Spent Li-Ion Battery Graphite Turned Into Valuable and Active Catalyst for Electrochemical Oxygen Reduction.

Employing Li-ion batteries (LIBs) in portable electronics has become a necessity in the modern world but, due to the short application time for any given battery (1-3 years), the quantity of spent LIBs (SLIBs) waste is becoming substantial. Herein, a novel strategy for recycling SLIB graphite and reforming it as a valuable catalyst material for electrochemical oxygen reduction reaction was proposed. SLIB graphite has been used as a precursor material for graphite oxide, which was thereafter doped with nitrogen to prepare nitrogen-doped graphene (NG-Bat). The prepared NG-Bat was characterized by various physical characterization methods and the electrochemical properties of the resulting catalyst material were investigated in alkaline media. It was found that NG-Bat prepared from SLIB had superior physical and electrochemical properties in comparison to commercial nitrogen-doped graphene. The findings clearly demonstrate the importance of the recycling of SLIB graphite and its great potential to be re-applied for various applications.

Studies on Pitting Corrosion of Al-Cu-Li Alloys Part II: Breakdown Potential and Pit Initiation.

Prediction of the accumulated pitting corrosion damage in aluminum-lithium (Al-Li) is of great importance due to the wide application of these alloys in the aerospace industry. The Point Defect Model (PDM) is arguably one of the most well-developed techniques for evaluating the electrochemical behavior of passive metals. In this paper, the passivity breakdown and pitting corrosion performance of AA 2098-T851 was investigated using the PDM with the potentiodynamic polarization (PDP) technique in NaCl solutions at different scan rates, Cl- concentrations and pH. Both the PDM predictions and experiments reveal linear relationships between the critical breakdown potential (Ec) of the alloy and various independent variables, such as aCl- and pH. Optimization of the PDM of the near-normally distributed Ec as measured in at least 20 replicate experiments under each set of conditions, allowing for the estimation of some of the critical parameters on barrier layer generation and dissolution, such as the critical areal concentration of condensed cation vacancies (ξ) at the metal/barrier layer interface and the mean diffusivity of the cation vacancy in the barrier layer (D). With these values obtained-using PDM optimization-in one set of conditions, the Ec distribution can be predicted for any other set of conditions (combinations of aCl-, pH and T). The PDM predictions and experimental observations in this work are in close agreement.

Studies on Pitting Corrosion of Al-Cu-Li Alloys Part III: Passivation Kinetics of AA2098-T851 Based on the Point Defect Model.

In this paper, the passivation kinetics of AA2098-T851 was investigated by a fundamental theoretical interpretation of experimental results based on the mixed potential model (MPM). The steady state passive layer formed on the AA2098-T851 in NaHCO3 solution in a CO2 atmosphere upon potentiostatic stepping in the anodic direction followed by stepping in the opposite direction was explored. Potentials were selected in a way that both anodic passive dissolution of the metal and hydrogen evolution reaction (HER) occur, thereby requiring the MPM for interpretation. Optimization of the MPM on the experimental electrochemical impedance spectroscopy (EIS) data measured after each potentiostatic step revealed the important role of the migration of Al interstitials in determining the kinetics of passive layer formation and dissolution. More importantly, it is shown that the inequalities of the kinetics of formation and dissolution of the passive layer as observed in opposite potential stepping directions lead to the irreversibility of the passivation process. Finally, by considering the Butler-Volmer (B-V) equation for the cathodic reaction (HER) in the MPM, and assuming the quantum mechanical tunneling of the charge carriers across the barrier layer of the passive film, it was shown that the HER was primarily controlled by the slow electrochemical discharge of protons at the barrier layer/solution (outer layer) interface.

Studies on Pitting Corrosion of Al-Cu-Li Alloys Part I: Effect of Li Addition by Microstructural, Electrochemical, In-situ, and Pit Depth Analysis.

To analyze the effect of lithium and microstructure on the pitting corrosion behavior of aluminum alloys, three types of aluminum alloys were studied via scanning electron microscopy, transmission electron microscopy, electrochemical polarization, and by immersion tests coupled with in-situ observation of pitting and statistical analysis of pit depths measured by surface profilometry. It was found that, with increasing lithium content, the resistance to pitting corrosion was enhanced and the passive range was enlarged. In-situ observation revealed that the development of pitting corrosion exhibited three stages, including an initial slow nucleation stage (Stage I), a fast development stage (Stage II), and a stabilized growth stage (Stage III). Higher lithium content contributed to shorter time periods of Stages I and II, resulting in faster pitting evolution and a higher number of pits. However, the pits were generally shallower for the specimen with the highest lithium content, which is in agreement with the results of the electrochemical analysis.

