Cathode Exchange Current Density Research Articles

Effect of ethanolamine as a steel corrosion inhibitor in realkalization of carbonated concrete

ABSTRACT This paper assessed the electromigration behavior of ethanolamine and its efficiency as a corrosion inhibitor of rebar during the realkalization. Cylindrical concrete specimen (diameter 45 mm, height 20 mm) with steel rebar (6 mm in diameter, 35 mm in length) were artificially carbonated and corroded in an accelerated manner with impressed anodic current. The specimens were realkalized in the electrolyte solution containing ethanolamine, while the steel rebars were connected to the cathodic current (200 mA·h, 1 A/m2). After 25 days of monitoring the repair process, experimental data revealed notable changes in electrochemical parameters. The corrosion potential increased from −627 mV to −236 mV, signifying a reduction in corrosion activity. The cathodic exchange current density decreased from 4.9 μA/cm2 to 2.3 μA/cm2, showing a decrease in the corrosion rate. Also, the pH value of the solution dropped to a comparatively lower level, the ethanolamine and potassium ion concentrations decreased from 22 to 30.54 g/L to 3.22 and 10.23 g/L, respectively. Moreover, nitrogen detection on the steel surface and varied levels of ethanolamine concentration at different depths in the concrete were also measured, both indicating a clear migration of inhibitor to the steel surface to form a passive film.

Effects of F− ions on the electrochemical and interface behavior of cathodes in zinc electrowinning

The increasing use of Zn metal in the energy and industrial sectors necessitates a higher level of research into the zinc electrowinning process. In this work, the effects of fluoride ions (F−) in zinc electrolyte on the cathodic kinetics and zinc product quality during zinc electrodeposition was systematically investigated via a series analysis. The results revealed that the addition of F− in the electrolyte showed a polarization effect, with an increase in the apparent cathodic exchange current density increased by 104 orders of magnitude, and a decrease in the zinc deposition overpotential by 46 mV at a concentration of 400 mg/L. However, F− also reduces the hydrogen evolution overvoltage, when the electrolyte contains 400 mg/L F−, the hydrogen evolution overvoltage on aluminum cathode and zinc cathode decreases by 121 mV and 97 mV, respectively. The promoted hydrogen evolution kinetics increases energy consumption and surface porosity. Additionally, F− ions corrode the Al2O3 oxide film on the cathode surface, accelerating the corrosion of the aluminum cathode plate. This results in increased adhesion of zinc deposition to the damaged aluminum substrate, making it difficult to peel off.

Oxygen scavenging activity of smart colophony microcapsules containing nitrite corrosion inhibitors for steel reinforced concrete

In this study, the electrochemical performance of microcapsules (MCs) containing NaNO2corrosion inhibitors for steel reinforcements was studied in 0.6 M chloride contaminated simulated concrete pore solutions (SCPS) with varying pH for a period of 28 days. The corrosion inhibition was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The polarization results for the MC samples showed improved corrosion resistance, with anicorrof 2.54 ×10–6A/cm2after 28 days exposure in SCPS. Oxygen scavenging activity from the MCs was observed by reduced cathodic kinetics, displaying decreased cathodic exchange current densities of 2.66 ×10−8A/cm2, thus imparting cathodic inhibition in conjunction with anodic corrosion inhibitors. The microcapsules additionally displayed improvement over free NaNO2inhibitors after sufficient release time. The decrease in cathodic and anodic kinetics, along with the improved corrosion resistance, show a dual synergistic corrosion inhibition of the NaNO2loaded colophony MC.

Which Exchange Current Densities Can Be Achieved in Composite Cathodes of Bulk-Type All-Solid-State Batteries? A Comparative Case Study.

The performance of bulk-type all-solid-state Li batteries (ASSBs) depends critically on the contacts between cathode active material (CAM) particles and solid electrolyte (SE) particles inside the composite cathodes. These contacts determine the Li+ exchange current density at the CAM | SE interfaces. Nevertheless, there is a lack of experimental studies on Li+ exchange current densities, which may be caused by the poor understanding of the impedance spectra of ASSBs. We have carried out a comparative case study using two different active materials, namely, single-crystalline LiCoO2 particles and single-crystalline LiNi0.83Mn0.06Co0.11O2 particles. Amorphous 0.67 Li3PS4 + 0.33 LiI particles act as a solid electrolyte within the cathode and separator, and lithiated indium acts as the anode. The determination of the cathode exchange current density is based on (i) impedance measurements on In-Li | SE | In-Li symmetric cells in order to determine the anode impedance together with the anode | separator interfacial impedance and (ii) variation in the composite cathode thickness in order to differentiate between the ion transport resistance and the charge transfer resistance of the composite cathode. We show that under the application of stack pressures in the range of 400 MPa, the Li+ exchange current densities can compete with or even exceed those obtained for CAM | liquid electrolyte interfaces.

