Development and experimental verification of a mathematical model of lithium ion battery

A model of the lithium ion battery is developed which takes into account intercalation and extraction of lithium ions in the active mass of negative and positive electrodes, the dependences of equilibrium electrode potentials on the concentration of intercalated lithium, the ion transfer in pores of electrodes and the separator, the kinetics of electrode reactions, and the electric double layer charging. As the active material for the negative electrode, UAMS graphite material is used. Lithium-nickel-cobalt oxide serves as the positive electrode. The porous structure of electrodes is studied by the method of standard contact porosimetry. Sufficiently high porosity values found for both electrodes (50% for anode and 27% for cathode) made it possible to consider the interface as regards the internal pore surface found from porosimetry data rather than as regards their external surface as in the previous studies. A comparison of calculated and experimental discharge curves demonstrates their closeness, which points to the correctness of the model. By the fitting procedure, the coefficients of solid-state diffusion of lithium ions and the rate constants for reactions on both electrodes are found.     

Synchrotron light scattering on nanostructured V/Ce oxide films intercalated with Li+ ions

Vanadium oxide and new V/Ce oxide films on a glass substrate were obtained by the sol-gel process. The morphology of these nanostructured and porous films was studied by grazing-incidence small-angle X-ray scattering (GISAXS) at the ELETTRA synchrotron (Italy, Trieste). The aim of performing GISAXS was to study changes, which might occur in the grain sizes and the porosity of vanadium oxide and V/Ce oxide at 38 and 55 atom % of V, upon the intercalation of Li+ ions. The average grain radius obtained by GISAXS varied with the layer thickness and upon the intercalation of Li+ ions. The layer structure in V/Ce oxides was revealed by the grazing-incidence X-ray reflectivity (GIXR) method. The average grain radius , obtained by GISAXS, was correlated with the intercalation of Li+ ions. The specific surface area of these films was also determined and generally varied from 0.5 nm(-1) to 0.03 nm(-1).     

The water-amorphous silica interface: analysis of the Stern layer and surface conduction

To explain why dynamical properties of an aqueous electrolyte near a charged surface seem to be governed by a surface charge less than the actual one, the canonical Stern model supposes an interfacial layer of ions and immobile fluid. However, large ion mobilities within the Stern layer are needed to reconcile the Stern model with surface conduction measurements. Modeling the aqueous electrolyte-amorphous silica interface at typical charge densities, a prototypical double layer system, the flow velocity does not vanish until right at the surface. The Stern model is a good effective model away from the surface, but cannot be taken literally near the surface. Indeed, simulations show no ion mobility where water is immobile, nor is such mobility necessary since the surface conductivity in the simulations is comparable to experimental values.     

Application of TOF-SIMS Method in the Study of Wetting the Iron (111) Surface with Promoter Oxides

In the present work, a simplified model of the Fe(111) surface’s promoter-oxide system was investigated in order to experimentally verify the previously proposed and known models concerning the structure and chemical composition of the surfaces of iron nanocrystallites in the ammonia-synthesis catalyst. It was shown that efficient oxygen diffusion from metal oxides to the clean Fe(111) iron surface took place even at temperatures lower than 100 °C. The effective wetting of the iron surface by potassium oxide is possible when the surface is covered with oxygen at temperatures above 250 °C. In the TOF-SIMS spectra of the surface of iron wetted with potassium, an emission of secondary FeOK⁺ ions was observed that implies that potassium atoms are bound to the iron surface atoms through oxygen. As a result of further wetting the iron surface with potassium ions, a heterogeneous surface structure was formed consisting of a thin K₂O layer, next to which there was an iron-oxide phase covered with potassium ions. Only a limited increase in calcium concentration was observed on the Fe(111) iron surface upon sample annealing at up to 350 °C. As a result of wetting the iron surface with calcium ions, an oxide solution of CaO-Fe_xO_y was formed. In the annealing process of the sample containing alumina, only traces of this promoter diffusing to the iron surface were observed. Alumina formed a solution with a passive layer on the iron surface and under the process conditions (350 °C) it did not wet the pure iron (111) surface. The decrease in Fe⁺-ion emission from the Fe-Ca and Fe-Al samples at 350 °C implies a reduction in the oxygen concentration on the sample surface at this temperature.     

