Nernst Equation Research Articles

The influence of electrolyte concentration and solvent on operational voltage of Li/CFx primary batteries elucidated by Nernst Equation

Fluorinated carbons (CFx) have the highest energy density as the cathode of lithium primary battery. They demonstrate distinct behaviors in different electrolytes. While, the reaction mechanism is still unclear. In this work, the influences of electrolyte in aspects of Li-ion concentration, anion species, and solvent species on the performances of Li/CFx batteries are explored. Contrary to conventional wisdoms that electrolytes play a role as a Li-ion conductor and only limit the kinetics, we found that the electrolyte can determine its thermodynamic behavior. In detail, a lower Li-salt concentration and a solvent solvating Li+ with more molecular numbers provide higher operational voltages in Li/CFx battery. This can be well elucidated by Nernst Equation. Interesting, in Li-free electrolyte (0 M DMSO), fluorinated graphene cathode can still work, offering an impeccable specific discharge capacity of 738 mAh g−1 with a specific energy of 1968 Wh kg−1 at 0.1C.

Dynamic modeling of long-term operations of vanadium/air redox flow battery with different membranes

The crossover rate of vanadium ions through the membrane and oxygen transport determines the capacity of vanadium/air redox flow battery due to the ion diffusion and the side reactions and the electro-migration and convection. The battery's high reaction temperature also impacts the diffusion coefficient. In this paper, the electrolyte concentration change is predicted, and battery performances with different membranes, including Nafion 115, CMS, and CMX, in different working conditions are compared using the developed dynamic model: Mass balance for each reaction ions and reaction temperature are studied by Fick's Law and Arrhenius Equation to predict; the voltage change of the battery can be calculated by the Nernst Equation. The partial differential equations are applied to predict the performance of the battery. It is observed that with a low crossover rate, the capacity of the battery using CMS is almost unchangeable for over 400 h, while with Nafion 115 the capacity decreases around 2% in each cycle steadily. However, Nafion 115 with the lowest inner resistance achieves the highest efficiency (0.85), while CMS is 13% lower and CMX is 27% lower than N115, respectively. The V2+ concentration in contact with the electrode and catalyst is also predicted to monitor this working efficiency model.

Mean activity coefficients of KCl in the KCl + SrCl2 + H2O solutions at 278.15 K determined by cell potential method and their application to the prediction of solid-liquid equilibria of the KCl + SrCl2 + H2O system

The cell potentials were determined by the cell without liquid junction K-ISE |KCl (m0) |Cl-ISE firstly. Using Nernst equation and the measured cell potentials, the response slope κ of the single-salt electrode and the standard cell potential E0 were fitted well. The total ionic strengths range from 0.0100 to 1.0000 mol·kg−1, the cell without liquid junction K-ISE |KCl (m1), SrCl2 (m2) |Cl-ISE is used to determine the mean activity coefficients of KCl in the KCl + SrCl2 + H2O solutions, the ionic strength fractions yb of SrCl2 are 0.8, 0.6, 0.4, 0.2 and 0. According to the measured cell potentials, the mean activity coefficients of KCl in the KCl + SrCl2 + H2O solutions were calculated by Nernst equation, and the relationship diagrams between the mean activity coefficients and total ionic strengths of the mixed solutions are drawn at 278.15 K. The mixed interaction parameters θK,Sr, and ψK,Sr,Cl in the Pitzer model were also obtained by regression of the mean activity coefficients of KCl in the mixed solutions. The mean activity coefficients of SrCl2, the osmotic coefficients, the water activities, and the excess Gibbs free energies of the mixed solutions were also calculated by Pitzer equations. Additionally, in order to verify the mixed ion parameters of Pitzer model fitted in this work, the isothermal dissolution equilibrium method is used to measure experimentally the phase equilibria of the mixed solutions at 278.15 K, and then the Pitzer equations and the mixed ion parameters are used to predict the solubilities of the salts in the mixed solutions at 278.15 K. The experimental and predicted phase diagrams are good agreement.

