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An advanced computational model based on the mixed potential theory (MPT) is presented, which is able to predict the progress of uniform as well as galvanic corrosion on car components made of zinc and steel (CR300). Previous approaches based on the MPT are computationally less challenging than other simulation models and are typically suitable for galvanic corrosion. In this work, an approach closer to reality is proposed by considering uniform corrosion aspects. Therefore, the metal surface is characterized by oxygen‐deficient and oxygen‐rich areas to model the anodic and cathodic reactions, respectively. Polarization curves are measured in 5 wt% NaCl electrolyte and are then used during finite element methods (FEM) simulation as respective boundary conditions on the metal surface, leading to a multiple microelectrode system. By randomly defining the microelectrodes as cathodes or anodes, that is, assigning polarization data from the oxygen‐rich or oxygen‐deficient electrolyte, the uniform corrosion is modeled. The independence of the corrosion rates from the arbitrary model parameters and surface width (up to 1 mm) is confirmed. The results from this FEM simulation for zinc and a low‐alloy steel are compared to the normed neutral salt spray (NSS) test and show good qualitative agreement. Further on, the galvanic corrosion of a zinc‐steel couple is modeled and the expected result for varying cathode‐anode surface ratio is reproduced. Uniform corrosion of zinc and steel is modeled by characterizing the surface in oxygen‐deficient and oxygen‐rich electrolyte. These polarization curves are used as alternating boundary conditions in the simulation approach based on the mixed potential theory. When galvanic corrosion is modeled, the noble metal corrodes less, depending on the ratio of anode and cathode surface area. The results agree reasonably well with experiments. [ABSTRACT FROM AUTHOR]

Mixed potential gas sensors with layered Au,Pt-YSZ electrode comprising a thick-film Pt-YSZ electrode and a covering thin-film Au layer deposited in two different thicknesses, respectively, were studied in this work. It was shown by GD-OES analysis that the Au layer is not uniformly admixed with the Pt-YSZ bulk after firing treatment at 850 °C, but results in a gradient of Au from top over the thickness of the electrode. Surprisingly, also this kind of layered electrode exhibits a mixed-potential characteristic, which was confirmed by open circuit potential measurement. Better sensitivity to CO was found for the electrode with thicker Au layer, and was attributed to the reduced catalytic activity for the oxygen reduction reaction by addition of Au. This aspect was investigated by cyclic voltammetry, and the dependence of electrochemical behaviors of the electrodes on temperature was studied as well. Over all, the experiments have clearly shown, that mixed potential formation at the Au,Pt-YSZ MPE can be dominated by a relatively thin Au,Pt-layer in the top part of the porous electrode material. [ABSTRACT FROM AUTHOR]

Gadolinia-doped ceria (GDC) prepared by the oxalate coprecipitation method was used as an oxygen-ion conducting solid electrolyte for a mixed-potential ammonia gas sensor with a WO 3 -sensitive electrode. The sensing performance of this sensor was compared with a sensor based on yttria-stabilized zirconia (YSZ) electrolyte. The influence of different oxygen-ion electrolytes on the performance of the gas sensor was evaluated. The test results show that the sensor device is much more sensitive (140.44 mV/decade) than the YSZ-based sensor device. Furthermore, the also shows good repeatability and stability. The electrochemical impedance measurements indicate that the GDC-based sensor’s high performance may benefit from the high conductivity of GDC. [ABSTRACT FROM AUTHOR]

The China high-speed trains use cable trays to neatly arrange the cables running through the distributed systems. On one hand, they protect cables against external electromagnetic interference and reduce external radiation from the cables. On the other hand, the cable trays create waveguide structures that affect the coupling among cables inside the cable trays. To simplify coupling analysis for cables going through a cable tray, a lumped circuit model was built using admittance blocks extracted from a mixed-potential integral equation (MPIE) formulation. In the MPIE formulation, either the half-free space or the waveguide dyadic Green's function was used depending on the region where the cables were. A test case was investigated. Results by the proposed circuit model were validated by measurement and full-wave simulation results. [ABSTRACT FROM PUBLISHER]

Copper (Cu) nanowires about 90 nm in mean diameter and lengths of about 50 μm were successfully synthesized by electroless deposition at 60°C in the presence of ethylenediamine (EDA). Without addition of EDA, only large Cu particles were formed in the solution. On the other hand, high quality nanowires were formed in the presence of 176 mM EDA. Below this amount, shorter Cu nanowires were observed. The mixed potential shifted to more negative values without EDA, indicating faster reduction rate. It is possible that EDA does not only act as a structure-directing agent, but also slows down Cu deposition. This condition favors formation of long and thin Cu nanowires. Then again, in all EDA concentrations experiment, the mixed potential is below the oxidation-reduction potential of the Cu(II)/Cu redox pair, suggesting Cu depositions occurs instantaneously at 60°C. Cu nanowire transparent conducting electrode attained a sheet resistance of about 197 Ω sq-1 at a 61% optical transmittance. [ABSTRACT FROM AUTHOR]

