Non-polarizable Electrodes Research Articles

Нейровизуализационный подход для выявления биомаркеров рабочей памяти у больных с хронической ишемией мозга

Verbal working memory (VWM) is a fundamental function responsible for temporary storage and short-term handling of verbal information. The study was aimed to determine the working memory biomarker associated with imaging of the source of infra-slow electrical activity in patients with chronic cerebral ischemia (CCI). A total of 50 patients with CCI took part in the study: 16 males and 34 females aged 50–85 years. VWM was evaluated by the Luria test. The subjects were divided into two groups matched by age with the VWM below and above the average level for the studied sample. The infra-slow, below 0.1 Hz, electrical activity, otherwise known as the DC potentials (DCPs) of the brain, was recorded with five monopolar leads: frontal, central, occipital, right and left temporal. The resting state fMRI was used to analyze brain regions with the activated BOLD (blood-oxygen-level-dependent) signal that were associated with the brain regions responsible for VWM and the DCP generation sources recorded with the non-polarizable electrodes. The differences in BOLD signal activation and infra-slow activity amplitude were found in two VWM groups. These resting-state neural networks, VWM and the neural network responsible for DCP generation, overlapped in frontal regions. There were significant differences in DCP recorded with the frontal lead in two VWM groups (р = 0.00004). In patients with CCI, infra-slow activity, recorded with the frontal lead that is generated by the neural network fragment representing an intersection of the VWM network and the part of the brain responsible for DCP generation in the frontal region, is a VWM biomarker.

Electrochemical behavior and electromotive force measurements of U3+/U0 in molten MgCl2-NaCl

The electrochemical behavior of UCl3 was investigated in molten MgCl2NaCl at 550 °C. Using electromotive force measurements, we have measured the formal reduction potential (Eo’) at 550 °C of U3+/U0 as +0.276 V vs. Mg/MgCl2 (-1.400 V vs. Ag/AgCl 5 mol%) on the molal scale. We also present the design and construction of a sealed Mg/MgCl2 reference electrode and have determined this system demonstrates ideal nonpolarizable electrode behavior, confirming it as an appropriate choice of reference electrode in molten chloride salts.

Experimental Study on the Performance of Steel Electrodes for Long-term Monitoring

Long-term monitoring of electromagnetic (EM) fields requires dense arrays of electrode buried underground for a long time. Steel electrodes are cheap and easy to deploy but are well known to be prone to the noise due to the electrochemical reaction on the metal-fluid interface. In this experiment, we bury an array of steel and non-polarizable electrodes in a realistic monitoring setting, and investigate the performance of steel electrodes with the non-polarizable electrodes as reference. The pilot experiment of 8 days has found significant drift in the data from the steel electrodes, but a detrending process that removes the long-period signals can make the steel and non-polarizable electrode data more consistent at the time scale of a few minutes. The results show that the steel electrodes can have performance comparable with that of the non-polarizable electrodes if signals at relatively short periods are concerned. This study offers inspiration of collecting electrical field data by dense steel electrode arrays for a variety of monitoring applications.

Using Ambient Pressure Photoelectron Spectroscopy to Investigate the Time Dependence of Electrostatic Potential Difference over the Interphase between an Electrode and an Electrolyte

Ambient pressure photoelectron spectroscopy (APPES) is a method well-suited for measuring the change ∆φ in electrostatic potential difference φ over an interphase between an electronic conductor and an insulator. APPES had previously been used to compare ∆φ over an interphase between an electrode and an electrolyte with the change in electrochemical potential difference ∆UWE-RE between the working and the reference electrode UWE-RE .[1] The relationship between ∆φ and ∆UWE-RE at low current-transient had been shown to follow two distinct trends depending on whether charge transfer of Li+ ions between an electrode and an electrolyte occurs or not.[1,2] In this work, APPES was used to investigate the time dependence of ∆φ after changing UWE-RE . The studied electrochemical system consisted of Au (working electrode), Li4Ti5O12 (reference electrode) and a second Li4Ti5O12 (counter electrode) with 0.008 M LiClO4 in propylene carbonate (PC) as the electrolyte. Pressure in the sample compartment was equal to the saturated PC pressure. APPES experiments were performed at HIPPIE beamline at MAX IV in Lund and were conducted as follows. After applying a potential step ∆UWE-RE , a C 1s spectrum was measured every 7 s. Incident photon energy was 1800 eV. Each spectrum was fitted using a Python code written especially for the obtained C 1s spectra. Time dependence of ∆φ was extracted from the shift in the kinetic energy ∆KE of the C=O peak (∆φ = ∆KE). Experiments were performed in both regimes, i.e. when the working electrode behaves as an ideal polarizable electrode and when it behaves as an ideal non-polarizable electrode, and have shown the time dependence of ∆φ to differ for the two regimes. Behaviour of ∆φ(t) as well as the experimental setup and spectral fitting using the Python code will be discussed.Figure 1: a) Schematic depiction of the electronic electrostatic potential φ between a working (WE) and a reference electrode (RE). Electrostatic potential profile is not to scale. b) An example of the experimentally obtained time dependence of the C=O peak kinetic energy KE(t). KE(t) is related to φ(t) as ∆φ(t) = ∆KE(t).

