Standard Reference Electrode Research Articles

Cathodic Decomposition Electrodes as Standard Reference Electrodes for Molten Salts: Example of the Lithium Eutectic Electrode for the LiCl-KCl Eutectic

Alternatives to the widely-used standard anodic decomposition reference electrodes in molten salts are necessary to enable more easily reproduced thermochemical and electrochemical data in molten salt electrolytes. The class of standard reference electrodes called cathodic decomposition electrodes (CDEs) are easily constructed and can be used to make thermochemical measurements in molten salts more directly compared to anodic decomposition electrodes. The lithium eutectic electrode (LEE) was chosen as a sample test case for validation and was applied to thermochemical measurements of electroactive species in molten LiCl-KCl eutectic. Transient measurements were made to measure the Li+/Li reduction potential at zero current in pure LiCl-KCl eutectic relative to a Li-alloy reference electrode to validate the reference potential of the LEE. Literature-reported electromotive force measurements against Li-alloy reference electrodes were used to generate a relationship between the LEE and the standard chlorine electrode and this relationship was used to evaluate measured and reported formal potential measurements for the LiCl-KCl-GdCl3 system. This work demonstrates the general framework for defining CDEs for any molten salt system and a method for calibrating external reference electrodes against a CDE standard reference electrode, improving the ease of obtaining thermochemical and electrochemical measurements in any molten salt system.

Development of a Disposable Polyacrylamide Hydrogel-Based Semipermeable Membrane for Micro Ag/AgCl Reference Electrode

Currently, Ag/AgCl-based reference electrodes are used in most electrochemical biosensors and other bioelectrochemical devices. However, standard reference electrodes are rather large and do not always fit within electrochemical cells designed for the determination of analytes in low-volume aliquots. Therefore, various designs and improvements in reference electrodes are critical for the future development of electrochemical biosensors and other bioelectrochemical devices. In this study, we explain a procedure to apply common laboratory polyacrylamide hydrogel in a semipermeable junction membrane between the Ag/AgCl reference electrode and the electrochemical cell. During this research, we have created disposable, easily scalable, and reproducible membranes suitable for the design of reference electrodes. Thus, we came up with castable semipermeable membranes for reference electrodes. Performed experiments highlighted the most suitable gel formation conditions to achieve optimal porosity. Here, Cl- ion diffusion through the designed polymeric junctions was evaluated. The designed reference electrode was also tested in a three-electrode flow system. The results show that home-built electrodes can compete with commercial products due to low reference electrode potential deviation (~3 mV), long shelf-life (up to six months), good stability, low cost, and disposability. The results show a high response rate, which makes in-house formed polyacrylamide gel junctions good membrane alternatives in the design of reference electrodes, especially for these applications where high-intensity dyes or toxic compounds are used and therefore disposable electrodes are required.

Home-Based Electrochemical Rapid Sensor (HERS): A Diagnostic Tool for Bacterial Vaginosis.

Bacterial vaginosis (BV) is the most frequently occurring vaginal infection worldwide, yet it remains significantly underdiagnosed as a majority of patients are asymptomatic. Untreated BV poses a serious threat as it increases one's risk of STI acquisition, pregnancy complications, and infertility. We aim to minimize these risks by creating a low-cost disposable sensor for at-home BV diagnosis. A clinical diagnosis of BV is most commonly made according to the Amsel criteria. In this method, a fish-like odor, caused by increased levels of trimethylamine (TMA) in vaginal fluid, is used as a key diagnostic. This paper outlines the development of a Home-Based Electrochemical Rapid Sensor (HERS), capable of detecting TMA in simulated vaginal fluid (sVF). Instead of odor-based detection of volatilized TMA, we identify TMA in trimethylammonium form by utilizing HERS and a potentiometric readout. We fabricated the ion selective electrode using a carbon-black-coated cotton string and a TMA-selective membrane consisting of calix[4]arene and sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate. When paired with a standard reference electrode, our device was able to quantify TMA concentration in deionized (DI) water, as well as sVF samples at multiple pH levels with a clinically relevant limit of detection (8.66 µM, and theoretically expected Nernstian slope of 55.14 mV/decade).

