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The resistive switching behavior is observed in the Cu/MoS2/Cu/ITO structures, which has been deposited by magnetron sputtering. With the increase in MoS2 thickness, the resistive switching behavior is gradually weakened. The optimal device with a MoS2 thickness of 120 nm has a lower Set voltage and Reset voltage, where Set voltage is 0.14–0.3 V and Reset voltage is −0.24 V to −0.08 V. The device also has a resistive switching ratio of up to 105 high resistance state/low resistance state, a data retention time over 104 s, and can endure more than 103 cycles. As the limiting current increases, the resistance switching (RS) characteristics of devices with MoS2 thickness of 200 nm at both positive and negative biases are improved. There is no RS behavior in ITO/MoS2/ITO devices fabricated by the same method, which indicates that sulfur vacancies have little effect on the RS characteristics of Cu/MoS2/Cu/ITO devices. Moreover, since the migration barrier and diffusion activation energy of Cu in MoS2 are lower than those of sulfur vacancy, combined with the data fitting structure, it is shown that the RS behavior is formed because Cu ions control the connectivity and fracture of conductive filaments through the diffusion and migration of MoS2 layer. [ABSTRACT FROM AUTHOR]

We compare the electrochemically measured Sand’s time, the time required for the cell potential to diverge when the applied current density exceeds the limiting current, with theoretical predictions for a 0.47 M poly(ethylene oxide) (5 kg mol−1)/LiTFSI electrolyte. The theoretical predictions are made using concentrated solution theory which accounts for both concentration polarization and polymer motion, using independently measured parameters that depend on concentration, c: conductivity (κ), salt diffusion coefficient (D), cationic transference number with respect to the solvent velocity ( t + 0 ), thermodynamic factor 1 + dln f ± dln c , and partial molar volume of the salt ( V ̅ ); f ± is the mean molar activity coefficient of the salt. We find quantitative agreement between experimental data and theoretical predictions. We derive a generalized analytical expression for Sand’s time for electrolytes based on dilute solution theory. This expression correctly predicts the divergence of the Sand’s time at the limiting current, in agreement with experimental data and concentrated solution theory predictions. When the applied current is large compared to the limiting current, the analytical expression approaches the standard expression for Sand’s time used in the literature.

In this study, we fabricated limiting current‐type oxygen microsensors capable of sensing a wide range of oxygen concentrations. The oxygen microsensors consist of yttria‐stabilized zirconia thin films on spiral Ta2O5 diffusion layers and high‐temperature micro‐hotplates. At temperatures above 575 °C, we observed a clear limiting current that increased proportionally with oxygen concentration between 0.4% and 94%. This wide‐range linearity is attributed to the Knudsen diffusion of the oxygen gas passing through the small gap in the spiral Ta2O5 diffusion layer. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

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Transport phenomena are key in controlling the performance of electrochemical energy-conversion technologies and can be highly complex, involving multiple length scales and materials/phases. Material designs optimized for one reactant species transport however may inhibit other transport processes. We explore such trade-offs in the context of polymer-electrolyte fuel-cell electrodes, where ionomer thin films provide the necessary proton conductivity but retard oxygen transport to the Pt reaction site and cause interfacial resistance due to sulfonate/Pt interactions. We examine the electrode overall gas-transport resistance and its components as a function of ionomer content and chemistry. Low-equivalent-weight ionomers allow better dissolved-gas and proton transport due to greater water uptake and low crystallinity but also cause significant interfacial resistance due to the high density of sulfonic acid groups. These effects of equivalent weight are also observed via in situ ionic conductivity and CO displacement measurements. Of critical importance, the results are supported by ex situ ellipsometry and X-ray scattering of model thin-film systems, thereby providing direct linkages and applicability of model studies to probe complex heterogeneous structures. Structural and resultant performance changes in the electrode are shown to occur above a threshold sulfonic-group loading, highlighting the significance of ink-based interactions. Our findings and methodologies are applicable to a variety of solid-state energy-conversion devices and material designs.

Copyright of Journal of the Chinese Society of Rare Earths is the property of Editorial Department of Journal of the Chinese Society of Rare Earths and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The formation of metal microstructures on metal substrates is theoretically analyzed by the example of local silver electrodeposition, using the numerical simulation of interrelated electrochemical and homogeneous chemical reactions. The silver electrodeposition localization and rate are shown to depend on the interrelation between full concentrations of ammonia, silver, and protons in solution. The ammonia relative concentration range is determined, which provided an acceptable combination of the silver electrodeposition localization and rate. By using some simplifications, the distributions of the concentrations of the participants in the reactions and the current density of silver ion reduction are numerically calculated for various concentrations of solution components and interelectrode distances. The degree of localization of metal deposition is shown to depend on the distribution of the concentrations of electroactive silver cations and the non-electroactive complex of this metal near the anode. The deposition rate was found to depend nonmonotonously on the interelectrode distances, which can be explained by difficulties in the reactants' delivery at small interelectrode distances and increase of the fraction of the silver electroactive ions diffusing toward solution bulk at large interelectrode distances. [ABSTRACT FROM AUTHOR]

