Change In Electrode Potential Research Articles

Application of an 800 Gold Microelectrode Array for Rapid Voltammetric Detection of Nitrite Pollution in Environmental Waters

Abstract A simple voltammetric procedure for direct determination of nitrites in natural water samples is described. Measurements are carried out in an inert medium of 0.1 M KCl. The procedure is based on the oxidation of N(III) to N(V) as a result of a change in electrode potential from +0.40 V to +0.96 V. The use of a combined electrode consisting of approximately 800 gold microelectrodes enables undisturbed determinations to be performed in the presence of high concentrations of organic compounds at a level of 20 mg L−1. The calibration plot for NO2− was linear in the range from 2 × 10−6 to 8 × 10−4 M with a detection limit of 6 × 10−7 M. The proposed procedure was successfully applied to nitrate determination in three natural water samples with passable results.

Redox potential shapes spatial heterogeneity of mixed-cultured electroactive biofilm treating wastewater

The core of bioelectrochemical systems (BESs) is electrochemically active microorganisms (EAMs), which exert spatial heterogeneity on electrode surface and influences BESs performance. Setting an optimal potential is an effective strategy for improving and optimizing BESs performance, however, how the electrode potential affects spatial structure of microbial community within anode biofilm is not known. Using a complex substrate-fed BES with a wastewater inoculum, this study investigated the community structure and composition of the stratified biofilm developed under the potential of −0.3 V, 0 V, +0.3 V and +0.6 V (vs. saturated calomel electrode) by freezing microtome method and high-throughput sequencing analysis. The spatial heterogeneity of biofilm community was found to be dependent on the electrode potential and a less-stratified community structure was observed for +0.6 V than other potentials. Within the biofilms, the inner layers selected more Geobacter and the outer layers enriched more Acinetobacter and Serratia, potentially suggested a stratification of electron transfer pathway and metabolite-based interspecies communications. The results demonstrated the response of spatial heterogeneity of anode biofilm community to the change of electrode potential, which help to understand the selective and enrichment of kinetically efficient anodic microbiome by electron potential.

Corrosion Degradation Behavior of Bending Aluminum and Copper Materials for Air Conditioning Refrigerant Piping