(Digital Presentation) Silver Electrode Potentials in NaCl–KCl–Cscl Eutectic Melts

Molten salts have a number of potential applications including metals’ electrowinning and electrorefining, pyrochemical spent nuclear fuels’ reprocessing. Considerable efforts were devoted over decades to investigation of various electrochemical processes in molten salts, especially in fused chlorides. Silver chloride electrode is one of convenient types of reference electrodes often employed in potentiometry measurements. This electrode has several advantages (especially compactness) compare to the standard chlorine reference electrode, potential of which in chloride melts is taken as zero. Surprisingly little attention was paid so far to the systematic study (covering the effect of temperature and concentration) of silver electrode potentials in molten chlorides, with majority of the works dating back to 1950-s and 60-s. Molten LiCl–KCl eutectic was, on obvious reasons, the best studied, and several other melts (NaCl, NaCl–KCl, LiCl–KCl–CsCl, NaCl–CsCl) were also looked at.The present study was directed at the systematic study of silver electrochemistry in fused alkali chlorides and determining silver electrode potentials. Here we present the results of the experiments performed in the melts based on the ternary NaCl–KCl–CsCl (30–24.5–45.5 mol. %) eutectic mixture at 823–1073 K. Electrode potentials of silver were determined using the electromotive force measurements method and the following galvanic cell:Ag|(NaCl–KCl–CsCl)+AgCl||(NaCl–KC1–CsCl)|Cl2 (C)Concentration of silver in the electrolyte varied from 0.1 to 5 wt. %.Silver electrode quickly equilibrated with the electrolyte and the potential remained stable over long time, Figure. Experimentally obtained electrode potentials were then used to calculate silver formal standard electrode potentials.Figure. An example of silver electrode potential evolution over time in (NaCl–KCl–CsCl)–AgCl (5 wt. %) melt at 823 K. 2Cl–/Cl2 reference electrode. Figure 1

Towards Electroanalytical Measurements in the Elemental Soup of Molten Salts Bearing Nuclear Fuel

Molten salt mixtures containing nuclear fuel present a complex and aggressive environment for electroanalytical measurements. These types of molten salt mixtures may be found within molten salt nuclear reactors (MSRs) or in used nuclear fuel (UNF) reprocessing units, such as an electrorefiner. These molten salts contain many elements from the periodic table at vastly varying concentrations creating a proverbial alphabet soup of elements. Adding to the challenge is that the ‘utensils’ available to probe this ‘soup’ are limited because of severe restrictions on suitable materials created by high temperatures, radioactivity, and harsh chemical environments.Electrochemical probes are a natural fit for real-time and in situ measurements in the ionic environment of molten salts due to their robust and simple construction. Responses from electrochemical probes can provide valuable information for characterizing and monitoring important species in nuclear processes. Monitoring the quantity of nuclear material in a process is required within a certain degree of accuracy and timeliness to deter the diversion of special nuclear material (SNM), such as uranium or plutonium, for nonpeaceful purposes. The degree of accuracy and timeliness is determined by domestic regulators, such as the United States Nuclear Regulatory Commission (NRC), and/or by the International Atomic Energy Agency (IAEA). Furthermore, the development and optimization of molten salt processes benefit from real-time feedback on the chemical composition and properties. However, due to the complex and aggressive environments, further refinement of sensor design and data analysis is required to achieve the needed accuracy and to apply electrochemical measurements over a greater range of conditions.Recent advancements in sensor design include more precise measurement and control of the working electrode area. However, additional issues still exist, such as the lack of standard reference electrodes and an inability to measure high concentrations of ions. Reference electrodes in molten salts are custom made resulting in a high degree of variation in construction and, therefore, reference potential. Recent results on a highly repeatable (±3 mV) and stable reference electrode for molten chloride salts will be presented. Furthermore, efforts to develop a thin layer sensor to perform bulk electrolysis techniques in molten salts containing analytes at high concentrations will be presented.Analyzing electrochemical measurements in nuclear fuel laden molten salts is complicated due to a high degree of signal overlap, as shown in Figure 1, and is limited due to a lack of advanced relations developed for electrodeposition (soluble-insoluble) reactions, which constitute most electrochemical reactions in molten salts. For example, semi-differentiation has been a powerful tool for improving peak separation for soluble-soluble reactions in potential sweep methods. However, relations for peak shapes and characteristic features (i.e., height and width) of semi-differentiated peaks for soluble-insoluble reactions are not well-established in the literature. Progress on the development of these relations through numerical methods will be presented and compared to experimental data. Additionally, a simple model developed for determining the number of electrons exchanged in a metal electrodeposition onto a foreign substrate will be presented. Lastly, the role and preliminary results of advance analytical techniques, such as partial least squares and principal component analysis, in analyzing the electrochemical responses in complex mixtures with a high degree of signal overlap will be discussed. Figure 1

