Flat Electrode Research Articles

Molecular Transport through TiO2 Mesoporous Thin Films: Correlation with the Partially Blocked Electrode Model

Mesoporous titania thin film (MTTF)-based electrodes are vastly popular due to their versatility and their potential use as sensors, catalysts, and photovoltaic devices. For these applications, understanding of diffusion through the pores along the thickness of the films is critical. Cyclic voltammetry with the use of a freely diffusing redox probe is a promising and simple strategy for the characterization of this kind of modified electrodes. However, the application of a mesoporous insulating material on a flat electrode greatly modifies the diffusion regimes in the vicinity of the reaction zone. This makes the use of traditional tools for data interpretation, such as the Randles–Ševčı́k equation, insufficient. In this work, the application of a model previously developed for partially covered electrodes (Matsuda et al., J. Electroanal. Chem. 1979, 101 (1), 29–38) is proposed to interpret experimental results. An excellent agreement between experimental and simulated voltammograms was achieved for MTTFs with different pore sizes and pore arrays. This analysis can be attributed to a lack of uniformity along the films related to differences in pore-to-pore connectivity within their thickness. At the same time, it is revealed that pore and neck sizes are determinant for diffusion within these materials. Thus, two dimensions govern the electrochemical results: nanopore sizes and arrays and microregions with different connectivities along the MTTF.

Electrical Properties of Transformer Oil with the Addition of Extremely Low Concentrations of Carbon Nanotubes

Electrical properties of transformer oil with additives of carbon nano-tubes are studied at the extremely low concentrations of the nano-tubes. Electrical strength of the mixtures is more than an order of magnitude lower than that of pure oil. Strengthening of the large gap is registered after several breakdowns in contrast to the small gap. The formation of a carbon bridge between flat electrodes is registered optically. This bridge is destroyed by an electrical discharge in the chain of bubbles generated on the bridge. Experiments with helium bubbles floating up in the mixture of carbon nano-tubes with transformer oil are performed at the deficiency of initiating electrons. Additives of carbon nano-tubes stimulate the partial discharges in the bubbles. Also, at lower voltages, the development of intense micro-flows in the liquid dielectric is observed that can be the result of the injection of free electrons from the nano-tubes.

Low voltage and robust InSe memristor using van der Waals electrodes integration

Memristors have attracted tremendous interest in the fields of high-density memory and neuromorphic computing. However, despite the tremendous efforts that have been devoted over recent years, high operating voltage, poor stability, and large device variability remain key limitations for its practical application and can be partially attributed to the un-optimized interfaces between electrodes and the channel material. We demonstrate, for the first time, a van der Waals (vdW) memristor by physically sandwiching pre-fabricated metal electrodes on both sides of the two-dimensional channel material. The atomically flat bottom electrode ensures intimate contact between the channel and electrode (hence low operation voltage), and the vdW integration of the top electrode avoids the damage induced by aggressive fabrication processes (e.g. sputtering, lithography) directly applied to the channel material, improving device stability. Together, we demonstrate memristor arrays with a high integration density of 1010 cm−2, high stability, and the lowest set/reset voltage of 0.12 V/0.04 V, which is a record low value for all 2D-based memristors, as far as we know. Furthermore, detailed characterizations are conducted to confirm that the improved memristor behavior is the result of optimized metal/channel interfaces. Our study not only demonstrates robust and low voltage memristor, but also provides a general electrode integration approach for other memristors, such as oxide based memristors, that have previously been limited by non-ideal contact integration, high operation voltage and poor device stability.

Unveiling the Working Mechanism of g-C3N4 as a Protection Layer for Lithium- and Sodium-Metal Anode.

