Electrode Polarization Effects Research Articles

Electro-fermentation and redox mediators enhance glucose conversion into butyric acid with mixed microbial cultures

Electro-fermentation (EF) is an emerging and promising technology consisting in the use of a polarized electrode to control the spectrum of products deriving from anaerobic bioprocesses. Here, the effect of electrode polarization on the fermentation of glucose has been studied with two mixed microbial cultures, both in the absence and in the presence of exogenous redox mediators, to verify the viability of the proposed approach under a broader and previously unexplored range of operating conditions. In unmediated experiments, EF (with the cathode polarized at −700 mV vs. SHE, Standard Hydrogen Electrode) caused an increase in the yield of butyric acid production provided that glucose was consumed along with its own fermentation products (i.e. acetic acid and ethanol). The maximum obtained yield accounted for 0.60 mol mol−1.Mediated experiments were performed with Neutral Red or AQDS at a concentration of 500 μM both in the absence and in the presence of the electrode polarized at −700 mV or −300 mV vs. SHE, respectively. Mediators showed a high selectivity towards the generation of n-butyric acid isomer from the condensation of acetate and ethanol, hence suggesting that they provided microbial cells with the required reducing power otherwise deriving from glucose in unmediated experiments.

Experimental investigation of water-in-oil nanoemulsion in sinking electrical discharge machining

ABSTRACTThe most common dielectric in sinking electrical discharge machining (EDM) is kerosene. However, kerosene is inflammable; besides, it can be decomposed and release harmful gases during machining process. And, owing to its low viscosity, using kerosene in sinking EDM has low machining efficiency. Accordingly, conventional sinking EDM using kerosene as dielectric has poor safety, unfriendly environment impact, and low machining efficiency. A new water-in-oil (W/O) nanoemulsion is presented in this paper. This W/O nanoemulsion not only can eliminate the hazards from kerosene to operator and environment but also improve the machining performance of conventional sinking EDM. This research aims to experimentally investigate the machining performance of W/O nanoemulsion in comparison with kerosene in sinking EDM at relatively low discharge energy. The effects of electrode material, electrode polarity, peak current, and pulse duration on machining performance are studied. The machined surface and recast layer of workpiece are characterized as well. The experimental results demonstrate that compared with kerosene, using W/O nanoemulsion in sinking EDM can obtain a higher material removal rate (MRR), a lower relative electrode wear rate (REWR), and a machined workpiece with fewer defects and thinner recast layer.

Electrical Impedance Spectroscopy for Characterization of Prostate PC-3 and DU 145 Cancer Cells.

The impedance profile of the human PC-3 and DU 145 prostate cancer cells were recorded and compared using Electrical Impedance Spectroscopy. Cells were measured in a special chamber using a four terminal setup to avoid parasitic effects of electrode polarization in low frequencies. Our results show that the two cancer cell lines are readily distinguishable by their impedance spectrum. As PC-3 cells have been shown to be spontaneously metastatic in previous xenograft experiments while DU 145 cells were non-metastatic, Electrical Impedance Spectroscopy has the potential to be developed into a simple diagnostic tool to distinguish metastatic from non-metastatic cells.

Tissue phantom to mimic the dielectric properties of human muscle within 20 Hz and 100 kHz for biopotential sensing applications.

Tissue-mimicking materials for phantoms are fabricated for research purposes to simulate the mechanical or electrical properties of real human tissues and promote better understanding of their properties. This research investigated the dielectric properties (from 20 Hz to 100 kHz) of five promising muscle mimicking materials including matrix materials (gelatin powder and agar powder), and fillers (sodium chloride, glycine and aluminum powder) for the development of muscle phantoms. The mechanical behaviors were verified as well. This research determined the effects of electrode polarization (EP) on the dielectric properties of each material and then used a mathematical model to reduce these unwanted effects. Additionally, the results indicated the very low dielectric properties of gels-only samples. Both electrical conductivity and relative permittivity increased with increasing concentrations of fillers. Moreover, all fillers had their own capabilities to alter the levels and trends in the increments of dielectric values, which provide a wider selection to muscle-mimicking materials. Theoretically, it is feasible to achieve desired dielectric properties by mixing these fillers together with certain ratios. In this way, low-cost muscle phantoms can be produced and used as experimental subjects for biopotential sensing application.