Investigation of Hydrogen Electrode Formation on the Surface of Noble Metals (Pd, Ir, Au) Exposed to Nitrogen Atmosphere: A Comprehensive Study Using Scanning Kelvin Probe

The importance of hydrogen evolution reaction (HER) in engineering and energy conversion related applications grows stronger and it is important to develop better catalysts to enhance the efficiency of the catalytic process. The introduction of computational chemistry (e.g., DFT) into the field of electrochemistry allows general prediction and understanding of activity trends. Great progress is made in modelling the electrochemical double layer under potentiostatic control [1]. However, a reliable and feasible experimental methodology providing in-depth experimental data for improving the theoretical model is lacking, as the electrochemical interface is usually buried under bulk electrolyte, which prevents most important surface analytical techniques to be applied for its investigation. However, it could be recently shown that a hydrogen electrode forms on a palladium surface even in nitrogen atmosphere, even at very low humidity [2] . The electrochemical double layer of this “hydrogen electrode in the dry” is confined just 1-2 monolayers of adsorbed water. However, it is still fully polarizable by adjusting the hydrogen activity from the backside of the electrode and it is even possible to measure full current-potential dependencies for reactions such as e.g. oxygen reduction [3]. Hence, this could be revolutionary new approach for investigating electrochemical electrodes in operando by standard surface analytical techniques. For this however, it needs to be investigated in how far this approach can be also applied beyond palladium. Since the potential of such “electrodes in the dry” cannot be measured with standard reference electrode a Kelvin probe is used instead [2,3]. Basically, the Kelvin probe measures the Volta potential difference between sample and probe (ψ KP - ψ S), and upon suitable calibration such measurement provides the electrode potential of the sample.Evers et.al has proposed the “Hydrogen electrode in dry” concept based on adjusting the hydrogen activity (cathodic charging) from one side of a palladium sample and measuring the work function on the other side using Kelvin probe [2]. In this work, the hydrogen electrode formation in dry (<0.1% R.H) as well as humid condition (>95% R.H) for Palladium (Pd), iridium (Ir) and gold (Au) was carried out using scanning Kelvin probe method by electrochemical charging of hydrogen from entry side and subsequently measuring the Volta potential on exit side (see fig.1). The measured potential on the exit side can be related to electrode potential. Palladium showed a 1:1 correlation between applied potential and measured potential at higher hydrogen activities (between 0 to 300 mVSHE) by establishing electrochemical equilibrium in both conditions, in accordance with [1]. Though the partial pressure of water is very low (0.23mbar) in dry condition, still the hydrogen electrode formation occurred on the palladium. In the case of Ir, it shows 1:1 correlation only in humid condition and not in dry condition. Further, the hydrogen electrode formation on Ir at different partial pressures of water was investigated by controlling the humidity on the exit side of the sample and the obtained results can be attributed to slight differences of thickness of the water layer in the monolayer and even sub-monolayer range. A linear decrease in the potential was observed when increasing the humidity from low to high humidity and the correlation between potential applied from the back and potential measure in the “dry” shows a decrease in responsiveness with decreasing humidity. No correlation was observed for iridium in dry conditions and it can be attributed to presence of insufficient amount of adsorbed water. For gold no correlation was observed in both the conditions. However, a slight behavior was observed at very high activities of hydrogen. This may be due to the initial hydrophobicity of gold, which has first to overcome by a formation of a double layer. On the whole, the effect of water layer adsorption on different metals and its influence on the establishment of a hydrogen electrode at a dry surface was studied.

Liquid Metal Fiber Mat as a Highly Stable Solid-State Junction for Inkjet-Printed Flexible Reference Electrodes.