Ultrasensitive sensing of pH and fluoride with enhanced constant potential coulometry at membrane electrodes

Minute potential changes at membrane electrodes may be translated to easily detectable current spikes if the cell potential is held constant and the change is imposed onto a capacitive element placed in series. While this results in a very important increase in measurement precision, the current transient passing through the sensing membrane contributes to measurement uncertainty and may not be applicable to all sensing materials. This limitation is overcome by treating the ion-selective electrode as reference electrode, which allows one to avoid current passing through the ion-selective membrane. The potential stability of the Ag/AgCl element upon passage of current was confirmed to be excellent, as expected for an ideally non-polarizable electrode. This greatly increases the reproducibility and precision of the method. The approach also allows one to use the LaF3 crystal-based fluoride sensitive membrane, for which passage of current transients gives deleterious effects. An electronic circuit was built to automate the control of the capacitive element. An improvement of precision (from 829 to 177 μpH) and a reduction of signal drift (from 1.89% of total charge to 0.38%) was demonstrated with membrane-based pH electrodes while fluoride sensing was achieved for the first time with constant potential coulometry at high reproducibility and precision (RSD of just 0.026% activity change).

A Gaussian field approach to the planar electric double layer structures in electrolyte solutions.

In this work, the planar, electric, double-layer structures of non-polarizable electrodes in electrolyte solutions are studied with Gaussian field theory. A response function with two Yukawa functions is used to capture the electrostatic response of the electrolyte solution, from which the modified response function in the planar symmetry is derived analytically. The modified response function is further used to evaluate the induced charge density and the electrostatic potential near an electrode. The Gaussian field theory, combined with a two-Yukawa response function, can reproduce the oscillatory decay behavior of the electric potentials in concentrated electrolyte solutions. When the exact sum rules for the bulk electrolyte solutions and the electric double layers are used as constraints to determine the parameters of the response function, the Gaussian field theory could at least partly capture the nonlinear response effect of the surface charge density. Comparison with results for a planar electrode with fixed surface charge densities from molecular simulations demonstrates the validity of Gaussian field theory.