Acidic and reductive dissolution of magnetite in aqueous sulfuric acid: Site-binding model and experimental results

The open circuit dissolution of ionic metal oxides in mineral acids is modelled assuming that the rate is controlled by the transfer of metal ions in hydrolytic equilibrium with bulk metal ions, from the metal oxide surface to the Stern plane. The site-binding model of the double layer metal oxide/electrolyte solution is used to obtain the pH dependence of surface and Stern potentials. The nature of the active sites is discussed and their surface concentration is assumed to be proportional to suface charge σ₀. Again, the site-binding model is used to detemine the pH dependence of σ₀. It is thus shown that the rate order in c_H⁺ is essentially defined by the potential dependence of the charge transfer process, for oxides with points of zero charge near neutrality that dissolve in mildly or strongly acidic solutions. The role of surface complexation is also discussed in terms of the site-binding model and the difficulties in interpreting dissolution experiments under constant external applied potential are discussed in terms of the complexity of the semiconductor oxide/electrolyte solution interfacial region in magnetite.An experimental study of the open circuit dissolution of magnetite in sulfuric acid is presented and interpreted according to the proposed model.The reductive dissolution of magnetite is modelled by extension of the Valverde-Wagner model of oxide dissolution. Experimental results are presented to demonstrate that the reductive dissolution rate of magnetite in ferrous containing solutions is controlled by the rate of electron transfer from adsorbed Fe(II) to Fe(III) surface states of magnetite.     

Evaluation of equilibrium parameters characterizing metal oxide/electrolyte solution interface

According to the surface complexation model (SCM), charging of a metal oxide surface in aqueous environment is due to interactions of active surface groups with ions from the bulk of the solution. Several models for mechanism of surface reactions were proposed. Interfacial equilibrium is determined by corresponding equilibrium constants, but also with the structure of the electrical interfacial layer (EIL). Therefore, evaluation of equilibrium parameters is not a simple task. Traditionally, the measurements of pH dependency of surface charge density was used for that purpose. This article shows that introduction of electrokinetic data produces more reliable results, especially in the case of specific adsorption. If surface charge density and/or adsorption data are not available, one may still deduce interfacial equilibrium constants from electrokinetic results combined with measurements of the surface potential.     

Structure‐Dependent Anchoring of Organic Molecules to Atomically Defined Oxide Surfaces: Phthalic Acid on Co3O4(111), CoO(100), and CoO(111)

We have performed a model study to explore the influence of surface structure on the anchoring of organic molecules on oxide materials. Specifically, we have investigated the adsorption of phthalic acid (PA) on three different, well‐ordered, and atomically defined cobalt oxide surfaces, namely 1) Co₃O₄(111), 2) CoO(111), and 3) CoO(100) on Ir(100). PA was deposited by physical vapor deposition (PVD). The formation of the PA films and interfacial reactions were monitored in situ during growth by isothermal time‐resolved IR reflection absorption spectroscopy (TR‐IRAS) under ultrahigh vacuum (UHV) conditions. We observed a pronounced structure dependence on the three surfaces with three distinctively different binding geometries and characteristic differences depending on the temperature and coverage. 1) PA initially binds to Co₃O₄(111) through the formation of a chelating bis‐carboxylate with the molecular plane oriented perpendicularly to the surface. Similar species were observed both at low temperature (130 K) and at room temperature (300 K). With increasing exposure, chelating mono‐carboxylates became more abundant and partially replaced the bis‐carboxylate. 2) PA binds to CoO(100) in the form of a bridging bis‐carboxylate for low coverage. Upon prolonged deposition of PA at low temperature, the bis‐carboxylates were converted into mono‐carboxylate species. In contrast, the bis‐carboxylate layer was very stable at 300 K. 3) For CoO(111) we observed a temperature‐dependent change in the adsorption mechanism. Although PA binds as a mono‐carboxylate in a bridging bidentate fashion at low temperature (130 K), a strongly distorted bis‐carboxylate was formed at 300 K, possibly as a result of temperature‐dependent restructuring of the surface. The results show that the adsorption geometry of PA depends on the atomic structure of the oxide surface. The structure dependence can be rationalized by the different arrangements of cobalt ions at the three surfaces.     

