Behavior Of Porous Electrodes Research Articles

Evaluation of Electrochemical Techniques for Characterizing the Kinetics of Porous Insertion-Type Electrodes

The composite-type porous electrode remains the most commonly used electrode for a wide variety of electrochemical energy storage devices, including lithium-ion batteries, electrochemical capacitors, Li-S/Li-air batteries, and even all-solid-state batteries. This is due to its ease of manufacturability and ability to maintain a high electrochemical surface area with adequate ion and electron transport. Understanding porous electrode kinetics is essential to maximize the active material utilization at high rates. A variety of electrochemical techniques exist to characterize the kinetic behavior of porous electrodes. The most popular ones include electrochemical impedance spectroscopy, galvanostatic charge/discharge, galvanostatic intermittent titration technique, and cyclic voltammetry. The purpose of this work was to evaluate which of these four techniques provides the most relevant kinetic information for understanding porous electrode kinetics. To do this, we utilized porous electrodes composed of LiCoO2 as a model insertion-type material, and with varying thicknesses (10 - 40 µm). We find that GITT is an accessible and reliable method for obtaining the effective diffusion coefficient of the porous electrode. It yields consistent results, regardless of electrode thickness and component ratio. On the other hand, the cyclic voltammetry peak current behavior can be easily compromised, even at slow scan rates of 0.01 - 0.1 mV/s, and when using a high conducting domain ratio. When comparing the dQ/dV plot and cyclic voltammetry for observing peaks indicating phase transitions in the insertion material, the dQ/dV plot is less kinetically limited. We utilized the differential relaxation time (DRT) method to analyze electrochemical impedance spectroscopy data. Our findings demonstrate that as thickness increases, charge transfer resistance decreases, while diffusion resistance increases. This study provides a comprehensive evaluation on the differences between electrochemical methods to characterize the kinetics of composite porous electrodes.

(Invited) Advances in Modeling Ion Transport in Micropores and Charging Behavior of Porous Electrodes: Merging Molecular Insights with Machine Learning for Energy Storage

Electric double layer (EDL) charging is a complex process coupling electro-osmotic flow, surface reactions, and ion concentration gradients. The charging dynamics depends on the properties of electrolyte and electrode structure, as well as initial and boundary conditions. While molecular dynamics (MD) simulations and first-principles calculations can encompass all factors, their computational demands are substantial even for simple electrochemical systems such as electrolytes near a planar surface. This presentation explores recent advancements in modeling ion transport in micropores and the charging behavior of porous electrodes with different theoretical and simulation methods. Illustrative examples will be discussed on the integration of molecular modeling and machine-learning techniques to enhance our understanding of complex electrochemical processes and improve the design of energy storage devices.

In Situ Determination of the Potential Distribution within a Copper Foam Electrode in a Zinc‐Air/Silver Hybrid Flow Battery

AbstractThis work describes a novel methodology for measuring the potential distribution within the porous copper foam electrode of a zinc‐air/silver hybrid (ZASH) flow battery by using local potential probes. The suitability of dynamic hydrogen electrodes (DHEs) and a quasi‐reference electrode as probes is evaluated, with the latter chosen in view of stability. Liquid and solid‐phase potentials are recorded at varying applied current densities over multiple charge‐discharge cycles. Various zinc structures are found within specific overpotential ranges, with moss‐like structures appearing between 7.8 mV and 13.2 mV and the desired boulder structures in the range of 22 mV to 100 mV. Regardless of the current density, the highest liquid‐phase potentials are always measured in the outermost region of the porous foam near to the separator. In practice, this means that increasing the thickness of the copper foam over about 5 mm does not provide significant performance benefits. Conversely, solid‐phase potentials across the copper foam remain nearly uniform, resulting in negligible effects on local overpotential. The presented technique provides unique insights into the behavior of porous electrodes in electrochemical energy conversion technologies, facilitating the determination of the optimal properties for maximum efficiency, such as electrode thickness.