An all-solid liquid-metal-fiber-mat-based membrane flexible reference electrode (LMFM-FRE) was developed by combining liquid metal eutectic gallium indium (EGaIn) and poly(styrene-block-butadiene-block-styrene) (SBS) as a liquid junction layer. Ag ink was printed and chlorinated by electroplating to form the AgCl layer. Then, agarose containing KCl was coated as the electrolyte layer, and LMFM was added as the liquid junction layer. The liquid junction layer can increase the hydrophobicity of the electrode surface, limit the loss of internal Cl-, and significantly improve the stability of the electrode. The potential fluctuation of LMFM-FRE does not exceed 1 mV within 1 h, and it is still the same after 1 month. In addition, its potential changes in ion species and concentration, pH value, and ambient light are small, and its cyclic voltammetry characteristics are consistent with the standard reference electrode. Even in the case of temperature change and mechanical deformation, the potential change of LMFM-FRE is minimal. In general, the materials used and fabrication by inkjet printing make it possible to manufacture the reference electrode on a large scale, which is particularly important in many electrochemical sensing fields.

Oxygen vacancy modulated MnO2 bi-electrode system for attomole-level pathogen nucleic acid sequence detection

Electrochemical nucleic acid detection has recently opened a relatively low budget, straightforward and speedy approach of detection with the aid of an electrochemically active redox probe. However, electrochemical sensors of nucleic acid amplification characteristically employ a tri-electrode geometry involving standard reference electrode usually made up of a noble metal that adds up the cost of detection. This work proposes a sensitive and rapid approach for detecting the endpoint of nucleic acid amplification test using a novel bi-electrode sensing geometry. The sensing layer of the electrode was comprised of a transition metal oxide to tune its electronic state for regulating its electrochemical response. The XPS analysis indicates a higher contribution of Mn3+ oxidation state than Mn4+ when annealed at elevated temperature, suggesting the formation of oxygen vacancies into the sensing layer. The formation of oxygen vacancies improved the electrical conduction of the layer as evident from the significant reduction in charge transfer resistance (Rct) value from electrochemical impedance spectroscopy (EIS) measurements. The fabricated device was then used to detect dengue virus sequence DNA (using rolling circle amplification) and Staphylococcus aureus genomic DNA (using polymerase chain reaction) with the limit of detection in the order of 103 target DNA copies

К вопросу использования алюминиевых электродов для контроля защищенности от коррозии стальных корпусов судов и кораблей

The article highlights the test results of a non-standard reference electrode made of a stripped of insulation strand of aluminum wiring, which were conducted on board an auxiliary marine vessel PM-15. The potential of the ship’s hull was measured at the same control point using three reference electrodes: silver chloride electrode No. 1; aluminum electrode No. 2; aluminum electrode No. 3. The vessel’s hull potential was measured over five days. All three reference electrodes were used daily. With the help of each electrode, fifty parallel measurements of the potential of the ship’s hull were carried out with a time interval between measurements of 5 seconds. To assess the accuracy of the measurement results, they were processed statistically. The factors that must be taken into account in the development of technologies for manufacturing non-standard reference electrodes are listed: using available inexpensive materials; avoiding expensive equipment in manufacturing the reference electrode; eliminating complex methods of storage of reference electrodes on ships. There has been given a diagram of measuring electrical circuits including the steel hull, a bulwark, a multimeter, a clamping device, switches, a silver chloride reference electrode, aluminum wires, etc. The results of the study can be used on sea-going vessels to organize the control of the protective effect of the hulls of ships and vessels in the absence of standard reference electrodes.

A Flow-through Microelectrode Sensor for Monitoring in Operando Concentrations in Redox Flow Batteries