Introduction Many types copper alloys of refrigerant piping are used for practical use owing to their high workability, thermal conductivity, and weather ability. However, there is concern about depletion, due to consume in large quantities via emerging country and new devices such as electric vehicle and so on. Recently, we focused on aluminum as light metal, and applied for refrigerant piping of air-conditioning equipment. We focused on corrosion factors of piping for inside (refrigerant passage) and outside (atmospheric exposure) and investigated simulated practical used straight sections. As a result, almost equal practicalities were confirmed for both cases of aluminum and copper [1].In actual refrigerant piping, bending sections are always appared utilized alongside straight pipes. When pipes are bent using a bender, tensile stress occurs on the outer surface and compressive stress on the inner surface. Stress corrosion cracking (SCC) can be induced under tensile stress in corrosive environments. Evaluating SCC potential in aluminum piping due to bending is crucial for its long-term use in refrigerant piping. Therefore, in this study, mechanical, electrochemical characteristics, and weather resistance characteristic of bending aluminum and copper piping under tensile stress were investigated to confirm practicality of Al refrigerant piping. Experiments A6063-T83(Al-T) and C1220-1/2H(Cu-H) were used for the aluminum materials and utilized copper materials, respectively. To confirm the electrochemical characteristics in order to investigate the difference in the bending curvature, natural electrode potential measurements were examined at eight bent points (four on the tensile side, four on the compressive side) and one straight segment. The natural potential of the samples was measured using a three-electrode method, with the samples, Pt wire, and Ag/AgCl as working, counter and reference electrodes, respectively, immersed in a 3.0 mol L-1 NaCl solution. Measurements were carried out using a potentiostat (HZ-5000, Hokuto Denko) at 303 K maintained by a constant-temperature water bath. To investigate the corrosion resistance of bending aluminum and copper piping, cyclic degradation test was performed according to the Japanese Automotive Standard JASO M610-92. Each cycle, lasting 8 hours, comprised three steps: 1. neutral saltwater spray (35°C, pH 6.5-7.2, 2h), 2. drying (60°C, 25% RH, 4h), and 3. humidification (50°C, 95% RH, 2h). Specimens were removed at 8h, 24h, 48h, 96h, 192h, 384h, and 496h during the cyclic degradation test for appearance observation. In addition, Samples at 496h, cross-sectional observations using SEM (JSM-7200F, JEOL) were performed after etching the samples at the tensile and compressive sides of the bent sections and the straight segment. Results & Discussion Fig.1 shows the time dependence in the natural electrode potential of tensile side of Cu-H. At all measurement points, stable natural potential of -0.27 V vs. Ag/AgCl(V) and no significant natural electrode potential changes were confirmed during the measurement time. Fig.2 shows the time dependence in the natural electrode potential of tensile side of Al-T. At all measurement points, the average natural potential value remained approximately -0.75 V vs. Ag/AgCl(V) across all measurement points, and no significant natural electrode potential changes were observed during the measurement time. However, deviations in the natural electrode potential values were also slightly observed at measurement points c and d with a large curvature in the bent part. These results suggested that regions with increased curvature due to bending might be occured to destroying to the oxide film on the surface of the Al piping, indicating subtle yet progressing oxidation. Fig 3. shows cross-section SEM images of the tensile and compressive sides of the bent sections and the straight segment of Cu-H after 496h cyclic degradation test. No significant were observed in all observation points.The results of this measurement indicate that the no evidence of corrosion of the copper tube due to tensile stress. Fig 4. shows cross-section SEM images of the tensile and compressive sides of the bent sections and the straight segment of Al-T after 496h cyclic degradation test. Thin oxide observed at all the measurement points, but there were no significant differences observed in its production at each of the measurement locations. In an environment of constant exposure to seawater, such as that encountered in the natural electrode potential measurements, chlorine can cause severe damage to the Al bending piping. On the other hand, cyclic degradation tests ,which simulated actual use for severe weather resistance performances, conditions suggested that the effects of Al bending are minimal, as the oxide film is re-formed during the wet-dry process. Thus we demonstrated that Al bending piping must use in practical useful.[1] S. Uchiyama, et., al., Mater Corros.(Wiley), 74, 344-351 (2023). Figure 1

Three modes of electrochemical impedance spectroscopy measurements performed on vanadium redox flow battery

This article presents an innovative approach to monitor working redox flow batteries using dynamic electrochemical impedance spectroscopy, diverging from the commonly sequential impedance methods carried out under potentiostatic or galvanostatic conditions close to the open circle voltage. The authors introduce a fresh variation of dynamic impedance measurement that leverages an amplitude-modulated multi-frequency alternating current perturbation signal. This technique leads to a reduction in measurement time, making it possible to monitor impedance in real-time under typical operational conditions. Consequently, it effectively addresses the limitations stemming from the absence of stationary conditions during impedance measurements. There is no doubt that measurement techniques enabling the study of processes during the operational life of a battery provide the most valuable insights into the properties of these systems. The potential of this proposed approach is exemplified through the examination of a full vanadium redox flow battery as a case study. Classical impedance measurements were also conducted under potentiostatic and galvanostatic conditions with sequential frequency signal change, which requires stopping the battery operation, resulting in electrode potential changes of over 200 mV compared to the working system. Spectra for all modes of measurements were compared. In the case of dynamic measurements, such significant differences in spectra during charging and discharging are not observed, which is characteristic of classical measurements. The authors deliberately and consciously refrain from analyzing the results by fitting equivalent circuits.

Partial Discharge Detection Method of Electrical Equipment Based on UHF Method

Partial discharge is an early symptom of insulation defects. In the field application, the detection method can not accurately identify those noise signals mixed in the partial discharge signal, which limits the detection to a certain extent. Based on UHF method, a partial discharge detection method for electrical equipment is designed. When partial discharge occurs, the exchange between charges, the radiation of electromagnetic waves and the consumption of energy will occur at the discharge position, causing the change of electrode potential. For the phase distribution spectrum, the signal characteristics produced by partial discharge are extracted from three aspects: statistical information, time domain information and frequency domain information. During detection, UHF sensor is placed on the basin insulator, and then UHF signal is received. Insulation defects are identified according to various differential discharge patterns formed by the discharge characteristics of different defects. Test results show that the signal spectrum detected by UHF partial discharge roughly matches the typical discharge spectrum, and it is determined that there is partial discharge in this area. This method has high positioning accuracy and meets the detection requirements of electrical equipment.