Parameter analysis from the modeling of high temperature proton exchange membrane fuel cells

High temperature proton exchange membrane fuel cells (PEMFCs) employing phosphoric acid (PA)-doped polymer membranes could be an alternative capable of overcoming the disadvantages of low temperature PEMFCs. Four critical membrane-electrode assembly (MEA) parameters (cathode exchange current density, cathode utilization, ohmic resistance, and cathode limiting current density) are selected and extracted from the modeling of twenty-two polarization curves measured from nineteen MEAs, which are fabricated and operated according to an experimental protocol that Samsung developed in the mid 2000s. MEA systems adopting three representative membranes (polybenzimidazole (PBI), poly(2,5-benzimidazole) (ABPBI), polybenzoxazine (PBOA)) are compared, and the effect of monomer ratio in two representative benzoxazine-benzimidazole copolymer membranes is analyzed. The evolution of the parameters during the break-in period of MEAs and the period of 2008 to 2018, when MEA performance was improved with the same specification of catalysts and membrane, is examined. Also, the impact of PA impregnation in the cathode is investigated when PA is additionally impregnated in the cathode in addition to a PA-doped membrane. Optimum values of the four parameters are combined to simulate the highest MEA performance, and the MEA performance is predicted in some cases where the parameters are varied. Overall, this approach expands the scope of previous literature on the modeling of high temperature PEMFCs, which have been mostly based on PBI membrane systems, by introducing new parameters such as the catalyst utilization and by applying the model to various membrane systems and phenomena.

Synergistic combination effect of clove essential oil extract with basil and atlas cedar oil on the corrosion inhibition of low carbon steel

Clove essential oil extracts was separately admixed with basil oil extract (CLB) and atlas cedar oil extract (CLA), and studied for their corrosion inhibition properties on low carbon steel in 0.5 M H2SO4 and HCl solutions by coupon analysis, potentiodynamic polarization, open circuit potential measurement and optical microscopy. Results showed the two admixed inhibitor compounds performed effectively at most concentrations with optimal inhibition efficiencies of 95.48% and 95.32% in H2SO4 solution while in HCl the corresponding values are 92.7% and 97.98%. CLB and CLA showed mixed inhibiting properties though shift in corrosion potential and Tafel slope values indicates dominant cathodic inhibition and higher cathodic exchange current density. Severe general deterioration was visible on the morphology of control (no inhibitor) steels in H2SO4 while the morphology of the control steel from HCl showed extensive localized deterioration. Addition of CLB and CLA significantly improved the morphology of the steel in both acid solutions signifying effective corrosion inhibition. The open circuit potential plots of the carbon steel in both acids showed significant potential transients due to thermodynamic instability in the presence of the inhibitors. However, the corrosion potential plots were significantly electropositive relative to the plot of the control specimen with final values −0.448V and −0.452V in H2SO4, and -0.476V in HCl (CLA).

Modeling the Effect of Electrolyte-to-Sulfur Ratio in the Cathode on the Systems-Level Performance of a Li-S Battery