The development of next-generation redox flow batteries (RFBs) heavily relies on the advancement of new component materials (e.g., redox electrolytes, membranes/separators) that enable low-cost, high-performance, and long-duration energy storage systems.1 The efficient evaluation of candidate materials thus requires simple and robust methods for investigating the evolution of system components during operation—in particular, near real-time monitoring of the battery state-of-health would enable timely interventions that extend lifetime or prevent safety incidents. Prior work has primarily comprised the measurement of electrolyte state-of-charge,2–4 and while this can qualitatively describe the state of the redox electrolyte, knowledge of the individual active species concentrations is needed to quantitatively assess the causes of performance loss. Accordingly, we have established the use of microelectrodes for studying the ex situ decomposition of RFB active materials, showing that this technique can simultaneously describe contributions from self-discharge reactions and molecular decomposition.5 However, considering the flow disturbances (e.g., pump oscillations, irregular flow, non-uniform mixing, etc.) associated with operating RFBs, it is especially challenging to integrate microelectrodes directly into flow cells, as the steady-state current can be highly variable due to undesired advection. Here, we seek to expand the versatility of microelectrodes by leveraging and directing this flow to study redox electrolytes within an operating cell.In this presentation, we describe the integration of microelectrodes into an in-line, flow-through electrochemical cell for use as an operando diagnostic tool to measure redox species concentrations in RFBs (see Figure). The cell consists of a three-electrode assembly, with a pseudo-reference electrode, to accurately quantify species concentrations via the steady-state current obtained from the microelectrode. First, we validate the proposed working principle using multi-physics simulations, and assess the measurement protocol ex situ under quiescent and flow conditions. Using a model electroactive compound (N-(2-(2-methoxyethoxy)ethyl)phenothiazine, MEEPT) prepared at varying states of charge, voltammetry reveals that the steady-state current can be reliably measured with a platinum wire pseudo-reference electrode, which can be used in place of standard fritted reference electrodes to reduce contamination and drift. Subsequent e x situ current measurements under steady flow yield a stable current response that increases with flow rate, in general agreement with simulation results. Importantly, as long as the flow conditions remain consistent throughout testing, the current remains linear with concentration, allowing the concentration to be determined from the steady-state current using an empirical mass transfer coefficient. As a proof-of-concept, we demonstrate the use of this sensor in a symmetric, non-aqueous redox flow cell using MEEPT. Finally, and perhaps most notably, this diagnostic tool is comprised of commercial off-the-shelf components, making it a readily accessible to any laboratory studying RFBs. Acknowledgments This work was funded by the National Science Foundation (NSF) under Award Number 1805566. B.J.N. and K.M.T. gratefully acknowledge the NSF Graduate Research Fellowship Program under Grant Number 1122374. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the NSF. References B. R. Chalamala, T. Soundappan, G. R. Fisher, M. R. Anstey, V. V. Viswanathan, and M. L. Perry, Proceedings of the IEEE, 102, 976–999 (2014).C. Stolze, J. P. Meurer, M. D. Hager, and U. S. Schubert, Chem. Mater., 31, 5363–5369 (2019).M. Skyllas-Kazacos and M. Kazacos, Journal of Power Sources, 196, 8822–8827 (2011).C. Stolze, M. D. Hager, and U. S. Schubert, Journal of Power Sources, 423, 60–67 (2019).J. A. Kowalski, A. M. Fenton, B. J. Neyhouse, and F. R. Brushett, J. Electrochem. Soc., 167, 160513 (2020). Figure 1

Application of nano electrode Ag/AgCl on potentiometric sensor based on molecularly imprinted polymer (MIP) to verify caffeine

Caffeine of Molecularly Imprinted Polymer (MIP) has been synthesized by the cooling-heating method and to obtain sensor material to detect caffeine. The caffeine is verified through a potentiometric method based on galvanic cells involving anodes and cathodes. MIP of caffeine that has been made function as a cathode or working electrode and the modified of the Ag/AgCl reference electrode that made by reducing the AgCl membrane to nano size (44.45 nm) function as an anode. Then the modified Ag/AgCl reference electrode performance test is compared to the standard AgCl reference electrode. The result has shown the modified Ag/AgCl reference electrode produces linearity of the calibration curve in testing caffeine solutions with a concentration range of 0.1 ppm to 5.0 ppm. Based on the result of the modified Ag/AgCl reference electrode’s test range, we got the linearity coefficient value of 0.9993, with a slope of 0.9693 and an intercept of 0.1306. Generated accuracy calculation resulted in a value of 98.85% and a precision of 0.951%. The result of the lower limit of detection (LoD) was at a concentration of 0.2 ppm and the limit of quantification (LoQ) at a concentration of 0.4 ppm. Thus, it concluded that the modified Ag/AgCl reference electrode has the same or equivalent capability as a standard electrode.

Rapid Microfluidic Electrochemical Sensor for the Detection of Heavy Metal Ions in Water Sample