The negative adsorption of chromium atoms on alloy-oxide film boundaries during oxidation in air and anodic passivation of Fe-Cr and Ni-Cr alloys

Equilibrium of Cr atoms between the surface layer and bulk of a binary alloy was analyzed. The Gibbs adsorption equation was used to obtain the dependence of the adsorption activity of atoms in the surface layer on their activity in the bulk. An approximate thermodynamic method was used to calculate the adsorption of Fe (Ni) and Cr atoms in the surface layers of Fe-Cr and Ni-Cr alloys. According to calculations, there was negative adsorption, X _Cr ≪ 1, in the surface layer of the alloys caused by a large difference between the Gibbs surface energies of Cr and Fe (or Ni). The negative adsorption of Cr shifted chemical reaction equilibria on the alloy-oxide film boundary both in oxidation in air and in anodic passivation, 3FeO (NiO) + 2Cr = Cr₂O₃ + 3Fe(Ni), toward oxide film enrichment in the FeO (or NiO) oxide. A unified method for calculating the composition of oxide films on alloys was used for both processes. The method was based on the use of the initial data on the Gibbs surface energy of metals constituting alloys. The calculated oxide film compositions were close to the experimental X-ray photoelectron spectroscopy data.     

Leaching of El-Missikat low-grade fluoritized uranium ore by sulfuric acid: mechanism and kinetic

A well-characterized low-grade fluoritized uranium samples from new occurrence in Gabal El-Missikat prospect, Eastern Desert, Egypt was subjected to sulfuric acid leaching. The effects of leaching parameters on uranium dissolution mechanism were investigated. The shrinking core model was used to model leaching reactions. The kinetics equations indicates that the reactions appear to be controlled by layer diffusion process. The activation energy for uranium dissolution was evaluated. Low activation energy value (2.54 kJ mol⁻¹) confirm the diffusion layer mechanism. The presence of fluoride ions in the solution increases the dissolution of uranium. The optimum process operating parameters were: sulfuric acid concentration: 1.5 M, solid–liquid ratio: 1:3, contact time 8 h; agitation speed rate 200 rpm; and ore particle size − 75 µm at temperature 60 °C, in the absence of an external oxidant. Under these experimental conditions, the extraction efficiency of uranium was about 91%.

     

Application of photoluminescence spectroscopy to elucidate photocatalytic reactions at the molecular level

The present review covers the outline of the application of photoluminescence (PL) spectroscopy to understand the photocatalytic reactions on the bulk semiconducting materials and highly dispersed metal oxide single-site heterogeneous catalysts at their working states. The first part focuses on the applications of PL spectroscopy to elucidate the surface active sites and surface band structures of the inorganic and organic bulk semiconducting photocatalysts at their working states. The second part describes the applications of in situ PL spectroscopy to elucidate the surface active sites of the highly dispersed metal oxide single-site heterogeneous catalysts and their roles in photocatalytic reactions at the molecular level. The last part is a brief conclusion and future direction of PL studies.

     

Removal of cadmium(II) and lead(II) ions from model aqueous solutions using sol–gel-derived inorganic oxide adsorbent

A study was conducted concerning the preparation and application of a novel synthetic oxide adsorbent of MgO-SiO₂ type. The material was prepared via a sol–gel route, utilizing magnesium ethoxide and tetraethoxysilane as precursors of magnesium oxide and silica respectively, and ammonia as a catalyst. The powder was comprehensively analyzed with regard to chemical composition (EDS method), crystalline structure, morphology, characteristic functional groups, electrokinetic stability and porous structure parameters (BET and BJH models). The synthesized oxide adsorbent is amorphous, with irregularly shaped particles, a relatively large surface area of 612 m²/g, and negative surface charge over almost the whole pH range. Comprehensive adsorption studies were performed to investigate the adsorption of Cd(II) and Pb(II) ions on the MgO–SiO₂ oxide adsorbent, including evaluation of adsorption kinetics and isotherms, the effect of pH, contact time and mass of adsorbent. It was shown that irrespective of the conditions of the adsorption process, the synthesized MgO–SiO₂ adsorbent exhibits slightly better affinity to lead(II) than to cadmium(II) ions (sorption capacity of 102.02 mg(Pb²⁺)/g and 94.05 mg(Cd²⁺)/g). The optimal time for removal of the analyzed metal ions was 60 min, although adsorption reached equilibrium within 10 min for Pb(II) and within 15 min for Cd(II) ions, which was found to fit well with a type 1 pseudo-second-order kinetic model. Additionally, adsorption efficiency was affected by the pH of the reaction system—better results were obtained for pH ≥7 irrespective of the type of metal ion.     