The practical application of lithium-/sodium-metal batteries is currently hindered by severe safety issues caused by uncontrolled continuous dendrite growth. Semiconductive nanoporous g-C3N4 film has been demonstrated to be an effective protection layer for lithium-/sodium-metal anode, which can suppress the growth of dendrite. However, the underlying mechanism of how this semiconductive flexible thin film works to suppress dendrite growth remains unclear. In this work, we investigate the detailed working mechanism of g-C3N4 protection layer employing both density functional theory calculations and ab initio molecular dynamics simulations. The calculation results indicate that g-C3N4 layers show strong adhesion toward the lithium-/sodium-metal surface. When contacting with lithium/sodium metal, the intrinsic triangular nanopores of g-C3N4 will be quickly filled with lithium/sodium atoms, turning the semiconductive g-C3N4 into a metallic material. Lithium/sodium atoms can migrate through the triangular nanopores of stacked g-C3N4 layers via a vacancy-mediated approach with moderate energy barriers of 0.42 and 0.61 eV, respectively. With a low current density, the newly deposited lithium/sodium atoms can permeate through the g-C3N4 protection layers, therefore resulting in a flat electrode surface with no dendrite; with a high current density, however, the newly deposited lithium/sodium atoms cannot transport across the protection layer timely, which will result in the aggregation of lithium/sodium atoms on the surface of the g-C3N4 protection layer.

Comparison of different chemical treatments of brush and flat carbon electrodes to improve performance of microbial fuel cells

Anodes in microbial fuel cells (MFCs) can be chemically treated to improve performance but the impact of treatment on power generation has not been examined for different electrode base materials. Brush or flat anodes were chemically treated and then compared in identical two-chambered MFCs using the electrode potential slope (EPS) analysis to quantify the anode resistances. Flat carbon cloth anodes modified with carbon nanotubes (CNTs) produced 1.42 ± 0.06 W m−2, which was 3.2 times more power than the base material (0.44 ± 0.00 W m−2), but less than the 2.35 ± 0.1 W m−2 produced using plain graphite fiber brush anodes. An EPS analysis showed that there was a 90% decrease in the anode resistances of the CNT-treated carbon cloth and a 5% decrease of WO3 nanoparticle-treated brushes compared to unmodified controls. Certain chemical treatments can therefore improve performance of flat anodes, but plain brush anodes achieved the highest power densities.

Study on the Analysis of Restrike Pattern and Radial Spectrum of AC Arc Discharge based on the Electrode Material

In this study, we designed and fabricated a system based on IEC-62606 and UL-1699 such that stable arc discharge could be produced. AC arc discharge was performed to interpret the restrike pattern and radiation spectrum according to the electrode material. In the voltage waveform analysis of flat copper electrodes, it was analyzed that the accompaniment cycle of the negative waveform was more unstable than the half cycle of the positive waveform. We observed that the radiation spectrum of copper electrodes occurred in the ultraviolet and visible light regions. Moreover, the voltage waveform of the carbon electrode was found to be similar to the pattern produced by the copper electrode. However, we observed that the restrike generated at the half cycle of the negative waveform was produced relatively faster. The radio spectra were strongest near 589 nm, 671 nm, and 766 nm. AC arc discharges using copper electrodes and carbon electrodes were found to be between the arc-discharge patterns of copper electrodes and carbon electrodes. It has been proven that depending on the material of the electrode, there are differences in voltage list like, current patterns, and radiated spectra bands.

Analysis of a method for measuring deposit impedance parameters using charge amplifier and lock-in voltmeter

Parameters such as capacitance and conductivity are measured to describe the properties of a medium, including its moisture content. These methods do not deliver highly accurate results in materials that are characterized by low homogeneity, varied porosity, high conductivity and high water content. This study proposes a more accurate method for estimating the parameters of any medium. In the experimental setup, a charge amplifier and a phase-sensitive voltmeter were applied to determine resistance and capacitance parameters of a medium based on the signals received by the measuring system. The proposed method can be applied to non-homogeneous media containing both dielectric and conductive materials. The described measuring system is composed of two flat electrodes whose size can be adapted to the dimensions of the analyzed medium. A method for processing the sensing signal to determine the impedance characteristics of a medium with the use of a phase-sensitive voltmeter was described. The measuring system was modeled in Matlab/Simulink, and the results were discussed.

