Electrode Components Research Articles

Exploring Binder and Solvent for Depositing Activated Carbon Electrode on Indium–Tin-Oxide Substrate to Prepare Supercapacitors

Supercapacitor electrode slurry is prepared for mass production by mixing activated carbon powder, conductive agent, and binder, which is then deposited on a substrate using the doctor-blade method. Polyvinylidene fluoride (PVDF) and 1-methyl-2-pyrrolidone (NMP) are used as binder and solvent, respectively, to form the electrode slurry on a metal substrate. In this study, ethyl cellulose (EC) is evaluated as a binder to prepare an electrode on an indium-tin-oxide (ITO) substrate obtaining transparent supercapacitors. Terpineol and isopropyl alcohol (IPA) are compared as suitable solvents for the EC binder. When terpineol is employed as a solvent, the conductive agent is uniformly deposited around the activated carbon powder. An electrode prepared using EC and terpineol exhibits slightly lower specific capacitance and rate performance than that using conventional PVDF and NMP. However, the electrode prepared using EC and terpineol securely adheres to the electrode components, resulting in a robust electrode. In contrast, an electrode prepared using EC and IPA exhibits high charge transfer resistance at the interface of the electrode/electrolyte, leading to a low specific capacitance and rate performance. Thus, ecofriendly EC and terpineol can substitute the conventional PVDF and NMP for depositing activated carbon powder on an ITO substrate, while improving the specific capacitance of manufactured electrodes.

Melanin’s Semiconductor Nature and His Polymer Structure Successfully Modifies Sulfur Cathode and Increases Efficiency on Li-S Batteries

Dynamics of change in impedance spectra and electrochemical parameters of the Li-S rechargeable batteries with non-aqueous liquid electrolyte 0.7 M LiIm, 0.25 M LiNO3, DME: DOL (2:1) during storage after assembly and cycling have been shown. For modification of the Sulfur cathode, we used the different types of melanin. Our results confirm that melanin can be used as a promising component of sulfur-based electrodes

Eco-Friendly Water-Processable Polyimide Binders with High Adhesion to Silicon Anodes for Lithium-Ion Batteries.

Silicon is an attractive anode material for lithium-ion batteries (LIBs) because of its natural abundance and excellent theoretical energy density. However, Si-based electrodes are difficult to commercialize because of their significant volume changes during lithiation that can result in mechanical damage. To overcome this limitation, we synthesized an eco-friendly water-soluble polyimide (W-PI) precursor, poly(amic acid) salt (W-PAmAS), as a binder for Si anodes via a simple one-step process using water as a solvent. Using the W-PAmAS binder, a composite Si electrode was achieved by low-temperature processing at 150 °C. The adhesion between the electrode components was further enhanced by introducing 3,5-diaminobenzoic acid, which contains free carboxylic acid (–COOH) groups in the W-PAmAS backbone. The –COOH of the W-PI binder chemically interacts with the surface of Si nanoparticles (SiNPs) by forming ester bonds, which efficiently bond the SiNPs, even during severe volume changes. The Si anode with W-PI binder showed improved electrochemical performance with a high capacity of 2061 mAh g−1 and excellent cyclability of 1883 mAh g−1 after 200 cycles at 1200 mA g−1. Therefore, W-PI can be used as a highly effective polymeric binder in Si-based high-capacity LIBs.

Polyethylene Oxide as a Multifunctional Binder for High-Performance Ternary Layered Cathodes.

Nickel cobalt manganese ternary cathode materials are some of the most promising cathode materials in lithium-ion batteries, due to their high specific capacity, low cost, etc. However, they do have a few disadvantages, such as an unstable cycle performance and a poor rate performance. In this work, polyethylene oxide (PEO) with high ionic conductance and flexibility was utilized as a multifunctional binder to improve the electrochemical performance of LiNi0.6Co0.2Mn0.2O2 cathode materials. Scanning electron microscopy showed that the addition of PEO can greatly improve the adhesion of the electrode components and simultaneously enhance the integrity of the electrode. Thus, the PEO-based electrode (20 wt% PEO in PEO/PVDF) shows a high electronic conductivity of 19.8 S/cm, which is around 15,000 times that of the pristine PVDF-based electrode. Moreover, the PEO-based electrode exhibits better cycling stability and rate performance, i.e., the capacity increases from 131.1 mAh/g to 147.3 mAh/g at 2 C with 20 wt% PEO addition. Electrochemical impedance measurements further indicate that the addition of the PEO binder can reduce the electrode resistance and protect the LiNi0.6Co0.2Mn0.2O2 cathode materials from the liquid electrolyte attack. This work offers a simple yet effective method to improve the cycling performance of the ternary cathode materials by adding an appropriate amount of PEO as a binder in the electrode fabrication process.