Electrochemical, theoretical, and analytical investigation of the phenylurea herbicide fluometuron at a glassy carbon electrode

For the first time, both theoretical and electrochemical behavior of the phenylurea herbicide fluometuron (FTN) were investigated using the glassy carbon electrode (GCE). The cyclic voltammetry (CV) performed in the presence of FTN showed an irreversible profile for the analyte with one well-defined anodic peak at ca. +1.2 V (vs. Ag/AgCl). The linear dependence of pH and peak potential was evaluated using the Nernst equation through CV measurements. The slope of 46 mV s−1 suggests an oxidation mechanism involving an equal number of protons and electrons. High-level quantum-mechanical calculations based on the density functional theory showed that the presence of defects on the GCE surface induces strong interaction leading to FTN dissociation and/or its adsorption with orientation parallel to the substrate which compromises the electroanalysis. Raman spectroscopy confirmed the surface fouling. Differential pulse voltammetry (DPV) was used for the electroanalytical determination of FTN under optimized conditions. The oxidation peak increased with increasing concentrations of FTN in the range of 207–3846 µg L−1; the theoretical detection limit was estimated as 63 µg L−1. To avoid surface fouling, the calibration curve was applied for the determination of FTN. The unmodified electrode offered proper selectivity in the presence of other pesticides and potential interfering species. Intra and inter-day precision was established. Recoveries were obtained in the range of 81.8–98.9% (n = 3) with the absence of matrix effects. The results showed that electroanalysis through the bare GCE might be used as a novel strategy to determine the persistent organic compound FTN in spiked river water and simulated serum samples and preliminary evaluations such as screening purposes.

The Nernst equation: using physico-chemical laws to steer novel experimental design.

The application of physico-chemical principles has been routinely used to explain various physiological concepts. The Nernst equation is one example of this, used to predict the potential difference created by the transmembrane ion gradient resulting from uneven ion distribution within cellular compartments and the interstitial space. This relationship remains of fundamental importance to the understanding of electrical signaling in the brain, which relies on current flow across cell membranes. We describe four distinct occasions when the Nernst equation was ingeniously applied in experimental design to illuminate diverse cellular functions, from the dependence of the action potential on Na+ influx to K+ buffering in astrocytes. These examples are discussed with the aim of inspiring students to appreciate how the application of seemingly textbook-bound concepts can dictate novel experimental design across physiological disciplines.

Electrochemical antioxidant capacity measurement: a downsized system and its application to agricultural crops.

An on-site electrochemical antioxidant capacity measurement system was developed using a screen print electrode (SPE) and circuit tester. The antioxidant capacities of eight antioxidants were evaluated with the handheld electrochemical antioxidant capacity measurement system to compare with those measured with spectroscopic methods, namely, oxygen radical absorbance capacity (ORAC) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging assays, as well as the reported electrochemical method with three conventional electrodes (a glassy carbon electrode, Ag/AgCl electrode and platinum wire electrode) and a potentiostat. Additionally, the potential shifts were proportional to the logarithm of the antioxidant concentration, which obeyed the Nernstian equation. Moreover, the antioxidant capacities of extracts from vegetables (green pepper, ginger and eggplant) were measured with a handheld electrochemical system. Each measurement was finished in only ca. 3min. The electrochemically obtained antioxidant data were comparable to those from DPPH free-radical scavenging assays and superoxide anion scavenging activity (SOSA) assays, as well as the total phenolic compound content.

Development of Chromium(III) Selective Potentiometric Sensors for Its Determination in Petroleum Water Samples Using Synthesized Nano Schiff Base Complex as an Ionophore.