Mathematical modelling of a membrane-less redox flow battery based on immiscible electrolytes

We present a mathematical model to study the steady-state performance of a membrane-less reversible redox flow battery formed by two immiscible electrolytes that spontaneously form a liquid-liquid system separated by a well defined interface. The model assumes a two-dimensional battery with two coflowing electrolytes and flat electrodes at the channel walls. In this configuration, the analysis of the far downstream solution indicates that the interface remains stable in all the parameter range covered by this study. To simplify the description of the problem, we use the dilute solution theory to decouple the calculation of the velocity and species concentration fields. Once the velocity field is known, we obtain the distribution of the mobile ionic species along with the current and the electric potential field of the flowing electrolyte solution. The numerical integration of the problem provides the variation of the battery current density Iapp with the State of Charge (SoC) for different applied cell voltages Vcell. A detailed analysis of the concentration density plots indicates that the normal operation of the battery is interrupted when reactant depletion is achieved near the negative electrode both during charge and discharge. The effect of the electrolyte flow on the performance of the system is studied by varying the Reynolds, Re, and Péclet, Pe, numbers. As expected, the flow velocity only affects the polarization curve in the concentration polarization region, when Vcell is well below the equilibrium potential, resulting in limiting current densities that grow with Re as jlim∼Re0.3. In addition, both the single-pass conversion efficiency ψ and the product ψjlim decrease with Re. Concerning the later, the decay rate with Re exhibits a power law with an exponent that almost doubles previous theoretical predictions obtained by imposing a prescribed velocity profile for the electrolyte in a membrane-less laminar flow battery with a liquid oxidant and gaseous fuel. The present work constitutes the first modelling attempt that simultaneously solves the fluid dynamical system formed by the two immiscible electrolytes and the electrochemical problem that determines the response of the membrane-less battery. The proposed model could be used as a valuable tool to optimize future flow battery designs based on immiscible electrolytes.

Nanostructured versus flat compact electrode for triboelectric nanogenerators at high humidity

The triboelectric nanogenerator (TENG) is a promising technology for mechanical energy harvesting. TENG has proven to be an excellent option for power generation but typically TENGs output power drops significantly in humid environments. In this work, the effect of electrode’s material on power output, considering smooth and nanostructured porous structures with various surface hydrophobicity, is investigated under various humidity conditions. A vertical contact-separation mode TENG is experimentally and numerically studied for four surface morphologies of Ti foil, TiO2 thin film, TiO2 nanoparticulated film, and TiO2 nanotubular electrodes. The results show that the TENG electrical output in the flat structures such as Ti foil and TiO2 thin film at 50% RH is reduced to 50% of its initial state, while in the nanoporous structures such as nanoparticle and nanotube arrays, this is observed at RH above 95%. The results show that the use of porous nanostructures in TENG due to their high surface-to-volume, and that the process of water adsorption on the pore leads to better performance than the flat surface in humid environments. Based on our study, employing nanoporous layers is vital for nanogenerators either for power generation or active sensor applications at high humidity conditions.

Electrochemical processes mediated via adsorbed Enzymes: Flat and porous electrodes Compared. Understanding Nano-confinement

• Adsorbed-enzyme-mediated electrochemical processes are investigated via simulations. • Potential dependent Michaelis constants are explained. • Four classes of voltammograms are introduced to help understand current responses. • Porous electrodes can create enhanced effective surface coverage and sensing ability. We present theory for electrolysis at electrode surfaces modified by a layer of electroactive enzyme which can mediate the reduction of a substrate to a product. In particular, we compare and contrast immobilisation on flat surfaces with that on porous surfaces. We identify the conditions under which the adoption of porous electrodes facilitates markedly improves turnover rates and develop the analysis on the basis of the porous layer conferring a much-increased effective surface coverage. For both types of electrode, the role of the electrode potential in controlling the thermodynamics of the binding of the substrate with the reduced layer of immobilised enzymes is quantified, and the observation of apparent potential dependent Michaelis constants are explained. Four distinct classes of voltammetric responses are categorised allowing bottom-up process optimisation.

Erratum to “Weld bead characterization of flat wire electrode in gmaw process part II: a numerical study”

Due to an unfortunate oversight during the conversion process, Reference [3] has been given erroneously in the XML version. The original article has been corrected.

