Interfacial Reaction Kinetics Research Articles

Evaluating the interfacial reaction kinetics of the bipolar membrane interface in the bipolar membrane fuel cell

A reaction kinetic model of the bipolar membrane interface in the bipolar membrane fuel cell (BPMFC) was proposed based on the p-n junction theory and chemical reaction kinetics. It verified the self-humidification feasibility of the BPMFC successfully.

Methyl Methacrylate (MMA)-Grafted Polypropylene (PP) Separator for Rechargeable Lithium Metal Battery

In this article the polypropylene (PP) separator grafted by methyl methacrylate (MMA) functional groups with plasma technique has been primarily investigated. The MMA groups are expected to form a stable interface with lithium metal electrode. In addition, the effect of the surface functional group MMA on the graphite and the LiFePO4 electrode has been also primarily examined. The cyclic voltammetry (CV) tests have exhibited faster deposition/dissolution reaction kinetics of lithium on stainless steel electrode. The impedance measurements have shown a smaller interface resistance between the electrolyte (PP-MMA separator) and the lithium metal electrode. The interface reaction kinetics of the electrolyte (separator)/lithium electrode can be effectively enhanced by the MMA surface functional groups. It is also found that the existence of the MMA-groups at the separator surface can increase the reversible capacity of both LiFePO4 and graphite electrode. Rechargeable secondary batteries with lithium metal as the negative electrode have a relatively high energy density in comparison with those with carbon-based materials as the negative electrode due to the high theoretical capacity of 3860 mAh/g. In the early stage of the researches on lithium battery systems, many attempts had been made to improve the cycle life of the lithium metal electrode. Later researchers paid their attention on the splendid appearance of the graphite-based carbon materials. As well-known, the carbon-based materials have been successfully used as the negative electrode in the commercial rechargeable Li-ion batteries nowadays. In fact, lithium metal electrode still has potential in the rechargeable lithium-based micro-batteries and the all-solid-state lithium batteries, etc. 1–6 For some devices such as the implantable medicine devices and microchips, the output power of the batteries is relatively small, but the cycle life must be long enough. Safety is the most important factor to the commercial applications; the solution leakage is absolutely not allowed in such systems. This type of battery is named as energy-type battery. The issue that the lithium metal anode faces is that the formation of the lithium dendrites leads to two main consequences. Firstly, the electrically isolated lithium is not to be used and will shed. Secondly, the penetration of fine lithium particles into the separator will cause the internal short. There are three main strategies that are used to improve the cyclic performance of the lithium metal electrode. The first strategy has been extensively investigated by researchers and is just on Li-alloys and Li-intermetallics. 2 The improvement of the cycle stability of the lithium electrode is expected by modifying the solid electrolyte interface (SEI) or by buffering the volume expansion. The second one is focused on the electrolyte additives, such as HF, CO2, sulfides and surfactants. 7 The additives play the role of decreasing the content of the deleterious impurities in SEI layers, stabilizing the SEI, modifying the morphology of SEI and weakening or delaying the formation of the lithium dendrites by the specific adsorption of these surfactants on the convex points of the surface that has a relatively high surface energy. Ishikawa and Morita 8 have compiled the related results. We thought that the first strategy came from the lithium metal itself; the second one originated from the electrolyte. There also exists the third strategy which is on the separator. After being assembled, the lithium metal electrode is in close contact with the separator. A more stable SEI layer can be constructed by modifying the surface of the separator and by grafting some functional groups into the separator surface. These functional groups are expected to improve the stability of the interface between the liquid electrolyte (separator) and the lithium metal electrode. In commercial lithium ion batteries, the separator is also in contact with the positive

Potentiostatic intermittent titration technique (PITT) for spherical particles with finite interfacial kinetics

The potentiostatic intermittent titration technique (PITT) is an electroanalytical method that has been widely used to study diffusion of solutes (such as lithium) in electrode materials. Here, we extend the conventional PITT method to account for finite interfacial reaction kinetics and derive analytic equations for electric current under PITT operations. Using the modified PITT, the lithium diffusion coefficient in host materials and the interfacial reaction kinetics can be determined simultaneously. We demonstrate this modified PITT by an example of lithium diffusion in graphite (mesocarbon microbeads, MCMB) and show the improvements of the modified PITT theory over the conventional PITT for investigating the kinetics of electrodes comprising spherical particles.