Many analytical techniques, such as X-ray fluorescence spectrometry, inductively coupled plasma-atomic emission spectrometry, and even traditional spectroscopic and fluorimetric methods, are used for the measurement of Cr(III) ions. These methods are sophisticated and very expensive, so thecheapest and low-cost ion selective electrodes were used. The quantification of Cr(III) ions in various samples of petroleum water using ion selective electrodes was suggested. Nano chromium modified carbon paste sensor (MCPE) and nano chromium modified screen printed sensor (MSPE) based on Schiff base Cr(III) complex are developed. The developed nano Cr(III) Schiff base chelate was characterized using elemental, spectroscopic, and thermal analysis techniques. The proposed nano Cr(III) has good properties for antibacterial and antifungal activity. The modified carbon paste and screen-printed sensors were fabricated for determination of Cr(III) ion. The proposed MCPE (sensor I) and MSPE (sensor II) obeys Nernstian equation upon incorporating nano Cr(III) ionophore in the paste at 25°C with a trivalent cationic slope of 18.8 ± 0.2 and 20.0 ± 0.4 mV/decade. They have showed fast response time around 8 and 5 s, and they may be used for at least 98 and 240 days without significant changes in MCPE and MSPE potential, respectively. The sensors I and II showed good selectivity for Cr(III) ion toward a wide variety of metal ions or anions as confirmed by potentiometric selectivity coefficients values. The detection and quantification limits were defined alongside the other process validation parameters. The results have been compared well to those obtained by atomic absorption spectrometry (AAS), and the data of F- and t-test indicated no significant difference between the proposed and AAS methods. These sensors have been used to determine Cr(III) ions in genuine spiked different petroleum well water samples with satisfactory percentage recoveries, low standard, and relative standard deviation values using direct potentiometric and standard addition methods. The proposed method of producing nano Cr(III) complex as a sensor material possesses the distinct advantages of being simple, easily reproducible, appropriate for operation, and highly selective and sensitive. Modified carbon paste and screen-printed electrodes were fabricated based on nano Cr(III) complex as ionophore. The electrodes follow Nernstian behavior, and they optimized according to IUPAC recommendation. They showed a high selectivity for Cr(III) ion over many bi- or trivalent metal ions and anions. The results obtained compared well with those obtained using AAS. They successfully applied for determination of Cr(III) in petroleum water samples.

Thermodynamic Properties of Ni–Nd Intermetallic Compounds Measured Electrochemically in Molten CaCl2–NdCl3

The electrochemical formation of Ni–Nd intermetallic compounds has been investigated in a molten CaCl2–NdCl3 system. For further understanding the thermodynamic properties of different Ni–Nd intermetallic compounds, an electrochemical investigating method was used. The temperature dependences of the Nd3+/Nd potential and two-phase coexisting potentials of the Ni–Nd intermetallic compounds were determined via open-circuit potentiometry using Mo and Ni flag electrodes, respectively. Expressing the two-phase coexisting potentials with respect to the Nd3+/Nd potential, the relative partial molar Gibbs energies of Nd were calculated. The Nernst and Gibbs-Duhem equations were used to determine the activities of Ni and Nd, respectively. The relative partial molar Gibbs energies of Ni were calculated using its activities. Thereafter, the relative partial molar enthalpies and entropies of Ni and Nd were obtained using the temperature dependences of the relative partial molar Gibbs energies. Finally, the standard Gibbs energies, enthalpies, and entropies of formation of the various Ni–Nd intermetallic compounds were calculated using the relative partial molar Gibbs energies of Nd and Ni. The obtained thermodynamic parameters were compared with previously reported values obtained by the CALPHAD method and modeling calculations.