We report a general approach for the synthesis of multishell mixed-metal oxyphosphide particles. Seven-layer Mn-Co oxide particles were first prepared by thermal treatment of Mn-Co coordination polymer precursors. Afterwards, these multishell Mn-Co oxide particles were further transformed into multishell Mn-Co oxyphosphide particles through a phosphidation reaction. This approach is very versatile and can be applied to synthesize other multishell mixed-metal oxyphosphide particles with different compositions. By applying a constant electrochemical potential, these multishell Mn-Co oxyphosphide particles can be activated to produce Mn-Co oxide/hydroxide species in their nanoshells and then show greatly enhanced electrocatalytic activity in the oxygen evolution reaction (OER). [ABSTRACT FROM AUTHOR]

Pt is a common redox electrode used to follow oscillations qualitatively in the Briggs-Rauscher (BR) and the Bray-Liebhafsky (BL) reactions from the time of their discovery. Although the potential oscillations of the electrode reflect the temporal pattern of the reaction properly, there is no general agreement as to how that potential is determined by the components of the reaction mixture. In this article, first we investigate how iodine species in different oxidation states affect the potential of a Pt electrode. It was found that I(+3) and I(+5) species do not affect the potential; only I-, I2, and HOI may have an influence. Although the latter three species are always present simultaneously as participants of the rapid iodine hydrolysis equilibrium, it was found that below and above the so-called hydrolysis limit potential (HLP, where the iodide and HOI concentrations are equal) the actual potential determining redox couple is different. Below the HLP, it is the traditional I2/I- redox couple, but above the HLP, it is the HOI/I2 redox pair that determines the potential of a Pt electrode. That change in the potential control mechanism was proven experimentally by exchange current measurements. In addition, from the potential response of the Pt electrode below and above the HLP, it was possible to calculate the equilibrium constant of the iodine hydrolysis as K°H = (4.97 ± 0.20) × 10-13 M², in rather good agreement with earlier measurements. We also studied the perturbing effect of H2O2 on the previously mentioned potentials. The concentration of H2O2 was 0.66 M, as in the BR reaction studied here. It was found that below the HLP, the perturbing effect of H2O2 was minimal but above the HLP, H2O2 shifted the mixed potential considerably down toward the HLP. In our experiments with the BR reaction, the potential oscillations of the Pt electrode crossed the HLP, indicating that from time to time the HOI concentration exceeds that of the iodide. We can conclude that although the perturbing effect of H2O2 prevents the calculation of concentrations from Pt potentials above the HLP, [I-]/[I2]1/2 ratios can be calculated as a good approximation from Pt potentials below the HLP. [ABSTRACT FROM AUTHOR]

A characteristic mode (CM) formulation is developed for the modal analysis of microstrip antennas. It is derived from the mixed-potential integral equation (MPIE) with spatial-domain Green’s functions for multilayered media, where spatial-domain Green’s functions take into account the effect of the multilayered media. The resultant characteristic currents and fields are orthogonal with each other among different orders of modes. Together with the eigenvalues and their deduced indicators, the CMs provide deep physical insights into the radiation mechanisms of microstrip antennas. Numerical results are presented to confirm CM formulation’s effectiveness and accuracy in determining the resonant frequencies, radiating mode currents, and modal fields of microstrip antennas. As opposed to the very popular CM formulation for conducting bodies, comparative studies are presented to show the quite different modal analysis results by considering the multilayered media. [ABSTRACT FROM AUTHOR]

Methanol crossover is one of the most critical issues hindering commercialization of direct methanol fuel cells since it leads to waste of fuel and significantly affects cathode potential, forming a so-called mixed potential. Unfortunately, due to the sluggish anode kinetics, it is not possible to obtain a reliable estimation of cathode potential by simply measuring the cell voltage. In this work we address this limitation, quantifying the mixed potential by means of innovative open circuit voltage (OCV) tests with a methanol-hydrogen mixture fed to the anode. Over a wide range of operating conditions, the resulting cathode overpotential is between 250 and 430 mV and is strongly influenced by methanol crossover. We show using combined experimental and modelling analysis of cathode impedance that the methanol oxidation at the cathode mainly follows an electrochemical pathway. Finally, reference electrode measurements at both cathode inlet and outlet provide a local measurement of cathode potential, confirming the reliability of the innovative OCV tests and permitting the evaluation of cathode potential up to typical operating current. At 0.25 A cm −2 the operating cathode potential is around 0.85 V and the Ohmic drop through the catalyst layer is almost 50 mV, which is comparable to that in the membrane. [ABSTRACT FROM AUTHOR]