The electrolysis of HCl to form Cl2 is an integral part of the production of polycarbonates and polyurethanes. In recent years, the direct gas-phase electrolysis was shown to be significantly more efficient than the current state-of-the-art process based on the oxidation of hydrochloric acid. Still, three phenomena significantly limit the performance and industrial applicability of this process and have so far only been investigated theoretically. Firstly, a limiting behavior in the HCl oxidation reaction was observed, which seems to be of purely kinetic origin. Secondly, also in the full-cell employing an oxygen depolarized cathode, a limiting behavior was detected, which however appears to have a different origin. Lastly, the performance of the oxygen reduction is significantly reduced in comparison to classical H2 PEM fuel cells. The present work utilizes a combined experimental and theoretical approach to confirm that the HCl oxidation is purely reaction limited while the limiting behavior in the full-cell system employing an oxygen depolarized cathode is caused by flooding at low reactor temperatures and, lastly, that the reduced performance of the oxygen reduction reaction is a consequence of significant HCl crossover that can be mitigated by means of increased cathode humidification. These insights are furthermore used to operate the HCl gas phase electrolyzer employing an oxygen depolarized cathode at current densities of more than 5000 A/m2 for the first time, while also substituting the previously employed platinum based cathode catalyst with RhxSy, decreasing the impact of HCl crossover and allowing for the lowest so far measured cell potentials over a wide interval of current densities.

The electrolysis of HCl to form Cl2 is an integral part of the production of polycarbonates and polyurethanes. In recent years, the direct gas-phase electrolysis was shown to be significantly more efficient than the current state-of-the-art process based on the oxidation of hydrochloric acid. Still, three phenomena significantly limit the performance and industrial applicability of this process and have so far only been investigated theoretically. Firstly, a limiting behavior in the HCl oxidation reaction was observed, which seems to be of purely kinetic origin. Secondly, also in the full-cell employing an oxygen depolarized cathode, a limiting behavior was detected, which however appears to have a different origin. Lastly, the performance of the oxygen reduction is significantly reduced in comparison to classical H2 PEM fuel cells. The present work utilizes a combined experimental and theoretical approach to confirm that the HCl oxidation is purely reaction limited while the limiting behavior in the full-cell system employing an oxygen depolarized cathode is caused by flooding at low reactor temperatures and, lastly, that the reduced performance of the oxygen reduction reaction is a consequence of significant HCl crossover that can be mitigated by means of increased cathode humidification. These insights are furthermore used to operate the HCl gas phase electrolyzer employing an oxygen depolarized cathode at current densities of more than 5000 A/m2 for the first time, while also substituting the previously employed platinum based cathode catalyst with RhxSy, decreasing the impact of HCl crossover and allowing for the lowest so far measured cell potentials over a wide interval of current densities.

The gas diffusion layer (GDL), as a key component of proton exchange membrane fuel cells (PEMFCs), plays a crucial role in PEMFC's polarization performance, particularly in mass transport properties at high current densities. To elucidate the correlation between GDLs' structure and their mass transport properties, a limiting current test with the H2 molecular probe was established and employed to investigate three representative GDLs with and without the microporous layer (MPL). By varying humidity and back pressure, the mass transport resistance of three GDLs was measured in an operating fuel cell, and an elaborate analysis of H2 transport was conducted. The results showed that the transport resistance (RDM) of GDLs was affected by the thickness and pore size distribution of the macroporous substrate (MPS) and the MPL. In the process of gas transport, the smaller pore size and thicker MPL increase the force of gas on the pore wall, resulting in an increase in transmission resistance. Through further calculation and analysis, the total transport resistance can be divided into pressure-related resistance (RP) and pressure-independent resistance (RNP). RP mainly originates from the transport resistance in both MPLs and the substrate layers of GDLs, exhibiting a linear relationship to the pressure; RNP mainly originates from the transport resistance in the MPLs. 29BC with thick MPL shows the largest RNP, and T060 without MPL shows the RNP = 0. This methodology enables in situ measurements of mass transport resistances for gas diffusion media, which can be easily applied for developing and deploying PEMFCs. [ABSTRACT FROM AUTHOR]