Enabling a Stable High-Power Lithium-Bromine Flow Battery Using Task-Specific Ionic Liquids

Hydrophobic task-specific ionic liquids (TSILs) can be the key to unlocking the potential of energy-dense lithium-bromine batteries for a wide variety of applications such as provision of sustainable power for transportation and the grid. In this paper, we describe a high efficiency catalyst-free lithium-bromine rechargeable fuel cell using highly concentrated bromine catholytes, with higher theoretical energy density than most lithium-ion cathode materials and catalyst-free lithium-air chemistries. Using a novel hydrophobic ionic liquid, we eliminate the organic electrolyte in the original Li-Br flow cell architecture with a flat graphite electrode, proposed by Bai and Bazant, and improve peak power density by ∼4× and the ionic conductivity of the solid electrolyte by almost an order of magnitude. The peak power density of 34.5 mW cm−2 at a potential of 3.45 V is the highest reported value for similar catalyst-free battery chemistries to date. It can also reversibly electrodeposit lithium in a dendrite-free manner at high current densities ∼10 mA cm−2 without any catalyst, with a >95% voltage efficiency for a 1 M Br2 in 9 M LiBr catholyte. Despite having chemical stability to lithium and bromine, suboptimal Li+ chelating affinity of the TSIL results in a depletion of ion concentration in the ionic liquid phase during operation, rendering stable long term cycling challenging. This can be addressed by the design of ionic liquid cations with higher Li+ affinity, while maintaining high chemical stability, hydrophobicity, and reasonable viscosity. This work is a proof-of-concept of the viability of this approach, and has potential for applicability in long-range transportation, beyond current Li-ion and Li-air batteries.

Textile Electrode-structure Effects and Motion Artifact Minimization in Heart Activity Signal Acquisition

The purpose of this study is to compare the heart activity signal sensing performance by textile electrodes (based on size and configuration method) in order to obtain the structural requirements of motion artifact-minimizing textile electrodes suitable for heart activity signal acquisition. Computer embroidery was used to create six types of contact textile electrodes for measuring heart activity by manipulating the electrode size and method of configuration. These electrodes were attached to separate chest belts worn sequentially by eight males in good physical health. Heart activity signals were detected while the subjects stood in a static posture for 60 seconds and while they walked in place at a rate of 80 beats per minute for 60 seconds. The measurements were repeated four times. To collect the heart activity signals, a BIOPAC Systems, Inc. ECG100 electrocardiogram amplifier was used at a sampling rate of 1 ㎑, and the detected raw signals were fed through a bandpass filter. The signal power ratio of the heart activity signal detected by each type of electrode was calculated, and statistical analysis was applied to determine the heart activity signal-acquisition performance of the six electrode configurations. The results of this study indicate that, with regard to the textile electrodes’ configuration method, convex electrodes detected higher-quality signals than flat electrodes; however, no significant performance difference was found in detecting heart activity signals among the three electrode sizes. Among the structural requirements of textile electrodes for heart activity signal acquisition, the electrode configuration method was found to be an important factor that affects heart activity signal sensing in static and dynamic states. Plans for implementing a wearable platform integrating the convex textile electrodes based on this study will be investigated in future studies, along with performance improvements to develop smart clothing technology that can detect high-quality heart activity signals without time or space limitations.

Mathematical modeling of a submerged jet of electric wind

Technological processes of electro-gas dynamics of dispersed systems are based on charging and transporting dispersed raw material particles in a strong electric field of a corona discharge. It is accompanied by turbulent gas motion caused by momentum transfer of ions to gas molecules. This accompanying motion is called electric wind. It must be considered when calculating the trajectories of particles and devices design. In recent years, equipment is being developed, the operation of which is based on the direct use of electric wind. In most cases these studies are based on experimental research and empirical calculation formulas, therefore, to make the design and construction of this equipment science oriented, it is necessary to develop mathematical models and methods for calculating this phenomenon. The object of the research is a unipolar electric corona discharge of direct current between a negative corona wire and a flat electrode in the form of a mesh. The calculation of a turbulent jet of an electric wind is considered both within the framework of the boundary layer theory and in a full-scale formulation using the k- и k- turbulence models in the Comsol program. Two new solutions for the velocity field of a submerged flat jet of electric wind are found and compared. They are an analytical solution based on the boundary layer theory and a numerical solution in a full-scale formulation based on the Reynolds equation integration. The novelty of the solutions is that they are applied for a two-dimensional problem and consider the turbulent motion of gas. The phenomenon of electric wind is widely applied in modern technologies that allow electric and gas cleaning, disinfection, and water purification from organic impurities, as well as treatment and disinfection of surfaces and air which is especially important recently. In the case of jet spread of electric wind in a closed channel, the boundary layer approximation conditions are satisfied, and a self-similar solution can be used. In the case of an open jet, the calculation should be carried out in a full-scale formulation of the problem based on the numerical solution of the Reynolds equation.

