Operando insights into ammonium-mediated lithium metal stabilization: surface morphology modulation and enhanced SEI development.

Lithium-ion batteries (LiBs) with graphite as an anode and lithiated transition metal oxide as a cathode are approaching their specific energy and power theoretical values. To overcome the limitations of LiBs, lithium metal anode with high specific capacity and low negative redox potential is necessary. However, practical application in rechargeable cells is hindered by uncontrolled lithium deposition manifesting, for instance, as Li dendrite growth which can cause formation of dead Li, short circuits and cell failure. The electrochemical behaviour of a protic additive (NH4PF6) in a carbonate-based electrolyte has been investigated by operando confocal Raman spectroscopy, in situ optical microscopy, and X-ray photoelectron spectroscopy, elucidating its functional mechanism. The ammonium cation promotes a chemical modification of the lithium metal anode-electrolyte interphase by producing an N-rich solid electrolyte interphase and chemically modifying the lithium surface morphology by electrochemical pitting. This novel method results in stable lithium deposition and stripping by a decreasing the local current density on the electrode, thus limiting dendritic deposition.

A Sustainable Gel Polymer Electrolyte for Solid-State Electrochemical Devices.

Nowadays, solid polymer electrolytes have attracted increasing attention for their wide electrochemical stability window, low cost, excellent processability, flexibility and low interfacial impedance. Specifically, gel polymer electrolytes (GPEs) are attractive substitutes for liquid ones due to their high ionic conductivity (10-3-10-2 S cm-1) at room temperature and solid-like dimensional stability with excellent flexibility. These characteristics make GPEs promising materials for electrochemical device applications, i.e., high-energy-density rechargeable batteries, supercapacitors, electrochromic displays, sensors, and actuators. The aim of this study is to demonstrate the viability of a sustainable GPE, prepared without using organic solvents or ionic liquids and with a simplified preparation route, that can substitute aqueous electrolytes in electrochemical devices operating at low voltages (up to 2 V). A polyvinyl alcohol (PVA)-based GPE has been cast from an aqueous solution and characterized with physicochemical and electrochemical methods. Its electrochemical stability has been assessed with capacitive electrodes in a supercapacitor configuration, and its good ionic conductivity and stability in the atmosphere in terms of water loss have been demonstrated. The feasibility of GPE in an electrochemical sensor configuration with a mediator embedded in an insulating polymer matrix (ferrocene/polyvinylidene difluoride system) has also been reported.

Crosslinked Chitosan Binder for Sustainable Aqueous Batteries.

The increased percentage of renewable power sources involved in energy production highlights the importance of developing systems for stationary energy storage that satisfy the requirements of safety and low costs. Na ion batteries can be suitable candidates, specifically if their components are economic and safe. This study focuses on the development of aqueous processes and binders to prepare electrodes for sodium ion cells operating in aqueous solutions. We demonstrated the feasibility of a chitosan-based binder to produce freestanding electrodes for Na ion cells, without the use of organic solvents and current collectors in electrode processing. To our knowledge, it is the first time that water-processed, freestanding electrodes are used in aqueous Na ion cells, which could also be extended to other types of aqueous batteries. This is a real breakthrough in terms of sustainability, taking into account low risks for health and environment and low costs.

Rheological Properties of Aqueous Sodium Alginate Slurries for LTO Battery Electrodes.

Rheological properties of electrode slurries have been intensively studied for manifold different combinations of active materials and binders. Standardly, solvent-based systems are under use, but a trend towards water-based electrode manufacturing is becoming more and more important. The different solvent is beneficial in terms of sustainability and process safety but is also accompanied by some disadvantages such as extraction of residual humidity and a higher complexity concerning slurry stability. Li4Ti5O12 (LTO) active material provides good long-term stability and can be processed in aqueous solutions. Combining the LTO active material with sodium alginate (SA) as a promising biobased polymer binder reveals good electrochemical properties but suffers from bad slurry stability. In this work, we present a comprehensive rheological study on material interactions in anode slurries consisting of LTO and SA, based on a complex interaction of differentially sized materials. The use of two different surfactants-namely, an anionic and non-ionic one, to enhance slurry stability, compared with surfactant-free slurry.

Study on Different Water-Based Binders for Li4Ti5O12 Electrodes.

In this study, Li4Ti5O12 (LTO) electrodes with different types of water-soluble binders are successfully coated upon aluminum foil. Electrodes containing solely sodium alginate (SA) as a binder or a mixed PVDF/carboxymethyl cellulose (CMC) binder show the most stable performance in 1 M LiPF6 in EC/DMC 1:1 in half cell vs. Li, with respect to cycle stability over 100 cycles at 1 C. The electrodes processed with a mixture of PVDF/SA show considerable fading and slightly worse values for rate capability. Each one of the different binders used is eco-friendly, and the whole processing can be performed without the use of organic solvents. Further advantages covering the whole production and recycling process, as well as safety issues during operation, encourage deeper research in this area.