Effect of electrode rinse solutions on the electrodialysis of concentrated salts

The data presented indicate that modest attention to the chemistry of the electrode rinse solution can yield as much as 56% improvement in process efficiency. When operating electrodialysis (ED) with salt concentrations greater than 10,000 mg/l (as NaCl) the amperage can be relatively high even at low voltages. To maximize the overall rate of ion transport from diluate to concentrate, there is a need to minimize resistances in the electrode cells since these can represent as much as 30% of the total resistances in the entire process and in this particular ED unit, represented resistance roughly equivalent to that within the membrane stack. This work describes the performance of a 10-cell pair, 200 cm2 (0.02 m2) per membrane, pilot ED unit operated in batch mode at 5 V potential. The feedstock to the stack was varied from 0.5% to 6% NaCl. Results from Volt-amp profiles (2.0–15 V) were used as the rationale for choosing the preferred electrode rinse solution, 90 g/l (kg/m3) disodium sulfate at pH 12.5. The recommended solution of 30 g/l (kg/m3) disodium sulfate at neutral pH was tested against stronger solutions (60, 90, and 120 g/l (kg/m3) disodium sulfate) at neutral pH and with 1 g/l (kg/m3) sodium hydroxide added to yield solutions at pH 12.5. There were stark differences in the performance of the ED unit between the solutions at pH 7 and those at pH 12.5. The slopes of the Volt-amp profiles improved indicating less resistance to ion flow at pH 12.5. Most of the difference can be attributed to the greater conductivity of sodium hydroxide compared to disodium sulfate, where even a modest addition of 1 g/l (kg/m3) sodium hydroxide increased the conductivity of the solution between 8 and 20% depending on the concentration of disodium sulfate. Most notably, the initiation voltage was 2.39 ± 0.08 V with solutions at pH 7 and 1.99 V ± 0.04 V when the rinse solutions were around pH 12.5, a difference of around 0.42 V. Since the full batch runs were performed at 5.0 V, this 0.42 V differential represented a loss of 8% in process efficiency. A series of tests showed a shift in initiation voltage occurred between pH 11.5 and 12.5. Nernst equations for water electrolysis are coupled with a simple flux model that estimates the concentration of hydroxide and hydronium ions at the electrode surfaces. This model indicates that the potential demanded by the electrodes is directly linked to the current. Furthermore, there is a steep drop in the potential demanded by the anode when there is sufficient hydroxide available to generate oxygen from hydroxide as opposed to generation from water. The voltage demand is minimal at pH 12.5 and reflective of the reference standard voltage (just over 1.23 V predicted at 0.1 amps). However, the flux model predicts that the voltage demanded by the electrodes at pH 7 is 1.61 V at 0.1 amps (the lowest amperage measurable with the power pack). Comparing this result to the reference standard (E0 = −1.23 V) yields a satisfactory explanation for the observed difference below reference standard of 0.42 V.

Measurements and Calculations mean activity coefficients of KI in the KI–KCl–H2O ternary system at 298.15 K

Compared to the current popular methods for measuring the mean activity coefficient of the ternary aqueous solution, electromotive force method has certain advantages of rapidity and sensitivity. Herein, The electromotive force measurements were performed on the cell of the type: K–ISE|KI (m1), KCl (m2)|I–ISE, which consists of a potassium-ion combination ion selective electrode (ISE) and iodide-ion combination ion selective electrode (ISE) without a liquid junction. We chose the total ionic strength I range from 0.0100 to 1.0000 mol·kg−1 for different ionic strength fractions yb of KCl with yb = (0.0, 0.2, 0.4, 0.6, 0.8). The experimental results show that the mean activity coefficients of KI can be calculated well by using the Pitzer models and Nernstian equation. Moreover, the Pitzer ion interaction parameters of θCl,I and ψK,I,Cl were fitted using Pitzer’s equations, and the two parameters were used to calculated the mean activity coefficients of KCl in the KI–KCl–H2O ternary system. Accordingly, the osmotic coefficients, water activities, and excess Gibbs free energies in the mixtures were studied in the KI–KCl–H2O ternary system.

Electrochemical Hydrogen Compression and Its Optimization through Computational Modeling