REVIEW OF IDENTIFIED SHORTCOMINGS IN AQUIFER VULNERABILITY ASSESSMENTS

Several studies have successfully carried out aquifer vulnerability evaluations using a combination of geophysical and biogeochemical methods. Unfortunately, some identified shortcomings have often led to inaccurate assessments. This review attempts to identify some of these drawbacks and suggest better ways to improve upon analysis and interpretation of results. Articles reviewed were sourced publicly and subjected to systematic analysis based on fundamental principles. The outcomes of each analysis were discussed, among which was a study that applied Ohmega Resistivity meter to acquire Self-Potential (SP) data without specifying the nature of electrode used. The result indicated large SP readings ≥200mV attributed to high fluid flow. According to analysis, when copper stakes are used, spurious SP readings occur in contrast to lower SP values of roughly 10 mV when suitable non-polarizable electrodes of Cu/CuSO4 porous pots are utilized to collect SP data. The review made clear the importance of providing detailed explanation of the nature of materials used. Another study solely collected samples for groundwater quality assessments during dry season, ignoring the effects of seasonal variation on water parameters. This must have had an impact on the results of the investigations. Research examined the aquifer problems in Gosa area of Abuja, utilizing only the Vertical Electrical Sounding (VES) technique. The study suggested basaltic intrusion as probable cause of borehole failures in the area. A different research which incorporated VES and data from the hill-shaded Shuttle Radar Topography Mission (SRTM), suggested insufficient interconnectivity within the fractures as conditions controlling groundwater occurrence in the area. The study illustrated the need for integrating geophysical methods for effective target detection. To map the infiltration of leachate into the subsurface, a study applied only the VES technique. Studies, however, showed that the VES method only provided average resistivity readings, suppressing some features. The study suggested the combination of VES and 2-D imaging for more accurate results. Another study obtained data via the ADMT Groundwater Detector. At the interpretation stage, the author interpreted ADMT data as VES, which was perceived as inaccurate as their principles and methodologies are different. Another study was noted to have presented results without categorizing the Aquifer Protective Capacity (APC) rating in percentages (%). It was assessed that a framework that accurately categorized the APC of each transversal using common statistics guidelines would have made it simpler to understand and aided decision-making. Future research is advised to take some of the noted flaws into account in order to enhance data processing and interpretation.

The joint seismic-and-electromagnetic monitoring with electromagnetic field separation

The magnetotelluric soundings (MTS) are a common tool in applied geophysics. The guidelines for electromagnetic (EM) monitoring should be updated because of new tools and software developed. Some techniques paragraphs have outdated sections. Some essential equipment requirements and its’ allowable parameters, MTS acquisition, are defined. We involve Research Station RAS patents (RU 175972 U1, 2017; RU 2701876 C1, 2018) to increase the long-term stability of electrical parameters of non-polarizable electrodes. We consider the irreversible rock deformations form sources of the electromagnetic field of endogenous origin as geodynamic processes. We offer MTS with an additional algorithm with electromagnetic field separation for studying the endogenous component of EM field as a lower half-space impedance. We explain the technology of MTS in seismically active zones with remote access on the example of the Tien Shan. We introduce these guidelines acquiring data system for the joint seismic-and-electromagnetic monitoring for the modern geodynamic processes. We show a result diagram for the energy characteristic of the endogenous component of EM field.

Delicate modulation of mixed conducting properties of PEDOT:PSS via crosslinking with polyvinyl alcohol

Despite possible toxicity issues, chemical reduction or non-polarizable electrodes incorporated with highly reactive chemical species have been utilized to control the operational characteristics of organic electrochemical transistors (OECTs) for bioelectronic interfacing applications. In this study, we demonstrate that crosslinking between highly conductive poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and biocompatible nonconductive polyvinyl alcohol (PVA) effectively modulates the mixed conducting properties of PEDOT:PSS. The PEDOT:PSS–PVA films prepared by simple PEDOT:PSS and PVA blending at various ratios, spin-coating, crosslinking, and sulfuric acid treatment were comprehensively studied using optical spectroscopy, x-ray diffraction, atomic force microscopy, and electrical/electrochemical device characterizations. With PVA contents up to 20 wt.%, the resultant PEDOT:PSS–PVA-based OECTs showed a linear threshold voltage shift with a marginal loss of transconductance, suggesting an effective modulation of the peak transconductance gate voltage. Furthermore, the PVA content also affects the ion transport dynamics, which is related to the crystallite size and ionic functional group density in the PEDOT:PSS–PVA system. The detailed mechanism of delicately controlled mixed conduction in the PEDOT:PSS–PVA system is proposed from the perspective of structure-property relations.

(Invited) Textile-based Electronic/fluidic Platforms Towards Wearable Diagnostic Sensor Systems

The fields of flexible electronics and microfluidic-based labs-on-a-chip continue to advance, with new devices and systems-level technologies reported on a daily basis. However, much of this advancement is limited to each of these fields separately, rather than development of platforms for combining flexible electronics and microfluidics together to realize wearable sensors and sensor systems. We present new approaches for combining electronics and microfluidic devices together on wearable textile-based substrates, resulting in combined systems that are highly portable, mechanically flexible, and can be easily integrated with clothing. We develop polymer materials traditionally used for artistic designs on clothing for use as engineering materials, i.e., as the base polymer for conductive electronics that can be integrated with polymer microfluidic channels printed in the same materials. Unlike other techniques, our technologies and materials are highly compatible with clothing-based textiles, and result in non-polarizable electrodes for improved frequency response. Our platforms can be laundered, facilitating rugged wearable devices and systems for biomedical and environmental monitoring. Application areas for our flexible and wearable platforms include health care, worker safety, food safety, consumer devices, personalized medicine and biomedical and environmental monitoring. We present technologies for specific applications that include: lighting and health monitors for safety vests; heart and perspiration (pH, lactate) monitors for athletic clothing; and wearable bioelectric and biochemical monitoring.