Interfacial Reaction Between CaO-SiO2-MgO-Al2O3 Flux and Fe-xMn-yAl (x = 10 and 20 mass pct, y = 1, 3, and 6 mass pct) Steel at 1873 K (1600 °C)

This study investigated the interfacial reaction kinetics and related phenomena between CaO-SiO2-MgO-Al2O3 flux and Fe-xMn-yAl (x = 10 and 20 mass pct, y = 1, 3, and 6 mass pct) steel, which simulates transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) steels at 1873 K (1600 °C). It also examines the effect of changes in the composition of the steel and slag phases on the interfacial reaction rate and the reaction mechanisms. The content of Al and Si in the 1 mass pct Al-containing steel was found to change rapidly within the first 15 minutes of the reaction, but then it remained relatively constant. The content of Al and Si in the 3 to 6 mass pct Al-containing steels, in contrast, changed continuously throughout the entire reaction time. In addition, the content of Mn in the 1 mass pct Al-containing steels initially decreased with increasing time, but the content did not change in the 3 to 6 mass pct Al-containing steels. Furthermore, the mass transfer coefficient of Al, kAl, in the 1 mass pct Al-containing systems was significantly higher than that in other systems; i.e., the kAl can be arranged such that 1 mass pct Al systems >> 3 mass pct Al systems ≥ 6 mass pct Al systems. The compositions of the final slags were close to the saturation lines of the [Mg,Mn]Al2O4 and MgAl2O4 spinels when the slags reacted with 1 mass pct Al and 3 to 6 mass pct Al-containing steels, respectively. These results, which show the effect of Al content on the reaction phenomena, can be explained by the significant increase in the apparent viscosity of the slags that reacted with the 3 to 6 mass pct Al-containing steels. This reaction was likely caused by the precipitation of solid compounds such as MgAl2O4 spinel and CaAl4O7 grossite at locally alumina-enriched areas in the slag phase. This analysis is in good accordance with the combination of Higbie’s surface renewal model and the Eyring equation.

Technical and commercial progress in the adoption of geopolymer cement

If formulated optimally, geopolymer cement made from fly ash, metallurgical slags and natural pozzolans could reduce by 80% the CO2 emissions associated with the manufacturing of cement. However, almost all standards and design codes governing the use of cementitious binders and concrete in construction are based on the use of Portland cement. The 100+ year track record of in-service application of Portland cement is inherently assumed to validate the protocols used for accelerated durability testing. Moreover, the entire supply chain associated with cementitious materials is based on the production of Portland cement. The geopolymerisation of aluminosilicates constitutes a radical change in construction materials chemistry and synthesis pathways compared with the calcium silicate hydrate chemistry which underpins Portland cement. Consequently, there are regulatory, supply chain, product confidence and technical barriers which must be overcome before geopolymer cement could be widely adopted. High profile demonstration projects in Australia have highlighted the complex regulatory, asset management, liability and industry stakeholder engagement process required to commercialise geopolymer cement. While the scale-up from the laboratory to the real-world is technically challenging, the core challenge is the scale-up of industry participation and acceptance of geopolymer cement. Demand pull by a carbon conscious market continues to be the key driver for the short term adoption of geopolymer cement. In the absence of an in-service track record comparable in scale and longevity to Portland cement, research is essential to validate durability testing methodology and improve geopolymer cement technology. Colloid and interface science, gel chemistry, phase formation, reaction kinetics, transport phenomena, comminution, particle packing and rheology, which are familiar concepts to minerals engineers, are also key building blocks in the development of geopolymer knowledge. Analysis of the nanostructure of geopolymer gels has enabled the tailored selection of geopolymer precursors and the design of alkali activator composition, aiding in establishing the relationship between geopolymer gel microstructure and durability.