Lithium-Sulfur (Li-S) batteries have received significant interest as a result of their high theoretical specific energy and non-toxic, naturally abundant and low-cost active material [1, 2]. Because of the complexity of the processes taking place in the sulfur cathode, performance of a Li-S battery is highly sensitive to the cathode design [1, 2]. Electrolyte-to-sulfur ratio (E/S) is one of the key design factors in a Li-S cathode defining both the electrochemical performance and the systems-level energy density of the battery. Increasing the E/S ratio improves the cathode kinetics and hence the discharge capacity and cyclability of the battery. On the other hand, an excess of electrolyte has an adverse impact on the energy density of the battery at the systems level. In this study, we present a systems-level analysis for a Li-S battery demonstrating the effect of E/S ratio on the energy density of the battery. The systems-level performance model for the Li-S battery has been developed based on the BatPaC model [2]. The performance model uses a 1-D electrochemical model in which the sulfur kinetics has been treated with a single kinetic parameter, cathode exchange current density (i0,PE) [1]. The model predicts the impact of the E/S ratio on the energy density firstly through this kinetic model parameter; i0,PE is defined as a linear function of the electrolyte amount in the electrochemical model. More importantly, cathode specific capacity is described with an empirical linear dependence on the E/S ratio. The dependence of the systems-level energy density on the E/S ratio has been predicted as a function of other critical design parameters such as the maximum cathode thickness, carbon-to-sulfur (C/S) ratio in the cathode and excess Li% in the anode. Figure 1 presents the effect of E/S ratio on the systems-level energy density of a Li-S battery at different C/S ratios. It can be seen in the figure that increasing the E/S ratio improves the energy density until around 9 mL/g S. Any further increase in the E/S ratio results in a significant decrease at the systems-level energy density after this point. This trend can be explained by the dependence of the specific capacity on the electrolyte amount. As mentioned earlier, cathode specific capacity or the sulfur utilization in other words, has been defined as a linear function of the E/S ratio in the model. Therefore, at low E/S ratios increasing discharge capacity with increasing E/S ratio results in higher energy densities. However, when the theoretical capacity has been reached, any further increase in the E/S ratio brings a volume penalty to the pack and thus decreases the energy density. Increasing E/S ratio also improves the cathode kinetics through increasing i0,PE; however, this influence is less significant. It can also be seen from the figure that this trend is independent of the C/S ratio. However, it is clear from the figure that energy density is more sensitive to the E/S ratio for higher C/S ratios. Figure 1.The effect of E/S ratio in the cell on the calculated energy density of a Li-S battery for different C/S ratios. In the model, specific capacity is defined as a linear function of the E/S ratio. Acknowledgment This work was partially supported by the Scientific and Technological Research Council of Turkey (TUBITAK), Grant No: 116M574.

Effect of Electrolyte-to-Sulfur Ratio in the Cell on the Li-S Battery Performance

The effect of electrolyte-to-sulfur (E/S) ratio on the electrochemical and cell- and systems-level performance of a Li-S battery is investigated through modeling efforts. A 1-D electrochemical model is proposed predicting the cell voltage at 60% discharge depth. In the model, increasing electrolyte amount improves the cell voltage by linearly increasing the cathode exchange current density, which is the single kinetic model parameter. Moreover, cathode specific capacity is either defined as a linear function of the E/S ratio or taken constant in the performance models. Increasing E/S ratio enhances the cell- and systems-level specific energy and energy density until 9 mL/g S when cathode specific capacity depends on the E/S ratio. However, when the cathode specific capacity is constant at 1200 mAh/g S, battery performance decreases continuously with increasing electrolyte amount. The effect of other critical design parameters -cathode thickness, carbon-to-sulfur ratio, S loading and excess Li%- are also considered in the analysis.

Effect of HCO3− on electrochemical kinetics of carbon steel corrosion in CO2-saturated brines

The effect of HCO3−(aq) on CO2 corrosion of carbon steel was investigated in deaerated 3.5 wt% NaCl solutions at 30 °C from pH 3.96 to 7.15. In the CO2-saturated solutions, the pH was adjusted with different HCO3−(aq) concentrations, c[HCO3−(aq)]. The corrosion rate decreased by a factor of 2 as the pH and c[HCO3−(aq)] increased. The cathodic current density during polarization increased at higher pH with higher c[HCO3−(aq)], indicating that HCO3−(aq) acted as an additional hydrogen source for the hydrogen evolution reaction. As the pH increased, the active dissolution regions displayed similar anodic Tafel slopes and suggested a modified Bockris mechanism for the Fe oxidation reaction. The exchange current densities for the half reactions were calculated to study kinetics of the anodic and cathodic half reactions independently. The anodic exchange current density (j0,a) increased by one order of magnitude in the presence of CO2, indicating the involvement of CO2(aq) in the Fe oxidation reaction. As the pH and c[HCO3−(aq)] increased, the cathodic exchange current density (j0,c) decreased by a factor of 50 because the increase in j0,c[HCO3−(aq)] was not high enough to compensate the decline from the other hydrogen sources, especially j0,c[H+(aq)]; and j0,a decreased by a factor of 2.4 because HCO3−(aq) may have competed with CO2(aq) for the surface coverage and the increase in j0,a[HCO3−(aq)] could not compensate the decrease in j0,a[CO2(aq)]. It suggests that the reaction rate constant of HCO3−(aq) was smaller than CO2(aq) for the anodic half reaction and was smaller than H+(aq) for the cathodic half reaction. The XPS results verified that the corrosion products transitioned from iron carbonate to hydroxide as the pH increased while iron carbonate remained the major product. As the pH increased with HCO3−(aq), a second time constant was observed at lower frequencies of the electrochemical impedance spectroscopy (EIS) results.

