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Robust time-averaged molecular dynamics has been developed to calculate finite-temperature elastic constants of a single crystal. We find that when the averaging time exceeds a certain threshold, the statistical errors in the calculated elastic constants become very small. We applied this method to compare the elastic constants of Pd and PdH0.6 at representative low (10 K) and high (500 K) temperatures. The values predicted for Pd match reasonably well with ultrasonic experimental data at both temperatures. In contrast, the predicted elastic constants for PdH0.6 only match well with ultrasonic data at 10 K; whereas, at 500 K, the predicted values are significantly lower. We hypothesize that at 500 K, the facile hydrogen diffusion in PdH0.6 alters the speed of sound, resulting in significantly reduced values of predicted elastic constants as compared to the ultrasonic experimental data. Literature mechanical testing experiments seem to support this hypothesis.
Recent theoretical and subsequent experimental studies suggest that the uptake and release of deuterium (D) in tungsten (W) under high flux ITER-relevant plasma exposure is controlled by dislocation microstructure. Thanks to numerical calculations, a comprehensive mechanism for the nucleation and growth of D bubbles on dislocation network was proposed. The process of bubble nucleation can be described as D atom trapping at a dislocation line, its in-core migration, the coalescence of several D atoms into a multiple cluster eventually transforming into a nano-bubble. This view implies that the initial microstructure might be crucial for D uptake and degradation of the sub-surface layer under prolonged plasma exposure. In this work, we apply several experimental techniques to investigate the microstructure and mechanical properties of surface and sub-surface layer of W in recrystallized and plastically-deformed condition exposed to the high flux plasma. We use transmission and scanning electron microscopy, thermal desorption spectroscopy as well as nano-indentation measurements.
Understanding the ratcheting effect of hydrogen and hydride accumulation in response to thermal cycling is important in establishing a failure criterion for zirconium alloy nuclear fuel cladding. We propose a simple discrete dislocation plasticity model to study the evolution of the dislocation content that arises as a micro-hydride repeatedly precipitates and dissolves over a series of thermal cycles. With each progressive thermal cycle, we find a steady growth in the residual dislocation density in the vicinity of the hydride nucleation site; this corresponds to a gradual increase in the hydrogen concentration and, consequently, the hydride population. The simulated ratcheting in the dislocation density is consistent with experimental observations concerning the hysteresis in the terminal solid solubility of hydrogen in zirconium, which can be correlated to the plastic relaxation of hydrides.
Growing interest in the use of CO2 as a feedstock for fuel generation has led to increased interest in solar CO2 electrolysis for renewable fuel generation which has a variety of applications ranging from providing renewable sources for energy-dense carbon fuels, to curbing high-density emissions from power plants, industries and automobiles. The challenges of integrated solar-to-carbon fuel converters, where the photovoltaic (PV) material is immersed in the electrolyte, are well-known: the need for unique PV cell designs; material incompatibility; corrosion; and optical losses. In this paper, a PV-electrolysis system is presented, where a flow-cell electrolyzer is power-matched to a high-performance solar PV module array which has two system design advantages: 1) use of standard PV cells external to the electrolyzer, which allows de-coupling the design, fabrication and operation of the PV system from that of the electrolyzer; and 2) enabling optimization of the PV configuration to maximize power coupling efficiency to the specific electrolyzer Tafel curve, with or without the use of electronic power-conditioning devices. The implemented system resulted in a peak SFE of 6.5%, a competitive solar-to-fuel efficiency (SFE) figure to those reported in literature.
This contribution reports the synthesis and characterization of La-based perovskites which can be used for the production of syngas via solar thermochemical splitting of H2O/CO2. The La-based perovskites were synthesized using a solution combustion synthesis approach. The derived perovskites were analyzed using powder X-ray diffractometer (PXRD), BET surface area analyzer (BET), and scanning/transmission electron microscope (SEM/TEM). The results associated with the synthesis and characterization of La-based perovskites is reported in detail.