Ion-exchange membranes (IEMs) have found potential applications in diverse areas, such as environment related issues and addressing energy. Due to their increasing importance, several studies have been made on the preparation, characterization, modification, and applications of IEMs. This paper first discusses IEMs, their use as new separation materials, and the methods to characterize them. Subsequent sections review IEM-based ion separation techniques, such as diffusion dialysis, Donnan dialysis, and particularly electrodialysis (ED). Importantly, the section on ED reviews concentration polarization (CP), which is especially relevant to the recent trends of research. More specifically, a discussion on monovalent ion permselective membranes and the methods to create them has been made in the paper. Layer-by-layer (LBL) adsorption of polyelectrolyte multilayers (PEMs) gives rise to remarkable monovalent to multivalent cation and anion selectivities > 1000 and > 100, respectively. However, such high selectivities are accompanied by lower current efficiencies (∼ 50%) and lower recoveries of the ions. Additionally, the PEMs assembled through LBL deposition method may start delaminating under an applied potential after a certain period of time. The later part of the paper suggests creating selective PEMs with a net charge matching the native charge of IEMs to reduce CP in ED. Suggestions to increase current efficiencies, percentage recoveries of ions of interest, and the possible ways to increase the stability of PEMs deposited on IEMs have also been discussed in the paper. [ABSTRACT FROM AUTHOR]

Abstract Leveraging the interactions between ionomer and catalyst can increase the performance of proton exchange membrane fuel cells. The impacts of the equivalent weight (EW) of perfluorosulfonic acid–based ionomers on the platinum group metal‐free electrode structure and fuel cell performance have not been fully explored. Four membrane electrode assemblies (MEAs) were prepared by using a commercial Fe–N–C catalyst, two perfluorosulfonic acid ionomers with different EWs, that is, Aquivion 720 (A720) and Nafion 1100 (N1100), and two ionomer‐to‐catalyst (I/C) ratios. The four MEAs were characterized to understand the impact of the ionomer EW and content on the capacitance, proton conductivity, and mass transport on the cathode. The mass transport resistance was measured for the first time using a new oxygen reduction reaction limiting current method enabling to couple the effects of oxygen diffusion with liquid water generation. Low EW ionomer combined with a moderate I/C results in improved performance due to its enhanced proton conductivity. However, when used at high I/C, it can cause severe water flooding at high current density due to the enhanced liquid water uptake, especially at high relative humidity, resulting in lower catalyst utilization and higher mass transport resistance.

(8YSZ)1−x(Cr2O3)x (x = 0, 0.05, 0.10, 0.15) are prepared by the co-precipitation method. Diffraction peaks of the samples belonged to the cubic fluorite structure. Conductivity decreases first and then increases with increasing Cr2O3 content. An oxygen sensor based on 8YSZ solid electrolyte and (8YSZ)0.85(Cr2O3)0.15 diffusion barrier is prepared by the Pt slurry bonding method. The sensor has a limiting current plateau at 2% oxygen concentrations within 720 ~ 870 °C. The oxygen sensor has a linear relationship between the log IL and 1000/T. At 850 °C, a linear relationship between the limiting current IL and oxygen concentration x(O2) is established for the oxygen sensor. The oxygen sensor is provided with a limiting current plateau within the experimental concentration division, and the limiting current plateau is not affected by x(CO2) and p(H2O). I-V curves of the oxygen sensor overlap, and the limiting current plateaus are almost equal under the long-term high-temperature operating conditions of 144 h. [ABSTRACT FROM AUTHOR]

Lithium metal is a promising anode material for next-generation rechargeable batteries, but non-uniform electrodeposition of lithium is a significant barrier. These non-uniform deposits are often referred to as lithium “dendrites,” although their morphologies can vary. We have surveyed the literature on lithium electrodeposition through three classes of electrolytes: liquids, polymers and inorganic solids. We find that the non-uniform deposits can be grouped into six classes: whiskers, moss, dendrites, globules, trees, and cracks. These deposits were obtained in a variety of cell geometries using both unidirectional deposition and cell cycling. The main result of the study is a figure where the morphology of electrodeposited lithium is plotted as a function of two variables: shear modulus of the electrolyte and current density normalized by the limiting current density. We show that specific morphologies are confined to contiguous regions on this two-dimensional plot.

Lithium metal is a promising anode material for next-generation rechargeable batteries, but non-uniform electrodeposition of lithium is a significant barrier. These non-uniform deposits are often referred to as lithium “dendrites,” although their morphologies can vary. We have surveyed the literature on lithium electrodeposition through three classes of electrolytes: liquids, polymers and inorganic solids. We find that the non-uniform deposits can be grouped into six classes: whiskers, moss, dendrites, globules, trees, and cracks. These deposits were obtained in a variety of cell geometries using both unidirectional deposition and cell cycling. The main result of the study is a figure where the morphology of electrodeposited lithium is plotted as a function of two variables: shear modulus of the electrolyte and current density normalized by the limiting current density. We show that specific morphologies are confined to contiguous regions on this two-dimensional plot.