Electrode polarization effects on interfacial kinetics of ionic liquid at graphite surface: An extended lagrangian-based constant potential molecular dynamics simulation study.

Computational models including electrode polarization can be essential to study electrode/electrolyte interfacial phenomena more realistically. We present here a constant-potential classical molecular dynamics simulation method based on the extended Lagrangian formulation where the fluctuating electrode atomic charges are treated as independent dynamical variables. The method is applied to a graphite/ionic liquid system for the validation and the interfacial kinetics study. While the correct adiabatic dynamics is achieved with a sufficiently small fictitious mass of charge, static properties have been shown to be almost insensitive to the fictitious mass. As for the kinetics study, electrical double layer (EDL) relaxation and ion desorption from the electrode surface are considered. We found that the polarization slows EDL relaxation greatly whereas it has little impact on the ion desorption kinetics. The findings suggest that the polarization is essential to estimate the kinetics in nonequilibrium processes, not in equilibrium. © 2019 Wiley Periodicals, Inc.

Characterization of the frequency dependence of the electrical properties of sandy soil with variable grain size and water content

The electrical properties of soil at low radio-frequencies are important for engineering applications. In this work the effects of excitation frequency (42 Hz-1 MHz) as well as soil characteristics and conditions on the electrical properties of soil are experimentally investigated using remolded soil samples. Several sandy soils were tested with variable water content (dry up to saturation) using guarded two-electrode arrangements. A method is proposed based on the Nyquist plot to estimate the critical frequency above which measurements of the electrical properties of wet soil are free from electrode polarization effects. The latter result in extremely high real permittivity values, which do not correspond to the response of soil. The critical frequency is higher for smaller grain size and higher water content and varies according to a power law with soil power-frequency conductivity. The real and (effective) imaginary relative permittivity decrease with increasing frequency whereas the effective conductivity increases; this is attributed to the distributed relaxation of the interfacial polarization mechanism associated with the particulate nature of soil. The values of soil electrical properties increase with increasing water content and decreasing grain size (increasing specific surface) as a consequence of enhanced polarization and conduction phenomena. The effective imaginary permittivity varies with frequency according to a power law with an exponent approximately −1; the multiplier coefficient of this law expresses losses and has been formulated as a function of the degree of saturation and soil specific surface.

Characterization of the frequency dependence of the electrical properties of sandy soil with variable grain size and water content

The electrical properties of soil at low radio-frequencies are important for engineering applications. In this work the effects of excitation frequency (42 Hz-1 MHz) as well as soil characteristics and conditions on the electrical properties of soil are experimentally investigated using remolded soil samples. Several sandy soils were tested with variable water content (dry up to saturation) using guarded two-electrode arrangements. A method is proposed based on the Nyquist plot to estimate the critical frequency above which measurements of the electrical properties of wet soil are free from electrode polarization effects. The latter result in extremely high real permittivity values, which do not correspond to the response of soil. The critical frequency is higher for smaller grain size and higher water content and varies according to a power law with soil power-frequency conductivity. The real and (effective) imaginary relative permittivity decrease with increasing frequency whereas the effective conductivity increases; this is attributed to the distributed relaxation of the interfacial polarization mechanism associated with the particulate nature of soil. The values of soil electrical properties increase with increasing water content and decreasing grain size (increasing specific surface) as a consequence of enhanced polarization and conduction phenomena. The effective imaginary permittivity varies with frequency according to a power law with an exponent approximately −1; the multiplier coefficient of this law expresses losses and has been formulated as a function of the degree of saturation and soil specific surface.