Design of stretchable and self-powered sensing device for portable and remote trace biomarkers detection

Timely and remote biomarker detection is highly desired in personalized medicine and health protection but presents great challenges in the devices reported so far. Here, we present a cost-effective, flexible and self-powered sensing device for H2S biomarker analysis in various application scenarios based on the structure of galvanic cells. The sensing mechanism is attributed to the change in electrode potential resulting from the chemical adsorption of gas molecules on the electrode surfaces. Intrinsically stretchable organohydrogels are used as solid-state electrolytes to enable stable and long-term operation of devices under stretching deformation or in various environments. The resulting open-circuit sensing device exhibits high sensitivity, low detection limit, and excellent selectivity for H2S. Its application in the non-invasive halitosis diagnosis and identification of meat spoilage is demonstrated, emerging great commercial value in portable medical electronics and food security. A wireless sensory system has also been developed for remote H2S monitoring with the participation of Bluetooth and cloud technologies. This work breaks through the shortcomings in the traditional chemiresistive sensors, offering a direction and theoretical foundation for designing wearable sensors catering to other stimulus detection requirements.

Potential Distribution across Model Membranes.

Membrane models assembled on electrodes are widely used tools to study potential-dependent molecular processes at or in membranes. However, the relationship between the electrode potential and the potential across the membrane is not known. Here we studied lipid bilayers immobilized on mixed self-assembled monolayers (SAM) on Au electrodes. The mixed SAM was composed of thiol derivatives of different chain lengths such that between the islands of the short one, mercaptobenzonitrile (MBN), and the tethered lipid bilayer an aqueous compartment was formed. The nitrile function of MBN, which served as a reporter group for the vibrational Stark effect (VSE), was probed by surface-enhanced infrared absorption spectroscopy to determine the local electric field as a function of the electrode potential for pure MBN, mixed SAM, and the bilayer system. In parallel, we calculated electric fields at the VSE probe by molecular dynamics (MD) simulations for different charge densities on the metal, thereby mimicking electrode potential changes. The agreement with the experiments was very good for the calculations of the pure MBN SAM and only slightly worse for the mixed SAM. The comparison with the experiments also guided the design of the bilayer system in the MD setups, which were selected to calculate the electrode potential dependence of the transmembrane potential, a quantity that is not directly accessible by the experiments. The results agree very well with estimates in previous studies and thus demonstrate that the present combined experimental-theoretical approach is a promising tool for describing potential-dependent processes at biomimetic interfaces.

Continuous measurements of gaseous oxygen production in Bray-Liebhafsky oscillatory reaction and its correlation with the reaction mechanism

• Experimental setup for evolved oxigen monitoring was constructed. • Bray-Liebhafsky reaction was investigated at 2 mixing rates in 5 replicates. • Lower mixing rate preserve higher content of dissolved gas. • Lower stirring facilitate oscillatory evolution. • Heterogeneous effects assist in triggering iodine oxidation. Upgraded design of the experimental setup for monitoring Bray-Liebhafsky (BL) oscillatory reaction dynamics allowed simultaneous recording of platinum electrode potential and gaseous pressure changes over time. Experiments were performed at two stirring rates (600 rpm and 1200 rpm) in five replicates. Evolved gas at two mixing rates is correlated with reaction induction period, number of oscillations, period between oscillations, oscillation amplitude and number of produced oxygen moles per oscillation. Obtained trends indicate that the amount of formed gas facilitates initiation of iodine oxidation. Results are in agreement with previous findings which point to the importance of heterogeneous effects in reaction of iodine oxidation.

