Preparation of silicon-metal nanocomposites based on electrophoretic deposition

Silicon has long been considered as one of the most promising anode material for lithium-ion batteries. However, the poor cycle life due to stress during charge/discharge cycling has been a major concern for its practical applications. In this report, novel Si-metal nanocomposites have been explored to accommodate the stress generated in the intercalation process. Several approaches have been studied with the aim of getting uniform mixing, good mechanical stability and high Si content. Among the three approaches being investigated, Si- Galinstan nanocomposite based on electrophoretic deposition showed the best promise by achieving at least 32.3% Si theoretical weight percentage, and our in current experiments we’ve already get 13% Silicon weight percentage, which gave us an anode material 46% more capacity than the current commercial product.

Cathodic protection of reinforced concrete:anodic processes in cements and related electrolytes

The nature and kinetics of electrode reactions and processes occurring for four lightweight anode systems which have been utilised in reinforced concrete cathodic protection systems have been studied. The anodes investigated were flame sprayed zinc, conductive paint and two activated titanium meshes. The electrochemical properties of each material were investigated in rapidly stirred de-oxygenated electrolytes using anodic potentiodynamic polarisation. Conductive coating electrodes were formed on glass microscope slides, whilst mesh strands were immersed directly. Oxygen evolution occurred preferentially for both mesh anodes in saturated Ca (OH)2/CaC12 solutions but was severely inhibited in less alkaline solutions and significant current only passed in chloride solutions. The main reactions for conductive paint was based on oxygen evolution in all electrolytes, although chlorides increased the electrical activity. Self-corrosion of zinc was controlled by electrolyte composition and the experimental set-up, chlorides increasing the electrical activity. Impressed current cathodic protection was applied to 25 externally exposed concrete slabs over a period of 18 months to investigate anode degradation mechanisms at normal and high current densities. Specimen chloride content, curing and reinforcement depth were also variables. Several destructive and non-destructive methods for assessing the performance of anodes were evaluated including a site instrument for quantitative "instant-off- potential measurements. The impact of cathodic protection on the concrete substrate was determined for a number of specimens using appropriate methods. Anodic degradation rates were primarily influenced by current density, followed by cemendtious alkalinity, chloride levels and by current distribution. Degradation of cementitious overlays and conductive paint substrates proceeded by sequential neutralisation of cement phases, with some evidence of paint binder oxidation. Sprayed zinc progressively formed an insulating layer of hydroxide complexes, which underwent pitting_ attack in the presence of sufficient chlorides, whilst substrate degradation was minimal. Adhesion of all anode systems decreased with increasing current density. The influence of anode material on the ionic gradients which can develop during cathodic protection was investigated. A constant current was passed through saturated cement paste prisms containing calcium chloride to central cathodes via anodes applied or embedded at each end. Pore solution was obtained from successive cut paste slices for anion and cation analyses. Various experimental errors reduced the value of the results. Characteristic S-shaped profiles were not observed and chloride ion profiles were ambiguous. Mesh anode specimens were significantly more durable than the conductive coatings in the high humidity environment. Limited results suggested zinc ion migration to the cathode region. Electrical data from each investigation clearly indicated a decreasing order of anode efficiency by specific anode material.

Aplicação de tecnologias eletroquímicas (oxidação via radicais hidroxila, oxidação mediada via cloro ativo e eletrocoagulação) para o tratamento de efluentes reais ou sintéticos