Climate change resulting from the heavy use of fossil fuels poses a serious threat to our environment. It is critically important to find alternatives to combustion-based energy technologies and promote renewable energy production. Hydrogen is a leading candidate for the transportation sector as a carbon-free fuel with high energy density. Hydrogen can be produced in a carbon-neutral manner via water electrolysis and other means. However, the establishment of the hydrogen infrastructure still faces serious challenges such as storage. Due to its lightweight nature, hydrogen is very difficult to store either as a compressed gas or as a liquid. Typically, hydrogen is compressed using mechanical compressors which contain moving parts that require frequent maintenance adding to their cost and complexity. Electrochemical compression (ECC) is a promising alternative to mechanical compressors. ECC is an electrochemical device that uses a proton exchange membrane (PEM) to compress the gas. When a voltage is applied across the PEM, low-pressure hydrogen supplied to the anode is oxidized to generate protons and electrons. The electrons are driven through the external circuit by the power source, whereas the protons travel through the PEM towards the cathode. The protons and electrons recombine via the cathodic reduction to obtain hydrogen at elevated pressure. The currently available knowledge base regarding electrochemical compressors has mainly resulted from experimental studies and less attention has been paid to modeling. The current work presents a comprehensive three-dimensional model of a single cell ECC that incorporates the relevant electrochemical phenomena as well as physical processes including water transport. It also takes into account the important phenomenon of back diffusion due to the pressure difference between the cathode and anode that limits the achievable pressure in the cathode compartment. Simulations were conducted for the pressurized cathode case . It was observed that back diffusion limits the compression ratio to a value well below that predicted by Nernst equation. Additionally, the effects of membrane thickness, temperature, and applied voltage on ECC performance are analyzed. The results show that there is a tradeoff between different objectives that must be addressed to optimize the ECC process. For example, thinner membranes permit faster compression rates but at the cost of increased back diffusion. Similarly, higher temperatures improve the pressure efficiency and the compression rate but at a higher operational cost. The results also show that ECC is more efficient at lower voltages because the associated compression ratio is smaller which consequently reduces back diffusion; however, such small voltages do not allow higher pressures. As a result of these tradeoffs, all design parameters need to be optimized simultaneously. This study offers valuable insights on the effect of different parameters on ECC performance. The results suggest that ECC is a viable alternative to conventional technologies for hydrogen compression. Back diffusion significantly reduces ECC efficiency; therefore, ECCs would benefit from membranes with low hydrogen diffusivity. The results provide a foundation for the modeling, analysis, and optimization of a full scale ECC system. Keywords—Hydrogen; Computational Model; Back Diffusion; Electrochemical Compression; Optimization;

Bioelectrochemistry in Undergraduate Curriculum and Research

Electrochemistry has a wide range of uses and applications, but undergraduate students do not appreciate this when the topic is first introduced in General Chemistry. Introducing more electrochemical methods in later chemistry courses can encourage interest in the field. In the chemistry department at Lebanon Valley College, the students first encounter electrochemistry through the typical introduction of redox reactions, the Nernst equation, and galvanic cells. The topic is expanded in Analytical Chemistry for third years during which the students learn about and perform electroanalytical methods, including potentiometric analysis, coulometry, amperometry, and voltammetry. Students who choose the advanced elective Chemical Sensors and Biosensors learn about electrochemical sensors as one unit of the course. This unit also includes a section on bioelectrochemical sensors. Students develop a hydrogen peroxide biosensor and use amperometry to evaluate its performance, giving them a better understanding of concepts like limit of detection, sensitivity, and dynamic linear range.In addition to the chemistry curriculum, students can choose to do electrochemical research in the department. Recent projects include fabricating and evaluating enzyme electrodes for a wide range of biologically relevant molecules, designing self-powered biosensors, and designing a biophotovoltaic device for solar energy conversion with plants. We also currently have a research project with the focus of developing an electrosynthesis experiment to be added to the organic lab sequence. Throughout these research projects, students gain experience with several electrochemical methods, analysis of electrochemical data, and general lab skills. They are also required to present their work, either in posters or oral presentations, a skill that will prepare them for their careers after college. Overall this combination of curriculum and research leads to more students being interested in electrochemistry. They learn that these methods can be used for every area of chemistry, not just analytical. It has lead to an increase in the number of graduating students who continue working in the field, whether in industry or academia.