Tailoring the pore accessibility using proteins in laser induced porous graphitic structures: Correlating the physicochemical & electrochemical characteristics

While the popular means of enhancing the sensor's electroanalytical performance involves novel nanomaterial modifications and functionalization, these are multistep procedures which require several material/electrode characterization studies and are resource intensive. Alternatively, the sensor's performance can also be greatly enhanced by appropriately choosing the electroanalytical technique and by tuning its associated parameters. While such optimization has been popularly addressed via one-parameter-at-a-time strategies, this method demands greater number of experiments and fails to factor in the interaction between variables. Such issues can be addressed via the DoE multivariate statistical technique, which, however has not been widely employed in the field of electroanalysis. Moreover, there is a significant dearth in DoE based works for optimizing the LIG electrode's electroanalytical performance. Hence, in this work we have performed the DoE, FFD-based SWV technique optimization in bare LIG electrodes and have demonstrated a label-free affinity sensing application. While the optimized parameters significantly improved the output signals, we observed counterintuitive traits of increasing current values with protein loading. Hence, to explain these contrary trends we evaluate the electrochemical and physicochemical traits of model protein, BSA modified LIG electrodes, wherein we report the eccentric porous electrode behavior ensuant upon protein modification, associated with pore accessibility in these electrodes. Subsequently, we attribute the pore accessibility traits to hydrophilicity & steric hindrance aspects, and correlate it to the CPE effects, relaxation times and diffusion resistance. While few LIG-based works have reported such contrary trends in label-free affinity sensing, they have not provided the plausible explanation, and this is the first report to comprehensively elucidate the reasons.

Modeling Contact Behavior of Multiparticles and Particle–Current Collector Contact in Porous Electrode

There are various component contacts in porous electrodes, such as the direct contact between the active particles and the particle–current collector, during electrode manufacturing and lithium‐ion battery electrochemical cycles. Herein, an electrochemical–mechanical representative volume element model is developed to study the contact behavior of porous electrodes. For the direct contact behavior of multiple particles, stronger battery constraints and larger size differences enhance the reduction in Li‐ion concentration in the contact area of the active particles in the porous electrode and the contact stress in the porous electrode particles. For the contact between the active particles and current collector, the decrease in the elastic modulus of the current collector slightly increases the contact radius and significantly reduces the contact stress. By comparing the contact area and contact stress of the smooth and rough current collectors, the latter has a smaller contact area and larger contact stress when in contact with active particles. These findings provide insights into designing Li‐ion batteries from the perspective of contact stress to minimize the mechanical failure of porous electrodes.

Elastoplastic model for chemo-mechanical behavior of porous electrodes using image-based microstructure

The microstructure of electrodes is intrinsically complex and thus should be determined prior to the analysis of the chemo-mechanical performance during charge/discharge cycles. In this study, a microstructurally resolved, fully coupled chemo-mechanical model was developed to investigate the structure–property relationship of electrodes in the framework of elastoplastic finite deformation. The active particles, binder, and pores of real electrode images were segmented and reconstructed using the region-growing method. The effects of the electrode microstructure on the diffusion-induced stress (DIS) distribution, local electric potential and electrical resistance, interaction between the binder and particles, and mechanical failure of the particle–binder interface (PBI) were elucidated considering the finite concentration effect, concentration-dependent modulus and yield strength. The results indicate that the microstructure of electrodes significantly influences the distribution of DIS, local electric potential, and electrical resistance. The elastoplastic finite deformation theory can accurately describe the stress singularities that occur near sharply concave regions. Additionally, the use of a relatively soft binder was found to accommodate the expansion of active particles and mitigate the effects of particle interaction. Furthermore, being able to ensure that the active particles maintain a simple convex shape can reduce the likelihood of particle pulverization and PBI debonding. These results will enhance the understanding of the evolution of stress generation, the local electric potential and electrical resistance, and the mechanical failure of the PBI within the microstructure of porous electrodes; the results also emphasize the need for an optimized microstructure design for porous electrodes.