Methodology and Electrochemical Techniques for Development of All-Solid-State Batteries

Despite some progress performed, state-of-the-art lithium ion batteries still require improvements in energy and power to extend the range of electric vehicles and reduce charging time. In this domain, all-solid-state batteries are viable alternatives to conventional batteries employing organic electrolytes because of their benefits, i.e., high power density, high energy density, long-life operation and safety. These advantages stem from the great features of inorganic solid electrolytes, which are single ion conductor, so a high lithium ion transport number, and no-liquid nature. In particular, the sulfide-based solid electrolytes possess favorable mechanical properties, allowing all-solid-state batteries to be easily prepared via simple mixing and cold-pressing processes, facilitating the scale-up.Sulfide-based solid-electrolytes can potentially be employed in conjunction with a lithium metal negative electrode and 5V-class high voltage positive electrode material. Indeed, lithium metal is believed to be the most promising negative electrode due to its specific large capacity (3862 mAh.g-1), low volumetric density (0.534 g.cm-3 at 20°C) and the lowest electrochemical potential (-3.03V vs ENH). Nevertheless, like most metal, lithium metal is morphologically dynamic. Its surface morphology is modified, since during the electrochemical cycling, a part of lithium migrates to the other electrode to react and is then plating on its surface heterogeneously, leading to a volume change and sometimes dendrite growth with potential internal short circuit and life-threatening accidents. Ceramic solid electrolytes have been considered to be the ideal solution to prevent dendrite growth because of their high shear modulus and high lithium transference number. In the same time, the chemical nature and composition of ceramic solid electrolyte can affect its reactivity with lithium metal. In the same time, the electrochemical stability of solid electrolyte depending of its nature and composition is a key parameter to mix it with the different components of positive electrode as active materials and electronic conductors to ensure the better percolation and performances. The oxide–based ceramic solid electrolytes can be shaped by sintering at high temperature, leading to a grain and –grain boundary microstructure with some porosity, facilitating the lithium dendrite growth through grain boundaries. Due to the low density and plasticity of sulfide based inorganic solid electrolyte, the dendrite growth through the particle-particle contact can be reduced but still present.Hence different parameters can influence the performances and aging of all solid state ceramic battery. To explore them, various electrochemical technics and associated specific treatments can be developed to extract and identify each phenomena and ensure the better development of this technology. A specific sequential methodology will be presented with different examples from the materials, interfaces with lithium metal, pseudo-composites and temperature effects up to aging of total all-solid–state ceramic battery based on sulfide technology. The extracted different parameters and the relationship between them will be presented.

NeocarbonixTM Electrodes for Li-Ion Batteries: Increased $/Kwh Savings and Scalability