Modelling and Analysis of the Corrosion Characteristics of Ferritic-Martensitic Steels in Supercritical Water.

The dependencies of weight gain of 9-12 Cr ferritic-martensitic steels in supercritical water on each of seven principal independent variables (temperature, oxygen concentration, flow rate, exposure time, and key chemical composition and surface condition of steels) have been predicted using a supervised artificial neural network (ANN). The relative significance of each independent variable was uncovered by fuzzy curve analysis, which ranks temperature and exposure time as the most important. The optimized ANN, not only satisfactorily represents the experimentally-known non-linear relationships between the corrosion characteristics of F-M steels and the key independent variables (demonstrating the effectiveness of this technique), but also predicts and reveals that the effects of oxygen concentration on the weight gains, to a certain degree, is influenced by the flow rate and temperature. Finally, according to the ANN predicted-results, departure of oxidation kinetics from the parabolic law, and basic cause of chromium content in steel substrate influencing the corrosion rate, and the synergetic effects of dissolved oxygen concentration, flow rate, and temperature, are discussed and analyzed.

The aggression behavior study of Cl- on the defect structure of passive films on copper.

The destructive role of chloride ions on the defect structure of barrier layers (bl) is vitally important for understanding the initial breakdown of passive films on metals. Here photo-electrochemical and density functional theory (DFT) were applied to investigate the influence of chloride on the defect structure of the bl in passive films. The results show a bl with a narrow band gap, in which the valence band maximum (VBM) increased upon introducing chloride into the electrolyte. DFT calculations indicate that an increase in the copper vacancy concentration, due to cation extraction at the bl/solution interface could increase the VBM while oxygen vacancy generation results in a decrease in the conduction band minimum (CBM). The combination of these results verifies the aggressive role of chloride as proposed by the Point Defect Model (PDM) where an enhancement of the cation vacancy concentration across the bl occurs in response to the absorption of Cl- into oxygen vacancies on the bl.

Oxygen-induced degradation of the electronic properties of thin-layer InSe.

Thin-layer indium selenide (InSe) compounds, as two-dimensional (2D) semiconductors, have been widely and intensively studied due to their high electron mobility and environmental stability. Here, we report a study demonstrating the oxygen-induced degradation of monolayer and bilayer InSe nanosheets using first-principles calculations and deformation potential theory. It is evident that O atoms prefer to substitute Se atoms instead of undergoing adsorption onto surfaces, while interstitial sites are the most stable adsorption sites of O atoms in the interior for both monolayer and bilayer InSe. Using the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, we calculated band structures and carrier mobility. The band gaps of a monolayer or bilayer InSe nanosheet with O atoms remained unchanged and corresponded to the pristine structure except for a slight decrease in the substituted cases. Additionally, no impurity levels are observed, indicating that the addition of O atoms has little effect on carrier concentrations. With the calculated mobility of monolayer InSe with and without O atoms, we show that the degradation is governed by the interstitial impurity of O atoms, whose electron mobility can decrease by 3-4 orders of magnitude. As for bilayer InSe, there is a one order of magnitude decrease at most, which indicates a stronger resistance to oxidation than that of the monolayer structure. Our calculations provide a detailed understanding of the degradation induced by O atoms from the aspects of structures and electronic properties, which is a foundation for the application and modification of thin-layer InSe.

Crack simulation of nano-bioceramic composite microstructures with cohesive failure law: effects of sintering, loads and time.

Crack behaviour of zirconia toughened alumina (ZTA) microstructures are simulated with a two-dimensional finite element simulation. Finite element models are developed using actual microstructure images of zirconia toughened alumina and a bilinear cohesive zone law. Simulation conditions are similar to those found at frictional contact between a femoral head and an acetabular cup of hip prosthesis. Effects of microstructures and contact stresses are investigated in terms of crack generation. Moreover, fatigue behaviour of a microstructure is determined by performing simulations under cyclic loading conditions. It is identified that total crack length observed in a microstructure increases with increasing the magnitude of applied contact stress. Cyclic simulation results show that progressive crack growth occurs with respect to number of fatigue cycles. In addition, it is demonstrated that zirconia grains resist crack growth in microstructures.