Calculation of Oxygen Potential Profile in Proton-Hole Mix Conductive Electrolyte and its Application for Evaluation of Practical Cells

In this work, IV characteristic and efficiency of protonic ceramic fuel cells and electrolysis cells were discussed based on the oxygen potential profile in mix conductive electrolyte. In protonic electrolyte such as barium zirconate, which exhibits partial hole conductivity in oxygen atmosphere, oxygen potential profile shows a steep slope where hole conductivity is low. As the result, hole blocking layer becomes extremely thin and the rest of the electrolyte shows a significant hole conductivity. Therefore, current leakage cannot be ignored even when the electrolyte material shows quite low electronic conductivity in one side of the electrolyte. When electronic leakage is significant, the analysis of electrochemical measurements becomes complicated. In such case, focusing on the net ionic current is a useful approach to evaluate the cell characteristics. Considering the effect of electrode polarization on the oxygen potential gap at electrode/electrolyte interface, electronic leakage becomes more serious in electrolysis mode. The simulation results showed that both improvement of ionic transportation number of electrolyte and reduction of polarization resistance of oxygen electrode are critical to achieve high efficiency in electrolysis cells.

Effect of Nickel Oxide on the Conductivity of Polymer Blend Electrolyte Doped with Sodium Iodide and Its Application in Dye-Sensitized Solar Cell

Ionic conductivity of electrolyte is one of the factor that influences the efficiency of dye-sensitized solar cell (DSSC). Herein, gel polymer electrolyte (GPE) consist of polyacrylonitrile (PAN), poly(1-vinylpyrrolidone-co-vinyl acetate) (P(VP-co-VAc)), sodium iodide (NaI) dopant and nickel oxide (NiO) additive was prepared using solution casting method. The ionic conductivity study revealed that after the inclusion of NiO, the conductivity was increased from 2.33 mS cm-1 (for polymer blend) to 4.84 mS cm-1. Besides the dielectric properties, the electrical modulus study was conducted to analyse the effect of electrode polarization and ionic conductivity of the GPE. Under the exposure of AM 1.5, the fabricated DSSC utilizing the prepared GPE exhibited photoenergy conversion efficiency of 3.98% with a short circuit current density (JSC) of 15.03mA cm-2, open circuit voltage (VOC) of 0.57 mV and fill factor (FF) of 44.0 %.

Effect of Nickel Oxide on the Conductivity of Polymer Blend Electrolyte Doped with Sodium Iodide and Its Application in Dye-Sensitized Solar Cell

Ionic conductivity of electrolyte is one of the factor that influences the efficiency of dye-sensitized solar cell (DSSC). Herein, gel polymer electrolyte (GPE) consist of polyacrylonitrile (PAN), poly(1-vinylpyrrolidone-co-vinyl acetate) (P(VP-co-VAc)), sodium iodide (NaI) dopant and nickel oxide (NiO) additive was prepared using solution casting method. The ionic conductivity study revealed that after the inclusion of NiO, the conductivity was increased from 2.33 mS cm-1 (for polymer blend) to 4.84 mS cm-1. Besides the dielectric properties, the electrical modulus study was conducted to analyse the effect of electrode polarization and ionic conductivity of the GPE. Under the exposure of AM 1.5, the fabricated DSSC utilizing the prepared GPE exhibited photoenergy conversion efficiency of 3.98% with a short circuit current density (JSC) of 15.03mA cm-2, open circuit voltage (VOC) of 0.57 mV and fill factor (FF) of 44.0 %.

Viscosity decoupled charge transport in surface functionalized ZnS nanoparticle dispersed imidazolium ionanofluids

The mechanism of charge transport in ionic liquid functionalized ZnS nanoparticles dispersed imidazolium-based ionanofluids are investigated combining impedance spectroscopy, viscosity measurement and diff ;erential scanning calorimetry. The viscosity enhances from 76 mPa S to 229 mPa S at room temperature in 0–20 wt% of functionalised nanoparticles addition in the ionic liquid. The conductivity and permittivity spectra are dominated on the low-frequency side by electrode polarization effects. Using the Poisson–Nernst–Planck (PNP) electro-diffusion equations enables us to determine the dc conductivity, ion diffusivity and hopping length of mobile ions and their nature of thermal activation. A decoupling of ion transport with viscosity is observed in the ionanofluids within the entire temperature range and for the 15.0 wt% nanoparticle inserted nanofluid conductivity reaches a maximum value (2.5 mS/cm at 30 °C). The physical explanation regarding the possible origin of the observed remarkable decoupling is proposed.