Thermodynamics of chalcocite dissolving in solutions of flotation reagents

This work describes the formation of the ionic composition of the sorption layer during the concentration of copper-lead and pyrite-copper-zinc ore. The thermodynamics of the sorption layer of a sulfhydryl collector (sodium diisobutyl thiophosphate and potassium butyl xanthate) on the surface of chalcocite under various conditions of its oxidation has been studied using pH- and redoxometry. The nature of the change in the chalcocite electrode potential depending on the type of modifier and storage device, as well as on pH, has been experimentally clarified. The differences in the collective action of a one-component accumulator and a mixture of flotation reagents were revealed based on the thermodynamics analysis of the flotation process reactions. In addition, the optimal conditions for the flotation were determined. It was found that the quality of the concentrate is mainly influenced by two factors, such as the pulp redox potential and the pH of the medium. Mathematical equations of the optimal reagent and hydrodynamic enrichment regimes with the maximum dissolution of ore minerals in solutions of flotation reagents were modeled.

Rate-controlling element in the self-discharge process in electrochemical double-layer capacitors

Suppression of self-discharge is crucial in the development of electrochemical double-layer capacitors (EDLCs). In this study, the rate-controlling element of the self-discharge process in EDLCs was explored without any new additives, and the anion was found to play a critical role in this process. The thickness ratio between the positive and negative electrodes (P/N ratio) was the primary factor used to control the self-discharge rate. As the P/N ratio increased, the anion density in the positive electrode decreased. The P/N ratio was increased to retain the anions for a longer period in the cell, which caused self-discharge suppression and led to a slow change in the positive electrode potential when held at an open-circuit status. Cells with a P/N ratio of 1.37 showed 26 to 32% reduced voltage decay than did those with a P/N ratio of 1.00 after 70 h.

Potentio-tunable FET sensor having a redox-polarizable single electrode for the implementation of a wearable, continuous multi-analyte monitoring device

The emerging field of wearable devices for monitoring bioanalytes calls for the miniaturization of biochemical sensors. The only commercially available electrochemical wearable monitoring medical devices for bioanalytes are the amperometric continuous glucose monitoring (CGM) systems. The use of such amperometric methods to monitor glucose levels requires a relatively large electrode surface area for sufficient redox species collection, allowing accurate measurements to be made. Consequently, miniaturization of such sensors bearing large electrodes is challenging. Furthermore, it is difficult to introduce and deploy more than one electrode–based sensor per device, thereby limiting the number of analytes that can be monitored in parallel. To address these limitations, we have employed a non-referenced, single polarizable electrode coupled to a fin-shaped field-effect transistor (Fin-FET). We have discovered that by passivating the FET area by a relatively thick oxide and/or polytetrafluoroethylene (PTFE) polymer, leaving only the polarizable working electrode (WE) exposed, we can monitor redox analytes at the micromolar to millimolar concentration range. We attribute this effect to the WE polarization by the solution redox species. We have exploited the superior sensitivity of the adjacent silicon-based Fin-FET to detect changes in sensor electrode potentials induced by the redox species. Furthermore, we demonstrated the correlation between a specific analyte and the biasing WE potential on the accumulation/depletion of the coupled Fin-FET channel as manifested by the transistor source-drain current. Moreover, we utilized the analyte-electrode potential interaction, which is analyte-specific, to tune the specificity of the sensor towards an analyte of choice. In addition, we demonstrated the use of a single-electrode potentiometric sweep to assist in identifying the accumulation/depletion as a result of analyte-WE state. Collectively, the tiny potentio-tunable electrochemical sensor (PTEchem sensor) area is ~50 × 50 µm, and dedicated wireless transducer facilitates the use of this sensor for wearable continuous, multi-metabolite monitoring.Graphical abstract

Synthesis of V-doped urchin-like NiCo2O4 with rich oxygen vacancies for electrocatalytic oxygen evolution reactions