Oxide-dependent adsorption of a model membrane phospholipid, dipalmitoylphosphatidylcholine: bulk adsorption isotherms

The importance of substrate chemistry and structure on supported phospholipid bilayer design and functionality is only recently being recognized. Our goal is to investigate systematically the substrate-dependence of phospholipid adsorption with an emphasis on oxide surface chemistry and to determine the dominant controlling forces. We obtained bulk adsorption isotherms at 55 degrees C for dipalmitoylphosphatidylcholine (DPPC) at pH values of 5.0, 7.2, and 9.0 and at two ionic strengths with and without Ca(2+), on quartz (alpha-SiO(2)), rutile (alpha-TiO(2)), and corundum (alpha-Al(2)O(3)), which represent a wide a range of points of zero charge (PZC). Adsorption was strongly oxide- and pH-dependent. At pH 5.0, adsorption increased as quartz < rutile approximately corundum, while at pH 7.2 and 9.0, the trend was quartz approximately rutile < corundum. Adsorption decreased with increasing pH (increasing negative surface charge), although adsorption occurred even at pH > or = PZC of the oxides. These trends indicate that adsorption is controlled by attractive van der Waals forces and further modified by electrostatic interactions of oxide surface sites with the negatively charged phosphate ester (-R(PO(4)-)R'-) portion of the DPPC headgroup. Also, the maximum observed adsorption on negatively charged oxide surfaces corresponded to roughly two bilayers, whereas significantly higher adsorption of up to four bilayers occurred on positively charged surfaces. Calcium ions promote adsorption beyond a second bilayer, regardless of the sign of oxide surface charge. We develop a conceptual model for the structure of the electric double layer to explain these observations.     

Electrochemical and surface analytical studies of self-assembled monolayers of three aromatic thiols on gold electrodes

Three thiols with three aromatic rings and different structure – terphenyl-4-methanethiol (TPMT), terphenyl-4-thiol (TPT), and anthracene-2-thiol (AT) – have been used to form self-assembled monolayers (SAM) on vapour-deposited and flame-annealed Au films on glass substrates. All three SAMs effectively block the anodic formation of Au oxide, indicating densely packed layers which prevent the access of water and hydrated ions through the organic layer to the metal surface. The film improves its inhibiting properties with duration of exposure to the thiol solutions, reaching completion after 1 hour [1]. The charge-transfer reaction of the Fe(CN)₆ ^3–/Fe(CN)₆ ^4– system is blocked for TPMT films with an insulation of the π-electron system from the Au surface by the methylene group. TPT and especially AT films show the current density of the redox reactions. It is proposed that the charge transfer occurs via the aromatic molecules of the SAMs to the Au surface. Electronic Publication     

Modification of Surface Forces by Metal Ion Adsorption

Abstract

Sorption of ions may lead to variations in interparticle forces and, thus, changes in the stability of colloidal particles. Chemical interactions between metal ions and colloidal particles modify the molecular structure of the surface, the surface charge, and the electrical potential between colloidal particles. These modifications to the surface and to the electrical double layer due to metal ion sorption are reflected in the interaction force between a particle and another surface, which is measured in this study by atomic force microscopy (AFM). Specifically, AFM is used to investigate the sorption of copper ions from aqueous solutions by silica particles. The influence of metal ion concentration and solution ionic strength on surface forces is studied under transient conditions. Results show that as the metal ion concentration is decreased, charge reversal occurs and a longer period of time is required for the system to reach equilibrium. The ionic strength has no significant effect on sorption kinetics. Furthermore, neither metal concentration nor ionic strength exhibits any effect on sorption equilibria, indicating that for the experimental conditions used in this study, the surface sites of the silica particle are fully occupied by copper ions.     

A gold electrode modified with amino-modified reduced graphene oxide,ion specific DNA and DNAzyme for dual electrochemical determination of Pb(II) and Hg(II)

Multilayered reduced graphene oxide (rGO) was functionalized with amino groups by treatment with nitrogen plasma. Raman spectroscopy showed plasma treatment not to substantially alter the chemical structure of rGO and that a wide range of functional nitrogen groups is evenly incorporated into the carbon lattice. The amino-modified rGO was used to design an electrochemical biosensor in which a DNAzyme, substrate DNA and Pb(II) and Hg(II) binding DNA were immobilized on the amino-rGO placed on a gold electrode. The high concentration of amino groups and the rough surface of the rGO favor DNA immobilization. Heavy metal ions are bound to the surface via specific interaction between DNA and the two ions which are detected by electrochemical impedance spectroscopy at a potential of 0.2 V (vs. Ag/AgCl). The detection limits for Pb(II) and Hg(II) are as low as 7.8 and 5.4 pM, respectively, and the analytical ranges extend from 0.01 to 100 nM. The sensor is highly specific and stable and therefore represents a highly promising tool for use in environmental monitoring.

