovery is also discussed including proofs of concept to scale up systems

3D-Printable Cathode Electrode for Monolithically Printed Microbial Fuel Cells (MFCs)

Introduction Biological fuel cells (BFCs) are an increasingly growing area of research as it beholds long-term sustainable advantages over conventional fuel cells. Microbial Fuel Cells (MFCs) are just one type of BFCs, which as the name implies, employ microbial electroactive species to facilitate the conversion of chemical energy stored in organic matter, into electricity. The properties of MFCs have successfully made the technology a primary source of energy for low-power autonomous robots 1 and off-grid urinal units 2. However, a hindrance to the mass production of MFC units is the time-consuming assembly process, which could perhaps be overcome using additive manufacturing (AM) processes. AM or 3D-printing has played an increasing role in advancing the MFC technology, by substituting essential structural components i.e. chassis and separators, with 3D-printed parts 3,4. This is precisely the line of work in the EVOBLISS project, which is investigating materials that can be extruded from the EVOBOT platform 5 for a potentially monolithically printed MFC. The development of such inexpensive, conductive, printable electrode material is described below as well as the advances of this material as a cathode electrode on air-breathing cathodes. Material and Methods Three triplicates of analytical size MFCs were assembled for this experiment using laser-cut acrylic sheets. The MFCs had a 25mL anode chamber, a CMI-700 cation exchange membrane (Membrane International, USA) as separator and three different electrodes forming the air-breathing cathodes. A gas diffusion electrode with polytetrafluoroethylene (PTFE) (60% wt. Sigma Aldrich, UK) painted carbon veil sheet that acted as the hydrophilic supporting material for a microporous layer (MPL) was used as the control. This was prepared with a mixture of activated carbon (80 g/120 mL solution. G Baldwin & Co, UK), PTFE and distilled water. The materials tested were a) a solid commercially available sintered Carbon Block CTO (Water Filter Man LTD, UK) and b) a custom made activated carbon-alginate paste which was made using ground activated carbon (80g) and alginate (Minerals Water Ltd, 20 g) that was then mixed with distilled water until a thick paste was made. The paste was then extruded from a syringe directly onto the membrane (10 ml) and dried/solidified on the bench for 24 hrs. The final weight of all the dried electrodes was 3.8 ± 0.2 g. The cells were inoculated with activated sludge (Wessex Water, UK) supplemented with full strength Tryptone Yeast Extract (1.5% w/v) and fed with human urine. Results The results showed that the MFCs using alginate electrode as cathode electron and oxygen receiver performed better compared to the MPL or sintered carbon having a maximum power transfer point at 286 μW, 98 μW and 85 μW respectively. An important factor to consider in the effort to improve the MFC performance is not only the power output but also the cost effectiveness of the materials, especially when using alginate. MPL cathode electrode requires a PTFE coated carbon veil sheet as well as a mixture of PTFE and carbon. PTFE is a highly toxic and expensive material (£138/500ml, Sigma Aldrich, 2017) compared to food grade alginate which only costs £8.76 per 500g. Moreover, the alginate electrode does not require a supporting material thus the cost was reduced further by removing the carbon veil from the assembly. Conclusion In conclusion, this experiment demonstrated that the development of an air-dried, extrude-able electrode material (similar to 3D printing) could successfully be incorporated in an MFC system and act as a cathode electrode. Such a development brings the field a step closer to monolithically printable MFCs, which can be made using the EVOBOT platform. References I. Ieropoulos, J. Greenman, C. Melhuish, and I. Horsfield, in Artificial Life Models in Hardware, p. 185–211 (2009). I. A. Ieropoulos et al., Environ. Sci. Water Res. Technol., 2, 336–343 (2016). J. You, R. J. Preen, L. Bull, J. Greenman, and I. Ieropoulos, Sustain. Energy Technol. Assessments, 19, 94–101 (2017). H. Philamore, J. Rossiter, P. Walters, J. Winfield, and I. Ieropoulos, J. Power Sources, 289, 91–99 (2015). A. Faíña, F. Nejatimoharrami, and K. Stoy, in IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), (2015)

Towards monolithically printed MFCs: Development of a 3D-printable membrane electrode assembly (MEA)

Additive manufacturing (3D-printing) and microbial fuel cells (MFCs) are two rapidly growing technologies which have been previously combined to advance the development of the latter. In the same line of work, this paper reports on the fabrication of novel membrane electrode assemblies (MEAs) using materials that can be 3D printed or extruded from the EvoBot platform. Materials such as air dry terracotta, air dry Fimo™ and standard terracotta were tested against conventional cation exchange membrane (CEM) material. The MEA was fabricated by painting the materials with custom made graphite coating. The results showed that the MFCs with the printable materials outperformed those using conventional CEM. Economic analysis showed that the utilization of ceramics-based separator can reduce significantly the overall costs. These findings suggest that monolithically printed MFCs may be feasible, as printable MEAs can improve MFCs performance, and help realise mass manufacturing at lower cost

Supercapacitive paper based microbial fuel cell: High current/power production within a low cost design

Microbial fuel cells (MFCs) with paper separators and liquid containing elements were investigated in supercapacitive mode. MFCs (15 mL) in a supercapacitive configuration, consisted of plain wrapped carbon veil anode (negative) and conductive latex cathode (positive). The internal supercapacitor is discharged galvanostatically and is self-recharged as red-ox reactions occur on both electrodes. MFCs were discharged at different current pulses varying from 1 mA to 7 mA. The MFCs had an equivalent series resistance of 41.2 ± 3.5 Ω caused mainly by the cathode. A maximum power of 1.380 ± 0.083 mW (0.092 ± 0.006 mW mL−1) was measured. Durability tests were conducted over 24 h collecting 1000 discharge cycles (0.5 s) and self-recharges (85 s) at a current of 1 mA. Over time the anode potential dropped causing a decline in performance perhaps due to evaporation of liquid from the pyramidal structure. Resistance and apparent capacitance measured during the durability test remained approximately constant during the cycles