Self-repairing nanoporous MCNT/Ag/AgCl composite electrode as a low-cost and long-term stable marine potentiometric sensor

Maintenance-free, cost-effective, and long-lasting potentiometric sensors are highly anticipated for marine detection. Solid-state silver/silver chloride (Ag/AgCl) is considered the most suitable non-polarizable electrode for that purpose. However, the conventional fabrication of thin-film or porous Ag/AgCl electrodes has limitations in the case of simultaneous cost-effectiveness and stability endurance. In the present study, the multi-walled carbon nanotube (MCNT)/Ag/AgCl composite electrode with a 70 mg/cm2 Ag load was prepared, having nanoporous MCNT/Ag conductive skeleton, and a three-dimensionally spreading Ag/AgCl thin layer. The prepared MCNT/Ag/AgCl composite electrode showed an excellent electrode performance, including low resistance, high exchange current density, and stable potential with long-term stability and low cost. The process kinetics and self-repairing mechanism between Ag and AgCl with the help of MCNT were elucidated. The usage of MCNT/Ag/AgCl composite electrode as a solid-state reference electrode and ocean electric field sensor was successfully evaluated, which provides a promising marine potentiometric sensor application for this nanoporous metal composite electrode via a novel preparation method.

Geoelectric studies of the Kozloduy nuclear power plant region, Bulgaria

The task of the work was geoelectrical studies using variations of the magnetotelluric (MT) field of the Kozloduy nuclear power plant (KNPP) region and the integration of its results with other geological and geophysical knowledge. This paper presents the determined interpretation parameters of the MT field. The KNPP is located on the right bank of the Danube River in close proximity to the river. This fact, together with the location of electrified railways determined the unique network of locations of observation points for MT field variations. Based on the analysis of Earthquake Catalogs of Bulgaria and international seismicity databases, a map of the seismicity of nuclear power plant areas was built. Over the past 50 years, about 750 earthquakes (mainly south of KNPP) have been recorded at a distance of 40—80 km from the KNPP. Two magnetotelluric stations GEOMAG-02 were used at measurement sites, but equipment for recording electrical channels was available only for one station (due to the lack of another set of non-polarizable electrodes). The MT field variations were observed at 21 points, which are located on the territory with sides approximately 30—35 km from east to west and 40—50 km from north to south. For all observation points on the profile, only the parameters of the vertical magnetic transfer function (VMPF) were determined, in the form of the real (Cu) and imaginary (Cv) parts of the induction vector. The steadily induction vector was defined for periods from 10—20 to 4900—10 800 s. For most points it was possible to estimate the values Cu, Cv with an error of 0.02—0.04 and AzCu, AzCv 3—5°. The analysis showed the presence of anomalous behavior of Cu, Cv in different intervals of periods at some points. In the shortest (about 20 s) and longest periods (600 to 1000 s), the Cu directions completely coincide and indicate the presence of anomalous conductivity of the quasi-longitudinal strike to the west of the study area. This behavior of the Cu vector is in good agreement with power isohypsum strike of the Cenozoic deposits. At intermediate periods of 50—200 s, the behavior of Cu is more complex. Approaching the zone of high seismicity, the direction of the Cu differs from the previous ones by almost 90°. On the Geoelectrical sections, obtained as a result of 1D inversions of MTS curves at 4 points located in the southern part of the region, anomalous layers are identified (ρ about 10 ohm · m, the depth of the center of the object is 15—20 km). It can be assumed that well-conducting objects in the Earth’s crust of the region, apparently, prevent the propagation of seismic waves from nearby earthquakes to the north towards the KNPP.