The theoretical analysis of the redox potentiometry of reducers and oxidizers is carried out, which involves the electrochemical characteristics of generalized analytical reactions and the development of simplified equations for calculating the sought concentration and the sensitivity of the method. The use of degrees of oxidation of atoms made it possible to elucidate the reaction stoichiometry and determine which atoms in complex compounds are involved in the electron transfer. The terminology of the redox potentiometric method is improved. [ABSTRACT FROM AUTHOR]

A high performance mixed potential type gas sensor based on stabilized zirconia (YSZ) and NiNb 2 O 6 as sensing electrode was fabricated and used for detection of acetone at 650 °C. NiNb 2 O 6 prepared via a facile sol–gel method and sintered at different temperatures was characterized using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM). The present study mainly focused on the effect of sintering temperature (800 °C, 1000 °C, 1200 °C) of NiNb 2 O 6 -SE materials on acetone sensing characteristics at 650 °C. Results indicated that the sensor using NiNb 2 O 6 -SE sintered at 1000 °C exhibited the largest sensitivity to acetone in the concentration range of 5–500 ppm at 650 °C, which the slope was −79 mV/decade. The response for the sensor attached with a NiNb 2 O 6 -SE sintered at 1000 °C to 100 ppm of acetone was approximately −113 mV. Moreover, the present sensor could detect even 500 ppb acetone with an acceptable response. The present device also displayed fast response and recovery times, good repeatability, slight sensitive effect to humidity, small drifts in 40 days measured periods, and acceptable selectivity at 650 °C. Additionally, the mixed potential mechanism was further demonstrated by polarization curve. [ABSTRACT FROM AUTHOR]

A novel mixed-potential type NO 2 sensor was fabricated using La 10 Si 6 O 27 electrolyte and WO 3 sensing electrode (SE). The sinterability of La 10 Si 6 O 27 was significantly improved by the introduction of Y 2 O 3 as sintering aid. WO 3 with different morphologies prepared by the citric acid (CA) assisted hydrothermal method was examined as the sensing electrodes of the mixed-potential type NO 2 sensors based on La 10 Si 6 O 27 electrolyte. The results showed that 6 wt% Y 2 O 3 added La 10 Si 6 O 27 electrolyte sample could get quite dense at a temperature as low as 1500 °C. The morphologies and phase constituents of WO 3 were influenced by the CA content. The sensor showed good response–recovery characteristics. Compared with the sensor based on the irregular WO 3 particles or nanorods, the sensor using WO 3 nanosheets-SE with hexagonal structure exhibited much higher sensitivity (195.6 mV/decade) to NO 2 at 550 °C. The response signals of the sensor were slightly affected by coexistent O 2 varying from 5 to 20 vol%. [ABSTRACT FROM AUTHOR]

Perovskite-type electrode materials of the compositions La 0.6 Ca 0.4 B′ 1− x B″ x O 3± δ (B = Mn, Cr; B″ = Ni, Co, Fe; x = 0, …, 0.6) were investigated with regard to their NO sensitivity and the cross-sensitivity to NO 2 and propylene in a potentiometric solid electrolyte measuring setup. The highest NO sensitivity was found for nickel and iron manganites with x = 0.2 and 0.3. Dependencies on the NO gas concentration were found using impedance spectroscopy. For some materials, the catalytic conversion of NO, NO 2 , methane and propene was determined by thermal investigation in the temperature range of 25–800 °C. [ABSTRACT FROM AUTHOR]