Energy storage electrodes are often limited in their electrochemical stability and electrical performance by polymer binders used in the active material layer. Binders are also used to adhere the active material to the current collector. Binders are usually polymeric resins used in electrodes to mechanically hold active material powders together. Active materials may be graphite, silicon-carbon, silicon oxides for anodes, and lithium metal oxides for cathodes in the case of lithium-ion batteries (LIBs). They can also be high surface area activated carbons, in the case of EDLCs. The binders are a passive component in energy storage electrodes and they carry limitations in terms of electrical conductivity, thermal stability and chemical stability.Capacity and C-rate capabilities in LIBs and ESR in EDLCs suffer because electrically insulating inactive binder material takes up space within the electrode material. Meanwhile lifetime at temperature and voltage can suffer as the binder material interacts with the internal electrochemical system of the energy storage device. Additionally, thermal stability of the electrode can be limited both by the electrochemical activity of the binder material as well as phase transitions of the binder material. Performance of energy storage systems using conventional electrodes in particularly high power applications may be limited by the thermal stability of the binder as well. Internal heat dissipation in those applications can be a serious concern when combined with ambient temperatures, especially in space-constrained environments or in applications where thermal management is at a premium. Energy density is also limited by the thickness of active materials that a standard coating process with binder-containing slurry can yield. Finally, cost of electrode production is dramatically impacted by the slurry drying step, as strong solvents with high boiling point (e.g. NMP) must be used to dissolve polymer binders, and are difficult to evaporate.Nanoramic has developed an alternate solution - NeocarbonixTM - an electrode platform technology that effectively replaces polymer high molecule binders PVDF. Results have been demonstrated for both LIB cathodes and EDLC electrodes. Nanoramic's Neocarbonix electrodes have significantly lower ESR, better C-rate capabilities, greater active material thickness for improved energy density, while also retaining or improving specific capacity. Lifetime at high temperature is also significantly improved, because of the increased thermal and chemical stability of the electrodes.Electrode production cost is also dramatically reduced, as the Neocarbonix process is solvent-agnostic. The solvent can be selected to speed up the drying process during coating, which dramatically improves the production throughput. Neocarbonix is compatible with standard roll-to-roll manufacturing equipment and is easily recyclable.In this presentation, Nanoramic will present a Neocarbonix Li-ion battery design combining high areal capacity loading (>5.2 mAh/cm2) Neocarbonix NMP/PVDF binder free NMC811 cathode and Si-C dominant anode electrodes which can achieve 350 Wh/kg and 900 Wh/L in energy density, and the cost of manufacturing such battery cell can be reduced from $97-116/kWh to ~$79/kWh, which improves 30% energy density and reduces 20% cost in $/kWh compared with conventional Li-ion battery NMC||Graphite technology as shown in the figure below. The battery cell prototype shows an excellent cycle life of 1000 cycles with 70% energy retention. Figure 1

Theoretical and Experimental Investigations into Composite Cathode Architectures for Solid-State Batteries

Solid-state batteries (SSB) are promising technologies for high energy density storage for automotive applications. Materials selection, property optimizations, architecture design and effective component integration are key parameters for successful applications of SSB. Material families that can meet ion transport criteria comparable to the state-of-the-art liquid electrolytes have been identified for solid ion conductors[1]. Integration of these materials into a high-performance battery stack is still far from realization[2]. The primary limitation is the lack of fundamental understanding of the interplay between charge transfer kinetics and transport within the system, specifically at the electrode | electrolyte interfaces[3]. A key challenge with SSB is the low areal capacity and the long-term stability of high voltage cathodes with areal capacities excess of 5 mAh cm-2 required for techno-economic feasibility. However, current SSBs only employ cathodes with loadings up to 0.5-2 mAh cm-2. Poor cathode architecture, improper utilization and cathode degradation are key factors that contribute to low areal capacity. In this work, the authors discuss a theoretical modeling framework for establishing solid electrolyte packing around a primary particle. Subsequently, this local architecture is used to estimate upper-bounds of the cell-level energy density. The developed model suggests an order of magnitude variation in the particle size of active material and the solid electrolyte in the composite cathode to achieve effective packing. In addition, the model predictions will be validated by experimental investigation using NMC622 based composite cathodes with a PEO-LLZO hybrid solid electrolyte. Initial experimental results indicate that the differential particle sizing for the components of composite electrodes leads to denser composite cathodes.[1] A. Manthiram, X. Yu, S. Wang, Nat. Rev. Mater. 2017, 2.[2] S. Randau, D. A. Weber, O. Kötz, R. Koerver, P. Braun, A. Weber, E. Ivers-Tiffée, T. Adermann, J. Kulisch, W. G. Zeier, F. H. Richter, J. Janek, Nat. Energy 2020, 5, 259.[3] K. B. Hatzell, X. C. Chen, C. Cobb, N. P. Dasgupta, M. B. Dixit, L. E. Marbella, M. T. McDowell, P. Mukherjee, A. Verma, V. Viswanathan, A. Westover, W. G. Zeier, ACS Energy Lett. 2020, 5, 922. Figure 1

