Search

Super-concentrated electrolyte solutions are of increasing interest for safer and more stable lithium and post-lithium batteries. The combination of 7Li and 17O (at natural abundance) nuclear magnetic resonance (NMR) and electrochemical characterization is proposed here as an effective approach to investigate the Li+ solvation structures and properties of electrolytes featuring tetraethylene glycol dimethyl ether (TEGDME) and lithium-bis(trifluoromethane sulfonyl) imide (LiTFSI). Five different formulations from salt-in-solvent to solvent-in-salt with LiTFSI at different concentrations (0.1 m, 0.5 m, 2 m, 4 m, 5 m) are investigated. The NMR results, also supported by physico-chemical characterizations such as thermal gravimetric analyses, differential scanning calorimetry, specific conductivity and viscosity, give information about the association of Li+ ions with anion and solvent molecules, allowing a deeper knowledge on the relationships among structure and functional properties of super-concentrated solutions.

In the past 10-15 years, the microbial fuel cell (MFC) technology has captured the attention of the scientific community for the possibility of transforming organics directly into electricity through microbially catalyzed anodic, and microbial/enzymatic/abiotic cathodic electrochemical reactions. In this review, several aspects of the technology are considered. Firstly, a brief history of abiotic to biological and subsequently, microbial fuel cells is presented. Secondly, the development of the concept of microbial fuel cell into a wider range of derivate technologies, called bioelectrochemical systems, is described introducing briefly microbial electrolysis cells, microbial desalination cells and microbial electrosynthesis cells. The focus is then shifted to electroactive biofilms and electron transfer mechanisms involved with solid electrodes. Carbonaceous and metallic anode materials are then introduced, followed by the electro catalysis of the oxygen reduction reaction and its behavior in neutral media is explained, from recent studies. Cathode catalysts based on carbonaceous, platinum-group metal and platinum-group-metal-free materials are presented, along with membrane materials with a view to future directions. Finally, microbial fuel cell practical implementation, with utilisation of energy output for practical applications, is described.

The Special Section “Microbial fuel cells: From fundamentals to applications” covers many diverse and multidisciplinary aspects of the entire microbial electrochemical field, with a special emphasis on microbial and abiotic/microbial electron transfer mechanisms at the anode and cathode electrodes. New materials are presented as low-cost catalysts for oxygen reduction or H2 evolution reactions, as alternatives to exotic/expensive metals. Different anode materials, structures, and configurations are shown with impressive results. Anodic biofilms have been identified and extensively studied, as well as newspecies and mixed-culture biofilms. Innovative designs and working conditions of microbial electrolytic cells for H2 production or NH3 recovery with outstanding results are also presented.

Supercapacitive microbial fuel cells with various anode and cathode dimensions were investigated in order to determine the effect on cell capacitance and delivered power quality. The cathode size was shown to be the limiting component of the system in contrast to anode size. By doubling the cathode area, the peak power output was improved by roughly 120% for a 10 ms pulse discharge and internal resistance of the cell was decreased by $47%. A model was constructed in order to predict the perfor- mance of a hypothetical cylindrical MFC design with larger relative cathode size. It was found that a small device based on conventional materials with a volume of approximately 21 cm3 would be capable of delivering a peak power output of approximately 25 mW at 70 mA, corresponding to 1300 W m"3.

Supercapacitors (SCs) are playing a key role for the development of self-powered and self-sustaining integrated systems for different fields ranging from remote sensing, robotics and medical devices. SC miniaturization and integration into more complex systems that include energy harvesters and func- tional devices are valuable strategies that address system autonomy. Here, we discuss about novel SC fabrication and integration approaches. Specifically, we report about the results of interdisciplinary ac- tivities on the development of thin, flexible SCs by an additive technology based on Supersonic Cluster Beam Deposition (SCBD) to be implemented into supercapacitive electrolyte gated transistors and supercapacitive microbial fuel cells. Such systems integrate at materials level the specific functions of devices, like electric switch or energy harvesting with the reversible energy storage capability. These studies might open new frontiers for the development and application of new multifunction-energy storage elements.

In this work, four different supercapacitive microbial fuel cells (SC-MFCs) with carbon brush as the anode and an air-breathing cathode with Fe-Aminoantipyrine (Fe-AAPyr) as the catalyst have been investigated using galvanostatic discharges. The maximum power (Pmax) obtained was in the range from 1.7 mW to 1.9 mW for each SC-MFC. This in-series connection of four SC-MFCs almost quadrupled Pmax to an operating voltage of 3025 mV and a Pmax of 8.1 mW, one of the highest power outputs reported in the literature. An additional electrode (AdHER) connected to the anode of the first SC-MFC and placed in the fourth SC-MFC evolved hydrogen. The hydrogen evolution reaction (HER) taking place at the electrode was studied on Pt and two novel platinum group metal-free (PGM-free) catalysts: Fe-Aminoantipyrine (Fe-AAPyr) and Fe-Mebendazole (Fe-MBZ). The amount of H2 produced was estimated using the Faraday law as 0.86 mMd-1cm-2 (0.132 LH2 day-1) for Pt, 0.83 mMd-1cm-2 (0.127 LH2 day-1) for Fe-AAPyr and 0.8 mMd-1cm-2 (0.123 LH2 day-1) for Fe-MBZ. Hydrogen evolution was also detected using gas chromatography. While HER was taking place, galvanostatic discharges were also performed showing simultaneous H2 production and pulsed power generation with no need of external power sources.

In this work, for the first time, we demonstrate a supercapacitive microbial fuel cell which integrates the energy harvesting function of a microbial fuel cell (MFC) with the high-power operation of an internal supercapacitor. The pursued strategies are: (i) the increase of the cell voltage by the use of high potential cathodes like bilirubin oxidase (BOx) or iron-aminoantipyrine (Fe-AAPyr); (ii) the use of an additional capacitive electrode (additional electrode, AdE) which is short-circuited with the MFC cathode and coupled with the MFC anode (MFC-AdE). The high working potential of BOx cathode and the low impedances of the additional capacitive electrode and the MFC anode permitted to achieve up to 19mW (84.4Wm-2, 152Wm-3), the highest power value ever reported for MFCs. Exploiting the supercapacitive properties of the MFC electrodes allows the system to be simpler, cheaper and more efficient without additional electronics management added with respect to an MFC/external supercapacitor coupling. The use of the AdE makes it possible to decouple energy and power and to achieve recharge times in the order of few seconds making the system appealing for practical applications.