In this paper, 3D urchin-like V-doped NiCo2O4 was synthesized as an efficient electrocatalyst for electrocatalytic oxygen evolution reaction (OER). NH4VO3 and VCl3 act as various dopants to provide V5+ and V3+ ions, and the valence effects of V dopants on the structural modulation of NiCo2O4 are examined systematically. XPS results show that the doping of V3+ to NiCo2O4 provides an extra 16.40% percentage of oxygen vacancies (Ov) than that of V5+ doping, which can significantly modulate the OH− adsorption on NiCo2O4. EPR tests further confirm that the content of Ov in V3+ doped NiCo2O4 (V(Ⅲ)-NiCo2O4) is 2.81 times higher than that in V5+ doped NiCo2O4 (V(V)-NiCo2O4). Besides, V(Ⅲ)-NiCo2O4 shows higher molar content of Co2+ comparing to V(V)-NiCo2O4, resulting in an increased probability of forming CoOOH catalytic active sites. Electrochemical investigations show that V(Ⅲ)-NiCo2O4 electrocatalyst achieves excellent OER catalytic activity with a low overpotential of 344 mV at 10 mA cm−2, and it holds superior OER stability of electrocatalysis at 100 mA cm−2 for 50 h without significant change in electrode potential. Thus, this paper shows the importance of the valence of dopant precursor to the doped structures, and these findings pave a new sight of designing heteroatom doped electrocatalysts for OER.

Investigating oxidative stability of lithium-ion battery electrolytes using synthetic charge-discharge profile voltammetry

Electrolytes are an integral part of any electrochemical energy storage systems, including batteries. Among the many properties which determine the applicability of a Li-ion battery electrolyte, electrochemical stability – and for high voltage electrodes, in particular anodic stability – is a key parameter to consider. Despite being simple and straightforward to employ, the conventional linear sweep voltammetry (LSV) technique often leads to an over-estimation of the oxidative stability. In this study, an alternative approach termed Synthetic Charge-discharge Profile Voltammetry (SCPV) is explored to investigate the oxidative electrolyte stability. We have found this to be a convenient method of quantifying the anodic stability of the electrolyte in a more practically representative manner, in which passivation kinetics and electrode potential changes at the electrode-electrolyte interface are more appropriately reproduced. The viability of this technique is explored with liquid electrolytes based on ether, carbonate, sulfone and carbonate-sulfone mixtures, all with lithium hexafluorophosphate (LiPF6) salt, tested for a potential profile equivalent to LiNi0.5Mn1.5O4 electrodes. The credibility of this technique is validated by correlations to the coulombic efficiencies of corresponding half-cells.

Comparative study of the crystallographic expansion of GSC and LSC porous electrodes

AbstractCharacteristics of the porous Gd0.15Sr0.85CoO3−δ and La0.6Sr0.4CoO3−δ cathodes were compared using the data measured at different electrode potentials and oxygen partial pressures. The electrochemical high‐temperature in situ XRD (HT‐XRD) method combined with electrochemical impedance spectroscopy has been used. The response of the crystallographic parameters and impedance values on the changes of electrode potential has been discussed. Reversible changes of the lattice parameters for both cathodes, slower for Gd0.15Sr0.85CoO3−δ compared with La0.6Sr0.4CoO3−δ, were observed depending on temperature (T), electrode potential (E), and oxygen partial pressure (pO2). The crystallographic parameters are determined by the vacancy formation kinetics as well as by vacancy formation energy in/at the cathode grain structure. Calculated impedance data were fitted to the experimental data and characteristics were obtained in context of crystallographic changes of the cathode materials studied.

Emergence of Temporal Instabilities during Electro-Dissolution of Nickel-Iron Alloy