Computational Study of the Effect of Electrode Polarity on Neural Activation Related to Paresthesia Coverage in Spinal Cord Stimulation Therapy

Using computer simulation, we investigated the effect of electrode polarity on neural activation in spinal cord stimulation and propose a new strategy to maximize the activating area in the dorsal column (DC) and, thus, paresthesia coverage in clinical practice. A new three-dimensional spinal cord model at the T10 vertebral level was developed to simulate neural activation induced by the electric field distribution produced by different typical four-contact electrode polarities in single- and dual-lead stimulation. Our approach consisted of the combination of a finite element model of the spinal cord developed in COMSOL Multiphysics and a nerve fiber model implemented in MATLAB. Five evaluation parameters were evaluated, namely, the recruitment ratio, the perception and discomfort thresholds, and the activating area and depth. The results were compared quantitatively. The dual-guarded cathode presents the maximum activating area and depth in single- and dual-lead stimulation. However, the lowest value of the ratio between the perception threshold in DC and the perception threshold in the dorsal root (DR) is achieved when the guarded cathode is programmed. Although the two versions of bipolar polarity (namely bipolar 1 and bipolar 2) produce higher activating area and depth than the guarded cathode, they are suitable for producing DR stimulation. Similarly, dual-lead stimulation is likely to activate DR fibers because the electrodes are closer to these fibers. The results suggest that the activating area in the DC is maximized by using the dual-guarded cathode both in single- and dual-lead stimulation modes. However, DC nerve fibers are preferentially stimulated when the guarded cathode is used. According to these results, the new electrode programming strategy that we propose for clinical practice first uses the dual-guarded cathode, but, if the DR nerve fibers are activated, it then uses guarded cathode polarity.

A label-free aptamer-based nanogap capacitive biosensor with greatly diminished electrode polarization effects.

A significant impediment to the use of impedance spectroscopy in bio-sensing is the electrode polarization effect that arises from the movement of free ions to the electrode-solution interface, forming an electrical double layer (EDL). The EDL screens the dielectric response of the bulk and its large capacitance dominates the signal response at low frequency, masking information particularly relevant for biological samples, such as molecular conformation changes and DNA hybridization. The fabrication of nanogap capacitors with electrode separation less than the EDL thickness can significantly reduce electrode polarization effects and provide enormous improvement in sensitivity due to better matching of the sensing volume with the size of the target entities. We report on the fabrication of a horizontal thin-film nanogap capacitive sensor with electrode separation of 40 nm that shows almost no electrode polarization effects when measured with water and ionic buffer solutions, thereby allowing direct quantification of their relative permittivity at low frequencies. Surface modification of the electrodes with thiol-functionalized single strand DNA aptamers transforms the device into a label-free biosensor with high sensitivity and selectivity towards the detection of a specific protein. Using this approach, we have developed a biosensor for the detection of human alpha thrombin. In addition, we also examine frequency dependent permittivity measurements on high ionic strength solutions contained within the nanogap and discuss how these support recent experimental observations of large Debye lengths. A large shift in the Debye relaxation frequency to lower frequency is also found, which is consistent with water molecules being in a rigid-like state, possibly indicating the formation of an ordered "ice-like" phase. Altogether, this work highlights the need for better understanding of fluids in confined, nanoscale geometries, from which important new applications in sensing may arise.