Biorefractory wastewater degradation in the cathode of constructed wetland-microbial fuel cell and the study of the electrode performance

In this study, azo dye decolorization and degradation were realized in the air cathode of constructed wetland-microbial fuel cells (CW-MFCs). Additionally, the relationship between cathode and anode was studied. The cathode diameter was varied from 20 to 30 cm to study the cathode degradation and electricity generation performances, the effects of the cathode on the anode, and the influence of plants in the cathode layer. Different external resistances were applied to study the effects of current intensity on degradation and electricity generation performances. Cathode decolorization performance increased with increasing cathode diameter. Electricity generation performance first increased and then decreased with increasing cathode diameter. The highest decolorization volume (397.64 mg/L) was observed in the CW-MFC with a cathode 25 cm in diameter when the external resistance was 620 Ω. Meanwhile, it had a chemical oxygen demand removal volume of 317.65 mg/L. The highest cathode exchange current density (0.539 A/m2) was observed in the CW-MFC with a cathode 27.5 cm in diameter when the external resistance was 200 Ω. There were more electricity generation generas in the anode layer and there were more anaerobes and amphimicrobes in the larger cathode layer.

Propagation of steel corrosion in concrete: Experimental and numerical investigations

This paper focuses on experimental and numerical investigations of the propagation phase of reinforcement corrosion to determine anodic and cathodic Tafel constants and exchange current densities, from corrosion current density and corrosion potential measurements. The experimental program included studies on RC specimens with various binder compositions, concrete cover thicknesses, and concrete cover crack widths. Modelling and fitting of experimental data using an electrochemical model allowed for the determination of parameters, which are key parameters for electrochemical modelling tools. The numerical model was, furthermore, used to identify electrochemical parameters, which are independent of concrete cover thickness and crack width and at the same time allow for determination of the corrosion current density and corrosion potential of concrete structures within an acceptable error.Very good comparisons between the experimentally measured and numerically simulated corrosion current densities and corrosion potentials were found for the various RC specimens. Anodic and cathodic Tafel constant between 0.01 and 0.369 V/dec and 0.01 and 0.233 V/dec, respectively, were found in the present study through numerical simulations of the experimental data. Anodic and cathodic exchange current densities ranged from 1.0E–12 to 1.0E–09 A/mm2 and 1.0E–12 to 1.1E–09 A/mm2, respectively.

A polarization model for solid oxide fuel cells with a Bi-layer electrolyte

A polarization model for a solid oxide fuel cell (SOFC) with a bi-layer electrolyte is developed and a set of explicit expressions for output current, maximum power and thickness ratio of bi-layer electrolyte are obtained. In the model, two dominating polarizations, activation polarization and ohmic polarization, are considered and the concentration polarization is neglected. The activation polarization at the electrodes is described by the Butler–Volmer equation. The ohmic polarization is represented by the charge transport equation, and this equation is solved with the assumption of constant ionic conductivity. To close the model equations, a supplemental relation is introduced by the energy conservation analysis. The modeling results compare well with the experimental data. The model is further used to study the effect of cathode exchange current density on the working characteristics of a solid oxide fuel cell with a bi-layer electrolyte.

Application of physical electric circuit modeling to characterize Li-ion battery electrochemical processes

A physical electric circuit model (PECM) was used to identify several electrochemical processes occurring in two commercial Li-ion batteries of different cathode materials (LixFePO4 and LixCoO2) via electrochemical impedance spectroscopy (EIS). Through defining these electrochemical processes in these two cells, it was determined that the charge transfer resistance (or exchange current density) observed via EIS was due to the cathodic exchange current densities in both the LixFePO4 and LixCoO2 full cells. In discussing the ionic diffusion of the examined cells, the anode of one cell and the cathode of the other were primarily responsible for the observed diffusion of the full cells. Lastly, the measured double layer capacitance was determined to be represented in EIS scans by the anodes of both full cells. The diffusion coefficient was calculated using Fick's1st Law estimation, and from this coefficient, the particle size was calculated and evaluated against scanning electron microscopy (SEM).