Electrical impedance guides electrode array in cochlear implantation using machine learning and robotic feeder

Cochlear Implant provides an electronic substitute for hearing to severely or profoundly deaf patients. However, postoperative hearing outcomes significantly depend on the proper placement of electrode array (EA) into scala tympani (ST) during cochlear implant surgery. Due to limited intra-operative methods to access array placement, the objective of the current study was to evaluate the relationship between EA complex impedance and different insertion trajectories in a plastic ST model. A prototype system was designed to measure bipolar complex impedance (magnitude and phase) and its resistive and reactive components of electrodes. A 3-DoF actuation system was used as an insertion feeder. 137 insertions were performed from 3 different directions at a speed of 0.08 mm/s. Complex impedance data of 8 electrode pairs were sequentially recorded in each experiment. Machine learning algorithms were employed to classify both the full and partial insertion lengths. Support Vector Machine (SVM) gave the highest 97.1% accuracy for full insertion. When a real-time prediction was tested, Shallow Neural Network (SNN) model performed better than other algorithms using partial insertion data. The highest accuracy was found at 86.1% when 4 time samples and 2 apical electrode pairs were used. Direction prediction using partial data has the potential of online control of the insertion feeder for better EA placement. Accessing the position of the electrode array during the insertion has the potential to optimize its intraoperative placement that will result in improved hearing outcomes.

Substrate Dependent Charge Transfer Kinetics at the Solid/Liquid Interface of Carbon‐Based Electrodes with Potential Application for Organic Na‐Ion Batteries

AbstractElectroactive organic semiconducting pigments represent a group of very promising electrode materials for the next generation of energy conversion and storage technologies. However, most pigments suffer from high solubility in organic electrolytes and poor electrical conductivity, which have severely impeded their practical applications. Among different strategies to improve their electrochemical performance, using conductive carbon substrates to form composite electrodes is one of the most used methods to solve these problems. In this work we investigate the role of conductive carbon substrates towards their charge transfer kinetics at the solid/liquid interface with potential application for organic sodium (Na)‐ion batteries. This study reveals that the role of conductive carbon is related not only to the optimal electronic path but also to the ionic path towards the electrode active material. Perylentetracarboxylicdiimide is used as the electrode active material coated on graphite/copper and carbon paper substrates. The morphology, structure, and chemical composition of our electrodes are investigated via scanning electron microscopy, X‐ray photoelectron and Raman spectroscopy. A thorough kinetic analysis is systematically implemented by cyclic voltammetry and electrochemical impedance spectroscopy. We performed a quantitative analysis of the resistance and capacitive components of the composite electrodes using the theory of the transmission line model and electrochemical impedance spectroscopy with symmetric cells. Our results indicate that a decrease in pore resistance is key to achieve high charge transfer kinetics in electrochemical systems. This work will therefore contribute towards future, efficient electrode design with low pore resistance and high charge transfer kinetics. This may prove of great importance for the development of energy conversion and storage technologies, including heterojunction solar cells, electrocatalysts/photocatalysts for water splitting, carbon dioxide (CO2) reduction and lithium (Li)‐ and Na‐ion batteries.

Multiphase, Multiscale Chemomechanics at Extreme Low Temperatures: Battery Electrodes for Operation in a Wide Temperature Range (Adv. Energy Mater. 37/2021)

Lithium-Ion Batteries In article number 2102122, Peter Cloetens, Kejie Zhao, Feng Lin, Yijin Liu and co-workers systematically elucidate multiphase, multiscale chemomechanical behaviors of composite lithium-ion battery cathodes under low-temperature conditions. Their results suggest that, in order to design batteries for use in a wide temperature range, it is critical to develop electrode components that are structurally and morphologically robust when the temperature is switched.