Detection of Chloride Using Microelectrodes in Closed Bipolar Electrode Scheme

Introduction: We present an electrochemical sensor to monitor Cl- concentration using a chloride specific silver electrode connected to electrodes of different surface areas and materials in a bipolar arrangement (figure 1). Using a bipolar arrangement may pose benefits for an ion selective electrode compared to traditional methods. Two key benefits are 1) the partition of the measurement versus reference compartments, and 2) the ability to apply various overpotentials across the system. These two attributes help eliminate the effect of some interference and may allow us to tune the linear range of the sensor.The sensor function relies on balancing the association of Cl- and Ag+ with the conversion of Prussian blue to Prussian white. The entire system is held at a defined potential using a potentiostat across working electrode 1 and reference electrode 1 (below). As Cl-are added to the sample compartment, Cl-will associate with Ag+ to form Ag/AgCl altering the potential across the bipolar electrode. To ensure the conservation of charge the ratio of Prussian blue to Prussian white will also shift. This change in ratio is measured using open circuit potential against a second working electrode. The open circuit potential response for each of these electrodes is then modeled using the Nernst equation, and mixed potential theory1–3. Methods: Deposition of Prussian blue was carried out using 1mL volume of 2.5mM FeCl3, and 2.5mM ferricyanide, in a supporting electrolyte of 0.1M hydrochloric acid and 0.1M KCl solution. An overpotential of 0.4V versus Ag/AgCl was applied to the working electrode for 3 cycles of 4 minutes while monitoring the current. After deposition, the electrode was vigorously rinsed in MQ water and activated using cyclic voltammetry. This procedure was carried out on both the gold and platinum electrodes.For proof of concept, the chloride sensitive electrode was fabricated by taking a single junction Ag/AgCl electrode and removing the silver wire. This wire was then anodized using a positive potential of 0.4V versus Ag/AgCl was held against a platinum counter electrode in 1M KCl solution. The electrode was stored in 1M KCl until further use.The various potentials applied across the entire cell were chosen by running cyclic voltammetry in 10mM potassium phosphate buffer with pH 7. The oxidation and reduction peaks were then selected, as well as the formal potential, which we calculated by taking the average of the 2 peaks. Results and Discussion: The bipolar reference electrode was tested against various interfering substances such as glucose, Na+, K+, and pH based on the in vivo environment (interstitial fluid ranges). The linear range, and limit of detection for Cl- was found across each electrode type and size. We also investigated the effect of applying different potentials across the cell and compare the limit of detection, and linear range. Based on this we found the reduction potential resulted in best limit of detection. Finally, the impact of the measurement compartment ion concentration was tested by changing the concentration of Cl- in the measurement compartment.

Coupled mutual diffusion in aqueous calcium sulphate + sulphuric acid solutions

Taylor dispersion method was used to measure binary mutual diffusion coefficients of calcium sulphate in water at concentrations ranging 0.0000 to 0.0100 mol dm−3 and at 298.15 K. Experimental results are discussed based on the Onsager-Fuoss and Pikal models and compared with theoretical diffusion coefficients, calculated using different values of the mean distance of closest approach of ions, a. The influence parameter a on the diffusion of this system is also discussed.Ternary mutual diffusion coefficients (Dik) measured by the same technique are reported for aqueous CaSO4 + H2SO4 solutions at 298.15 K and concentrations up to 0.0100 mol dm−3. The coupled diffusion of CaSO4 (1) and H2SO4 (2) is significant, as indicated by the large negative cross-diffusion coefficients. Nernst equations are used to predict transport coefficients from limiting ionic conductivities and help to interpret both concentration dependence of the diffusion coefficients and the electrostatic mechanism for the coupled diffusion of the solutes.

Measurement of Transport Number of Lithium in Glycerol Assisted by Fourier Transform Spectroscopy Analysis: Progress towards Elaboration of Optimal Electrolyte of Friendly Environmental Battery

Up to now, a great deal of research investigations on lithium ion conductors has been carried out, because they are potentially utilized in the solid electrolytes of the batteries and the electrochemical devices. However, in order to elaborate new ecological batteries of lithium, it becomes primordial to study and understand the properties of transport of the lithium electrolytes using eco-friendly solvents, with view perhaps to find out the best electrolyte for such devices. In fact, the electromotive forces (EMFs) of lithium chloride electrolyte in the hydrogen-bonded solvents glycerol, were measured using the concentration cells (CCs) 0.005/0.05 and 0.05/0.5. Then the transport numbers of the lithium-ion were deduced by means of the Nernst equation in combination with the Debye-Huckel limiting law. Whilst the activation energy values were calculated from the parameters of the fitting of the transference number data to the empirical power law, yielding a regression coefficient of 95.9% for the most concentrated concentration cell. The structure and interactions in the lithium electrolyte solution were studied by vibrational Infra-Red spectroscopy. The experimental data were discussed and compared to those obtained previously, using impedance spectroscopy of glass-forming glycerolate lithium electrolytes for the same purpose. Despite the enormous difference between their viscosities; glycerol shows similar activation energy (i.e. 31.40 kJ.mol–1) with water (i.e. 31.73 kJ.mol–1), in particular at very low concentration, confirming both solvents being hydrogen-bonded. Besides, this study suggests the utilization of the glycerol-lithium ion electrolyte for future conception of ecological lithium-ion battery, rather than those using ion electrolyte polymer currently on the market. Similarly to relaxation and conductivity, the transport number data suggests that the diffusion of conformational states is also monitoring the overall lithium ion transport mechanism.