Mucoadhesive Buccal Films for Local Delivery of Lactobacillus brevis.

The aim of this work was to prepare mucoadhesive buccal films for local release of Lactobacillus brevis CD2, which shows interesting anti-inflammatory properties due to its high levels of arginine deiminase. Hydroxypropylmethylcellulose-based films were prepared by means of a modified casting method, which allowed L. brevis CD2 loading on one side of the film, before its complete drying. Three batches of films were prepared, stored at +2-8 °C and +23-25 °C for 48 weeks and characterized in terms of physico-chemical and functional properties. For each batch, the L. brevis viable count and arginine deiminase activity were evaluated at different time points in order to assess functional property maintenance over time. Moreover, the mucoadhesive properties and ability of the films to release L. brevis CD2 were evaluated. A good survival of L. brevis CD2 was observed, particularly at the storage temperature of +2-8 °C, while the activity of arginine deiminase was maintained at both temperature values. Films showed good mucoadhesive properties and guaranteed a prolonged release of viable lactobacilli, which can be directed towards the whole buccal cavity or specific mucosa lesions. In conclusion, the proposed preparative method can be successfully employed for the production of buccal films able to release viable L. brevis CD2 cells that maintain the anti-inflammatory enzymatic activity.

Oxygen Redox Reaction in Ionic Liquid and Ionic Liquid-like Based Electrolytes: A Scanning Electrochemical Microscopy Study.

Improving the stability of the cathode interface is one of the critical issues for the development of high-performance Li/O2 batteries. The most critical feature to address is the development of electrolytes that mitigate side reactions that bring about cathode passivation. It is well-known that the superoxide anion (O2•-) plays a critical role. Here, we propose scanning electrochemical microscopy (SECM) as an analytical tool to screen the electrolyte of Li/O2 batteries. We demonstrate that by using SECM it is possible to evaluate the stability of O2•- and of the cathode to the passivation process occurring during the oxygen redox reaction. Specifically, we report a study carried out at a glassy carbon electrode in 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and in tetraethylene glycol dimethyl ether with LiTFSI, the latter ranging from the salt-in-solvent to solvent-in-salt regions.

A robust, modular approach to produce graphene-MOx multilayer foams as electrodes for Li-ion batteries.

Major breakthroughs in batteries would require the development of new composite electrode materials, with a precisely controlled nanoscale architecture. However, composites used for energy storage are typically a disordered bulk mixture of different materials, or simple coatings of one material onto another. We demonstrate here a new technique to create complex hierarchical electrodes made of multilayers of vertically aligned nanowalls of hematite (Fe2O3) alternated with horizontal spacers of reduced graphene oxide (RGO), all deposited on a 3D, conductive graphene foam. The RGO nanosheets act as porous spacers, current collectors and protection against delamination of the hematite. The multilayer composite, formed by up to 7 different layers, can be used with no further processing as an anode in Li-ion batteries, with a specific capacity of up to 1175 µA h cm-2 and a capacity retention of 84% after 1000 cycles. Our coating strategy gives improved cyclability and rate capacity compared to conventional bulk materials. Our production method is ideally suited to assemble an arbitrary number of organic-inorganic materials in an arbitrary number of layers.

Microbial fuel cells: From fundamentals to applications. A review.

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 organic waste 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 fuel cells and subsequently, microbial fuel cells is presented. Secondly, the development of the concept of microbial fuel cell into a wider range of derivative 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 an explanation of the electro catalysis of the oxygen reduction reaction and its behavior in neutral media, 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, through the utilization of energy output for practical applications, is described.

Graphite//LiNi0.5 Mn1.5 O4 Cells Based on Environmentally Friendly Made-in-Water Electrodes.

The performance of graphite//LiNi0.5 Mn1.5 O4 (LNMO) cells, both electrodes of which are made using water-soluble sodium carboxymethyl cellulose (CMC) binder, is reported for the first time. The full cell performed outstandingly over 400 cycles in the conventional electrolyte ethylene carbonate/dimethyl carbonate-1 m LiPF6 , and the delivered specific energy at the 100th, 200th, 300th, and 400th cycle corresponded to 82, 78, 73, and 66 %, respectively, of the initial energy value of 259 Wh kg-1 (referring to the sum of the two electrode-composite weights). The good stability of high-voltage, LNMO-CMC-based electrodes upon long-term cycling is discussed and the results are compared to those of LNMO-composite electrodes with polyvinylidene fluoride (PVdF). LNMO-CMC electrodes outperformed those with PVdF binder, displaying a capacity retention of 83 % compared to 62 % for the PVdF-based electrodes after 400 cycles at 1 C. CMC promotes a more compact and stable electrode surface than PVdF; undesired interfacial reactions at high operating voltages are mitigated, and the thickness of the passivation layer on the LNMO surface is reduced, thereby enhancing its cycling stability.