Диагностика утечек загрязненных вод с территории полигона отходов химического производства методом естественного электрического поля

The main goal of the research is a diagnostic assessment of polluted water leaks from the chemical waste landfill site using the self-potential method integrated with other methods. The following tasks were to be solved: locating zones of contaminated water leakage from the drainage canals; detecting polluted water leaks from the sludge reservoir; identifying the discharge zones of contaminated groundwater into the swamps adjacent to the landfill. Electrical prospecting equipment ERA-MAX with non-polarizable electrodes of the VIRG system was used for field measurements. Two measuring techniques of the self-potential method were used: the fixed-base method (the measurement interval was 5 m) and the potential gradient method (measuring line MN = 5 m). The additional methods were as follows: geomagnetic microsurvey and phytoindication. The following diagnostic indicators were estab-lished for the zones of infiltration of contaminated waters from canals and sludge reservoirs: negative fixed-base potential anomalies or negative potential gradient anomalies of the natural electric field, which are characterized by the amplitude of 10-40 mV. The area of discharge of polluted groundwater into the surficial unit is indicated by a positive anomaly of the natural electric field (+ 20-47 mV), spatially associated with the zone of degradation of swamp vegetation

3ε-A Versatile Operando Analytics Toolbox in Energy Storage.

The performance and safety of lithium-ion batteries are plagued by several diverse, nonlinear aging mechanisms influenced by the electrochemical thermal interactions at the electrodes, usage history, and operating conditions. Understanding and deconvoluting the fundamental reaction mechanisms responsible for electrode degradation are key for developing technologies in Li-ion battery diagnostics and prognostics. Hence, there exists a need for high-precision operando techniques to investigate and characterize distinct electrode degradation modes over a gamut of operational variability. Cells embedded with a stable, nonpolarizable reference electrode offer an in situ and operando tool to decouple the complex electrochemical interplay between the electrode pair by measuring individual electrode responses simultaneously with the cell response in the time and frequency domains. This perspective comprehensively looks at 3-electrode (3ε) analytics as a versatile toolbox, highlighting recent techniques and parameters developed with an emphasis on degradation diagnostics and control strategies that is expected to drive the futuristic design of battery management systems.

Performance Evaluation of Copper and Stainless-steel Electrodes in Electrical Tomographic Imaging

Geophysicists use electrical methods to investigate and characterise the earth’s subsurface geology. This study aims to evaluate the performance of copper and conventional stainless-steel electrodes in subsurface tomographic investigations using electrical resistivity tomography (ERT) and induced polarisation (IP) at two sites in Penang, Malaysia. Site 1 and Site 2 employed profile lengths of 200 m and 100 m, with electrodes spacing of 5.0 m and 2.5 m, respectively. In the results of the final data inversion, it was observed that the ERT and IP tomographic models of Site 1 have the best convergence limits with percentage relative differences (copper as reference model) ranging from –70% to 70%, while Site 2 recorded –8% to 8%. The electrodes performance evaluation showed that population root mean square (RMS) error and population mean absolute percentage error (MAPE) of data points between copper and stainless-steel electrodes yielded large values for Site 1 with values above 28% and that of Site 2 was less than 4%. Hence, copper (good electrical conductivity and non-polarisable) electrodes have improved the quality and quantity of infield data which give low values of population RMS error and population MAPE compared to conventional stainless-steel electrodes, especially for large unit electrode spacing surveys. Most notably, this work has contributed to the understanding of the capability of copper electrodes in providing precise and reliable inversion models for subsurface tomographic investigations in pre- and post-land uses (engineering work), hydrogeology/groundwater, environmental studies, etc.

Couple of Nonpolarized/Polarized Electrodes Building a New Universal Electrochemical Energy Storage System with an Impressive Energy Density.

Herein, we propose a new concept of energy storage system composed of a nonpolarized electrode and a polarized electrode (PPE) with an impressive energy density. It offered nearly 4 times higher energy density than that of carbon-based supercapacitor. Among the suggested potential PPE system, we introduced an electrodeposited nanozinc on the copper foam as the nearly nonpolarized electrode and a Zn-2,5-dihydroxyterephthalic acid (DHTA) metal-organic framework (MOF)-derived activated porous carbon as a nearly polarized electrode in KOH-ZnO electrolyte to constitute the C|Zn PPE system prototype. The C|Zn system achieved an impressive energy density of 84.5 Wh kg-1 at 1000 W kg-1, 4 times higher than that of the C|C supercapacitor. It also shows a high capacitance retention rate of 94.5% at 10 A g-1 after 10 000 cycles. Therefore, the amazing results indicate that the PPE energy system integrates the advantages of supercapacitors and secondary batteries. It will be a promising and effective energy device for higher-performance electric vehicles.