In this paper, the series connection of resonant tunneling diodes (RTDs) will be analyzed with respect to their stability properties. An alternative approach to the commonly used loadline construction for the analysis of circuits utilizing the series connection of RTDs is presented. Furthermore, the basins of attraction of multiple operating points will be determined analytically by Brayton-Moser's mixed potential function. Therewith, the jump postulate by Andronov et al. will be generalized for series connected N-type nonlinearities. In addition, the numerical results will be verified by measurements. At the end, the discussed method is applied to the monostable-bistable transition logic element, which today is one of the most promising logic circuits in nanoelectronics. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A series of mixed potential type gas sensors using stabilized zirconia and M 3 V 2 O 8 (M: Zn, Co and Ni) sensing electrode were fabricated and applied for detecting acetone at 600 °C. Among the sensors utilizing these composite oxides (Zn 3 V 2 O 8 , Co 3 V 2 O 8 and Ni 3 V 2 O 8 )–SEs prepared via a facile sol–gel method, the sensor attached with Zn 3 V 2 O 8 –SE exhibited the highest response to acetone at 600 °C. Therefore, the present study mainly focused on acetone sensing performance for YSZ-based sensor using Zn 3 V 2 O 8 –SE at 600 °C. Results showed that the sensor attached with Zn 3 V 2 O 8 –SE could detect even 1 ppm acetone with an acceptable response. Moreover, Δ V of the sensor attached with Zn 3 V 2 O 8 –SE exhibited segmentally linear relationship to the logarithm of acetone concentration in the ranges of 1–10 ppm and 10–400 ppm, which the sensitivities were −16 and −56 mV/decade, respectively. The present device also displayed good repeatability, small drifts in 30 days measured period, and the excellent sensitivity and relatively good selectivity in the presence of various interfering gases before and after 30 days high-temperature-aging of 600 °C. Additionally, polarization curve was measured to further demonstrate the mixed potential mechanism. [ABSTRACT FROM AUTHOR]

Methanol crossover is a barrier that limits the widespread deployment of direct methanol fuel cell (DMFC) technology. As methanol crossover can be reduced, but cannot be completely eliminated, efforts should be focused on reducing the adverse impacts of permeated methanol on the cathode, i.e.: the problems of mixed potential and Pt poisoning. In this work, we propose a novel cathode structure involving an additional thin reaction layer that is interfaced with the membrane. The reaction layer, conducting ions but being insulated to electrons, is able to chemically consume permeated methanol to reduce the methanol concentration on the cathode. Experimental results show that the adoption of the proposed cathode not only increases the open-circuit voltage due to a reduced mixed-potential loss, but also decreases the desorption peaks of intermediates on the cathode catalyst (Pt) surfaces as a result of an alleviation in Pt-poisoning. Hence, the overall fuel cell performance exhibits a substantial improvement. [ABSTRACT FROM AUTHOR]

In this paper, a high performance YSZ based mixed-potential type sensor based on three-dimensional three-phase boundary (TPB) and a new type composite oxide Co 3 V 2 O 8 as sensing electrode (SE) was fabricated for NO 2 detection at 700 °C. The Co 3 V 2 O 8 material was synthesized through sol–gel method, and the YSZ particle was mixed uniformly with Co 3 V 2 O 8 in different mass fraction (0 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt% and 50 wt%) to form different three-dimensional TPB. The present study mainly focused on the effect of the TPB on NO 2 sensing performances of sensor. Results showed that the sensor using sensing electrode Co 3 V 2 O 8 + 40 wt% YSZ displayed the largest sensitivity in an NO 2 concentration range of 10–400 ppm at 700 °C, which the slope was 85 mV/decade. The response for the sensor to 100 ppm NO 2 was approximately 130 mV. Furthermore, the present sensor also displayed relatively good linearity, repeatability, stability, and cross-sensitivities. Such an enhancing effect on the sensing characteristics of the sensor may be ascribed to the enlargement of three-phase boundary through constructing the three-dimensional TPB. [ABSTRACT FROM AUTHOR]

This paper reports a comparative study on the calculation of equilibrium potential (also known as Open Circuit Voltage) of co-electrolysis of H 2 O and CO 2 in a Solid Oxide Electrolyzer Cell. We start with the thorough examination of literature and investigation of physical principles governing the development of such a potential difference. Based on that review, we compare the use of three different models. A standard model refers to the use of Nernst equation for fuel electrode's reaction H 2 O/H 2 or CO 2 /CO. An oxygen partial pressure model refers to the use of Nernst referring to oxygen partial pressure difference across the cell. A mixed potential model refers to the phenomena described by Fleming et al. as the Mixed Potential Theory (MPT), i.e. the observable potential difference is the superposition of all above potential differences. We conclude that the oxygen partial pressure model suffices for modern cells operated at temperature above 800 °C and if the concentration of CO 2 in the gas mixture is below 25%. Above this limit, MPT model is more accurate and thus recommended. The standard model exhibit large error in all cases and is not recommended. We also present the values of parameters, used in conjugation with MPT model, fitted to a cell with Ni-YSZ fuel electrode operated at 800 °C. [ABSTRACT FROM AUTHOR]