Novel Self-Calibrating Amperometric and Ratiometric Electrochemical Nanotip Microsensor for pH Measurement in Rat Brain.

Brain pH has been proven to be a key factor in maintaining normal brain function. The relationship between local pH fluctuation and brain disease has not been extensively studied due to lack of the accurate in situ analysis technology. Herein, we have for the first time proposed a voltammetric pH sensor by measuring the ratio of current signals instead of the previously reported potential based on the Nernst equation. Single-walled carbon nanotubes (CNT) were first self-assembled on the electrode surface of a carbon-fiber nanotip electrode (CFNE). Then, poly-o-phenylenediamine (PoPD) molecules were deposited as pH-responsive molecules through in situ electrochemical polymerization. The compact CFNE/CNT/PoPD exhibited a good redox process with the on-off-on ratiometric electrochemical response to pH ranging from 4.5 to 8.2, providing self-correction for in situ pH detection. Thus, the proposed sensor enabled the accurate measurement of pH with excellent selectivity even in the presence of proteins or electroactive species. In addition, the sensor showed high repeatability, reproducibility, and reversibility in measuring pH and even demonstrated good stability when it was exposed to air for 5 months. Finally, we successfully detected the fluctuation of pH in rat brains with cerebral ischemia and rat whole blood. Overall, this research not only provides a good tool for the detection of rat brain pH but also provides a new strategy for further designing nanosensors for intracellular or subcellular pH.

Feasibility of multifunction calibration of H+-responsive glass electrodes in seawater (IUPAC Technical Report)

Abstract Seawater pH values are of the highest relevance in marine chemistry studies, not only through being acidity indicators but also due to the control provided by H+(aq) over the various simultaneous equilibria occurring in seawater. Although the concept of p H = − l g a H + = − lg ( m H + γ H + / m 0 ) $\mathrm{p}\mathrm{H}=-\mathrm{l}\mathrm{g}{\mathit{a}}_{{\mathrm{H}}^{+}}=-\mathrm{lg}\left({\mathit{m}}_{{\mathrm{H}}^{+}}{\mathit{\gamma }}_{{\mathrm{H}}^{+}}/{\mathit{m}}^{0}\right)$ , where m H + ${m}_{{\text{H}}^{+}}$ is the relative (molality basis) activity, γ H + ${\gamma }_{{\text{H}}^{+}}$ is the molal activity coefficient of the hydrogen ion H+ at molality m H + ${m}_{{\text{H}}^{+}}$ , and m 0 is the standard molality, was introduced in 1910 and reaffirmed on successive occasions by relevant bodies, different conceptual definitions and alternative measurement procedures have been adopted and are in use by some, namely among oceanographers, often leading to confusion. This leads to major difficulties with the use of data, e.g., on what concerns comparison of results in space and time. Primary pH values, the highest quality level in terms of the metrological chain, have been assigned to primary reference pH buffer solutions of low ionic strength, by a primary method based on measurements of the Harned cell potential in association with the Nernst equation, as well as on the adoption of extra-thermodynamic model assumptions for electrolyte solutions. Although equivalent types of recommendations dealing with standards and procedures based on metrological traceability are still lacking for higher ionic strength media, as it is in the case of seawater, reference Tris–Tris·HCl buffer solutions in artificial seawater have been suggested for use in the calibration of pH meter systems. In this work, Tris–Tris·HCl buffer saline solutions of three different molality ratios mTris:mTris.HCl, m/mol kg−1 H2O, have been assigned reference values for free p H = − lg a H + $\mathrm{p}\mathrm{H}=-\mathrm{lg}\,{a}_{{\text{H}}^{+}}$ and total pH T = − lg ( m H + * / m 0 ) ${\mathrm{pH}}^{\mathrm{T}}=-\text{lg}\left({m}_{{\text{H}}^{+}}^{\text{{\ast}}}/{m}^{0}\right)$ , where m 0 = 1 mol kg−1 and m H + * = lim m → m SW [ m ( H + ) + m ( HSO 4 − ) ] ${m}_{{\text{H}}^{+}}^{\text{{\ast}}}=\underset{m\to {m}_{\text{SW}}}{\mathrm{lim}}\left[m\left({\mathrm{H}}^{\mathrm{+}}\right)+m\left({\mathrm{HSO}}_{4}^{\mathbf{-}}\right)\right]$ . Multi-point calibration of pH meters in terms of either pH or pHT is thus possible and supports measurement of their respective values under routine conditions at a high metrological level.