The Holes of Zn Phosphate and Hot Dip Galvanizing on Electrochemical Behaviors of Multi-Coatings on Steel Substrates

The aim of this investigation is focused on the evaluation of distinctive coatings commonly applied in the automotive industry. The resulting corrosion behavior is analyzed by using electrochemical impedance spectroscopy (EIS), equivalent circuit (EC) and potentiodynamic polarization curves. The novelty concerns a comparison between tricationic phosphate (TCP), cataphoretic electrodeposition (CED) of an epoxy layer, TCP + CED and HDG (hot-dip galvanized) + TCP + CED multi-coatings. Both the naturally deposited and defect-induced damage (incision) coatings are examined. The experimental impedance parameters and corrosion current densities indicate that multi-coating system (HDG + TCP + CED layers) provides better protection. Both planar and porous electrode behaviors are responsible to predict the corrosion mechanism of the majority of samples examined. Although induced-damage samples reveal that corrosion resistances decreased up to 10×, when compared with no damaged samples, the same trend of the corrosion protection is maintained, i.e., TCP < CED < TCP + CED < HDG + TCP + CED. It is also found that the same trend verified by using electrochemical parameters is also observed when samples are subjected under salt spray condition (500 h). It is also found that porous electrode behavior is not a deleterious aspect to corrosion resistance. It is more intimately associated with initial thickness coating, while corrosion resistance is associated with adhesion of the CED layer on TCP coating. The results of relative cost-to-efficiency to relative coating density ratios are associated with fact that a CED coating is necessary to top and clear coating applications and the TCP + CED and the HDG/TCP + CED coating systems exhibit the best results.

EIS Investigation of the Corrosion Behavior of Steel Bars Embedded into Modified Concretes with Eggshell Contents

This investigation is focused on evaluation of the corrosion behavior of embedded steel bars (SB) into concretes. Conventional and modified concretes with eggshell are prepared. Although the effect of calcium carbonate on mechanical behavior is recognized and reported, their effects as eggshell (ES) particles replacing portions of sand and cement contents are reasonably scarce. Corrosion behavior is evaluated by electrochemical impedance spectroscopy (EIS) and the potentiodynamic polarization technique. Equivalent circuit and porous electrode behavior are also considered. The novelty concerns a promising use of concrete with ES content to maintain corrosion resistance concatenated with reasonable structural properties. For this purpose, three distinct concrete mixtures are proposed, i.e., a reference and two modified concretes. One replaces 10 wt.% with cement and another 10 wt.% with sand content. It is found that porous electrode behavior helps to predict the corrosion mechanism. Finer ES particles in concrete mixture provides a rapidly passivation on rebar. This reflects positively in corrosion current density after long-term immersion. Additionally, an environmentally friendly aspect associated with economical factor constitutes a promise use of the concrete.

Effect of added porosity on a novel porous Ti-Nb-Ta-Fe-Mn alloy exposed to simulated body fluid

Porous titanium materials have gained interest as prosthesis materials due to their similar mechanical properties to the human bone, biocompatibility, and high corrosion resistance. The presence of pores in the metal matrix implies a decrease in the elastic modulus and an increase in the active area, perhaps improving the osseointegration. Corrosion resistance is a critical consideration as corrosion may lead not only to mechanical failure but also the release of ions and/or particles to the bloodstream. In this work, a novel Ti-Nb-Ta-Fe-Mn alloy with varying percentage of porosity (25, 31 and 37 v/v%) was exposed to simulated body fluid (SBF) at 37°C and its corrosion resistance was investigated using electrochemical techniques and surface analysis as a function of exposure time. Open circuit potential and polarization curves revealed that the effect of porosity was mainly on the shift of the corrosion potential to more negative values with a slight increase in the anodic current. A passive range was also observed, which was not influenced either by increased exposure time or increased porosity. Therefore, a change in the surface specific area could have taken place during the exposure, which is not necessarily related to a corrosion process. Moreover, a typical porous electrode behavior was identified by electrochemical Impedance spectroscopy, without any significant change over time. No release of metal ions was detected by on line ICP-AES, either at the open circuit potential or upon polarizing the samples up to 2V vs. SCE, whereas only traces elements (Fe and Mn 1nmol/scm2) were detected in the electrolyte accumulating all released ions during 30days of exposure. Additionally, the surface analysis showed thickening of the oxide layer with exposure time. Therefore, the stability of the passive layer and low release of ions indicate that the porous alloys are suitable for further study as prosthesis materials.