Salt concentration and temperature dependent dielectric properties of blend solid polymer electrolyte complexed with NaPF6

Solid polymer electrolytes consisted of poly (ethylene oxide) (PEO) and poly (vinyl) pyrrolidone (PVP) with sodium hexafluorophosphate (NaPF6) salt has been prepared by solution cast technique. The influence of salt concentration and temperature on the complex permittivity, complex conductivity, loss tangent, and complex modulus have been analyzed systematically. The complex permittivity decreases with the increase of frequency and high value of dielectric permittivity in the low-frequency window is attributed to the electrode polarization effect. The peak in the loss tangent plot shift toward high frequency with the addition of salt and increase of temperature clearly indicates the decrease of the relaxation time. The temperature dependent analysis suggests that dielectric properties, dc conductivity, and the molecular chain segmental dynamics increase with the increase of temperature owing to the thermal activation of dielectric properties. The ion migration and dc conductivity are effectively improved by the addition of salt. Aforementioned estimated results strongly convincing its use for the device applications

Self-Similar Interfacial Impedance of Electrodes in High Conductivity Media: II. Disk Electrodes.

Electrode polarization effects were investigated using impedance spectroscopy measurements for planar and nanorod-structured gold disk electrodes at 100 Hz to 1 MHz frequency range and in 0.25 S/m to 1.5 S/m conductivity KCl solutions. Diameters of planar electrodes were varied from 50 μm to 2 mm to examine the effect of electrode size on impedance spectra. Normalizing the impedance magnitude with the spreading resistance and frequency with the characteristic time scale, all experimental data collapsed onto a universal curve, proving self-similarity. Experimental impedance results were compared well with that obtained from the numerical solution of Poisson-Nernst-Planck equations in axisymmetric domain. The influence of surface morphology was also investigated by generating cylindrical nanorods on a planar electrode. The 500 μm diameter electrode surface was covered with cylindrical nanorods with known height, diameter, and separation distance, which were characterized using scanning electron microscopy. The characteristic time scale for the nanorod-structured electrode increased by the surface enlargement factor obtained by cyclic voltammetry measurements. Self-similar interfacial impedance of electrodes was modeled using a constant phase element model. Current findings describe the coupled effects of electrode diameter, electrolyte conductivity, and electrode surface morphology on the impedance spectra of electrode/electrolyte system when the electric double layer between the nanorods does not overlap.

A novel microfluidic high-throughput resistive pulse sensing device for cells analysis

Microfluidic impedance-based devices offer a simple method for counting and sizing particles and cells in fields of biomedical research and clinical diagnosis. In this work, we present design, fabrication and operational characteristics of a novel high throughput original MEMS-based Coulter counter. This microfluidic device possesses two sub channels including two pairs of coplanar Au/Cr electrodes in each channels which allows double detection of the particles simultaneously and increases the throughput. The present design provides minimizing the cross talk and obviating the need for hydrodynamic focusing of the sample particles by adjusting Y shape insulation obstacle in direction of flow. Moreover, reducing coincidence events and removing electrode polarization effect were purposed by applying optimum sizes for electrodes considering the ease of fabrication and low costs. The reliability of the novel device was evaluated for polystyrene particles and cancer cells in conductive solutions. Results, which were recorded as relative resistance pulses across four sensing zones, illustrate the capability of the double-channel proposed device in detecting, counting and sizing 10 and 20 µm polystyrene particles. The superiority of present design was proved by relative counting error of below 3 and 11% for the 10 µm and 20 µm particles, respectively and a throughput of hundreds particles per second. Aiming at demonstrating the functionality of the proposed device in the biomedical area, counting of SP2/0 cells was performed. The measured counting outputs for cells in the size range of 5.63–17.6 µm were validated with results of hemocytometer cell counter, with relative error less than 7%.