Characterization of Vegard strain related to exceptionally fast Cu-chemical diffusion in Cu_2Mo_6S_8 by an advanced electrochemical strain microscopy method

Electrochemical strain microscopy (ESM) has been developed with the aim of measuring Vegard strains in mixed ionic-electronic conductors (MIECs), such as electrode materials for Li-ion batteries, caused by local changes in the chemical composition. In this technique, a voltage-biased AFM tip is used in contact resonance mode. However, extracting quantitative strain information from ESM experiments is highly challenging due to the complexity of the signal generation process. In particular, electrostatic interactions between tip and sample contribute significantly to the measured ESM signals, and the separation of Vegard strain-induced signal contributions from electrostatically induced signal contributions is by no means a trivial task. Recently, we have published a compensation method for eliminating frequency-independent electrostatic contributions in ESM measurements. Here, we demonstrate the potential of this method for detecting Vegard strain in MIECs by choosing Cu_2Mo_6S_8 as a model-type MIEC with an exceptionally high Cu chemical diffusion coefficient. Even for this material, Vegard strains are only measurable around and above room-temperature and with proper elimination of electrostatics. The analyis of the measured Vegards strains gives strong indication that due to a high charge transfer resistance at the tip/interface, the local Cu concentration variations are much smaller than predicted by the local Nernst equation. This suggests that charge transfer resistances have to be analyzed in more detail in future ESM studies.

Assembling and Testing a Series of Ion-Selective Electrodes in Analytical Chemistry

Ion-selective electrodes are among the oldest and most important potentiometric sensing methods. In this experiment, students assemble their own reusable ion-selective electrode from glass tubes with an attached PTFE membrane, [(CH3CH2CH2CH2CH2CH2CH2CH2)3NCH3]X ion exchanger, and both internal and external Ag/AgCl reference electrodes. Students then evaluate the electrode response as a function of specific-ion activity, measure the activity of an unknown-concentration solution, and determine the electrode selectivity by repeating the analysis in the presence of a fixed amount of interfering ion. With a choice of chloride, nitrate, acetate, and sulfate specific-ion electrodes and a variety of interfering ions, each student in a lab section can do a different experiment while keeping both the lab cost for consumables and the setup time low. The obtained selectivity values are in agreement with the Hofmeister series. Students practice analytical laboratory skills by designing and preparing a calibration curve, see benefits and limitations of ion-selective electrodes, and make use of the Nernst equation.

A new method to determine AgCl(1% mol)/Ag electrode potential versus the standard chloride electrode potential in a LiCl-KCl eutectic

In this work, an innovative method was utilized to determine the AgCl(1% mol)/Ag reference electrode potential versus Cl2/Cl− at 673 K. Instead of directly measuring the chlorine electrode potential, the AgCl(1% mol)/Ag electrode potential versus Cl2/Cl− was calculated from the decomposition voltage of LiCl and the equilibrium potential of Li+/Li versus AgCl(1% mol)/Ag in a LiCl-KCl melt. The decomposition voltage of LiCl in the LiCl-KCl melt was calculated using the Nernst equation and the equilibrium potential of Li+/Li was determined by chronopotentiometry, open circuit chronopotentiometry and potentiodynamic scan techniques, and the deviation is within 5 mV. The AgCl(1% mol)/Ag electrode potential was determined to be −1.130 V vs Cl2/Cl− at 673 K. Since it does not involve direct injection of chlorine gas, this method is more convenient and safer than existing approaches. Furthermore, it also has the potential to be used to calibrate reference electrodes in a variety of melts.