Combining Cyclic Square Wave Voltammetry Experiment and Modeling to Quantify Unknown Electron Transfer Mechanisms for Applications in Relevant Electrochemical Systems

Understanding and controlling electron transfer process(es) is of significant importance to electrochemical systems that employ Faradaic reactions, as knowledge of reaction mechanisms enables improvements on the device level (e.g., reducing the kinetic overpotential, minimizing undesirable homogeneous reactions). Therefore, developing robust and inexpensive techniques capable of diagnosing electron transfer mechanisms is highly desirable. Currently, many methods are able to quantify specific electron transfer mechanisms. For example, the Nicholson Method can determine the heterogeneous rate constant of a quasi-reversible one-electron transfer; further, voltammetric simulations can capture the behavior of more complex electron transfer phenomena.1,2 However, while these previous studies have successfully combined modeling and experiment to quantify various electrode mechanisms, such approaches require a priori knowledge of the electron transfer pathway to extract meaningful information. If a system has multiple possible electron transfer pathways, the approach used in these previous studies provides inadequate information regarding which pathway is the correct one, limiting its utility in novel or poorly understood systems. Thus, this protocol would be even more powerful if it could both determine relevant parameters for an appropriate electron transfer pathway and correctly select unknown electron transfer pathways. We successfully address this shortcoming using a robust and accessible protocol that determines electron transfer mechanisms of different redox couples by combining voltammetry, modeling, and statistical analysis. Specifically, we couple cyclic square wave voltammetry, due to its increased sensitivity to Faradaic processes as compared to conventional voltammetry,3 with model selection criteria based on statistical inference (e.g., Akaike Information Criterion, Bayesian Information Criterion), to determine the most appropriate electron transfer model. Our protocol requires only experimental data and essential inputs (e.g., simulated points per second, number of initial guesses tested) and uses an extensive library of electron transfer models derived using an approach similar to that of previous researchers.3,4 As the field becomes cognizant of the utility model selection criteria offer, researchers are starting to use them to differentiate between electron transfer mechanisms. However, the work done thus far has only been validated for moderately simple electron transfer mechanisms (at most, four reactions in series) and is ultimately targeted towards the specific application of analyzing porous electrode behavior in batteries and fuel cells.5 This protocol can be applied to an even wider variety of applications (e.g., post-mortem testing, deeper mechanistic understanding of complex electrode processes), but to do so, it must be shown to be successful for more complicated electron transfer pathways present in these applications. We pursue this goal and demonstrate its viability by extending our protocol to consider these complicated pathways. In this presentation, we first demonstrate the successful validation of our extensive model library using well-known model redox couples studied on a planar surface. We then illustrate the predictive capability of our protocol using relevant redox flow battery couples, demonstrating strong agreement with literature values. We finally discuss future work, including the addition of appropriate electron transfer models to enable this protocol’s implementation in specific, targeted applications.

Supercapacitive properties, anomalous diffusion, and porous behavior of nanostructured mixed metal oxides containing Sn, Ru, and Ir

Different nanostructured mixed metal oxide (MMOs) electrodes containing Sn, Ru, and Ir supported on titanium with the nominal composition Ti/[Sn0.5Ru(0.5−x)Ir(x)]O2 were prepared using the drop-coating method. SEM analysis revealed the presence of oxide islands in the microsized domains of ca. 50 μm separated from each other by cracks. On the contrary, analysis of the nanosized domains revealed the presence of nanostructures containing rectangular grains with an average diameter of ca. 200 nm. The discrepancy between the nominal and real oxide compositions was attributed to volatilization of Sn during the heat treatment. XRD analysis revealed a poor degree of crystallinity and an average crystallite size of 15 ± 4 nm. Different electrochemical studies revealed higher specific pseudocapacitances in the range of 175–222 F g−1 for the MMO containing 50 mol% Ir. The low values obtained for the morphology factor (0.11 ≤ φ ≤ 0.33) indicate a relatively narrow interval of 11–33% for the active surface regions confined to the inner surface regions of the oxide layers. The chronoamperometric findings obtained for short times (t ≤ 50 ms) permitted evaluation of the electrical double-layer capacitance (Cedl), with verified maximum values in the range of 68–75 F g−1 for the MMO containing 50 mol% Ir. On the contrary, the experimental findings obtained for long times (0.1 s ≤ t ≤ 3 s) revealed that the reversible solid-state Faradaic reactions did not exhibit a Fickian behavior. The impedance analysis revealed that MMOs exhibit a porous electrode behavior (De Levie’s model) permitting the determination of the pseudocapacitance and the resistance of the electrolyte inside the pores.