Characterizing oxygen transport resistances in different components of a polymer electrolyte membrane fuel cell (PEMFC) is essential to achieve better cell performance at high current under low Pt loading. In this work, a macroscopic three-dimensional model, together with a novel agglomerate model was proposed to analyze impacts of operating conditions on these resistances via limiting current strategy. By introducing a focusing factor obtained with lattice Boltzmann method at mesoscopic level, the structure-dependent local transport resistance in ionomer thin-film of the electrode was comprehensively captured and validated by existing experimental studies. Contributions of the cell components to the total transport resistance were dissected. Results show that the present agglomerate model could well reproduce the local transport behaviors of oxygen in catalyst layer by fully considering the detailed nanoscale diffusion and adsorption processes. A small mass fraction of oxygen was favored to minimize the relative deviation of the local transport resistance from its intrinsic one due to the water production and heat generation, which can reach 7% for the mass fraction of oxygen of 1%. Contribution of the in-plane diffusion of oxygen in the inactive electrode is around 1%. The total transport resistance increased with the absolute pressure, mainly due to the dominated molecular diffusion mechanism in gas channel and gas diffusion layer. Gas convection accounted for 26% of the oxygen transport resistance originated from gas channel. The transport resistance of catalyst layer increased significantly with the reduction of Pt loading, and decreased with relative humidity and operating temperature, particularly at high Pt loading. • A novel agglomerate model considering oxygen local transport behavior is proposed. • Parameter analyses of operating conditions on transport resistances are performed. • Relative deviation of local transport resistance and its intrinsic one is analyzed. • High Pt-loaded electrode resistance decreases with operating temperature and RH. [ABSTRACT FROM AUTHOR]

Hydrogen sensors, especially those operating at high temperatures, are essential tools for the emerging hydrogen economy. Monitoring hydrogen under process conditions to control the reactions for detecting confined species is crucial to the safe, widespread use and public acceptance of hydrogen as fuel. Hydrogen sensors must have a sensitivity ranging from traces of hydrogen (parts per million (ppm)) up to levels near the lower explosive limit (LEL = 4% H2 in the air) for safety reasons. Furthermore, they need to operate in cryogenic, ambient, and high-temperature environments. Herein, emphasis is given to hydrogen sensors based on solid oxide electrolytes (operating at high temperatures), in particular oxygen ion and proton conductors. The review is devoted to potentiometric, amperometric, and combined amperometric-potentiometric hydrogen sensors. Experimental results already reported in the international literature are presented and analyzed to reveal the configuration, principle of operation, and the applied solid electrolytes and electrodes of the high-temperature hydrogen sensors. Additionally, an amperometric sensor able to detect hydrogen and steam in atmospheric air through a two-stage procedure is presented and thoroughly discussed. The discussion reveals that high-temperature hydrogen sensors face different challenges in terms of the electrodes and solid electrolytes to be used, depending on the operating principle of each sensor type. [ABSTRACT FROM AUTHOR]

The present communication describes the results of the performance and the assessment of a sensor based on a solid oxide electrolyte with a composition of 0.9ZrO2 + 0.1Y2O3 (YSZ), equipped with a ceramic diffusion barrier for measuring the water vapor and hydrogen content in air. The possibility of determining the concentration of water vapor and hydrogen in the air is based on the measurement of the limiting current value. For the calculation of the steam and hydrogen concentration in ambient air, analytical expressions were obtained and applied, using the limiting current values measured in air with a standard oxygen concentration of 20.9 vol.% and in the analyzed air. A two-stage method for the determination of the hydrogen and steam amount in ambient air is proposed. It is stated that the sensor operates successfully at the temperature of 700 °C and can be applied for the continuous determination of steam or hydrogen concentrations in air. [ABSTRACT FROM AUTHOR]

The current experimental study looks at how the limiting current density is approached on using rotating 2-stage 4- blade flat turbine promoters to improve mass transfer coefficient in an open electrolytic cell. The mass transfer data are obtained at microelectrodes fixed on the cell wall and electrode support using an electrochemical method. The electrolyte was equimolal in potassium ferricyanide, potassium ferrocyanide and excess sodium hydroxide. The mass transfer coefficients were calculated using limiting current data from a diffusion-mediated electrode reduction reaction at the microelectrodes attached to the electrode supports. The limiting current technique has been particularly chosen in view of its accuracy, simplicity, negligible chemical polarization, and absence of any physical change to the reacting surface even after long exposure. The effects of geometric parameters such as turbine diameter (0.05-0.09 m), blade width (0.005-0.015m), turbine rotational speeds (250-1250 rpm) and electrolyte velocity (0.567x10-3 to 7.93x10-3 m/s) were investigated. The mass transfer coefficients were increased by the turbulence created by rotation of the promoter turbines. The mass transfer correlation was formed in terms of dimensionless numbers: Schmidt number (Sc), Sherwood number (She), rotational Reynolds number (Rer), and flow Reynolds number (Ref).