In this work the degradation of real and synthetic wastewater was studied using electrochemical processes such as oxidation via hydroxyl radicals, mediated oxidation via active chlorine and electrocoagulation. The real effluent used was collected in the decanter tank of the Federal University of Rio Grande do Norte (ETE-UFRN) of Effluent Treatment Plant and the other a textile effluent dye Ácido Blue 113 (AB 113) was synthesized in the laboratory. In the electrochemical process, the effects of anode material, current density, the presence and concentration of chloride as well as the active chlorine species on site generated were evaluated. Electrodes of different compositions, Ti/Pt, Ti/Ru0,3Ti0,7O2, BDD, Pb/PbO2 and Ti/TiO2-nanotubes/PbO2 were used as anodes. These electrodes were subjected to electroanalytical analysis with the goal of checking how happen the anodic and cathodic processes across the concentrations of NaCl and supporting electrolyte used. The potential of oxygen evolution reaction were also checked. The effect of active chlorine species formed under the process efficiency was evaluated by removing the organic matter in the effluent-ETE UFRN. The wastewater treatment ETE-UFRN using Ti/Pt, DDB and Ti/Ru0,3Ti0,7O2 electrodes was evaluated, obtaining good performances. The electrochemical degradation of effluent-UFRN was able to promote the reduction of the concentration of TOC and COD in all tested anodes. However, Ti/Ru0,3Ti0,7O2 showed a considerable degradation due to active chlorine species generated on site. The results obtained from the electrochemical process in the presence of chloride were more satisfactory than those obtained in the absence. The addition of 0.021 M NaCl resulted in a faster removal of organic matter. Secondly, was prepared and characterized the electrode Ti/TiO2-nanotubes/PbO2 according to what the literature reports, however their preparation was to disk (10 cm diameter) with surface area and higher than that described by the same authors, aiming at application to textile effluent AB 113 dye. SEM images were taken to observe the growth of TiO2 nanotubes and confirm the electrodeposition of PbO2. Atomic Force Microscope was also used to confirm the formation of these nanotubes. Furthermore, was tested and found a high electrochemical stability of the electrode Ti/TiO2-nanotubes/PbO2 for applications such as long-term indicating a good electrocatalytic material. The electrochemical oxidation of AB 113 using Ti/Pt, Pb/PbO2 and Ti/TiO2-nanotubes/PbO2 and Al/Al (electrocoagulation) was also studied. However, the best color removal and COD decay were obtained when Ti/TiO2-nanotubes/PbO2 was used as the anode, removing up to 98% of color and 92,5% of COD decay. Analysis of GC/MS were performed in order to identify possible intermediates formed in the degradation of AB 113.

Towards eco-friendly batteries: concepts for lithium and sodium ion batteries

Several possibilities are arising aiming the development of “greener”, more sustainable energy storage systems. One point is the completely water-based processing of battery electrodes, thus being able to renounce the use of toxic solvents in the preparation process. Despite its advantage of lower cost and eco-friendlyness, there is the need of similar mechanical and electrochemichal behavior for boosting this preparation mode. Another point – accompanying the water-based processing - is the replacement of solvent-based polymer binders by water-based ones. These binders can be based on fluorinated, crude-oil based polymers on the one side, but also on naturally abundant and economic friendly biopolymers. The most common anode materials, graphite and lithium titanate (LTO), have been subjected a water-based preparation route with different binder systems. LTO is a promising anode material for lithium ion batteries (LIBs), as it shows excellent safety characteristics, does not form a significant SEI and its volume change upon intercalation of lithium ions is negligible. Unfortunately, this material suffers from a rather low electric conductivity - that is why an intensive study on improved current collector surfaces for LTO electrodes was performed. In order to go one step ahead towards sustainable energy storage, anode and cathode active materials for a sodium ion battery were synthesized. Anode active material resulted in a successful product which was then subjected to further electrochemical tests. In this PhD work the development of “greener” energy storage possibilities is tested under several aspects. The ecological impact of raw materials and required battery components is examined in detail.

Synthesis and characterization of prussian blue analogue materials for post-Li ion batteries

Energy issues have always been a subject of concern to people. During the past 30 years, rechargeable Li-ion batteries (LIBs) have been widely used in portable electronic devices and power tools because of their high energy density and efficiency among practical secondary batteries. While the unevenly distribution of Lithium sources and the increasing cost of lithium-raw material can not satisfy the requirement for further cost reduction, especially for the grid-scale energy storage. Post-lithium ion batteries as promising replacement for LIBs have attracted wide attention, owing to their high abundant resources and adequate insertion potential. Similar with Li-ion batteries, finding a suitable electrode material is the key for the research and application of the post-Li ion batteries. In our project, we focus our study on Prussian blue analogues (PBAs), with formula AxM[M’(CN)6]1-y□y•zH2O (0≤x≤2, 0anode material for both Li-ion and post-Li batteries. The most commonly studied PBAs are metal haxacyanoferrate, with the carbon-sites of -CN- ligands fix connected with Fe. Here, we synthesized three different PBAs: manganese hexacynoferrate (MnHCF), zinc hexacynoferrate (ZnHCF) and titanium hexacynoferrate (TiHCF), using co-precipitation method, and their electrochemical properties were tested in both aqueous Na+, K+, Mg2+, Zn2+ and organic Li+, Na+ electrolytes. Various X-ray techniques were employed to study their electronic and structural properties of electrodes and electrochemical reaction mechanism during cycling.