We investigate numerically the effect of non-linear interaction on conductance statistics in one dimensional disordered systems with δ peak potentials. It is shown that the non-linearity can either localize or delocalize the electronic states depending on its sign. For an attractive nonlinear interaction, we found that the mean conductance decays as g ≈ L − γ . The exponent γ is found to be sensitive to the kind of the potential. It seems to be independent of the strength of the non-linearity in the case of disordered barrier potentials, while it varies with this strength for well and mixed potentials. The conductance probability distribution shows a deviation from its log-normal form (linear case) when the nonlinearity is increased and the fluctuations of conductance decrease indicating the delocalization of the eigenstates. [ABSTRACT FROM AUTHOR]

Abstract: A one-dimensional mathematical model is developed for the study of the mixed potential associated with the hydrogen peroxide oxidation reaction (HPOR) at the cathode of hydrogen peroxide-based fuel cells. The complicated physicochemical processes, including mass transport, charge transport, and three simultaneous electrochemical reactions (the hydrogen peroxide reduction, hydrogen peroxide oxidation, and oxygen reduction reactions) are considered. The model is experimentally validated and shows good agreement with the literature experimental data. The model is then applied to the study of the mixed potential by varying the current density. It is found that the largest potential loss due to the HPOR occurs under the open-circuit condition (OCC), and the potential loss decreases with the superficial current density. In addition, the numerical results suggest that under the OCC, an increase in the concentrations of hydrogen peroxide and H+ ions leads to a decrease in the potential loss, but an increase in the hydrogen peroxide decomposition rate and the oxygen evolution rate. [Copyright &y& Elsevier]

Abstract: Monoclinic ZnWO4 has been investigated the first time for the sensing electrode of the yttria-stabilized zirconia (YSZ) based mixed-potential hydrogen sensors. The sensor of ZnWO4/YSZ/Pt indicated a good sensitivity to hydrogen in a concentration range of 0.5–3.0vol% and excellent selectivity over some possible interferents such as CO, propane and NO2 at 600°C in a background of 10vol% oxygen balanced with nitrogen. The response repeatability of the sensor and sensor to consistency was investigated. The half-month long-term performance of the sensor to different concentrations of hydrogen at 600°C was also examined. The sensor demonstrated significantly potential to be developed for a selective hydrogen sensor. [Copyright &y& Elsevier]

Highlights: [•] Activated carbon increased the dissolution current densities of enargite. [•] Activated carbon modified the semiconducting properties of enargite. [•] The dissolution of enargite was interpreted in terms of mixed-potential theory. [ABSTRACT FROM AUTHOR]

This study demonstrates how the potentiometric mode of the scanning electrochemical microscope (SECM) can be used to sensitively probe and alter the mixed potential due to two independent redox processes provided that the transport of one of the species involved is controlled by diffusion. This is illustrated with the discharge of hydrogen from nanostructured Pd hydride films deposited on the SECM tip. In deareated buffered solutions the open circuit potential of the PdH in equilibrium between its β and α phases (OCPβ→α) does not depend on the tip-substrate distance while in aerated conditions it is found to be controlled by hindered diffusion of oxygen. Chronopotentiometric and amperometric measurements at several tip-substrate distances reveal how the flux of oxygen toward the Pd hydride film determines its potential. Linear sweep voltammetry shows that the polarization resistance increases when the tip approaches an inert substrate. The SECM methodology also demonstrates how dissolved oxygen affects the rate of hydrogen extraction from the Pd lattice. Over a wide potential window, the highly reactive nanostructure promotes the reduction of oxygen which rapidly discharges hydrogen from the PdH. The flux of oxygen toward the tip can be adjusted via hindered diffusion. Approaching the substrate decreases the flux of oxygen, lengthens the hydrogen discharge, and shifts OCPβ→α negatively. The results are consistent with a mixed potential due to the rate of oxygen reduction balancing that of the hydride oxidation. The methodology is generic and applicable to other mixed potential processes in corrosion or catalysis. [ABSTRACT FROM AUTHOR]

As an important interface converter, the three-phase voltage-source rectifier (VSR) connects the grid to DC-input converters. The constant power load (CPL) characteristic of the converter-load often causes large-signal stability problems. In order to solve this problem, the stability boundary of the VSR with CPL is analyzed based on the mixed potential theory, and the stability condition under large-signal disturbance is obtained; thus, the jump range of the load power can be estimated. To improve the stability of the system, a voltage loop control scheme based on ADRC is proposed. A theoretical analysis based on the mixed potential theory shows the proposed scheme expands the power jump range of the VSR with CPL effectively, and improves its disturbance rejection performance. Finally, experimental results prove the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]