Fabrication of SiO2nanofiber-integrated all-inorganic electrodes for safer Li-ion batteries

Energy density, rate capability, and safety are often compromised in lithium-ion batteries (LIBs). To overcome this dilemma, novel electrode structure design is considered as one of the most promising routes. However, simple and scalable fabrication methods are currently very limited. Here, an electrostatic self-assembled three-dimensional Li4Ti5O[Formula: see text] (3D-LTO) electrode with high-energy density as a whole and excellent thermal stability was fabricated by regulating the zeta potential of electrode components. Such a 3D electrode features an intergraded current collector layer of SiO2/ketjen black (KB) and active material layer of SiO2/KB/LTO/carbon fiber (CF). Benefiting from its well-designed electronic conductive 3D skeleton and desirable chemical affinity with the liquid electrolyte, outstanding cyclability (capacity retention of 85% over 80 cycles) and rate capability (125 mAh g[Formula: see text] at 5 C) could be achieved for Li/3D-LTO cells with a high LTO mass loading of 10 mg cm[Formula: see text]. Excellent thermal-tolerance of the 3D electrode enables the cell with good operability and safety at an elevated temperature of 80[Formula: see text]C. The discharge capacity of the Li/3D-LTO half-cell remains 160 mAh g[Formula: see text] at 1 C after 100 cycles. This simple and scalable method for the fabrication of the 3D electrodes boosts the energy density, rate capability, and high-temperature operability, which is promising for next-generation LIBs.

Multiphase, Multiscale Chemomechanics at Extreme Low Temperatures: Battery Electrodes for Operation in a Wide Temperature Range

AbstractUnderstanding the behavior of lithium‐ion batteries (LIBs) under extreme conditions, for example, low temperature, is key to broad adoption of LIBs in various application scenarios. LIBs, poor performance at low temperatures is often attributed to the inferior lithium‐ion transport in the electrolyte, which has motivated new electrolyte development as well as the battery preheating approach that is popular in electric vehicles. A significant irrevocable capacity loss, however, is not resolved by these measures nor well understood. Herein, multiphase, multiscale chemomechanical behaviors in composite LiNixMnyCozO2 (NMC, x + y + z = 1) cathodes at extremely low temperatures are systematically elucidated. The low‐temperature storage of LIBs can result in irreversible structural damage in active electrodes, which can negatively impact the subsequent battery cycling performance at ambient temperature. Beside developing electrolytes that have stable performance, designing batteries for use in a wide temperature range also calls for the development of electrode components that are structurally and morphologically robust when the cell is switched between different temperatures.

In situ potential measurement in a flow-electrode CDI for energy consumption estimation and system optimization

Flow electrode capacitive deionization (FCDI) is a promising electrochemical technique for brackish water desalination; however, there are challenges in estimating the distribution of resistance and energy consumption inside a FCDI system, which hinders the optimization of the rate-limiting compartment. In this study, energy consumption of each FCDI component (e.g., flow electrodes, membranes and desalination chamber) was firstly described by using in situ potential measurement (ISPM). Results of this study showed that the energy consumption (EC) of the flow electrodes dominated under most conditions. While an increase in the carbon black content in the flow electrodes could improve the energy efficiency of the electrode component, consideration should be given to the contribution of ion exchange membranes (IEMs) and the desalination chamber to the EC. Based on the above analysis, system optimization was carried out by introducing IEMs with relatively low resistance and/or packing the desalination chamber with titanium meshes. Results showed that the voltage-driven desalination capability was increased by 39.3% with the EC reduced by 17.5% compared to the control, which overcame the tradeoff between the kinetic and energetic efficiencies. Overall, the present work facilitates our understanding of the potential drops across an FCDI system and provides insight to the optimization of system design and operation.

Self-healing, stretchable, and highly adhesive hydrogels for epidermal patch electrodes

Flexible, self-healing and adhesive conductive materials with Young's modulus matching biological tissues are highly desired for applications in bioelectronics. Here, we report self-healing, stretchable, highly adhesive and conductive hydrogels obtained by mixing polyvinyl alcohol, sodium tetraborate and a screen printing paste containing the conducting polymer Poly (3,4-ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) and diol additives. The as prepared hydrogels exhibited modelling ability, high adhesion on pig skin (1.96 N/cm2), high plastic stretchability (>10000%), a moderate conductivity, a low compressive modulus (0.3−3.7 KPa), a good strain sensitivity (gauge factor = 3.88 at 500% strain), and remarkable self-healing properties. Epidermal patch electrodes prepared using one of our hydrogels demonstrated high-quality recording of electrocardiography (ECG) and electromyography (EMG) signal. Because of their straightforward fabrication, outstanding mechanical properties and possibility to combine the electrode components in a single material, hydrogels based on PVA, borax and PEDOT:PSS are highly promising for applications in bioelectronics and wearable electronics. Statement of significanceSoft materials with electrical conductivity are investigated for healthcare applications, such as electrodes to measure vital signs that can easily adapt to the shape and the movements of human skin.Conductive hydrogels (i.e. gels containing water) are ideal materials for this purpose due softness and flexibility.In this this work, we report hydrogels obtained mixing an electrically conductive polymer, a water-soluble biocompatible polymer and a salt. These materials show high adhesion on skin, electrical conductivity and ability to self-repair after a mechanical damage.These hydrogels were successfully used to fabricate electrode to measure cardiac and muscular electrical signals.