Study of ethanol electro-oxidation in acid environment on Pt(3)Sn/C anode catalysts prepared by a modified polymeric precursor method under controlled synthesis conditions

A carbon-supported binary Pt(3)Sn catalyst has been prepared using a modified polymeric precursor method under controlled synthesis conditions This material was characterized using X-ray diffraction (XRD). and the results indicate that 23% (of a possible 25%) of Sn is alloyed with Pt, forming a dominant Pt(3)Sn phase. Transmission election microscopy (TEM) shows good dispersion of the electrocatalyst and small particle sizes (3 6 nm +/- 1 nm) The polarization curves for a direct ethanol fuel cell using Pt(3)Sn/C as the anode demonstrated Improved performance compared to that of a PtSn/C E-TEK. especially in the intrinsic resistance-controlled and mass transfer regions. This behavior is probably associated with the Pt(3)Sn phase. The maximum power density for the Pt(3)Sn/C electrocatalyst (58 mW cm(-2)) is nearly twice that of a PtSn/C E-TEK electrocatalyst (33 mW cm(-2)) This behavior is attributed to the presence of a mixed Pt(9)Sn and Pt(3)Sn alloy phase in the commercial catalysts (C) 2009 Elsevier B V All rights reserved

Electrode surface modifications improve cathode hydrogen production and anode capacity in Ni-MH batteries

This paper reports results from electrochemical evaluations of electrodes used as cathodes for a hydrogen evolution reaction and anodes in Ni-MH batteries that had been surface-modified by micro-encapsulation, co-deposition and sol-gel methods. The surface modifications produced actual improvements in the corresponding electrochemical reactions by enhancing the performance and/or the mechanical stability of the electrode material. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

Microstructural and electrical properties of the sofc anode precursor YSZ/NiO composite prepared by A liquid mixture technique

A detailed study of the microstructural and electrical properties of the yttria-stabilized zirconia/nickel oxide (YSZ/NiO) composite was performed. This material is the precursor to the solid oxide fuel cell anode cermet YSZ/Ni. A liquid mixture technique was developed to produce the YSZ/NiO composite to fabricate high-performance SOFC anodes. This technique resulted in fine and homogeneous powders and specimens with high electrical conductivity. The combined results showed that this technique is suitable for the production of the anode cermet.

PtSnIr/C anode electrocatalysts: Promoting effect in direct ethanol fuel cells

This study investigates the promoting effect of PtSnIr/C (1:1:1) electrocatalyst anode, prepared by polymeric precursor method, on the ethanol oxidation reaction in a direct ethanol fuel cell (DEFC). All of the materials used were 20% metal m/m on carbon. X-ray photoelectron spectroscopy (XPS) analysis showed the presence of Pt, PtOH 2, PtO 2, SnO 2 and IrO 2 at the electrocatalyst surface, indicating a possible decorated particle structure. X-ray diffractometry (XRD) analysis indicated metallic Pt and Ir as well as the formation of an alloy with Sn. Using the PtSnIr/C electrocatalyst prepared here with two times lower loading of Pt than PtSn/C E-tek electrocatalyst, it was possible to obtain the same maximum power density found for the commercial material. The main reaction product was acetic acid probably due to the presence of oxides, in this point the bifunctional mechanism is predominant, but an electronic effect should not be discarded. © 2012 Sociedade Brasileira de Química.

PtSnIr/C Anode Electrocatalysts: Promoting Effect in Direct Ethanol Fuel Cells

This study investigates the promoting effect of PtSnIr/C (1:1:1) electrocatalyst anode, prepared by polymeric precursor method, on the ethanol oxidation reaction in a direct ethanol fuel cell (DEFC). All of the materials used were 20% metal m/m on carbon. X-ray photoelectron spectroscopy (XPS) analysis showed the presence of Pt, PtOH2, PtO2, SnO2 and IrO2 at the electrocatalyst surface, indicating a possible decorated particle structure. X-ray diffractometry (XRD) analysis indicated metallic Pt and Ir as well as the formation of an alloy with Sn. Using the PtSnIr/C electrocatalyst prepared here with two times lower loading of Pt than PtSn/C E-tek electrocatalyst, it was possible to obtain the same maximum power density found for the commercial material. The main reaction product was acetic acid probably due to the presence of oxides, in this point the bifunctional mechanism is predominant, but an electronic effect should not be discarded.