Heavy metals are naturally found in the earth’s crust. A relatively dense metal or metalloid which is known for its potential toxicity in an environmental context is termed as Toxic Heavy Metal. They include cadmium, mercury, lead, arsenic, copper, silver etc. to name a few. Human activities like mining, production of industrial wastes, vehicle emissions, manufacturing paints, disposal of microplastics in water bodies are few examples of how these metals are exposed to open vicinities that lead to their direct interaction with living beings. Plants uptake heavy-metal polluted water is then consumed by animals. Ingestion of these plants and animal further becomes the largest source of heavy metal concentration in humans. They are hard to metabolize that causes them to bioaccumulate in the system of the living being. These metals bind to vital cellular components, such as structural proteins, enzymes, and nucleic acids, and interfere with their proper functioning. The symptoms and effects vary as per the concentration of the metal or metal compound. In most cases, carcinogenic effects have been observed in central and peripheral nervous system, and circulatory system of the organism. Therefore, there is a need to develop a fast, convenient, accurate, and cost-effective microfluidic sensor platform for heavy metal ions in water bodies of both urban and rural scenarios.In this project, a microfluidic device design (as shown in the Figure 1) is developed adapting a logical sequence of microchannels and microstructures representing the mixing, detection, and separation zones with consideration of desired operation. This is followed by incorporation of an optical and electrochemical sensing system for increased precision of heavy metal ion detection. The electrochemical system includes three electrodes such as working electrode, counter electrode and reference electrode. The potential at working electrode start with -0.4 V and switching potential at 1.2 V while the counter electrode at 0 V and standard reference electrode at 0.23 V. The three-electrode cell configuration consists of a nanoporous gold film (NPGF) as working electrode, Pt wire as the counter electrode and Ag/AgCl as the reference electrode. The electrode behavior is investigated using cyclic voltammetric studies in the presence of the electrolyte 10mM K3Fe(CN)6 in 0.1M KCl. The inlet velocity achieved through hydrodynamic focusing facilitates the rapid detection of heavy metal ions in the electroanalysis unit.In this study, a simulation model has been created using COMSOL Multiphysics® Modelling Software using both laminar flow physics for Fluid Transport and Electroanalysis modules to obtain Cyclic Voltammetry results for heavy metal ion detection within the microfluidic platform. The transport properties of water are used for simulation studies. Diffusion coefficient for the two species K3Fe(CN)6 and KCl (K3Fe(CN)6)= 7.6x10-10 m2/s ; (KCl) = 2.47x10-9 m2/s. Starting concentrations of the two species, C1 (K3Fe(CN)6) = 10 mM = 10 mol/m3and C2 (KCl) = 0.1M = 100 mol/m3. The scan rate applied is 0.1V/s. Figure 2 represents the results for the simulation model. These simulation results are in good agreement with the experimental results of the same. Further investigation on the microfluidic sensor for selective detection of heavy metal ions in water samples is in progress. Figure 1

Reference Electrodes for Electrochemical Sensors Based on Redox Couples Immobilized within Nafion Films.

The immobilization of both components of a redox couple within films of the sulfonated tetrafluoroethylene polymer, Nafion, on the surface of carbon electrodes is reported. In particular, cationic and/or water-insoluble species are used to develop stable and robust reference electrodes by adjustment and optimization of both the film thickness and the level of doping of the film, as an alternative to using standard commercial reference electrodes. Different redox couples were evaluated: methyl viologen dication/cation (MV2+/MV+), tris(2,2'-bipyridyl)ruthenium(II)/ruthenium(III) (Ru(bpy)32+/Ru(bpy)33+), ferrocene/ferrocenium (Fc/Fc+), and poly(vinylferrocene)/poly(vinylferrocenium) (PVFc/PVFc+). These reference electrodes demonstrate a good stability over 10 days and 1000 successive scans; in particular, Nafion-confined Fc/Fc+PF6- was shown to display the best performance. This type of reference electrode, as a solid-state electrolyte-free reference electrode, has several advantages, including full retention of the redox species within the films together with ease of both fabrication and miniaturization.

State-of-charge monitoring for redox flow batteries: A symmetric open-circuit cell approach

A method for the real-time monitoring of the state-of-charge of redox flow batteries is presented, which provides half-cell resolution. The well-known standard procedure for the state-of-charge monitoring, which utilizes the equilibrium potential of the monitored electrolyte versus a standard reference electrode in an open-circuit cell, is modified. It is demonstrated that the flow battery electrolyte itself provides a stable reference potential if used in the reference compartment of a symmetric open-circuit cell. This reference potential can be used to monitor the state-of-charge of a flow battery electrolyte during battery operation. The proposed method is validated with N,N,N-2,2,6,6-heptamethylpiperidinyloxy-4-ammonium chloride (TEMPTMA) catholytes and N,N′-dimethyl-4,4-bipyridinium dichloride (MV) anolytes in aqueous flow batteries using both a symmetric open-circuit cell and a standard open-circuit cell with a Ag/AgCl reference electrode. Reference potential drift rates are determined and drift mechanisms are investigated, demonstrating that the utilization of a symmetric open-circuit cell reduces the reference potential drift. It is validated that the exchange of the in-situ producible reference electrolyte can replace time-consuming re-calibration procedures.