Growth kinetics of the solid-state interfacial reactions in the Sn–Cu/Co and Sn/Co–Cu couples

Two different Sn–Cu/Co and Sn/Co–Cu reaction couples were examined at temperatures ranging from 150 °C to 200 °C to examine the Cu alloying effect by varying Cu contents. Two reaction phases, CoSn 3 and (Cu,Co) 6Sn 5, were observed simultaneously at the interfaces of the Sn–Cu/Co couples (0.1 wt%–3 wt%Cu). The CoSn 3 layer was much thicker than (Cu,Co) 6Sn 5, and CoSn 3 exhibited a linear growth rate at the initial reaction stage. Remarkably, minor Cu addition into the solders resulted in strongly suppressing the layer growth. On the other hand, the potential Co–Cu alloy substrate was also considered because of its impact on decreasing the growth rate. Sn/Co–Cu (less than 10 wt%Cu) interfacial reactions were carried out. Only one CoSn 3 phase layer was produced. In addition, the temperature dependence of the reaction layer growth was also examined. Compared with the binary Sn/Co couple, the layer growth rates in the Sn–Cu/Co and Sn/Co–Cu couples are relatively lower and more temperature-sensitive.

Interfacial reaction kinetics in Au stud/Sn bumps during annealing and current stressing

Annealing and current stressing were performed at 125∼160 °C with 5 × 10 4 A/cm 2 conditions in order to investigate the interfacial reaction and growth kinetics of the Intermetallic Compound (IMC) in Au stud/Sn bumps. AuSn, AuSn 2, and AuSn 4 phases were formed at the interfaces between the Au studs and Sn after bonding. AuSn 2 phases continued to grow with stressing time while the thickness of the AuSn 4 phase decreased. The current stressing accelerated the interfacial IMC reaction. The apparent activation energies for the growth of the AuSn 2 phase during the annealing and current stressing were 0.89 eV and 0.51 eV, respectively. The activation energies for current stressing were lower than that for annealing, which might be closely related to the acceleration of the interfacial reaction by electron wind force.

Dependence of an Interfacial Diels-Alder Reaction Kinetics on the Density of the Immobilized Dienophile: An Example of Phase-Separation

Interfacial reactions kinetics often differ from kinetics of bulk reactions. Here, we describe how the density change of an immobilized reactant influences the kinetics of interfacial reactions. Self-assembled monolayers (SAMs) of alkanethiolates on gold were used as a model interface and the Diels-Alder reaction between immobilized quinones and soluble cyclopentadiene was used as a model reaction. The kinetic behavior was studied using varying concentrations of quinones. An unusual threshold density of quinones (<TEX>${\Gamma}_c$</TEX> = 5.2-7.2%), at which the pseudo-first order rate constant started to vary as the reaction progressed, was observed. This unexpected kinetic behavior was attributed to the phase-separation phenomena of multi-component SAMs. Additional experiments using more phase-separated two-component SAMs supported this explanation by revealing a significant decrease in <TEX>${\Gamma}_c$</TEX> values. When the background hydroxyl group was replaced with carboxylic or phosphoric acid groups, <TEX>${\Gamma}_c$</TEX> was observed at below 1%. Also, more phase-separated thermodynamically controlled SAMs produced a lower critical density (3% < <TEX>${\Gamma}_c$</TEX> < 4.9%) than that of the less phaseseparated kinetically controlled SAMs (6.5% < <TEX>${\Gamma}_c$</TEX> < 8.9%).

Isotope Tracing Study of GeO Desorption Mechanism from GeO2/Ge Stack Using 73Ge and 18O

GeO desorption from a GeO2/Ge stack is a critical concern in Ge metal oxide semiconductor field effect transistors (MOSFETs). In this contribution, we focus on a uniform-desorption region and unveil the GeO desorption mechanism from a GeO2/Ge stack by 73Ge and 18O isotope tracing in thermal desorption spectroscopy (TDS) analysis, in which the Ge and O diffusion kinetics in GeO2 and the interfacial reaction kinetics have been investigated. Through 73Ge isotope tracing, we have clarified that Ge in the desorbed GeO dominantly comes from the GeO2 surface. Moreover, the self-diffusivity of oxygen was evaluated to be much larger than Ge in GeO2. Furthermore, owing to the difference among GeO desorptions from GeO2/Ge stacks with various substrate orientations, the reaction at the GeO2/Ge interface was attributed to the redox reaction kinetics. On the basis of our experimental findings, we have proposed an oxygen vacancy diffusion model of the GeO desorption mechanism.