PtSnIr/C anode electrocatalysts: promoting effect in direct ethanol fuel cells

This study investigates the promoting effect of PtSnIr/C (1:1:1) electrocatalyst anode, prepared by polymeric precursor method, on the ethanol oxidation reaction in a direct ethanol fuel cell (DEFC). All of the materials used were 20% metal m/m on carbon. X-ray photoelectron spectroscopy (XPS) analysis showed the presence of Pt, PtOH2, PtO2, SnO2 and IrO2 at the electrocatalyst surface, indicating a possible decorated particle structure. X-ray diffractometry (XRD) analysis indicated metallic Pt and Ir as well as the formation of an alloy with Sn. Using the PtSnIr/C electrocatalyst prepared here with two times lower loading of Pt than PtSn/C E-tek electrocatalyst, it was possible to obtain the same maximum power density found for the commercial material. The main reaction product was acetic acid probably due to the presence of oxides, in this point the bifunctional mechanism is predominant, but an electronic effect should not be discarded.

Molecular plating of thin lanthanide layers with improved material properties for nuclear applications

In der vorliegenden Arbeit werden Experimente beschrieben, die zu einem vertieften Verständnis fundamentaler Prozesse bei der elektrochemischen Herstellung von Dünnschichten, sog. Targets, für kernphysikalische und -chemische Studien führten. Targets wurden mittels 'Molecular Plating' (MP) hergestellt, indem eine Elektrodeposition aus organischem Medium in der Regel bei konstantem Strom in Zwei-Elektroden-Zellen. Die Resultate erlaubten, optimierte Herstellungs-bedingungen zu ermitteln, welche die Produktion deutlich verbesserter Targets erlaubten. MP bei konstantem Strom ist ein massentransportkontrollierter Prozess. Der angelegte Strom wird durch einen konstanten Fluss elektroaktiver Spezies zur Kathode – auf der die Schicht wächst – und Anode aufrechterhalten. Die Untersuchungen zeigten, dass das Zellenpotential des Elektrodepositionsystems immer durch den Ohm'schen Spannungsabfall auf Grund des Widerstandes der verwendeten Lösung dominiert wurde. Dies erlaubte die Herleitung einer Beziehung zwischen dem Zellenpotential und der Konzentration der elektroaktiven Spezies. Die Beziehung erlaubt die Erklärung des gemessenen zeitlichen Verlaufs des Zellenpotentials während der Abscheidung als Funktion der Elektrolytkonzentration. Dies dient als Basis, auf der nun ein umfassenderes Bild der Prozesse, die für die charakteristischen Minima im Potentialverlauf einer Abscheidung verantwortlich sind, gewonnen werden kann. Es konnte gezeigt werden, dass die Minima mit der fast vollständigen Entfernung (durch Abscheidung) der aus einem gelösten Salz erzeugten Nd-Ionen korrespondieren. Die abgeschiedene Spezies wurde als Nd3+ identifiziert, vermutlich als Carboxylat, Oxid oder Hydroxid, was auf Grund der hohen negative Werte des Standardredoxpotentials der Lanthanide verständlich erscheint. Von den vorliegenden elektroaktiven Spezies tragen die Nd3+ Ionen nur zu knapp 20% zum Gesamtstrom bei. Durch Elektrolyse tragen auch die Lösungsmittelkomponenten zu diese Strom bei. Die Gegenwart von elektrolysiertem Lösungsmittel wurde in Analysen der Dünnschichten bestätigt. Diese waren immer mit chemi- und physisorbierten Lösungsmittelmolekülen bedeckt. Die Analyse der Dünnschichten zeigte, dass die Oberflächen von einem furchenartiges Netz durchzogen waren, und dass diese während des Trocknen der Schichten nach dem MP entstanden. Ob die Schichten an Luft oder in inerter Atmosphäre trockneten, hatte keinen Einfluss. Es wurden Experimente mit mehreren Lösungsmitteln durchgeführt, die sich deutlich in ihren physikalischen Eigenschaften, v.a. dem Siedepunkt, unterschieden. Furchenfreie Dünnschichten konnten insbesondere bei MP in N,N-dimethylformamide (DMF) erzeugt werden. Die Verwendung von DMF in Kombination mit einer Abscheidung auf sehr glatten Substraten erlaubte die Produktion von sehr homogenen, glatten und defektfreien Schichten. Diese waren vermutlich geringeren inneren Spannungen während des Trocknens ausgesetzt, als Schichten auf raueren Substraten oder solche, die aus flüchtigeren Lösungsmitteln hergestellt wurden. Die Oberflächenrauigkeit des Substrats und das gewählte Lösungsmittel wurden so als Schlüsselfaktoren für die Produktion hochqualitativer Schichten identifiziert. Es konnte gezeigt werden, dass mit MP eine sehr effiziente Methode zur Herstellung homogener Schichten mit exzellenter Ausbeute ist. In weiteren Experimenten mit dem primordialen Alpha-Emitter 147Sm als Modellisotop wurde die Eignung solcher Schichten als Alpha-Quelle untersucht. Sowohl die Energieauflösung als auch der Anteil der Alpha-Teilchen, die den Detektor erreichten, waren von den Quelleneigenschaften abhängig. Die Effekte wurden verschiedenen Variablen der Dünnschicht zugeordnet, welche die Alpha-Spektren beeinflussten. Dominant war die Wahl des Lösungsmittels und die Rauigkeit des Substrats. Dies beeinflusste Schichtdicke und -morphologie sowie die Art des Schichtwachstums und veränderte die Detektionseffizienz in Alpha-Messungen bis zu 15%. Nur homogene, ebene Schichten, die aus DMF auf glatten Substraten abgeschieden wurden, eignen sich optimal als Alpha-Quelle. Die gewonnenen Ergebnisse erlauben die optimierte Herstellung nuklearer Targets durch MP. Künftige Anwendungen beinhalten insbesondere die Herstellung von Targets für neutroneninduzierte Spaltexperimente und untergrundarmeAlpha-Messungen sehr kleiner Aktivitäten.

