Development of new nanostructured electrodes in Microbial Fuel Cells (MFCs)

The aim of my thesis work is to investigate new nanostructured materials, obtained by the electrospinning technique, in order to design 3D arrangement of the electrodes, leading thus to improve the energy efficiency of energy production devices, such as microbial fuel cells (MFCs). The carbon nanofibers reveal to be the most promising material in the field of bio electrochemistry; in fact, up to now the best performing microbial fuel cells are fabricated using carbon and carbon based material electrodes. To further enhance the performances of bio anodes and bio cathodes, a set of properties are then required to be overcome, such as a proper surface morphology and chemistry, good biofilm adhesion and electron transfer, and a good electrical conductivity. This work aims to demonstrate that the electrospun nanofibers own all the necessary properties, revealing themselves as the most innovative and promising structures for anodes and cathodes for microbial fuel cells. The nanofibers ensure all the properties listed above; in particular, during my Ph.D. I have investigated and studied the carbon based nanofibers to be applied as cathode and as anode in these kind of the devices. In this thesis, it will be demonstrated that the nanostructured electrodes improve the efficiency devices thanks both to the low impedance and to the interaction with the microorganisms. The high micrometric porosity characteristics of the realized anodic material create the ideal habitat for the microorganism’s proliferation. Moreover, different solution for the cathode material have been developed using ceramic nanofibers, such as MnxOy nanofibers and carbon nanofibers, in order to improve the performance of the devices. The layer made of these nanofibers, in fact, catalyzes the oxygen reduction reaction if the oxygen is used as terminal electron acceptor in the devices; thus these catalysts can substitute the platinum layer, which is the most used today, granting a cheaper and eco friendlier material

3D Composite PDMS/MWCNTs Aerogel as High-Performing Anodes in Microbial Fuel Cells

Porous 3D composite materials are interesting anode electrodes for single chamber microbial fuel cells (SCMFCs) since they exploit a surface layer that is able to achieve the correct biocompatibility for the proliferation of electroactive bacteria and have an inner charge transfer element that favors electron transfer and improves the electrochemical activity of microorganisms. The crucial step is to fine-tune the continuous porosity inside the anode electrode, thus enhancing the bacterial growth, adhesion, and proliferation, and the substrate’s transport and waste products removal, avoiding pore clogging. To this purpose, a novel approach to synthetize a 3D composite aerogel is proposed in the present work. A 3D composite aerogel, based on polydimethylsiloxane (PDMS) and multi-wall carbon nanotubes (MWCNTs) as a conductive filler, was obtained by pouring this mixture over the commercial sugar, used as removable template to induce and tune the hierarchical continuous porosity into final nanostructures. In this scenario, the granularity of the sugar directly affects the porosities distribution inside the 3D composite aerogel, as confirmed by the morphological characterizations implemented. We demonstrated the capability to realize a high-performance bioelectrode, which showed a 3D porous structure characterized by a high surface area typical of aerogel materials, the required biocompatibility for bacterial proliferations, and an improved electron pathway inside it. Indeed, SCMFCs with 3D composite aerogel achieved current densities of (691.7 ± 9.5) mA m(−2), three orders of magnitude higher than commercial carbon paper, (287.8 ± 16.1) mA m(−2)

Semiconducting Electrospun Nanofibers for Energy Conversion

Nowadays, semiconducting thin films, thanks to their unique and excellent properties, play a crucial role for the design of devices for energy conversion and storage, such as solar cells, perovskite solar cells, lithium-ion batteries (LIBs), and fuel cells. Since the nanostructured arrangements can improve the behavior of the materials in several application fields, in this chapter we propose the electrospinning process as electro-hydrodynamic deposition to obtain semiconducting materials, in the form of nanofiber mats. The nanostructured mats are able to provide high surface-area-to-volume ratio and a microporous structure, which are crucial aspects for energetic application. In this chapter, we deeply describe the electrospinning process and how nanofibers obtained can be used in energy devices, satisfying all the requirements to improve overall final performances

The Role of Material Selection and Microfluidics for Optimized Energy Conversion in Microbial Fuel Cells

This chapter book aims to present some key aspects, which play a crucial role to optimize the energy conversion process occurring in microbial fuel cells (MFCs): fluid dynamics and the materials selected as anodic electrodes. MFCs are (bio)-electrochemical devices that directly convert chemical energy into electrical energy, thanks to the metabolic activity of some bacteria. In the anodic compartment, these bacteria, named exoelectrogens, are able to oxidize the organic matter, directly releasing the electrons to the anode surface. The conversion process can be deeply influenced by how the electrolyte solution, containing the carbon-energy source, moves inside the device. For this reason, fluid dynamic modeling is an important tool to explain the correlation between the fluid flow and power output production, optimizing also the overall MFC performance. Moreover, the morphology of anode electrodes results to be essential to guarantee and enhance the bacteria proliferation on them, improving the energy conversion