Electrochemical Etching of Zinc Oxide for Silicon Thin Film Solar Cell Applications

A novel approach is presented for introducing a surface morphology with beneficial light scattering properties to sputter-deposited ZnO:Al films, being used as front contact in Si thin film photovoltaic devices. Electrochemical anodization was used to trigger local corrosion, leading to interfacial structures complementary to those commonly prepared by an etching step in diluted HCl. By systematic variation of electrochemical etching conditions and electrolytes, sensible experimental parameters were evaluated for the preparation of ZnO films that can be applied in Si thin film solar cells. The prepared films were characterized by scanning electron microscopy, four-point resistance and Hall measurements. Furthermore, the kinetics of the heterogeneous interfacial reaction during the corrosion process were studied utilizing electroanalytical techniques. This allowed the identification of the processes occurring at the solid/liquid interface. Application of such films in microcrystalline Si single junction solar cells has shown promising initial results.

Investigation of interfacial reaction kinetics of I −(aq) with Ag 2O(s) on Ag substrate: Determining mass transport and surface reaction rates

The reaction kinetics of AgI formation by reaction of Ag 2O films with aqueous iodide were followed by monitoring the open-circuit potential ( E OC). Previous studies have shown that complete conversion of Ag 2O to AgI is indicated by an abrupt transition in the E OC from a value close to the equilibrium potential for the Ag|Ag 2O|H 2O system to one close to that for Ag|AgI|I −, allowing an easy determination of the total reaction time, τ f . The solid–solution interfacial kinetic parameters can then be determined by measuring τ f as a function of the initial amount of Ag 2O and the I − concentration. In this study, the application of the technique was extended to examine the effect of I −(aq) transport to an Ag 2O surface by measuring τ f as a function of electrode rotation rate. By studying the chemical conversion as a function of electrode rotation rate we are able to separate mass transport effects from the reaction kinetics. The interfacial reaction follows kinetics typical of a sequential binary-reaction system consisting of mass transport to, followed by reaction at, the surface. The mass transport rate was proportional to the square root of the electrode rotation rate, consistent with the well-established diffusion-boundary layer model for a rotating disc. Varying the rotation rate allows a quantitative extrapolation of the data to the infinite rotation rate to determine the chemical reaction rate at the surface.

Active low temperature oxidation as a route to minimize electrode–oxide interface reactions in nanoscale capacitors

The electrical characteristics of reactive metal–oxide interfaces are largely dependent on the thermodynamics and kinetics of interfacial reactions that may occur during synthesis and further processing conditions. Such reactions may lead to undesirable properties such as increased loss tangent, frequency dispersion, or asymmetric capacitance. Metals such as Ni are being explored as electrodes in various electronic packaging as well as on-chip decoupling capacitors and this presents a challenge to advance processing routes that render utilization of high-dielectric constant oxide thin films. In this work, we demonstrate that photon-assisted oxidation enables a unique low temperature processing route to synthesize reduced loss (Ba,Sr)TiO3 thin film based capacitors with Ni bottom electrodes. Our results show a decrease in the dielectric loss tangent in photon-assisted oxidized films compared to conventionally re-oxidized at an applied field of 0.33 MV/cm, tan δ of 0.08 versus 0.63, respectively. Leakage currents showed a significant decrease, 7.8 A/cm2 for conventional re-oxidation versus 0.046 A/cm2 for photon assisted, at an applied field of 0.33 MV/cm. The results are of relevance to processing reactive materials wherein athermal routes are necessary to avoid interfacial reactions.

Kinetics of interfacial ion-transfer reactions studied using the indirect laser-induced temperature jump technique: Theory