Surface bioelectric dry Electrodes: A review

The surface bioelectric sensors in contact with human skin is a key component of Long-term wearable health monitoring systems (LWHMs), bioelectric signals generated by living cells or tissues are closely related to the health status of the human body, and bioelectric sensors are used to record such signals. Compared to conventional Ag/AgCl wet electrodes, surface bioelectric dry electrodes (SBDEs) offer significant advantages in terms of ease of use, biocompatibility and long-term stability. Therefore, the research focus has shifted to the study of dry electrodes, which can be used without gels. This paper provides a detailed overview of the research progress of SBDEs and a comprehensive introduction to their measurement principles, different types of SBDEs (flat film dry electrodes, surface micro/nano-structured dry electrodes and textile dry electrodes) and evaluation test methods, analyzes the advantages and disadvantages of SBDEs and their prospects, and provides some inspiration for the development of high-performance SBDEs.

Honeycomb meshed working electrodes based on microsphere lithography for high-resolution chemical image sensor

The chemical image sensor has attracted much attention because of its ability to visualize the spatial distribution of biochemical species in solution. However, the lateral diffusion of photo-generated carriers generated by illuminating backside of the substrate limits the spatial resolution of the sensor and the sharpness of the image. In this study, honeycomb meshed metal array based on microsphere lithography as working electrodes of the sensor is proposed. A focused light spot illuminates a plurality of periodic and ordered mesh holes and the metal electrodes adjacent to the mesh holes. For chemical imaging performance, sensors with honeycomb meshed working electrodes are developed for comparison with the sensor the flat working electrodes, and their spatial resolution is tested under the focused light spot with different sizes. Three interpretations of improved spatial resolution including enhanced recombination of the photo-generated holes by electrons during the initial stage of lateral diffusion and two boundary cases of modulated light illuminating meshed working electrodes on the substrate are elaborated. The experimental results show that the spatial resolution of sensor chips with honeycomb meshed working electrodes is better than that of the sensor with the flat working electrodes and is higher under the illumination condition of smaller light spots.

Stable Acidic Water Oxidation with a Cobalt–Iron–Lead Oxide Catalyst Operating via a Cobalt‐Selective Self‐Healing Mechanism

AbstractThe instability and expense of anodes for water electrolyzers with acidic electrolytes can be overcome through the implementation of a cobalt‐iron‐lead oxide electrocatalyst, [Co–Fe–Pb]Ox, that is self‐healing in the presence of dissolved metal precursors. However, the latter requirement is pernicious for the membrane and especially the cathode half‐reaction since Pb2+ and Fe3+ precursors poison the state‐of‐the‐art platinum H2 evolving catalyst. To address this, we demonstrate the invariably stable operation of [Co–Fe–Pb]Ox in acidic solutions through a cobalt‐selective self‐healing mechanism without the addition of Pb2+ and Fe3+ and investigate the kinetics of the process. Soft X‐ray absorption spectroscopy reveals that low concentrations of Co2+ in the solution stabilize the catalytically active Co(Fe) sites. The highly promising performance of this system is showcased by steady water electrooxidation at 80±1 °C and 10 mA cm−2, using a flat electrode, at an overpotential of 0.56±0.01 V on a one‐week timescale.

Stable Acidic Water Oxidation with a Cobalt-Iron-Lead Oxide Catalyst Operating via a Cobalt-Selective Self-Healing Mechanism.