Solid-state gas sensors composed of complex oxide electrolytes offer great potential for analyzing various atmospheres at high temperatures. While relatively simple gas mixtures (H2O+N2, O2+N2) have been successfully studied by means of ZrO2-based sensors, the precise detection of more complex compounds represents a challenging task. In this work, we present our findings regarding the analysis of lower alkanes (CH4, C2H6, and C3H8) mixed with nitrogen as an inert gas, utilizing an amperometric ZrO2-based sensor. This sensor, serving as an electrochemical cell with a diffusion barrier, was tested at 500–600 °C to measure the limiting current, which depends on the gas composition and can be further used as a basis for calibration curves. In addition, the diffusion coefficients of the specified gas mixtures were successfully found and compared with references, confirming the applicability of the fabricated sensor for studying diffusion processes in wide concentration and temperature ranges.

Rotating disk electrode systems are widely used to study the kinetics of electrocatalytic reactions that may suffer from insufficient mass transfer of the reactants. Kinetic current density at certain overpotential calculated by the Koutecky-Levich equation is commonly used as the metrics to evaluate the activity of electrocatalysts. However, it is frequently found that the diffusion limiting current density is not correctly identified in the literatures. Instead of kinetic current density, the measured current density normalized by diffusion limiting current density (j/jL) has also been frequently under circumstance where its validity is not justified. By taking oxygen reduction reaction/hydrogen oxidation reaction/hydrogen evolution reaction as examples, we demonstrate that identifying the actual diffusion limiting current density for the same reaction under otherwise identical conditions from the experimental data is essential to accurately deduce kinetic current density. Our analysis reveals that j/jL is a rough activity metric which can only be used to qualitatively compare the activity trend under conditions that the mass transfer conditions and the roughness factor of the electrode are exactly the same. In addition, if one wants to use j/jL to compare the intrinsic activity, the concentration overpotential should be eliminated. [ABSTRACT FROM AUTHOR]

The processes of mass transfer in the metal electrodeposition on a rotating disk electrode from the solution containing three sorts of ions (electroactive metal cation and indifferent electrolyte containing inactive cation and anion) are studied theoretically. The Nernst–Planck equations in the approximation of the solution electroneutrality reduced to a dimensionless form, which takes into account the elecrodiffusion and convective transfer of all types of ions, are used as the mathematical model. The numerical solution of the mathematical model is carried out by the finite volume method using a non-uniform grid. As a result of the numerical solution, the distributions of potential and ion concentrations are obtained with taking into account the interaction between the electric and hydrodynamic fields in the solutions with various concentrations of supporting electrolyte at various diffusion coefficients of ions of all sorts. The dependences of the limiting current of metal electrodeposition on the concentration of supporting electrolyte are obtained. When calculating the limiting current density in the absence of convection, the thickness of the Nernst diffusion layer is calculated taking into account the effective diffusion coefficient of the solution with three sorts of ions at various concentrations of supporting electrolyte. Using several examples with various ratios between the diffusion coefficients of the anion and inactive cation of the electrolyte, the error in the limiting current calculated using the Nernst diffusion layer approximation, as compared with the limiting current obtained taking into account the convective transport of ions, is estimated. [ABSTRACT FROM AUTHOR]

The gas diffusion layer (GDL), as a key component of proton exchange membrane fuel cells (PEMFCs), plays a crucial role in PEMFC’s polarization performance, particularly in mass transport properties at high current densities. To elucidate the correlation between GDLs’ structure and their mass transport properties, a limiting current test with the H2 molecular probe was established and employed to investigate three representative GDLs with and without the microporous layer (MPL). By varying humidity and back pressure, the mass transport resistance of three GDLs was measured in an operating fuel cell, and an elaborate analysis of H2 transport was conducted. The results showed that the transport resistance (RDM) of GDLs was affected by the thickness and pore size distribution of the macroporous substrate (MPS) and the MPL. In the process of gas transport, the smaller pore size and thicker MPL increase the force of gas on the pore wall, resulting in an increase in transmission resistance. Through further calculation and analysis, the total transport resistance can be divided into pressure-related resistance (RP) and pressure-independent resistance (RNP). RP mainly originates from the transport resistance in both MPLs and the substrate layers of GDLs, exhibiting a linear relationship to the pressure; RNP mainly originates from the transport resistance in the MPLs. 29BC with thick MPL shows the largest RNP, and T060 without MPL shows the RNP = 0. This methodology enables in situ measurements of mass transport resistances for gas diffusion media, which can be easily applied for developing and deploying PEMFCs.