Electrochemical impedance spectroscopy of iron corrosion in H2S solutions

Corrosion of iron exposed to H2S saturated solution at pH 4 was studied by electrochemical impedance spectroscopy, weight loss coupons and surface analysis. Hydrogen permeation was also used as indirect means of evaluating the intensity of the proton reduction reaction leading to hydrogen entry into the metal.Since corrosion in this type of test solution results in the rapid build-up of a conductive and highly porous iron sulfide scale, a specific contribution of the film has to be considered. An impedance model was thus proposed. The faradaic anodic impedance consists of a two-step reaction with charge transfer and adsorption – desorption. An additional contribution, associated with the conductive and highly porous iron sulfide film was added in parallel. This contribution, mostly visible in the low frequency domain, presents a 45° tail associated with a porous electrode behavior. This model was well adapted to describe impedance diagrams measured at various exposure times, up to 620 h. Charge transfer resistance determined from impedance analysis allowed calculating the evolution with time of the corrosion current density. A very good correlation was found between this corrosion current density and the hydrogen permeation current density. As expected in our experimental conditions, a permeation efficiency close to 100% is demonstrated. Corrosion rate of 490 μm/year was measured by weight-loss specimens, confirming the validity of the impedance analysis, which resulted in a calculated corrosion rate of 530 μm/year.

Experimental Validation of the Transmission Line Model Via Impedance Spectroscopy of an Ordered Array on Porous Carbon Electrode

In this paper, the interface of a porous substrate with an arranged and well-defined geometry is investigated for the impedance response with different electrolytes by using the well known electrochemical technique of Electrochemical Impedance Spectroscopy (EIS). Based on De Levie's Transmission Line Model (TLM) for porous electrodes a modification has been done in the model by incorporating the CPE behavior to reflect the non-ideal behaviour for real electrodes at low frequencies. The geometry used to validate the proposed model was fabricated from a smooth Glassy carbon electrode (GCE) surface to correlate the EIS response to that obtained by the model. The desired array was obtained by using laser micromachining tool on a glassy carbon substrate with a goal to study the influence of different electrolytes, varying electrolyte concentrations, the morphological features of pore- depth and radii of pore as well as different pore shapes. The outcomes of the experiments carried out on the in-house setup are compared with the MATLAB simulated results of the impedance. The transition from resistive to capacitive behavior is found to be shifted to lower frequency side and TLM behavior at high frequencies is more apparent as the concentration is increased. For the same concentration, different electrolytes are found to behave differently due to varying conductivity and ion sizes. In all the experiments carried out the impedance response showed CPE (constant phase element) behavior at the low frequency end while for high frequencies the nature/appearance of TLM behavior is found to be dependent on the pore depth to radius ratio. In addition the concept of time constant is also dealt with which exhibits differences for different geometries of the pores on glassy carbon. The results suggest that the GC electrode engaged here could provide a tractable model for studying electrochemical impedance behavior of porous electrodes without using any surface area analysis or pore volume analysis technique. Keywords: Transmission Line Model, Glassy carbon, EIS, MATLAB

A Mathematical Model for Mechanically-Induced Deterioration of the Binder in Lithium-Ion Electrodes

This study is concerned with modeling detrimental deformations of the binder phase within lithium-ion batteries that occur during cell assembly and usage. A two-dimensional poroviscoelastic model for the mechanical behavior of porous electrodes is formulated and posed on a geometry corresponding to a thin rectangular electrode, with a regular square array of microscopic circular electrode particles, stuck to a rigid base formed by the current collector. Deformation is forced both by (i) electrolyte absorption driven binder swelling, and; (ii) cyclic growth and shrinkage of electrode particles as the battery is charged and discharged. The governing equations are upscaled in order to obtain macroscopic effective-medium equations. A solution to these equations is obtained, in the asymptotic limit that the height of the rectangular electrode is much smaller than its width, that shows the macroscopic deformation is one-dimensional. The confinement of macroscopic deformations to one dimension is used to obtain boundary conditions on the microscopic problem for the deformations in a 'unit cell' centered on a single electrode particle. The resulting microscale problem is solved using numerical (finite element) techniques. The two different forcing mechanisms are found to cause distinctly different patterns of deformation within the microstructure. Swelling of the binder induces stresses that tend to lead to binder delamination from the electrode particle surfaces in a direction parallel to the current collector, whilst cycling causes stresses that tend to lead to delamination orthogonal to that caused by swelling. The differences between the cycling-induced damage in both: (i) anodes and cathodes, and; (ii) fast and slow cycling are discussed. Finally, the model predictions are compared to microscopy images of nickel manganese cobalt oxide cathodes and a qualitative agreement is found.