Development of New Nanostructured Electrodes for Electrochemical Conversion: Energy and Fuels from the Environment

During the last decade, carbon-based nanofibers emerged as an important class of materials for the fabrication of electrodes for electrochemical energy conversion. Indeed carbon-based nanofibers combine high electrochemical stability and high porosity to high mechanical flexibility and low weight, resulting in a unique and versatile material for the design and fabrication of energy-related devices. This chapter aims to show and analyze new nanostructured materials, obtained by electrospinning technique, in order to design 3D arrangement of the electrodes and to improve the energy efficiency of energy production devices. Indeed, the design of new 3D nanostructured electrodes enhances the energy efficiency of these devices, optimizing the energy production, obtained by new renewable energy technologies. The chapter is focused on those devices able to generate power output through the electrochemical conversion of different fuels, like wastes, and environmental compounds, such as CO2

Electrospun PEO/PEDOT:PSS Nanofibers for Wearable Physiological Flex Sensors

Flexible sensors are fundamental devices for human body monitoring. The mechanical strain and physiological parameters coupled sensing have attracted increasing interest in this field. However, integration of different sensors in one platform usually involves complex fabrication process-flows. Simplification, even if essential, remains a challenge. Here, we investigate a piezoresistive and electrochemical active electrospun nanofibers (NFs) mat as the sensitive element of the wearable physiological flex sensing platform. The use of one material sensitive to the two kinds of stimuli reduces the process-flow to two steps. We demonstrate that the final NFs pH-Flex Sensor can be used to monitor the deformation of a human body joint as well as the pH of the skin. A unique approach has been selected for pH sensing, based on Electrochemical Impedance Spectroscopy (EIS). A linear dependence of the both the double layer capacitance and charge transfer re-sistance with the pH value was obtained by EIS, as well as a linear trend of the electrical resistance with the bending deformation. Gauge factors values calculated after the bending test were 45.84 in traction and 208.55 in compression mode, reflecting the extraordinary piezoresistive behavior of our nanostructured NFs

Design and Optimization of Piezoresistive PEO/PEDOT:PSS Electrospun Nanofibers for Wearable Flex Sensors

Flexible strain sensors are fundamental devices for application in human body monitoring in areas ranging from health care to soft robotics. Stretchable piezoelectric strain sensors received an ever-increasing interest to design novel, robust and low-cost sensing units for these sensors, with intrinsically conductive polymers (ICPs) as leading materials. We investigated a sensitive element based on crosslinked electrospun nanofibers (NFs) directly collected and thermal treated on a flexible and biocompatible substrate of polydimethylsiloxane (PDMS). The nanostructured active layer based on a blend of poly(ethylene oxide) (PEO) and poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS) as the ICP was optimized, especially in terms of the thermal treatment that promotes electrical conductivity through crosslinking of PEO and PSS, preserving the nanostructuration and optimizing the coupling between the sensitive layer and the substrate. We demonstrate that excellent properties can be obtained thanks to the nanostructured active materials. We analyzed the piezoresistive response of the sensor in both compression and traction modes, obtaining an increase in the electrical resistance up to 90%. The Gauge Factors (GFs) reflected the extraordinary piezoresistive behavior observed: 45.84 in traction and 208.55 in compression mode, which is much higher than the results presented in the literature for non-nanostructurated PEDOT

Enhanced Power Extraction with Sediment Microbial Fuel Cells by Anode Alternation

Sediment microbial fuel cells (SMFCs) are energy harvesting devices where the anode is buried inside marine sediment, while the cathode stays in an aerobic environment on the surface of the water. To apply this SCMFC as a power source, it is crucial to have an efficient power management system, leading to development of an effective energy harvesting technique suitable for such biological devices. In this work, we demonstrate an effective method to improve power extraction with SMFCs based on anodes alternation. We have altered the setup of a traditional SMFC to include two anodes working with the same cathode. This setup is compared with a traditional setup (control) and a setup that undergoes intermittent energy harvesting, establishing the improvement of energy collection using the anodes alternation technique. Control SMFC produced an average power density of 6.3 mW/m2 and SMFC operating intermittently produced 8.1 mW/m2. On the other hand, SMFC operating using the anodes alternation technique produced an average power density of 23.5 mW/m2. These results indicate the utility of the proposed anodes alternation method over both the control and intermittent energy harvesting techniques. The Anode Alternation can also be viewed as an advancement of the intermittent energy harvesting method