Intermetallic ternary nanoalloys (NA) have increasingly gained prominence as excellent catalysts. But, their size, morphology and chemical compositions affect their catalytic and interfacial activities significantly. In this study, we present laser-induced breakdown spectroscopy (LIBS) for rapid quantitative elemental composition characterization of ternary NAs with different elemental ratios. Specifically, we use a calibration-free approach with LIBS to estimate the elemental ratios of PtCuCo ternary NAs with various stoichiometric ratios synthesized via our in-house laser ablation synthesis in solution-galvanic replacement reactions (LASiS-GRR) technique. The size and morphology of the samples are determined from transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) measurements. The LIBS quantitative estimations for the NA samples are compared with results from inductively coupled plasma-optical emission spectroscopy (ICP-OES). The elemental ratio results of quantitative LIBS show good agreement with ICP-OES results, while being devoid of any external standard requirements or extensive sample preparations.
In this work, we successfully synthesized rhombic dodecahedral Cu2O nanocrystals with a size of 300 – 400 nm using a facile hydrothermal method. The as-prepared photocatalyst with narrow bandgap is activated using low power visible LED light sources and shows high efficiency in degrading aromatic organic compounds including toluene and chlorobenzene. The OH substitution leads to oxidation/ionization potential drops while the nature of the p-type Cu2O contributes to an effective single electron transfer reaction.
We report on a wide-range Density Functional Theory (DFT) investigation of the g-C3N4 photocatalysis systems combined with metals/nonmetals, especially those available in plants and involved in the natural photosynthesis process, such as K, Mg, Mn, Mo, Fe, Co, Cr, S and B. It is found that doping increases the range at which light absorption occurs to significantly large regions of the visible spectrum. These findings suggested that the g-C3N4 can be a promising system for the photosynthesis process.
In this study, Ni based ferrite nanomaterials were synthesized using sol-gel method for solar thermochemical splitting of CO2 using a thermogravimetric analyzer. To synthesize the ferrite materials, the corresponding metal precursors were dissolved in ethanol (with required molar ratios). After achieving the dissolution, propylene oxide (PO) was added to achieve the gel formation. Freshly synthesized gels were aged, dried, and calcined by heating up to 600°C in air. Powder x-ray diffractometer (XRD), BET surface area, as well as scanning (SEM) and transmission (TEM) electron microscopy characterized the calcined powders. The sol-gel derived ferrites were further tested towards their thermal reduction and CO2 splitting ability using a high temperature thermogravimetric analyzer (TGA).
This paper highlights experimental and theoretical efforts dedicated to developing plasmonic-enhanced electrodes for the photo-electrochemical ethanol oxidation reaction (EOR) at room temperature in alkaline media. However, decoupling the electrocatalytic dark response from the plasmon-enhanced improvement presents a difficult challenge. To understand the plasmonic-enhancement of the photo-electrochemical EOR, multiple Au-Fe2O3 were fabricated and evaluated in parallel with discrete dipole approximation (DDA) modeling. Different Au-Fe2O3 were synthesized with Au nanoparticles located at variable positions within and/or on the Fe2O3 layer(s). The configurations investigated include thin film, embedded, surface and sandwich layered electrodes to facilitate optimal electrode design considerations for plasmonic-enhancement. The design strategies and configurations were guided by DDA simulations to assess absorption, scattering, and near-field enhancements within or near the semiconductor band edge, as well as the solution/electrode interface. For the different Fe2O3 loadings and Au nanoparticle sizes/distributions considered, it is determined that the Au-Fe2O3 surface configurations significantly enhanced the EOR in terms of a large positive current density enhancement, an increased photo-voltage and a lower onset potential relative to the other electrode designs.
Herein, commercial Ni foam coated with self-assembled and linearly-aligned Ni wires is utilized as a cost-effective current collector for application in Li-O2 battery. The Ni wires are furthered deposited with graphene layers (g-Ni wire) to improve electrical conductivity. Multivalent Mn oxides consisting of Mn3O4, Mn2O3 and MnCO3 are used as effective oxygen reduction (ORR) and evolution reaction (OER) catalysts deposited on g-Ni wire current collectors. Specific capacities are respective ∼100 and ∼170 mAh g-1 without or with O2 introduction into the cell. The relative facile synthesis process requiring merely solution-based synthesis at ambient pressure, low temperature and short process time renders the Mn oxides/g-Ni wire electrode promising for Li-O2 battery application.