Evidence for enhanced catalytic activity of magnesium arising from anodic dissolution

The increasing rate of hydrogen evolving from magnesium (Mg) surfaces under anodic polarization is nowadays well documented and often termed the so-called “negative difference effect” (NDE). Recently, this behavior has been explained by a theory involving an increase in the cathodic exchange current density that arises from the anodic dissolution itself rather than a commonly-mentioned theory involving the formation of univalent Mg and its subsequent chemical reaction with water to produce hydrogen gas. In this work, a series of electrochemical tests were performed to provide evidence in support of the enhanced catalytic surface theory explaining the NDE. Potentiostatic, galvanostatic, and potentiodynamic polarization experiments using high purity Mg electrodes indicated substantial increases in the ability to support the rate of the cathodic reaction following discrete periods of anodic dissolution.

Concepts for Ultra-High Power Density Solid Oxide Fuel Cells (SOFC)

Over the past two decades, considerable work has been reported on solid oxide fuel cells (SOFC) [1-3]. While progress has been made, there has not been significant further gain in performance (at 800oC), beyond that achieved about fifteen years ago (~2 Wcm-2), despite using many different cathodes. Thus in many cases, the cathode may not be limiting the performance. To achieve further improvements in cell performance beyond what has been discussed in previous studies [4,5], it will require accurate identification of various polarization losses, their sources, and dependence on material and microstructural parameters, atmosphere and temperature. The majority of the modeling studies do not provide the required guidance as they rely on a number of often not so easily measurable parameters thus necessitating a somewhat arbitrary selection of such parameters. The objective of this work is to estimate various polarization losses based on out-of-cell measurements made using micro-fabricated electrodes, microstructural measurements on cells, and cell electrochemical performance measurements using a parametric model. Such an approach may identify where the dominant losses are and how to further improve cell performance. The minimum number of independent parameters necessary to model cell performance for an anode-supported SOFC with five distinct layers are 9 and they are: Deff1 O2-N2 and Deff2 O2-N2 , the effective binary diffusivities through the cathode current collector and the cathode functional layer, respectively; Deff1 H2-H2Oand Deff2 H2-H2O , the effective binary diffusivities through the anode support and the anode functional layer, respectively; cathode exchange current density (i0c ); anode exchange current density ((i0a ), cathode transfer coefficient (αc), anode transfer coefficient (αa), and ohmic resistance Ri. The parametric model is given by equation (1). V(i)=E0-iRi-(RT/2F)arcsinh(i/2i0 c)-(RT/2F)arcsinh(i/2i0 a)+( RT/2F)ln(pH2'(i)pH2Oo /( pH2o pH2O')+ ( RT/4F)ln(pO2'(i)/ pO2o ) (1) where pO2o and pO2'(i) are the oxygen partial pressures just outside the cathode current collector and close to the cathode functional layer/electrolyte interface, respectively; pH2o and pH2'(i) are the hydrogen partial pressures in the fuel just outside the anode support and close to the anode functional layer/electrolyte interface, respectively; pH2Oo and pH2O' are the water vapor partial pressures in the fuel just outside the anode and close to the anode functional layer/electrolyte interface, respectively. In equation (1), both transfer coefficients are assumed to be 0.5. As seen in Fig. 1, at low current density, the most dominant contribution is cathodic activation polarization for a cathode grain size of 2 mm. However, beyond about 1.3 A/cm2, the ohmic contribution is the dominant one, and underscores its importance. In Figs. 2a to 2b, the cathode functional layer grain size is varied from 2 μm to 0.2 μm. This increases the maximum power density by 0.3 W/cm2. However, if the ohmic resistance can be somehow reduced from 0.1 to 0.05 Ωcm2, the maximum power density increases by 1.2 W/cm2 (Figs. 2b and 2c) even in a thin electrolyte, anode-supported cell. This shows the profound role of ohmic contribution on cell performance. By contrast, a change from LSM/YSZ to Pt/YSZ only leads to a modest increase in maximum power density of about 0.4 W/cm2 (Figs. 2c and 2d). This is consistent with the observation that cells with several very different cathodes exhibit similar performance. Further work is thus required in lowering the ohmic contribution. Many cathodes that have been developed over the years appear quite satisfactory and not limiting cell performance for operation at 800oC. Funded by DOE EFRC Grant Number DE-SC0001061 as a flow-through from the University of South Carolina.

A polarization model for a solid oxide fuel cell with a mixed ionic and electronic conductor as electrolyte

A polarization model for a solid oxide fuel cell (SOFC) with a mixed ionic and electronic conductor (MIEC) electrolyte is developed based on charge transport equation and a constant ionic conductivity assumption. The electrochemical reaction at the electrode is described by the Butler–Volmer equation and the energy conservation equation is included as an additional condition to complete the model. The modeling results agree well with experimental data. Utilizing this model the effects of key parameters, including conductivities of electrolyte, electrolyte thickness and cathode exchange current density on the performance of the SOFC are analyzed. The distribution of oxygen partial pressure in the electrolyte is also obtained.