Graphite for lithium-ion batteries: mineral analysis and global Material Flow Analysis

Graphite is a mineral commodity used as anode for lithium-ion batteries (LIBs), and its global demand is doomed to increase significantly in the future due to the forecasted global market demand of electric vehicles. Currently, the graphite used to produce LIBs is a mix of synthetic and natural graphite. The first one is produced by the crystallization of petroleum by-products and the second comes from mining, which causes threats related to pollution, social acceptance, and health. This MSc work has the objective of determining compositional and textural characteristics of natural, synthetic, and recycled graphite by using SEM-EDS, XRF, XRD, and TEM analytical techniques and couple these data with dynamic Material Flow Analysis (MFA) models, which have the objective of predicting the future global use of graphite in order to test the hypothesis that natural graphite will no longer be used in the LIB market globally. The mineral analyses reveal that the synthetic graphite samples contain less impurities than the natural graphite, which has a rolled internal structure similar to the recycled one. However, recycled graphite shows fractures and discontinuities of the graphene layers caused by the recycling process, but its rolled internal structure can help the Li-ions’ migration through the fractures. Three dynamic MFA studies have been conducted to test distinct scenarios that include graphite recycling in the period 2022-2050 and it emerges that - irrespective of any considered scenario - there will be an increase of synthetic graphite demand, caused by the limited stocks of battery scrap available. Hence, I conclude that both natural and recycled graphite is doomed to be used in the LIB market in the future, at least until the year 2050 when the stock of recycled graphite production will be enough to supersede natural graphite. In addition, some new improvement in the dismantling and recycling processes are necessary to improve the quality of recycled graphite.

Effect Of Platform Connection And Abutment Material On Stress Distribution In Single Anterior Implant-supported Restorations: A Nonlinear 3-dimensional Finite Element Analysis.

Although various abutment connections and materials have recently been introduced, insufficient data exist regarding the effect of stress distribution on their mechanical performance. The purpose of this study was to investigate the effect of different abutment materials and platform connections on stress distribution in single anterior implant-supported restorations with the finite element method. Nine experimental groups were modeled from the combination of 3 platform connections (external hexagon, internal hexagon, and Morse tapered) and 3 abutment materials (titanium, zirconia, and hybrid) as follows: external hexagon-titanium, external hexagon-zirconia, external hexagon-hybrid, internal hexagon-titanium, internal hexagon-zirconia, internal hexagon-hybrid, Morse tapered-titanium, Morse tapered-zirconia, and Morse tapered-hybrid. Finite element models consisted of a 4×13-mm implant, anatomic abutment, and lithium disilicate central incisor crown cemented over the abutment. The 49 N occlusal loading was applied in 6 steps to simulate the incisal guidance. Equivalent von Mises stress (σvM) was used for both the qualitative and quantitative evaluation of the implant and abutment in all the groups and the maximum (σmax) and minimum (σmin) principal stresses for the numerical comparison of the zirconia parts. The highest abutment σvM occurred in the Morse-tapered groups and the lowest in the external hexagon-hybrid, internal hexagon-titanium, and internal hexagon-hybrid groups. The σmax and σmin values were lower in the hybrid groups than in the zirconia groups. The stress distribution concentrated in the abutment-implant interface in all the groups, regardless of the platform connection or abutment material. The platform connection influenced the stress on abutments more than the abutment material. The stress values for implants were similar among different platform connections, but greater stress concentrations were observed in internal connections.