Dynamics instabilities are often observed in many systems, such as biological, chemical, physical, and others. Some very commons examples are the circadian rhythms that regulates biological process during the rotation of the Earth every 24 hours, and dunes formations where the topographical structures are built with large masses of sand accumulated. These instabilities can be classified as spatial, where the vicinity affect the emergence of instabilities, and temporal, when the instabilities are time dependent. In chemical systems there is a well-known Belousov-Zhabotinsky reaction where the instabilities rise between citric acid, bromate ions and ceric ions (or similar set of substances) and is possible to emerge spatial and temporal instabilities.Among many chemical systems the electrochemical has been of great interest due to the fine adjustment that is possible by the potential or current control. Another advantage is that electrochemical setup is relatively simple, formed in most cases by a working electrode, counter-electrode and reference electrode emerging from an electrolyte inside a container. Anodic dissolution of metals has been studied since 1828, with the reports by Fechner. Many studies were performed using different metals like Cu, Fe, Ni, among others, as electrochemical oscillators using single or multielectrode configuration coupled under different network topologies, where the latter configuration has been made often using similar electrodes. In this present work, we report experimental studies of the coupling between two different electrochemical oscillators during the electro-dissolution of Ni and Fe, not as two separated electrodes but like an alloy.To perform the experiments was utilized a glass electrochemical cell with 3 electrodes, a platinum sheet as counter-electrode, a saturated calomel electrode as reference electrode, and a Ni-Fe(80-20) alloy embedded in Teflon with a cylindrical shape and a diameter of 0.5 cm as working electrode. For comparison, all experiments were performed also using a pure Ni and a pure Fe with the same geometry of the alloy as working electrode. All experiments were carried out using H2SO4 1 mol L-1 as electrolyte and before each electrochemical experiment the working electrode was polished to ensure that the surface will be the same, i.e., the absent of oxides and other substances on the surface. The phenomenon observed during the experiments is described in terms of stationary and dynamic electrochemical techniques such as chronoamperometry and cyclic voltammetry, varying the external resistance Rext of the system. For each Rext applied there is a different potential range where the oscillations occur during cyclic voltammetry and by different Rext applied was built a bifurcation diagram (Rext vs. E). In each region of oscillations was performed chronoamperometry experiments, choosing different potential applied values, where is possible to note the electrode potential change, revealing that occurs a separation of the activation and passivation processes during an oscillatory cycle.Comparing with the Ni and Fe pure electrodes, these results suggest that there is a change in the mechanism during the emergence of the oscillations in the Ni-Fe alloy. For the alloy at low potentials, there is a mixed contribution from both Ni and Fe dissolution on the oscillations, that occurs before the Flade potential, while the pure Ni dissolution occurs in the transpassive domain with range of ~1.2 to 1.5 V vs. SCE (both with Rext 392 Ω cm2) and the pure Fe dissolution ~0.4 to 0.6 vs. SCE (without Rext). The mixed contribution produced by Ni and Fe in the alloy during the oscillatory electro-dissolution are caused because of their oxides and salts present in the passivation step, which impacts on the instabilities generated during the nonlinear dynamics of the system. With these results we can conclude that a small amount of Fe (only 20%) on the Ni electrode at electro-dissolution process is enough to induce a change in the mechanism during the emergence of oscillations, suggesting that a new process is taking place, from high potentials for Ni (~1.2 to 1.5 V) to lower overpotentials for Ni-Fe alloy (~-0.1 to 0.1 V). Also, there is a suppression of the transpassive state, i.e, is observed in pure Ni and absent in the Ni-Fe alloy. The Figure compares the shape and period of the oscillations for each electrode at some fixed potentials, Ni (a), Ni-Fe (b), and Fe (c).As perspectives of the work we are working to observe the instabilities using other conditions to be able to understand more deeply the mechanism found by the Ni-Fe alloy. We also intend to develop simulations to describe this phenomenon more accurately. Figure 1

Ionic liquid–metal interface: The origins of capacitance peaks

The complex nature of electrode charge screening is well-known for ionic liquids (ILs). Due to strong ion–ion correlations, these electrolytes form a distinctive layered structure at interfaces. Variations in electrode potential cause structural changes that are reflected in a peculiar shape of differential capacitance–potential dependence with characteristic peaks. Although the differential capacitance for various ILs in conjunction with metal electrodes accessed via molecular dynamics (MD) simulations has been reported in the literature, retrieving a capacitance-potential curve, C(U), from the MD trajectories is not a trivial task. In this work, we present the results of the MD simulations of the IL 1-butyl-3-methylimidazolium hexafluorophosphate at a single-crystalline Au (100) surface. The discussion focuses on the simulation data treatment for C(U) curve fitting. It is shown that the resulting C strongly depends on the fitting method used. Four capacitance peaks and three structural reorganization types were identified in the studied system. With the help of a semi-quantitative approach in the framework of the original bilayer model of electric double layer (EDL), it is argued that the ions’ reorientation is in the origin of the capacitance peaks. Also, it is shown that under the conditions of this study, the multilayer structure, characteristic of EDL in ILs on the whole, is far from the “lattice saturation” regime. The multilayer structure possesses a steric packing effect that impedes structural changes, decreasing the capacitance.