Silver Nanoneedle Probes Enable Sustained DC Current, Single-Channel Resistive Pulse Nanopore Sensing.

Resistive pulse sensing using ion channel proteins (biological nanopores) has been evolving as a single-molecule approach to detect small biomolecules owing to atomically precise pore size reproducibility, high signal-to-noise ratio, and molecular selectivity. The incorporation of biological nanopores in sensing platforms requires a stable lipid membrane that can be formed by a variety of methods such as the painting method and droplet-based techniques. However, these methods are limited by the fragility of the unsupported bilayer or the need for specific microdevices. Electrode-supported bilayers, in which a metal electrode is used as a support structure, have been recently developed using a fine gold nanoneedle. We previously described the utility of the gold nanoneedle-supported ion channel probe to detect small molecules with high spatial resolution; however, it exhibited a channel current decay over time, which affected the binding frequency of the target molecule to the protein pore as well. Here, we introduce a silver nanoneedle probe to support the lipid bilayer formation and ion channel measurements. The silver nanoneedle mitigates the current decay observed on gold electrodes and produces stable DC channel currents. Our findings propose the formation of a AgCl layer creating a nonpolarizable electrode. The new nanoneedle is successfully applied for single-molecule detection of sulfonated β-cyclodextrin (S7βCD) using αHL as a test bed protein. We believe that this new silver nanoneedle platform has great potential given the relative ease of lipid bilayer formation and stable open channel currents.

Operation mechanism of organic electrochemical transistors as redox chemical transducers

Designing OECTs to amplify chemical redox reactions reliably requires: (1) separating reaction from the OECT (2) operating the OECT potentiometrically (3) utilizing non-polarizable gate electrode (4) maximizing transconductance of channel material.

Highly sensitive interfaces of graphene electrical-electrochemical vertical devices for on drop atto-molar DNA detection

The development of novel high-sensitivity DNA-based biosensors is beneficial, as these devices have applications in the identification of genetic risk factors, medical diagnostics, and environmental monitoring. Herein, we report on the first robust device capable of detecting DNA on a microliter drop with a zepto-molar (10−21) concentration. To accomplish this, we engineered an electrical-electrochemical vertical device (EEVD) that comprises a novel drain and source terminal in a short-circuited configuration, paired with an ideal non-polarizable reference electrode. Vertical electron transfer occurs perpendicularly to the graphene plane, while the electronic current flows through the graphene van der Waals (vdW) heterojunctions. Ferrocene adsorbed on graphene was strategically chosen as the vdW heterojunction redox component. Charge carrier insertion into the graphene makes the EEVD 10 times more sensitive than traditional graphene field-effect transistors. Interfacial potential changes were measured for single-stranded DNA detection with an unprecedented zepto-molar limit of detection.

Faradaic effects in electrochemically gated graphene sensors in the presence of redox active molecules

Field-effect transistors (FETs) based on graphene are promising devices for the direct sensing of a range of analytes in solution. We show here that the presence of redox active molecules in the analyte solution leads to the occurrence of heterogeneous electron transfer with graphene generating a Faradaic current (electron transfer) in a FET configuration resulting in shifts of the Dirac point. Such a shift occurs if the Faradaic current is significantly high, e.g. due to a large graphene area. Furthermore, the redox shift based on the Faradaic current, reminiscent of a doping-like effect, is found to be non-Nernstian and dependent on parameters known from electrode kinetics in potentiodynamic methods, such as the electrode area, the standard potential of the redox probes and the scan rate of the gate voltage modulation. This behavior clearly differentiates this effect from other transduction mechanisms based on electrostatic interactions or molecular charge transfer doping effects, which are usually behind a shift of the Dirac point. These observations suggest that large-area unmodified/pristine graphene in field-effect sensors behaves as a non-polarized electrode in liquid. Strategies for ensuring a polarized interface are discussed.