The instability and expense of anodes for water electrolyzers with acidic electrolytes can be overcome through the implementation of a cobalt-iron-lead oxide electrocatalyst, [Co-Fe-Pb]Ox , that is self-healing in the presence of dissolved metal precursors. However, the latter requirement is pernicious for the membrane and especially the cathode half-reaction since Pb2+ and Fe3+ precursors poison the state-of-the-art platinum H2 evolving catalyst. To address this, we demonstrate the invariably stable operation of [Co-Fe-Pb]Ox in acidic solutions through a cobalt-selective self-healing mechanism without the addition of Pb2+ and Fe3+ and investigate the kinetics of the process. Soft X-ray absorption spectroscopy reveals that low concentrations of Co2+ in the solution stabilize the catalytically active Co(Fe) sites. The highly promising performance of this system is showcased by steady water electrooxidation at 80±1 °C and 10 mA cm-2 , using a flat electrode, at an overpotential of 0.56±0.01 V on a one-week timescale.

Scalable Fabrication of Flexible Single‐Layer Strain and Double‐Layer Pressure Sensors by Inkjet Printing for Subtle Vibration Detection

AbstractFlexible sensors have attracted tremendous attentions in subtle force/vibration detection, human motion/health monitoring, and other related application fields. Although various sensors are developed to meet this growing demand, it is still a huge challenge to prepare satisfactory sensors with ultrahigh sensitivity and superior stability. In this work, a double‐layer flexible sensor is successfully prepared via an efficient and designable inkjet printing approach. Metallic silver layers are deposited onto polyurethane acrylate substrates with or without microstructures to form the flexible electrodes. The combination of a flat electrode and a microstructured electrode finally becomes a durable double‐layer flexible sensor with ultrahigh sensitivity and superior stability. Besides, the flexible flat electrodes can also be applied as single‐layer sensors. An ultrahigh sensitivity (maximum gauge factor of >1100), favorable durability (>1000 cycles), and fast response time (≈90 ms) are achieved simultaneously in a flat single‐layer sensor, while the combined double‐layer sensor presents quick response capability to small pressures (≈250 Pa). Moreover, these single‐layer and double‐layer sensors can monitor a variety of physiological signals (e.g., human pulse waveform, breathing behavior, and voice recognition), indicating their promising applications in wearable electronics.

Electrochemical safety limits for clinical stimulation investigated using depth and strip electrodes in the pig brain

Objective. Diagnostic and therapeutic electrical stimulation are increasingly utilized with the rise of neuromodulation devices. However, systematic investigations that depict the practical clinical stimulation paradigms (bipolar, two-electrode configuration) to determine the safety limits are currently lacking. Further, safe charge densities that were classically determined from conical sharp electrodes are generalized for cylindrical (depth) and flat (surface grid) electrodes completely ignoring geometric factors that govern current spreading and trajectories in tissue. Approach. This work reports the first investigations comparing stimulation limits for clinically used electrodes in two mediums: in benchtop experiments in saline and in vivo in a single acute experiment in the pig brain. We experimentally determine the geometric factors, the water electrolysis windows, and the current safety limits from voltage transients, for the sEEG, depth and surface strip electrodes in both mediums. Using four-electrode and three-electrode configuration measurements and comprehensive circuit models that accurately depict our measurements, we delineate the various elements of the stimulation medium, including the tissue-electrode interface impedance spectra, the medium impedance and the bias-dependent change in the interface impedance as a function of stimulation parameters. Main results. The results of our systematics studies suggest that safe currents in clinical bipolar stimulation determined in vivo can be as much as 24 times smaller than those determined from benchtop experiments (for depth electrodes at a 1 ms pulse duration). Our detailed circuit modeling attributes this drastic difference in safe limits to the greatly dissimilar electrode/tissue and electrode/saline impedances. Significance. We established the electrochemical safety limits for commonly used clinical electrodes in vivo and revealed by detailied electrochemical modeling how they differ from benchtop evaluation. We argue that electrochemical limits and currents are unique for each electrode, should be measured in vivo according to the protocols established in this work, and should be accounted for while setting the stimulation parameters for clinical applications including for chronic applications.