Control of Reactions on Bipolar Electrodes Using Ion-Selective Membranes

Bipolar electrochemistry is promising in realizing simultaneous multiplexed detection. In open bipolar systems, a potential gradient is formed in a solution. When an isolated electrode (bipolar electrode: BPE) that is not in contact with an external device is placed in the potential gradient, interfacial potential difference develops between the BPE and the solution (Figure 1A). As a result, oxidation and reduction reactions occur simultaneously on both poles (Figure 1B) [1]. The progress of the reduction reaction on the cathodic pole can be measured by coupling the reaction with a reaction that generates electrochemiluminescence (ECL) [2]. However, a problem with this method is that the interfacial potential difference on the BPE is not precisely controlled. In other words, the potential profile with respect to the electrode potential changes (Figure 1C). To solve this problem, we used an ion-selective membrane (ISM) on a part of the BPE. The ISM has an effect to fix the interfacial potential difference at the location without current generation through the interface (Figure 1D).Arrays of BPEs were formed with gold and Na+ ISM was formed on a part of each BPE. The surface of the BPE was insulated with a polyimide layer except for the anodic and cathodic poles and the active area of the ISM. To form the ISM, a layer of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS) was first coated on an exposed area of the BPE. The Na+ ISM was formed on the PEDOT/PSS layer. The solution to form the ISM contained 43.97 wt% polyvinyl chloride (PVC) dissolved in 1 mL tetrahydrofuran (THF). 53.38 wt% of nitrophenyl octyl ether (NPOE), 2.04 wt% of sodium ionophore X, and 0.61 wt% (w/w) of sodium tetrakis(4-fluorophenyl)borate (NaTFPB) were added to the PVC solution and mixed well. After forming the ISM, its peripheries were fixed with a silicone adhesive.In the experimental setup shown in Figure 1A, platinum wires (diameter: 0.5 mm) were used for the driving electrodes. The distance between the driving electrodes was 30 mm. To cause the ECL reaction, 10 mM phosphate buffer solution (pH 6.9) containing 5.0 mM tripropylamine (TPA) and 1.0 mM [Ru(bpy)3]2+ was used. Oxygen dissolved in the solution was used as an analyte. The experiments were conducted at 25°C.To control the potential of the BPEs, we previously used Ag/AgCl for the potential control. However, a problem was that current flowed through the non-polarizable metal/solution interface, affecting the ECL intensity. With regard to this, the ISM is superior because current does not flow. The effect of placing the ISM on a part of the BPE was first examined using BPEs of the same length and changing the location of the ISM (Figure 2). The ion selective electrode (ISE) was effective and the ECL intensity changed by changing the location of the ISE. The effect of the ISM was also demonstrated using folded double BPE structures with the ISM formed at either or both ends. Brighter ECL was observed with the folded structure compared with a single BPE. From these experiments, the effect of placing the ISM on BPEs was clearly observed. As an application to biosensing, we also tested the detection of glucose by immobilizing glucose oxidase and osmium polymer on the cathodic pole. The ECL was also observed accompanying the production of hydrogen peroxide by glucose oxidase and following the reduction of hydrogen peroxide.The effect of placing the ISM was also examined in closed bipolar systems. In the closed bipolar systems, solutions in the cathode and anode side are separated in different compartments. In this study, 15 mm-long electrodes were used and the electrodes extended in the two compartments. The anodic pole was exposed to the solution for ECL, whereas the cathodic pole was immersed in a Na2SO4 solution. A voltage (2.4 V) was applied between the driving electrodes immersed at the end of the solutions. The brightest ECL was observed on the BPE with the ISM nearest to the cathodic pole. The result indicates that the ISM is also effective in controlling the potential for closed bipolar systems.[1] S. E. Fosdick, K. N. Knust, K. Scida, R. M. Crooks. Bipolar electrochemistry. Angewandte Chemie International Edition, 52 (2013) 10438-10456. doi:10.1002/anie.201300947[2] K. F. Chow, F. Mavré, R. M. Crooks. Wireless electrochemical DNA microarray sensor. Journal of the American Chemical Society, 130 (2008) 7544-7545. doi:10.121/ja802013q Figure 1