Synchrotron X‐Ray Tomography for Rechargeable Battery Research: Fundamentals, Setups and Applications

Understanding the complicated interplay of the continuously evolving electrode materials in their inherent 3D states during the battery operating condition is of great importance for advancing rechargeable battery research. In this regard, the synchrotron X-ray tomography technique, which enables non-destructive, multi-scale, and 3D imaging of a variety of electrode components before/during/after battery operation, becomes an essential tool to deepen this understanding. The past few years have witnessed an increasingly growing interest in applying this technique in battery research. Hence, it is time to not only summarize the already obtained battery-related knowledge by using this technique, but also to present a fundamental elucidation of this technique to boost future studies in battery research. To this end, this review firstly introduces the fundamental principles and experimental setups of the synchrotron X-ray tomography technique. After that, a user guide to its application in battery research and examples of its applications in research of various types of batteries are presented. The current review ends with a discussion of the future opportunities of this technique for next-generation rechargeable batteries research. It is expected that this review can enhance the reader's understanding of the synchrotron X-ray tomography technique and stimulate new ideas and opportunities in battery research.

Organic Solvent Free Process to Fabricate High Performance Silicon/Graphite Composite Anode

Cycling stability is a key challenge for application of silicon (Si)-based composite anodes as the severe volume fluctuation of Si readily leads to fast capacity fading. The binder is a crucial component of the composite electrodes. Although only occupying a small amount of the total composite mass, the binder has major impact on the long-term electrochemical performance of Si-based anodes. In recent years, water-based binders including styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) have attracted wide research interest as eco-friendly and low-cost alternatives for the conventional poly(vinylidene difluoride) (PVDF) binder in Si anodes. In this study, Si-based composite anodes are fabricated by simple solid mixing of the active materials with subsequent addition of SBR and CMC binders. This approach bypasses the use of toxic and expansive organic solvents. The factors of binder, silicon, and graphite materials have been systematically investigated. It is found that the retained capacities of the anodes are more than 440 mAh/g after 400 cycles. These results indicate that organic solvent free process is a facile strategy for producing high performance silicon/graphite composite anodes.

A study of the effect of electrode composition on the electrochemical reduction of CO2

The composition of the catalyst layer plays an important role in the carbon dioxide reduction reaction (CO2RR), since it influences greatly the mass diffusion rate and the accessibility of active sites. Until now, tremendous efforts have been dedicated to the development of cathode materials with innovative characteristics, while scarce efforts have been concentrated on the study of the catalyst layer aiming at maximizing the performance of the electrodes toward the CO2RR. This work focuses on a full investigation of the key electrode components and their effects on the CO2RR performance. It is found that all key components such as Nafion binder, zinc oxide catalyst and carbon black conductor significantly affect the current density and the faradaic efficiency for carbon monoxide (CO) formation.

Evidence of a Streamlined Extracellular Electron Transfer Pathway from Biofilm Structure, Metabolic Stratification, and Long-Range Electron Transfer Parameters.