Reducing mass-transport losses in polymer-electrolyte fuel cells (PEFCs) is essential to increase their power density and reduce overall stack cost. At the same time, cost also motivates the reduction in expensive precious-metal catalysts, which results in higher local transport losses in the catalyst layers. In this paper, we use a hydrogen-pump limiting-current setup to explore the gas-phase transport losses through PEFC catalyst layers and various gas-diffusion and microporous layers. It is shown that the effective diffusivity in the gas-diffusion layers is a strong function of liquid saturation. In addition, it is shown how the catalyst layer unexpectedly contributes significantly to the overall measured transport resistance. This is especially true for low catalyst loadings. It is also shown how the various losses can be separated into different mechanisms including diffusional processes and mass-dependent and independent ones, where the data suggests that a large part of the transport resistance in catalyst layers cannot be attributed to a gas-phase diffusional process. The technique is promising for deconvoluting transport losses in PEFCs.

This work describes a comprehensive assessment of operating parameters of a bench-scale electrodialysis (ED) plant for nutrient concentration from an Anaerobic Membrane BioReactor (AnMBR) effluent. The ED bench-scale plant serves a dual purpose. Firstly, to generate a concentrated stream with a high nutrient content, and secondly, to produce high-quality reclaimed water in the diluted stream, both sourced from real wastewater coming from the effluent of an AnMBR. Two sets of experiments were conducted: 1) short-term experiments to study the effect of some parameters such as the applied current and the type of anionic exchange membrane (AEM), among others, and 2) a long-term experiment to verify the feasibility of the process using the selected parameters. The results showed that ED produced concentrated ammonium and phosphate streams using a 10-cell pair stack with 64 cm2 of unitary effective membrane area, working in galvanostatic mode at 0.24 A, and operating with an Acid-100-OT anionic exchange membrane. Concentrations up to 740 mg/L and 50 mg/L for NH 4 –N and PO 4 –P, respectively, were achieved in the concentrated stream along with removal efficiencies of 70% for ammonium and 60% for phosphate in the diluted stream. The average energy consumption was around 0.47 kWh·m−3. [Display omitted] • ED can effectively concentrate NH 4 -N and PO 4 -P from AnMBR real effluent. • Lower current values are preferable when working with real urban wastewater. • Selecting an adequate AEM is crucial due to low PO 4 -P recovery efficiencies. • Increasing the number of cell pairs in the ED stack enhances recovery and removal efficiencies. • Determining the most suitable parameters is critical for reducing energy consumption. [ABSTRACT FROM AUTHOR]

A dual chamber solid-oxide sensor for simultaneous measurement of methane and water vapor concentrations in CH4 + H2O + N2 gas mixtures was designed and tested in the temperature range of 450–600 °C. The sensor consisted of two isolated electrochemical cells based on yttria-stabilized zirconia (YSZ) electrolyte and Pt electrodes; each cell had a gas chamber connected with the outside atmosphere via a ceramic capillary. Both cells operated in the amperometric mode, one of them was designed for measuring humidity, while the other one for measuring CH4 concentration. The limiting currents of the cells measured in the temperature range of 450–600 °C were shown to rise linearly as concentrations of CH4 and H2O increased. The sensor demonstrated satisfactory response times and good reproducibility of data. The present research shows that the dual chamber amperometric sensor allows to simultaneously measure the methane and water vapor concentrations in CH4 + H2O + N2 gas mixtures and can be used, in particular, for measuring methane humidity. [ABSTRACT FROM AUTHOR]

The features of the electrochemical behavior of experimental heterogeneous ion-exchange membranes with different mass fractions of sulfonated cation-exchange resin (from 45 to 65 wt%) have been studied by voltammetry during electrodialysis. Electromembrane systems with 0.01 M NaCl solution and with a mixed 0.01 M NaCl + 0.05 M phenylalanine (Phe) solution have been investigated. A significant influence of the ion-exchanger content on the parameters of current-voltage curves (CVCs) was established for the first time. Electrodialysis of the sodium chloride solution revealed a decrease in the length of the limiting current plateau and in the resistances of the second and third sections of the CVCs with an increase in the resin content in the membrane. The fact of the specific shape of the CVCs of all studied cation-exchange membrane samples in mixed solutions of the mineral salt and the amino acid was established. A specific feature of current-voltage curves is the presence of two plateaus of the limiting current and two values of the limiting current, respectively. This phenomenon in electromembrane systems with neutral amino acids has not been found before. The value of the first limiting current is determined by cations of the mineral salt, which are the main current carriers in the system. The presence of the second plateau and the corresponding second limiting current is due to the appearance of additional carriers due to the ability of phenylalanine as an organic ampholyte to participate in protolytic reactions. In the cation-exchange electromembrane system with the phenylalanine containing solution, two mechanisms of H+/OH− ion generation through water splitting and acid dissociation are shown. The possibility of the generation of H+/OH− ions at the enriched solution/cation-exchange membrane interface during electrodialysis of amino acid containing solutions is shown for the first time. The results of this study can be used to improve the process of electromembrane demineralization of neutral amino acid solutions by both targeted selection or the creation of new membranes and the selection of effective current operating modes.