Fabrication of Robust Reference Tips and Reference Electrodes for Kelvin Probe Applications in Changing Atmospheres.

The scanning Kelvin probe (SKP) is a versatile method for the measurement of the Volta potential difference between a sample and the SKP-tip (ΔψsampleSKP-tip). Based on suitable calibration, this technique is highly suited for the application in corrosion science due to its ability to serve as a very sensitive noncontact and nondestructive method for determining the electrode potential, even at buried interfaces beneath coatings or on surfaces covered by ultrathin electrolyte layers, which are not accessible by standard reference electrodes. However, the potential of the reference (i.e., the SKP-tip) will be influenced by variations of the surrounding atmosphere, resulting in errors of the electrode potential referred to the sample. The objective of this work is to provide a stable SKP-tip which can be used in different or changing atmosphere, e.g., within a wide range of relative humidity (approximately 0-99%-rh) or varying O2 partial pressure, without showing a change of its potential (note that the work functions measured in non-UHV atmospheres are electrochemical in nature [Hausbrand et al. J. Electrochem. Soc. 2008, 155 (7), C369-C379], and hence in the following we will refer to the potential of the SKP-tip instead of its work function). In that regard, the SKP-tip is in a first approach modified with self-assembled monolayers (SAMs) in order to create a hydrophobic barrier between the metallic surface and the surrounding atmosphere. The changes in potential upon varying relative humidity (ΔErh) of different bare metallic substrates are quantified, and it is shown that these potential differences cannot be minimized by SAMs. On the contrary, the ΔErh increases for every examined material system modified with SAMs. The major explanation for this observation is the dipole layer at the interface metal|SAM, causing an interfacial adsorption of water molecules even in a preferred orientation of their dipole moments, which leads to a changed work function and consequently to the correlated electrode potential. However, thin paraffin coatings were found to lead to a strongly reduced ΔErh, finally validated with novel robust Ag/Ag+ reference electrodes. It is also shown that nickel as SKP-tip material is seemingly more stable in varying atmospheric conditions compared to widely used Ni/Cr, stainless steel, or gold as SKP-tip material.

Processable and Moldable Sodium‐Metal Anodes

Sodium-ion batteries are similar in concept and function to lithium-ion batteries, but their development and commercialization lag far behind. One obstacle is the lack of a standard reference electrode. Unlike Li foil reference electrodes, sodium is not easily processable or moldable and it deforms easily. Herein we fabricate a processable and moldable composite Na metal anode made from Na and reduced graphene oxide (r-GO). With only 4.5 % percent r-GO, the composite anodes had improved hardness, strength, and stability to corrosion compared to Na metal, and can be engineered to various shapes and sizes. The plating/stripping cycling of the composite anode was significantly extended in both ether and carbonate electrolytes giving less dendrite formation. We used the composite anode in both Na-O2 and Na-Na3 V2 (PO4 )3 full cells.

Processable and Moldable Sodium‐Metal Anodes

AbstractSodium‐ion batteries are similar in concept and function to lithium‐ion batteries, but their development and commercialization lag far behind. One obstacle is the lack of a standard reference electrode. Unlike Li foil reference electrodes, sodium is not easily processable or moldable and it deforms easily. Herein we fabricate a processable and moldable composite Na metal anode made from Na and reduced graphene oxide (r‐GO). With only 4.5 % percent r‐GO, the composite anodes had improved hardness, strength, and stability to corrosion compared to Na metal, and can be engineered to various shapes and sizes. The plating/stripping cycling of the composite anode was significantly extended in both ether and carbonate electrolytes giving less dendrite formation. We used the composite anode in both Na‐O2 and Na‐Na3V2(PO4)3 full cells.