Impedance analysis of ASTM A416 tendon steel corrosion in alkaline simulated pore solutions

The corrosion behavior of ASTM A416 steel in alkaline simulated pore solution under active aeration was studied by cyclic voltammetry, electrochemical impedance spectroscopy, and measurement of open-circuit potential and polarization curves. The electrochemical impedance spectra were interpreted by use of a model that accounted for porous electrode behavior and for the contributions of both anodic and cathodic reactions. The open-circuit corrosion rate for a stationary working electrode immersed in the active-aerated electrolyte was 64μm/year shortly after the cathodic pre-treatment was completed, but was too small to be detected after steady-state was reached.

High-Voltage, High-Frequency Electrochemical Capacitor

Electric double layer capacitors (EDLCs) with electrical performance like aluminum electrolytic capacitors have been developed.(1) They can be smaller in size and offer higher reliability. Operation of such devices relies on charge stored on vertically oriented graphene nanosheet (VOGN) carbon. Vertically oriented graphene nanosheets are prepared using RF plasma enhanced chemical deposition of a hydrocarbon feed gas.(2) Under proper growth conditions, VOGN are ohmically connected to the metal current collector on which they grow, offer high electronic conductivity, and have an “open” structure totally free of porous electrode behavior. Each of these characteristics is necessary for efficient operation at frequencies of 1 kHz and higher.EDLC cells, like battery cells, operate at low voltage. Thus cells must be series connected to operate at high-voltage. Figure 1 shows an approach devised for interconnecting the EDLC cells to create a high-voltage, high-frequency EDLC. It involves interconnecting planar EDLC cells using the substrate metallization. As shown, interdigitated gaps are created in the VOGN that has been grown on a thin metal layer covering an insulating substrate, for instance, nickel on alumina. The gap is created using a laser to cut through the VOGN and metal down to the insulating substrate. This then creates multiple electrically-isolated regions (six are shown in the figure). Two adjacent regions become a single EDLC after electrolyte is applied over the gap and the surface of that region. To make a series connection of cells, each gap must be individually covered with an electrolyte, making sure that the electrolyte band does not touch the neighboring bands. This is a “bipolar” design in two dimensions, the substrate metallization serving as the bipolar plate. Connecting M cells in series each rated at voltage Vo with capacitance Co and series resistance Ro yields a capacitor with a voltage rating M·Vo, capacitance Co/M, and series resistance M·Ro. The frequency response of this high-voltage capacitor is nearly identical to that of one of its cells because the interconnects add minimal resistance. Voltage-balance resistors can be added using, for instance, thick-film printing processes. Details of the fabrication process are described and electrical performance data on these high-voltage, high-frequency electric double layer capacitors is presented. References 1J.R. Miller el al, “Graphene Double-Layer Capacitor with ac Line-Filtering Performance”, Science 329 , 1637 (2010). 2Cai M, Outlaw RA, Butler SM, and Miller JR, “A High Density of Vertically-Oriented Graphenes for Use in Electric Double Layer Capacitors”, Carbon 50, 5481–5488 (2012)..