Towards a Physical Description for the Origin of Enhanced Catalytic Activity of Corroding Magnesium Surfaces

The so-called “negative difference effect” (NDE) exhibited by corroding magnesium (Mg) surfaces, where the rate of hydrogen evolution increases with the extent of anodic polarization, has been well documented. Recently this behaviour has been explained by a theory involving an increase in the cathodic exchange current density that occurs during anodic polarization, rather than the popular theory involving the formation of a univalent Mg+ ion and its subsequent chemical reaction with water to produce hydrogen. The present study reports on the results of transmission electron microscopy (TEM) conducted on focused ion beam (FIB) prepared cross-section lamellae of the dark film formed on a corroding area of a Mg surface from which hydrogen evolved. The film was found to consist of an outer columnar mixed magnesium oxide-hydroxide layer on top of a magnesium oxide-rich inner layer. X-ray energy dispersive spectroscopy (EDS) reveals iron (Fe)-rich particles embedded in the columnar outer layer. Subsequent cathodic polarization measurements showed that the corroded surface became cathodically activated relative to a non-corroded surface. These observations demonstrate that a surface film enriched in more noble metals can catalyze the cathodic process, provide physical evidence towards support of the enhanced catalytic surface theory explaining the NDE, and validate the chemistry and structure of the surface film that forms upon corroding regions during anodic polarization.

Parameter sensitivity examination for a complete three-dimensional, two-phase, non-isothermal model of polymer electrolyte membrane fuel cell

Parameter sensitivity analysis is carried out for a complete three-dimensional, two-phase, non-isothermal model of polymer electrolyte membrane (PEM) fuel cell with a parallel flow field design. The model couples the two-phase flow of the multi-component reactants and liquid water, species transport, electrochemical reactions, proton and electron transport, and the electro-osmosis transport, back diffusion of water in the membrane, and energy transport. Twenty nine parameters, which are classified into the structural or transport parameters of porous layers (tortuosity, porosity, permeability, proton conductivity, electron conductivity, and thermal conductivity) as well as the electrochemical parameters (anodic and cathodic exchange current densities, anodic and cathodic transfer coefficients for anode and cathode reactions), are used to implement individual parameter investigation. The results show the parameters can be divided in to strongly sensitive, conditional sensitive and weak sensitive parameters according to its effect on the cell polarization curve. The optimization of parameters of cathode gas diffusion layer (GDL) and catalyst layer (CL) is more important to improve cell performance than that of anode GDL and CL because liquid water transport and removal affect significantly membrane hydration and reactant transport. Electrochemical parameters determine the activation potential and the slope of ohmic polarization hence these parameters can be used to fit experimental polarization curve more effectively than the other parameters.

Exchange Current Density of Solid Oxide Fuel Cell Electrodes

It is desired to develop computational procedures to simulate an internal current density, anode/cathode gas concentrations and a temperature distribution in solid oxide fuel cell (SOFC) systems. In this study, the influences of various operational conditions on the exchange current density which is the essential parameter to simulate SOFC performance were discussed. The anodic exchange current density depended strongly on the humidity of H2, and it exhibited the highest value at around 40% H2O. The cathodic exchange current density was strongly affected by the operational temperature. Parameters necessary to describe dependences of exchange current density on the operational conditions were determined by fitting measured exchange current density with the empirical equations.

A simplified model to predict the current–voltage relationship of an electro-chlorination cell

A simplified model is described to predict the Current–Voltage (I–V) relationship of a parallel plate electro-chlorination cell containing aqueous NaCl solution as electrolyte. The simplifications allowed obtaining an analytical solution without recourse to computationally intensive numerical solutions like finite element method. The anodic and cathodic exchange current densities and symmetry factors for the model were obtained using linear sweep voltammetry experiments for two different electrodes, viz. graphite and mixed metal oxide coated titanium. Using them, anodic and cathodic overpotential values (for a particular device current I) were predicted using the Butler–Volmer equation. The solution potential drop for the same device current was determined using a modified Nernst–Plank equation. The predicted device voltage (for the device current I), which is the sum of equilibrium electrode potentials, electrode overpotentials and solution potential drop, was compared with experimental (I–V) data for the two electrochemical cells as mentioned above. Results showed that the simplified model could predict the I–V data well, when the electrode surface area was assumed to be twice the superficial area.