ABSTRACTA strain of Geobacter sulfurreducens, an organism capable of respiring solid extracellular substrates, lacking four of five outer membrane cytochrome complexes (extABCD+ strain) grows faster and produces greater current density than the wild type grown under identical conditions. To understand cellular and biofilm modifications in the extABCD+ strain responsible for this increased performance, biofilms grown using electrodes as terminal electron acceptors were sectioned and imaged using electron microscopy to determine changes in thickness and cell density, while parallel biofilms incubated in the presence of nitrogen and carbon isotopes were analyzed using NanoSIMS (nanoscale secondary ion mass spectrometry) to quantify and localize anabolic activity. Long-distance electron transfer parameters were measured for wild-type and extABCD+ biofilms spanning 5-μm gaps. Our results reveal that extABCD+ biofilms achieved higher current densities through the additive effects of denser cell packing close to the electrode (based on electron microscopy), combined with higher metabolic rates per cell compared to the wild type (based on increased rates of 15N incorporation). We also observed an increased rate of electron transfer through extABCD+ versus wild-type biofilms, suggesting that denser biofilms resulting from the deletion of unnecessary multiheme cytochromes streamline electron transfer to electrodes. The combination of imaging, physiological, and electrochemical data confirms that engineered electrogenic bacteria are capable of producing more current per cell and, in combination with higher biofilm density and electron diffusion rates, can produce a higher final current density than the wild type.IMPORTANCE Current-producing biofilms in microbial electrochemical systems could potentially sustain technologies ranging from wastewater treatment to bioproduction of electricity if the maximum current produced could be increased and current production start-up times after inoculation could be reduced. Enhancing the current output of microbial electrochemical systems has been mostly approached by engineering physical components of reactors and electrodes. Here, we show that biofilms formed by a Geobacter sulfurreducens strain producing ∼1.4× higher current than the wild type results from a combination of denser cell packing and higher anabolic activity, enabled by an increased rate of electron diffusion through the biofilms. Our results confirm that it is possible to engineer electrode-specific G. sulfurreducens strains with both faster growth on electrodes and streamlined electron transfer pathways for enhanced current production.

Sub-Microstructure of Surface and Subsurface Layers after Electrical Discharge Machining Structural Materials in Water

The material removal mechanism, submicrostructure of surface and subsurface layers, nanotransformations occurred in surface and subsurface layers during electrical discharge machining two structural materials such as anti-corrosion X10CrNiTi18-10 (12kH18N10T) steel of austenite class and 2024 (D16) duralumin in a deionized water medium were researched. The machining was conducted using a brass tool of 0.25 mm in diameter. The measured discharge gap is 45–60 µm for X10CrNiTi18-10 (12kH18N10T) steel and 105–120 µm for 2024 (D16) duralumin. Surface roughness parameters are arithmetic mean deviation (Ra) of 4.61 µm, 10-point height (Rz) of 28.73 µm, maximum peak-to-valley height (Rtm) of 29.50 µm, mean spacing between peaks (Sm) of 18.0 µm for steel; Ra of 5.41 µm, Rz of 35.29 µm, Rtm of 43.17 µm, Sm of 30.0 µm for duralumin. The recast layer with adsorbed components of the wire tool electrode and carbides was observed up to the depth of 4–6 µm for steel and 2.5–4 µm for duralumin. The Levenberg–Marquardt algorithm was used to mathematically interpolate the dependence of the interelectrode gap on the electrical resistance of the material. The observed microstructures provide grounding on the nature of electrical wear and nanomodification of the obtained surfaces.

Electronically conductive MXene clay-polymer composite binders for electrochemical double-layer capacitor electrodes

Electrochemical double-layer capacitors recently attract strong attention because of their fast and stable charge/discharge characteristics and their high-power density. To improve the performance of EDLCs, it is necessary to conduct comprehensive studies on electrode, including the binder. An ideal binder for an EDLC must have high adhesion ability to the electrode components and should be electronically conductive. Here, we synthesize a composite binder consisting of MXene clay and poly(acrylonitrile-co-butyl acrylate) using an in-situ emulsion polymerization. This is a first report of an in-situ polymerization method to make a conducting composite binder with good mechanical, adhesion, and electronic conducting properties. An EDLC containing electrodes of activated carbon and MXene clay/poly(acrylonitrile-co-butyl acrylate) composite binder shows a high specific power of 8510 W kg−1 with a high specific energy of 23.6 Wh kg−1. This is a significant improvement over EDLC electrodes containing only activated-carbon and poly(acrylonitrile-co-butyl acrylate). The excellent performance is attributable to the binder's high conductivity and toughness due to improved interactions among the electrode components.