High oxygen transport resistance in the cathode is a main cause of the low performance of high temperature proton exchange membrane fuel cell (HT-PEMFC), and therefore to determine the contribution of different mass transport processes to the oxygen transport resistance is beneficial to the subsequent research work. In this paper, the molecular diffusion resistance (R M) in the cathode was successfully calculated by measuring the limiting currents with using different diluent gases. And the oxygen transport resistance in phosphoric acid (R P A ) was analyzed by changing the humidity and temperature. It was found that the total oxygen transport resistance (R t o t a l ) increased obviously with the increase of the humidify, and the variation of R t o t a l under different conditions was mainly related to the change of R P A . Combined with the phenomenon that the experimental value of R M was less than the calculated value at high humidity, but higher than that at high operation temperature, we speculate that the cause of that R P A increased obviously at high humidity is the occupancy or blockage of gas phase transport channel in catalyst layer (CL) by phosphoric acid due to the water absorption of phosphoric acid in CL and the swelling of membrane. This consequence indicates that it is the change of phosphoric acid distribution that dominate C i s the R t o t a l at high humidity. Image 1 • The separation of molecular diffusion resistance from the total mass transport resistance of HT-PEMFC cathode was realized. • The relationship between the oxygen transport resistance in phosphoric acid and operating conditions was obtained. • The cause of the variation of oxygen transport resistance at different operating conditions was preliminarily analyzing. [ABSTRACT FROM AUTHOR]

The effect of complex formation on the mass transfer during the metal electrodeposition on a rotating disk electrode from the solution containing three types of ions (metal cation, cationic complex, and non-electroactive anion) is studied theoretically. The dimensionless Nernst–Planck equations in the approximation of solution electroneutrality, which take into account the electro-diffusion and convective transfer of all types of ions and the homogeneous reaction of complex formation, are used as the mathematical model. The kinetics of electrochemical reactions is taken into account using the Butler–Volmer equations. In contrast to the known works, the approximations of the Nernst layer, equal diffusion coefficients of all types of ions, and equilibrium complex formation reaction are not used. As a result of numerical solution, the distributions of concentration, potential, and the rate of complex formation reaction are obtained at various parameters of the system under consideration. It is shown that the equilibrium and rate constants of complex formation reaction and the ratio between the diffusion coefficients of complex cation and anion have the strongest effect on the mass transfer. [ABSTRACT FROM AUTHOR]

• A new solid-state gas sensor was designed for humidity analysis (HA) in inert gases. • The sensor consists of two (oxygen- and proton-conducting) electrolytes. • HA was performed by reading a limiting current level (I lim). • Calibration curves of i lim were obtained at different t and inert gases. An amperometric solid electrolyte sensor with a diffusion barrier for measuring gases humidity at the temperatures above 500°C has been developed and analyzed. Simple inert gases with a desired humidity value were used to evaluate the humidity sensitivity of the sensor and to obtain the sensor volt-ampere characteristics. The electrochemical sensor with diffusion barrier is a double electrochemical cell, in which the first cell is made on the basis of solid electrolyte with oxygen ionic conductivity and the second one is made on the basis of solid electrolyte with hydrogen ionic conductivity. The sensor allows obtaining a linear dependence of limiting currents on the humidity of the gases under analysis ranging from 0.3% to 8% at the temperatures ranging from 500 to 700 оС. Apart from that the concentration of oxygen admixtures, which was present in the inert gases under analysis, was measured. The sensor dynamic humidity sensing characteristicswere obtained for the operating temperature of 500оС using argon as an analyzed gas and proved good reproducibility of results and fast operation of the device. [ABSTRACT FROM AUTHOR]

Featured Application: The wedge-shaped cells with static mixers simulated in this research can be applied to innovative high-performance toroidal vanadium redox flow battery (VRB/VRFB) designs for commercial development in public settings/urban environments. The world is moving to the next phase of the energy transition with high penetrations of renewable energy. Flexible and scalable redox flow battery (RFB) technology is expected to play an important role in ensuring electricity network security and reliability. Innovations continue to enhance their value by reducing parasitic losses and maximizing available energy over broader operating conditions. Simulations of vanadium redox flow battery (VRB/VRFB) cells were conducted using a validated COMSOL Multiphysics model. Cell designs are developed to reduce losses from pump energy while improving the delivery of active species where required. The combination of wedge-shaped cells with static mixers is found to improve performance by reducing differential pressure and concentration overpotential. Higher electrode compression at the outlet optimises material properties through the cell, while the mixer mitigates concentration gradients across the cell. Simulations show a 12% lower pressure drop across the cell and a 2% lower charge voltage for improved energy efficiency. Wedge-shaped cells are shown to offer extended capacity during cycling. The prototype mixers are fabricated using additive manufacturing for further studies. Toroidal battery designs incorporating these innovations at the kW scale are developed through inter-disciplinary collaboration and rendered using computer aided design (CAD). [ABSTRACT FROM AUTHOR]