Design and Fabrication of Ag / AgCl Composite Reference Electrode Based on Microfluidic Chip

Polydimethylsiloxane (PDMS) has been widely used in chip fabrication. However, PDMS itself is a non-conducting polymer, and the adhesion between metal and PDMS is also really weak. Hence, integrating microelectrodes on PDMS microchips has become a technical bottleneck in many applications such as miniaturized electrochemical (EC) sensing systems. A new method was presented to integrate Ag/AgCl electrode on microfluidic chips by using a new conductive composite. It was made of the mixture of PDMS and silver powders, so good electrical conductivity was achieved. Two chloridizing methods were selected to fabricate Ag/AgCl reference electrode. In the electrolysis method, Ag-PDMS composite electrode (as anode) was electrolyzed for 24 hours in saturated KCl solution. In the second one, silver chloride powder was uniformly mixed with silver powders and PDMS pre-polymer, and then cured 1 hour at 90 oC. These composite materials could be efficiently shaped as different electrode structures. Its potential response was measured in different chloride solutions, and its stability was also measured in water (10 days) and 3 mol/L KCl solution (14 days), respectively. Electrochemical characteristics of the electrode were also analyzed in potentiometric and amperometric measurements. SEM pictures showed that the surface of the electrode was fluffy and of rough morphology, which might increase its contacting area with solution, so as to improve the measuring adequacy and accuracy. The electrodes had a fast and stable potential response toward Cl− concentration change.The much tiny potential fluctuation indicated that the composite electrode was stable, which could be served as a good reference for EC measurements. Its CV curves showed its performance was almost as good as a standard reference electrode. Based on its excellent properties, the composite material can be widely applied in microfluidic field. The new method has many advantages such as simple operation, low cost and no special environmental requirements.

OPTIMIZATION OF SCREEN PRINTED REFERENCE ELECTRODE BASED ON CHARGE BALANCE AND POLY (BUTYL ACRYLATE) PHOTOCURABLE MEBRANE

&lt;p class="TRANSAffiliation"&gt;&lt;span&gt;This research focus on transforming the traditional design of reference electrode into all-solid-state reference electrode front-end using Ag/AgCl screen- printed electrodes. By replacing the internal reference solution of a traditional reference electrode by a solid photocurable membrane, an all-solid-state reference electrode can be achieved. The solid-state screen-printed reference electrode was designed using a photocurable acrylic film containing immobilized sodium tetrakis [3,5-bis(trifluoromethyl)phenyl] borate (NaTFPB) and trimethylocthylammonium chloride (TOMA-Cl). An optimum ratio of NaTFPB:TOMA-Cl = 1:1 produced a stable reference electrode. In the anions interference studies, all anions i.e. NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt;, Cl&lt;sup&gt;-&lt;/sup&gt;, Br&lt;sup&gt;-&lt;/sup&gt; and SO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;2-&lt;/sup&gt; does not give effect to the SPRE except perchlorate anions. The all-solid-state reference electrodes was applied to the detection of potassium ions and ammonium ions. Validation of the all-screen-printed reference electrode was performed with reference electrode standard gel type. The validation results showed that all-solid-state screen-printed reference electrode demonstrated performance that was comparable to standard reference electrode. &lt;/span&gt;&lt;/p&gt;

Absolute Potentials of the Standard Hydrogen Electrode (4.20 V), Standard Reference Electrodes & Aqueous Redox Couples of Elements

For more than two centuries after Volta (1745 – 1827) (http://www.ecsblog.org/the-birthplace-of-electrochemistry), aqueous redox potentials have been conventionally referred to that of the standard hydrogen electrode (SHE) as zero, in the absence of a proper knowledge of the latter. The author demonstrated for the first time (Heyrovska, 2009) a new simple linear relation between the gaseous ionization potentials (I) and the aqueous standard redox potentials (E0) using the existing data for the elements of various Groups in the Periodic Table. It was astonishing that all these straight lines converged to one point at I = 0, yielding the absolute potential of SHE, E0 I=0 = 4.20 (+/- 0.03)V. This value was found to be close to the theoretical value (4.44V) obtained earlier by Trasatti (1986) (Pure & Appl. Chem. 58 (1986) 955) and to the experimental value, 4.2 (+/-0.4V) obtained by Donald et al, (2008) (J. Am. Chem. Soc. 130 (2008) 3371). Thus, by knowing the absolute value of SHE, the absolute aqueous redox potentials, Eo abs = Eo - Eo I =0, of all the elements of the Periodic Table (Heyrovska, 2010) as well as of the standard reference electrodes were obtained and tabulated (Heyrovska, 2009, 2010, 2011). Full list of references in: http://www.jh-inst.cas.cz/~rheyrovs/publs.htm. Some selected references are given below.