Remarkable impact of water on the discharge performance of a silicon-air battery.

Here, we report on a Si-air/ionic liquid electrolyte battery whose performance improves with small amounts of water in the electrolyte. The shift of the generation zone of the SiO(2) discharge product from the air cathode surface into the bulk region of the liquid electrolyte, caused by water addition, is demonstrated through various means. Addition of 15 vol% water leads to an increase of 40% in the discharge capacity as compared to the capacity obtained using a pure ionic liquid electrolyte. If the water content increases above 20 vol%, the Si-air cell capacity dramatically decreases. The water-ionic liquid electrolyte mixture shows a maximum in the ionic conductivity with a water content of 10 vol%. In-depth studies indicate a reduced amount of discharge product at the air electrode using 15 vol% H(2)O electrolyte. The morphology of the anode surface, as well as the developed surface film in the presence of water-containing ionic liquid, is reported. This study shows that exposing a Si-air battery to a humid environment does not result in capacity losses, but rather improves cell performance.

Dielectric relaxation in dimethyl sulfoxide/water mixtures studied by microwave dielectric relaxation spectroscopy.

Dielectric spectra of dimethyl sulfoxide (DMSO)/water mixtures, over the entire concentration range, have been measured using the transmission line method at frequencies from 45 MHz to 26 GHz and at temperatures of 298-318 K. The relaxation times of the mixtures show a maximum at an intermediate molar fraction of DMSO. The specific structure of mixtures in different concentration regions was determined by the dielectric relaxation dynamics, obtained from the effect of temperature on the relaxation time. A water structure "breaking effect" is observed in dilute aqueous solutions. The average number of hydrogen bonds per water molecule in these mixtures is found to be reduced compared to pure water. The increase in the dielectric relaxation time in DMSO/water mixtures is attributed to the spatial (steric) constraints of DMSO molecules on the hydrogen-bond network, rather than being due to hydrophobic hydration of the methyl groups. The interaction between water and DMSO by hydrogen bonding reaches a maximum at a DMSO molar fraction of 0.33, reflected by the maximum activation enthalpy for dielectric relaxation in this concentration, suggesting the formation of a stoichiometric compound, H2O-DMSO-H2O. In highly concentrated solutions, negative activation entropies are observed, indicating the presence of aggregates of DMSO molecules. A distinct antiparallel arrangement of dipoles is obtained for neat DMSO in the liquid state according to the Kirkwood correlation factor (g(K) = 0.5), calculated from the static permittivity. The similarity of the dielectric behavior of pure DMSO and DMSO-rich mixtures suggests that dipole-dipole interactions contribute significantly to the rotational relaxation process in these solutions.

Two-port transmission line technique for dielectric property characterization of polymer electrolyte membranes.

Performance improvements of perfluorosulfonic acid membranes, such as Nafion and Flemion, underline a need for dielectric characterization of these materials toward a quantitative understanding of the dynamics of water molecules and protons within the membranes. In this Article, a two-port transmission line technique for measuring the complex permittivity spectra of polymeric electrolytes in the microwave region is described, and the algorithms for permittivity determination are presented. The technique is experimentally validated with liquid water and polytertrafluoroethylene film, whose dielectric properties are well-known. Further, the permittivity spectra of dry and hydrated Flemion SH150 membranes are measured and compared to those of Nafion 117. Two water relaxation modes are observed in the microwave region (0.045-26 GHz) at 25 degrees C. The higher-frequency process observed is identified as the cooperative relaxation of bulk-like water, whose amount was found to increase linearly with water content in the polymer. The lower-frequency process, characterized by longer relaxation times in the range of 20-70 ps, is attributed to water molecules that are loosely bound to sulfonate groups. The loosely bound water amount was found to increase with hydration level at low water content and levels off at higher water contents. Flemion SH150, which has an equivalent weight of 909 g/equiv, displays higher dielectric strengths for both of these water modes as compared to Nafion 117 (equivalent weight of 1100 g/equiv), which probably reflects the effect of equivalent weight on the polymers' hydrated structure, and in particular its effect on the extended ionic cluster domains.