Evaluation of Electrochemical Process Improvement Using the Computer-Aided Nonlinear Frequency Response Method: Oxygen Reduction Reaction in Alkaline Media.

The intensification of an electrochemical process by forced periodic operation was studied for the first time using the computer-aided Nonlinear Frequency Response method. This method enabled the automatic generation of frequency response functions and the DC components (Faradaic rectification) of the cost (overpotential) and benefit (current density) indicators. The case study, oxygen reduction reaction, was investigated both experimentally and theoretically. The results of the cost–benefit indicator analysis show that forced periodic change of electrode potential can be superior when compared to the steady-state regime for specific operational parameters. When the electrode rotation rate is changed periodically, the process will always deteriorate as the dynamic operation will inevitably lead to the thickening of the diffusion layer. This phenomenon is explained both from a mathematical and a physical point of view.

On the utilization of supercapacitor electrode materials

Representative supercapacitor electrode materials: activated carbon for an electrochemical double layer capacitor, MgCo2O4 showing redox, i.e. non-pseudocapacitive, and MnO2 showing pseudocapacitive behavior have been examined and compared regarding mass utilization as a function of active layer thickness, i.e. mass loading, of rate of electrode potential change and current density. Conclusions regarding degree of utilization and rational design of active material layer thickness are highlighted, suggestions for suitable reporting of data for rational comparison of results are offered.

Theoretical Analysis of Changes in the System’s Composition in the Course of Oxidative Electrolysis of Bromide Solution: pH Dependence

Changes in the indicator electrode potential (at zero current) E and (quasi) equilibrium composition of aqueous solution in the anode chamber of the model electrolyzer, which initially contained 0.5 M concentration of bromide anions, provided that the solution was kept at a constant pH and constant (together with the gas phase above it) total number of Br atoms in all its compounds, are calculated. Theoretical analysis was carried out for four different hypotheses regarding the possible extent of electrolysis and the nature of the processes are theoretically analyzed. They are: (1) no formation of bromine compounds with positive oxidation states occurs, i.e., electrolysis only leads to the formation of molecular bromine in its various forms (the dissolved state of Br2, as well as phases of liquid bromine $${\text{Br}}_{{\text{2}}}^{{{\text{liq}}}}$$ , and bromine vapor in the gas space above the $${\text{Br}}_{{\text{2}}}^{{{\text{vap}}}}$$ solution); (2) oxidation of bromide ions leads to the formation of bromine compounds in its oxidation state up to +1 inclusive; (3) the process proceeds with the formation of both bromate ion (BrO3-) and compounds of bromine with lower oxidation states in solution ( $${\text{Br}}_{{\text{3}}}^{ - },$$ $${\text{Br}}_{{\text{5}}}^{ - },$$ Br2, $${\text{Br}}_{{\text{2}}}^{{{\text{liq}}}},$$ $${\text{Br}}_{{\text{2}}}^{{{\text{vap}}}},$$ BrO–, HBrO); (4) in addition to the components specified in clause (3), the formation of the perbromate anion $$\left( {{\text{BrO}}_{{\text{4}}}^{ - }} \right)$$ is also taken into consideration. All electrochemical and chemical reactions involving bromine-containing species have been taken into consideration in the hypothesis framework of the system’s evolution (1), (2), (3), or (4), are assumed to be in a (quasi)equilibrium state. Predictions for all hypotheses (1), (2), (3), or (4) have been compared at three different pH values of the solution (2, 6 and 10 of Br-containing anolyte composition’s evolution in the course of electrolysis.