High conducting nanocomposite electrospun PVDF-HFP/ $$\hbox {TiO}_{2}$$ TiO 2 quasi-solid electrolyte for dye-sensitized solar cell

A high conducting electrospun nanocomposite polymer PVDF-HFP with a crystalline $$\hbox {TiO}_{2}$$ fillers were synthesized and treated with various redox couple electrolytes for dye-sensitized solar cells is reported. The as-spun nanocomposite membranes were characterized using DSC, XRD and FTIR to study the thermal behaviour, crystallinity and interaction between polymer and fillers. The electrolyte uptake behaviour and impedance response of the electrolyte-activated quasi-solid electrolyte membranes were analyzed. A high conductivity of $$1.41\times 10^{-2}\, \text{S cm}^{-1}$$ were achieved for 6 wt% of crystalline $$\hbox {TiO}_{2}$$ fillers with LiI based redox couple and 4-tert-butylpyridine (TBP) as additive. In order to interpret the conducting mechanism and dielectric response involved in the ion dynamics and relaxation of charge carriers of the prepared quasi-solid electrolytes were analysed by the random barrier model along with the effect of electrode polarization and Havarliak–Negami formalism. The photovoltaic performance of all the prepared electrolytes were investigated for all the fabricated DSSC and obtained an efficiency of 5.93% for electrospun nanocomposite (PVDF-HFP/6wt% of $$\hbox {TiO}_{2}$$ ) polymer with LiI based redox couple and TBP additive, as quasi-solid electrolyte.

Effect of Na2SO4 substitution for Na2O on the structural and electrical properties of a sodium borophosphate glass

The effects of Na2SO4 substitution to Na2O on the structural and electrical properties of a sodium borophosphate glass system prepared by the melt/quenching method were investigated by means of different techniques. The amorphous nature of the glass was evidenced by X-ray diffraction (XRD). Differential scanning calorimetry (DSC) has showed a decrease of glass transition temperature (Tg) while density measurements showed an increase of the molar volume Vm of the glass with the addition of Na2SO4. Raman and infrared (FTIR) spectroscopies have revealed a significant structural change which confirms the behavior of Tg and Vm of the glass. Impedance measurements showed that the overall electrical behavior originates from bulk contribution, whereas the frequency dependence of ac conductivity does not seem to follow the simple Jonscher's power law due to the electrode polarization effects. Moreover, the dc conductivity exhibits an Arrhenius-type behavior with temperature. The decrease of the activation energy and the increase of the electrical conductivity with the addition Na2SO4was discussed based on the results of the structural investigation of the glass.

Physical properties of Ag/Ca doped Lantanium manganite

La0.6Ca0.3Ag0.1MnO3 system has been synthesized using the cheap solid–solid process. Structural analysis indicates that the sample exhibits a single phase of intragranular. Electrical and dielectric data, over a wide temperature range and frequencies have been recorded with impedance spectroscopy. We visualize the conductivity, whose activation energy is low, as a successive hopping of electrons as polaron does. Further, the conductivity is governed by the small polaron hopping model at higher temperature region while it fits well with the variable range hopping model at a lower temperature range. Dielectric data has been represented in different alternative complex formalisms, from which complementary information has been extracted. The complex impedance diagram suggests the contribution of only two active microstructures, ruling out the electrode polarization effect. We adopt the spectrum of the imaginary component of the electric modulus M″ to distinguish long range hopping from short range hopping. The relative permittivity spectrum permits to identify the possibility of the existence of electric polarizations. Further, it reveals colossal static dielectric constant, which makes it suitable for multitude potential applications in electronic industrial fields.

Interplay of \u03b1/\u03b2-Relaxation Dynamics and the Shape of Ionomer Building Blocks

The relation between the α/β relaxations and the shape of the building blocks of ionomer materials is a key factor for programming an important temperature-dependent property: the memory of shape. However, the morphology of ionomers is indirectly obtained via modeling of small angle X-ray scattering (SAXS) data owing to the hardly accessible image characterization of the nanometric building blocks ‒ micelle-like cylindrical polymeric aggregates (radius ~2–6 nm and length >100 nm). Herein, broadband dielectric spectroscopy (BDS) measurements, free from electrode polarization effects, allowed identifying the time and temperature dependence of the polarization of different length scales of the ionomer matrix, and more importantly, by directly providing the aspect ratio of the radius and length of the polymeric aggregates for each desired temperature. This finding is essential for controlling the shape of ionomer based functional products under several stimuli conditions, thereby advancing remarkable applications, such as four dimensional (4D) printing.