The universal linear scan voltammogram measurement on the rotating disk electrode (RDE) has been identified as a simple method to investigate the oxygen reduction activity of electrocatalysts. The steady‐state limiting current density Ilim indicates the maximum diffusion current density in the oxygen reduction reaction (ORR) during RDE measurement, which should be a fixed value in theory for a 4e ORR in a particular concentration solution and at a certain rotate speed. However, in experiments, Ilim is always variable and smaller than theoretical value even though with the same the catalyst, electrode, and rotator. So the impact of various experimental operating parameters on Ilim is highly necessary to be investigated. In this paper, factors, such as catalyst loading, O2 inlet condition, O2 flow rate, gas tightness, solution concentration, and purity, have been investigated for their effects on the Ilim of ORR on three typical catalysts (20 % commercial Pt/C, Iron/Nitrogen/Carbon‐catalyst and N‐doped carbon nanotubes). The results indicate that the catalyst loading and O2 inlet condition are the key factors influencing the Ilim of ORR. While, the O2 flow rate, gas tightness, solution concentration, and purity have little influence on the Ilim of ORR. The correct Ilim could be obtained under the optimized catalyst loading and the O2 inlet with an extended sand core tube. [ABSTRACT FROM AUTHOR]

Analytical equations for the steady-state current at shallow electrochemical cells with embedded interdigitated electrode (IDE) arrays were found by solving the diffusion equation in steady state using conformal transformations. These equations consider the cases where the IDE is used with an external counter electrode (four-electrode configuration) and where one of its arrays is used as internal counter electrode (three- and two-electrode configuration). Since the expressions for the current depend on Jacobian elliptic functions, we found approximations which depend only on trigonometric and hyperbolic functions which can ease the calculations at the expense of an error below 5%. Additionally, we provide expressions for steady-state voltammograms for the case of Nernstian (reversible) electrode reactions. The obtained theoretical results agree with theoretical and simulation results from the literature and with our own experiments. These results can be useful as criteria for designing electrochemical cells based on IDEs, and as benchmarks for assessing their performance, especially for polymer- or paper-based microfluidics. • Analytical expressions were obtained for interdigitated arrays in shallow cells. • All expressions were obtained by solving the diffusion equation in steady state. • The model includes expressions for concentration profile, current density and current. • Voltammogram equations are given for four-, three- and two- electrode configurations. • Trigonometric/hyperbolic expressions approximate the current in tall/shallow cells. [ABSTRACT FROM AUTHOR]

Lithium metal is a promising anode material for next-generation rechargeable batteries, but non-uniform electrodeposition of lithium is a significant barrier. These non-uniform deposits are often referred to as lithium “dendrites,” although their morphologies can vary. We have surveyed the literature on lithium electrodeposition through three classes of electrolytes: liquids, polymers and inorganic solids. We find that the non-uniform deposits can be grouped into six classes: whiskers, moss, dendrites, globules, trees, and cracks. These deposits were obtained in a variety of cell geometries using both unidirectional deposition and cell cycling. The main result of the study is a figure where the morphology of electrodeposited lithium is plotted as a function of two variables: shear modulus of the electrolyte and current density normalized by the limiting current density. We show that specific morphologies are confined to contiguous regions on this two-dimensional plot.

This work reports the unusual results on studying the operability and capability of a solid state electrochemical sensor based on a proton-conducting material to analyze the oxygen concentration in a gas media at elevated temperatures. This sensor consists of two ceramic parts made of CaZr 0.9 In 0.1 O 3–δ , one of which acts as a hydrogen pump element, while another as a potentiometric detection element. A limiting current, occurring at a certain voltage value applied to the former element, is a sensor's response; it forms the concentration or temperature calibration curves, which can be used for the subsequent electrochemical analysis at high temperatures. The presented results expand the possibilities for utilizing the proton-conducting materials in new electrochemical (analytical) directions. Unlabelled Image • A proton-conducting material, CaZr 0.9 In 0.1 O 3–δ (CZI), was used as a sensor's basis. • The sensor consists of two PtǀCZIǀPt cells for hydrogen pumping and detection. • The limiting current (i limit) is an electrochemical response of the sensor. • Concentration and temperature dependences of i limit were obtained. • Such dependences can be further utilized for analysis of H 2 O + O 2 + N 2 gas mixtures. [ABSTRACT FROM AUTHOR]