Co-generation of hydrogen and power/current pulses from supercapacitive MFCs using novel HER iron-based catalysts.

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 L day-1) for Pt, 0.83 mMd-1cm-2 (0.127 L day-1) for Fe-AAPyr and 0.8 mMd-1cm-2 (0.123 L 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.

Miniaturized supercapacitors: key materials and structures towards autonomous and sustainable devices and systems.

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 functional 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 activities 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.

Supercapacitive microbial fuel cell: Characterization and analysis for improved charge storage/delivery performance.

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 10ms pulse discharge and internal resistance of the cell was decreased by ∼47%. A model was constructed in order to predict the performance 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 21cm(3) would be capable of delivering a peak power output of approximately 25mW at 70mA, corresponding to ∼1300Wm(-3).

Self-feeding paper based biofuel cell/self-powered hybrid µ-supercapacitor integrated system.

For the first time, a paper based enzymatic fuel cell is used as self-recharged supercapacitor. In this supercapacitive enzymatic fuel cell (SC-EFC), the supercapacitive features of the electrodes are exploited to demonstrate high power output under pulse operation. Glucose dehydrogenase-based anode and bilirubin oxidase-based cathode were assembled to a quasi-2D capillary-driven microfluidic system. Capillary flow guarantees the continuous supply of glucose, cofactor and electrolytes to the anodic enzyme and the gas-diffusional cathode design provides the passive supply of oxygen to the catalytic layer of the electrode. The paper-based cell was self-recharged under rest and discharged by high current pulses up to 4mAcm(-2). The supercapacitive behavior and low equivalent series resistance of the cell permitted to achieve up to a maximum power of 0.87mWcm(-2) (10.6mW) for pulses of 0.01s at 4mAcm(-2). This operation mode allowed the system to achieve at least one order of magnitude higher current/power generation compared to the steady state operation.

Self-powered supercapacitive microbial fuel cell: The ultimate way of boosting and harvesting power.

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 19 mW (84.4 Wm(-2), 152 Wm(-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.

The effect of ring nitrogen atoms on the homolytic reactivity of phenolic compounds: understanding the radical-scavenging ability of 5-pyrimidinols.

Six substituted 5-pyrimidinols were synthesized, and the thermochemistry and kinetics of their reactions with free radicals were studied and compared to those of equivalently substituted phenols. To assess their potential as hydrogen-atom donors to free radicals, we measured their O-H bond dissociation enthalpies (BDEs) using the radical equilibration electron paramagnetic resonance technique. This revealed that the O-H BDEs in 5-pyrimidinols are, on average, about 2.5 kcal mol(-1) higher than those in equivalently substituted phenols. The results are in good agreement with theoretical predictions, and confirm that substituent effects on the O-H BDE of 5-pyrimidinol are essentially the same as those on the Obond;H BDE in phenol. The kinetics of the reactions of these compounds with peroxyl radicals has been studied by their inhibition of the AIBN-initiated autoxidation of styrene, and with alkyl and alkoxyl radicals by competition kinetics. Despite their larger O-H BDEs, 5-pyrimidinols appear to transfer their phenolic hydrogen-atom to peroxyl radicals as quickly as equivalently substituted phenols, while their reactivity toward alkyl radicals far exceeds that of the corresponding phenols. We suggest that this rate enhancement, which is large in the case of alkyl radical reactions, small in the case of peroxyl radical reactions, and nonexistent in the case of alkoxyl radical reactions, is due to polar effects in the transition states of these atom-transfer reactions. This hypothesis is supported by additional experimental and theoretical results. Despite this higher reactivity of 5-pyrimidinols towards radicals compared to phenols, electrochemical measurements indicate that they are more stable to one-electron oxidation than equivalently substituted phenols. For example, the 5-pyrimidinol analogues of 2,4,6-trimethylphenol and butylated hydroxytoluene (BHT) were found to have oxidation potentials approximately 400 mV higher than their phenolic counterparts, but reacted roughly one order of magnitude faster with alkyl radicals and at about the same rate with peroxyl radicals. The 5-pyrimidinol structure should, therefore, serve as a useful template for the rational design of novel air-stable radical scavengers and chain-breaking antioxidants that are more effective than phenols.