For fast, interfacial ion-transfer (adsorption/desorption) reactions, I demonstrate the development of a relationship describing the time dependence of the open-circuit potential change (Δ V oc( t)) initiated by the coulostatic temperature perturbation associated with the indirect laser-induced temperature jump (ILIT) technique. The form of this relationship is exactly the same as the one developed for interfacial electron-transfer (ET) reactions of solution-dissolved redox couples. However, the definitions of the parameters associated with this relationship (e.g., the measured rate constant ( k m,a/d) and the mass-transfer parameter ( P 75,a/d)) are unique to and are functions of the chemical kinetic and (some of) the thermodynamic properties of the adsorption/desorption reactions. An additional analysis of the time dependence of the ILIT-induced open-circuit potential change (Δ V oc,et( t)) effected by the ET reaction of a reversibly adsorbed redox couple (where only the adsorbed redox species undergo the ET reaction) also results in a relationship that is the same as that developed for solution-dissolved redox couples, but the definitions of k m,et and P 75,et are, again, different for the reversibly adsorbed redox moieties. The analyses associated with these developments are relevant to possible studies (using ILIT or other coulostatic perturbation techniques) of the adsorption/desorption reactions pertinent to many technologically important electrochemical processes.

Study of Diffusion of Co(II) and Co(II)-DEHPA Complex in a Microfluidic Device

The use of microfluidic devices as analytical tools to probe the kinetics of interfacial reactions between heterogeneous phases such as those that occur in solvent extraction systems can provide important information on the interfacial processes that control these reactions. A number of studies have proposed the use of microfluidic devices for lab-on-a-chip processing. In either case, a detailed understanding of the hydrodynamic and diffusion behavior of the fluids in these devices is essential.In this study, the diffusion of Co(II) in an aqueous phase and the diffusion of the cobalt(II)-di-(2-ethylhexyl)-phosphate (Co(II)-DEHPA) complex in an organic phase were investigated in a double-Y-type microfluidic device. Diffusion experiments were carried out over a range of flow rates in the laminar flow region of the microfluidic device.A computational Fluid Dynamics (CFD) simulation of the flow field was carried out and the detailed velocity distribution in the channel was obtained; this distribution was used to predict the rate of diffusion of a solute. Furthermore, a simplified calculation mesh was developed for reducing the simulation time. The diffusion coefficients of Co(II) and the Co(II)-DEHPA complex were determined by the simulation to be 6.6×10−10 m2/s and 3.2×10−10 m2/s, respectively.

Fabrication and evaluation of Ni-GDC composite anode prepared by aqueous-based tape casting method for low-temperature solid oxide fuel cell

Large-size, 8 cm × 8 cm, NiO-Gd 0.1Ce 0.9O 1.95 (Ni-GDC) composite anodes have been successfully fabricated by aqueous-based tape casting method for anode-supported solid oxide fuel cell (SOFC). The pre-sintered anode green tape was coated with a GDC electrolyte film by spray coating method and then co-sintered together to obtain electrolyte/anode bi-layer. The cathode, which is made of La 0.8Sr 0.2Co 0.2Fe 0.8O 3-GDC (LSCF-GDC) was screen printed onto the electrolyte film and sintered to form a complete anode-supported SOFC. The performance of the cell was evaluated on an in-house developed test station between 500 and 650 °C. Due to the limitation of the test station for large-cell testing, small-size samples with dimensions of 2.5 cm × 2.5 cm were cut out from the large-cell. For the single cell with humidified hydrogen as fuel and air as oxidant, the maximum power density achieved 909, 623, 335 and 168 mW cm −2 at 650, 600, 550 and 500 °C, respectively. Impedance analysis confirmed that the performance of single cells below 600 °C was retarded primarily due to the slow interfacial reaction kinetics at reduced temperatures. Development of catalytically active electrode materials, especially the cathode material and improvement of the electrode microstructure are thus crucial for achieving a high performance low-temperature SOFC.

Studies on Interface of SiCf/Ti55 Composite

Abstract The SiC fiber reinforced Ti55 composite (SiC f /Ti55) was fabricated by Fiber Coating Method (FCM) and Hot Isostatic Pressing (HIP). After the composites were thermally exposed in vacuum under different conditions, the study on the order of interfacial reaction products and the kinetics of interfacial reaction was performed. The results show that only C, Ti and Si elements take part in the interfacial reaction. The order of interfacial reaction products of SiC f /Ti55 composite exposed at 1000 °C can be identified as SiC | Ti 3 SiC 2 | Ti 5 Si 3 +TiC | TiC | Ti55. However, the Ti 3 SiC 2 does not exist in the composites exposed at low temperature. The interfacial reaction layer growth is controlled by diffusion and follows a role of parabolic rate, and the activation energy Q k and the pre-exponential factor k 0 of SiC f /Ti55 composite are 198.16 kJ·mol −1 and 1.79×10 −3 m·s −1/2 , respectively. Compared with the SiC f /Ti composite and SiC f /Ti 2 AlNb composite, there is an interface with higher stability in SiC f /Ti55 composite. However, the interfacial reaction between SiC fiber and matrix takes place easier in SiC f /Ti55 composite than in the SiC f /Ti600 composite and SCS-6 SiC f /super a 2 composite.