Corrosion Behavior of ASTM A416 Steel in Simulated Pore Solution

Cable used in post-tensioned bridges usually consists of multiple strands encased within a plastic sleeve. The annulus or space between the steel tendon and the plastic sleeve is filled with grout, which is intended to provide corrosion protection for the steel. Often the grout does not provide adequate protection due to a number of factors, including insufficient grout-cover, i.e., air voids; insufficient grout quality and/or strength; faulty grouting procedure; or inadequate waterproofing sealant. Because post-tensioned concrete members rely on tensile strength of prestressed steel to resist loading, the loss of even a few wires or strands could have catastrophic results. And yet, because these members are encased in grout, a method to detect corrosion or corrosion risk does not yet exist. Since post-tensioning technology is still relatively new, these problems were not evident until the 1980’s. The first instance occurred in 1980 when the southern outer roof of the Berlin Congress Hall collapsed 23 years after it was constructed. Soon thereafter, two bridges were found with similar serious corrosion issues – the Taf Fawr Bridge on A470 in Wales, England and the Angel Road Bridge on the A406 North Circular in London, England.1 The Taf Fawr Bridge was demolished in 1986, and the Angel Road Bridge was significantly retrofitted in 1982. In 1985, the single-span segmental post-tensioned Ynys-y-Gwas Bridge in Wales collapsed as a result of corrosion of longitudinal tendons at its segmented joints. This structure was only 32 years old, and there had been no previous indication of distress prior to collapse. In 1992, the British Department of Transportation conducted a study on these corrosion issues and concluded that there was no method that could guarantee complete corrosion prevention. Later that year, post-tensioned bridges were effectively banned in the United Kingdom.2 The United Kingdom was not the only country with post-tensioned bridge issues. The post-tensioned Melle Bridge, which was built in Belgium in 1956, collapsed in 1992. In this instance, the bridge had been inspected, load tested, re-waterproofed, declared adequate, and just restored to service two years prior to its collapse. More recently, the Saint Stefano Bridge in Italy (1999) and the Lowe’s Motor Speedway footbridge in North Carolina (2000) collapsed due to similar corrosion-related failures.3 Locally, in Florida, corrosion in post-tensioned bridges is a major concern as well. The first reported observation of post-tension corrosion was at the 18-year old Niles Channel Bridge in the Keys (1999).4 Similar issues were reported at the 7-year old Mid Bay Bridge in the Western Panhandle (2001)5 and the 15-year old Sunshine Skyway Bridge in Tampa (2002).6 As part of an effort to develop an impedance-based sensor for detecting corrosion of pre-stressed tendons, experiments were conducted using rotating and stationary disk electrodes fashioned out of the tendon steel and immersed in a simulated alkaline pore solution. A model for the impedance response was developed that accounted for a porous electrode behavior that gradually disappeared over a period of 36 hours. In some cases, a small corrosion rate could be discerned from the impedance response, but, in general, the metal was stable under these conditions. References Proverbio, E. and Bonaccorsi, L. M. (2002). Failure of prestressing steel induced by crevice corrosion in prestressed concrete structures. Proceedings 9th International Conference on the durability of building materials and components, Brisbane, Australia, March 17-21. Lewis, A. (1996). A moratorium lifted. Concrete, November/December, 25-27. Goins, D. (2000). Motor speedway bridge collapse caused by corrosion. Materials Performance, 36 (7) 18-19. Sagüés, A. A., Kranc, S. C., and Hoehne, R. H (2000). Initial development of methods for assessing condition of post-tensioned tendons of segmental bridges. Final Report Florida Department of Transportation, Tallahassee, FL, May. Hartt, W. H. (2002). Corrosion evaluation of post-tensioned tendons on the mid bay bridge in Destin, FL. Final Report, Florida Department of Transportation, Tallahassee, FL, April 15. Sagüés, A., Powers, R. G., and Wang, H (2008). Mechanism of corrosion of steel strands in post tensioned grouted assemblies. NACE International, paper no. 03312.

Thermodynamics in Porous Electrodes: A Monte Carlo Simulation Study

Thermodynamic behavior of porous electrodes is qualitatively different from that of planar electrodes when the pore size is comparable to the ion size. We performed Monte Carlo simulation and investigated the thermodynamics behavior of porous electrodes as functions of the pore size, the ion size, and the applied voltage. We found that thermodynamic properties such as surface charge density, ion density, and pressure exerted in the porous electrodes on applying voltage show quite nonlinear behaviors as functions of voltage. The mechanism of the thermodynamic behaviors is explained in terms of the balance between the electrostatic and volume exclusion interactions.

Modeling of Volume Change Behavior of Porous Electrodes

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Modeling of Volume Change Behavior of Porous Electrodes

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