A nanofilm of reduced graphene oxide was first modified with amino groups by treatment with nitrogen plasma. A special DNA was then anchored to the surface to obtain a biosensor for simultaneous detection of Pb(II) and Hg(II). The sensor has detection limits as low as 7.8 and 5.4 pM and is highly selective.

     

Evolution of surface chemistry during sintering of water-atomized iron and low-alloyed steel powder

Water-atomized iron and steel powder is commonly used as the base material for powder metallurgy (PM) of ferrous components. The powder surface chemistry is characterized by a thin surface oxide layer and more thermodynamically stable oxide particulates whose extent, distribution, and composition change during the sintering cycle due to a complex set of oxidation–reduction reactions. In this study, the surface chemistry of iron and steel powder was investigated by combined surface and thermal analysis. The progressive reduction of oxides was studied using model sintering cycles in hydrogen atmospheres in a thermogravimetric (TG) setup, with experiments ended at intermediate steps (500–1300°C) of the heating stage. The surface chemistry of the samples was then investigated by means of X-ray photoelectron spectroscopy (XPS) to reveal changes that occurred during heating. The results show that reduction of the surface oxide layer occurs at relatively lower temperature for the steel powder, attributed to an influence of chromium, which is supported by a strong increase in Cr content immediately after oxide layer reduction. The reduction of the stable oxide particulates was shifted to higher temperatures, reflecting their higher thermodynamic stability. A complementary vacuum annealing treatment at 800°C was performed in a furnace directly connected to the XPS instrument allowing for sample transfer in vacuum. The results showed that Fe oxides were completely reduced, with segregation and growth of Cr and Mn oxides on the particle surfaces. This underlines the sequential reduction of oxides during sintering that reflects the thermodynamic stability and availability of oxide-forming elements.     

Aluminum chloride as a solid is not a strong Lewis acid

Aluminum chloride is used extensively as Lewis acid catalyst in a variety of industrial processes, including Friedel-Crafts and Cl/F exchange reactions. There is a common misconception that pure AlCl3 is itself a Lewis acid. In the current study, we use experimental and computational methods to investigate the surface structure and catalytic properties of solid AlCl3. The catalytic activity of AlCl3 for two halide isomerization reactions is studied and compared with different AlF3 phases. It is shown that pure solid AlCl3 does not catalyze these reactions. The (001) surface of crystalline AlCl(3) is the natural cleavage plane and its structure is predicted via first principles calculations. The chlorine ions in the outermost layer of the material mask the Al3+ ions from the external gas phase. Hence, the experimentally found catalytic properties of pure solid AlCl3 are supported by the predicted surface structure of AlCl3.     

Contact angles in thin liquid films : III. Interaction forces in Newton black soap films

The interaction parameters of Newton black soap films stabilized by NaDS, as derived from contact angle experiments, have been interpretated in terms of the structure and the interaction forces in the films. From the film thickness and the difference between the surface excess of the salt in the film and at the bulk surface it is concluded that (a) the diffuse double-layer overlap in the film is practically complete; (b) the film only contains absorbed DS⁻ ions and an equal amount of Na⁺ counterions, but no salt; and (c) the double layer at the bulk surface is still partly diffuse. A model for the structure of the NB films is proposed according to which the adsorbed DS⁻ ions with their counterions form a two-dimensional square lattice at each film surface. It is found that the interaction free energy of the NB films can be explained by taking into account the electrostatic interactions between the discrete ions in the two opposing surface lattices. The model of the NB film is qualitatively in agreement with the experimental results of other workers.     

Oxidation, Diffusion and Segregation in CuNi(Mn) Films Studied by AES

 The surface and in-depth compositions of sputter-deposited Cu_0.57Ni_0.42Mn_0.01 thin films were studied by Auger electron depth profiling after thermal treatment. The samples were thermally cycled to maximum temperatures of 300 °C to 550 °C in air, argon and forming gas (N₂, 5 vol. % H₂). Linear least-squares fit to standard spectra and factor analysis were applied to separate the overlapping Auger transitions of Cu and Ni. Under bombardment by 4 keV argon ions, CuNi(Mn) layers display bombardment-induced surface enrichment of Ni in the same extent as binary CuNi alloys. At sufficiently high oxygen partial pressures, a duplex oxide layer is formed and a thick surface copper oxide overgrows the initial nickel oxide. In reducing atmosphere selective oxidation of manganese takes place. A capping NiCr layer prevents CuNi(Mn) from being oxidized, but the film configuration is degraded with increasing annealing temperature due to formation of a surface chromium oxide and diffusion of Ni from the CuNi(Mn) layer into the NiCr/CuNi(Mn) interface.