Modeling of PEG Hydrogel Membranes for Biomedical Applications

AbstractA mathematical model has been developed for surface‐initiated photopolymerization of PEG‐DA forming cross‐linked hydrogel membranes on the surface of a substrate. The existing model was extended to apply the NF technique, which made it possible to describe the progression of photopolymerization through gelation, and to calculate gelation time, cross‐link density of the gel and soluble phases. The model provides a tool for understanding and studying the kinetics of interfacial photopolymerization reactions, which are important in processes such as cell encapsulation by hydrogel membranes formed through free radical photopolymerization. It will also be useful for applications in tissue engineering, where protein gradients are required for optimizing engineered tissue formation.magnified image

RECOVERY OF NI2+ BY DI-(2-ETHYLHEXYL) PHOSPHORIC ACID (HDEHP)

This paper dealts with solvent and bulk liquid membrane extraction of Ni2+ from its chloride solutions by HDEHP in n-heptane. Effects of extraction time, initial pH and Ni2+ concentration in the feed as well as HDEHP concentration in the organic phase were investigated. Solvent extraction equilibrium was established within 10 minutes. Ni2+ showed to be extracted into the organic phase preferentially as Ni(DEHP), complexes. The Ni2+ extraction yield decreased with increasing initial Ni2+ concentration, with decreasing pH and/or HDEHP concentration. The later is not only due to shifting equilibrium of Nils extraction reaction, but also due to concurent extraction of HCI. Results of bulk liquid membrane extraction could be described by the kinetics of interfacial pseudo-first order reactions. Observed rate constants were determined ⁓ 2,30.10-2 ⁒ 2,68.10-2 min-1 for concentration range [Ni2+]0 ⁓ 10-3 ⁒ 10-2 mol/l.

Studies of polyamines transport through liquid membranes with D2EHPA as a carrier

The transport of polyamines through the liquid membranes with di-2-ethylhexyl phosphoric acid (D2EHPA) was investigated. The study was performed in three main steps: liquid-liquid extraction (LLE), bulk liquid membrane (BLM) extraction, and supported liquid membrane (SLM) extraction. Equilibrium distribution experiments allowed determining the extraction constants and stoichiometric coefficients for each polyamine. It turned out that one amino group binds two molecules of carrier (one D2EHPA dimer) and the extractability of polyamine rises with the increase in number of function groups in the molecule. The BLM and SLM experiments showed that despite considerable differences in distribution ratio between various polyamines the extraction efficiencies for all of them are very approximate. The smaller diamines compensate the lowest affinity to membrane phase with faster interface reaction kinetics and higher diffusivity. Finally, the SLM extraction conditions were optimized. The main parameters that influence the transport are the pH of the donor and acceptor phases. The extraction efficiencies obtained for polyamines are high (80-90%) and give hope for an application in bioanalytical chemistry.

Electrospray Mass Spectrometric Detection of Products and Short-Lived Intermediates in Aqueous Aerosol Microdroplets Exposed to a Reactive Gas

The intermediates ISO3- (m/z=207) and IS2O3- (m/z=239) generated in aqueous (NaI/Na2S2O3) microdroplets traversing dilute O3 gas plumes are detected via online electrospray mass spectrometry within approximately 1 ms, and their stabilities gauged by collisionally induced dissociation. The simultaneous detection of anionic reactants and the S2O62-, HSO4-, IO3-, and I3- products as a function of experimental conditions provides evidence of genuinely interfacial reaction kinetics. Although O3(aq) reacts about 3 times faster with I- than with S2O32- in bulk solution, only S2O32- is significantly depleted in the interfacial layers of [I-]/[S2O32-]=10 microdroplets below [O3(g)] approximately 50 ppm.