Fluorescence of CdSe/ZnS Quantum Dots in Toluene: Effect of Cyclic Temperature

Quantum dots (QDs) are the potential material for the application in optical thermometry, and have been successfully applied to solar cells, LEDs, bio-labeling, structural health monitoring, etc. In this paper, we study the fluorescence properties of CdSe/ZnS QDs in toluene under the action of heating-cooling cycles. The experimental results show that, in a heating-cooling cycle, increasing temperature causes red-shift of the emission peak and the decrease of the PL intensity, and decreasing temperature causes blue-shift of the emission peak and the increase of the PL intensity. The surface structures of the QDs likely are dependent on the cycle numbers, which cause the change of the excited energy state of the QDs in toluene. The results presented in this paper reveals the strong effects of cyclic temperature on the photoluminescence characteristics of QDs

Thermal Control of Electronics for Nuclear Robots via Phase Change Materials

AbstractAn effective thermal control is highly desired due to the increased heat generated from tight integration of electrical components. It is more difficult when the electronics are operating in high temperature, narrow space and strong nuclear radiation. In this paper, motor drivers of nuclear robots were taken as a case to study the thermal control methods and their effects on keeping the safe operation of electronics. Phase change materials (PCM) was found could lower the temperature by 20 oC and stabilize below 70 oC for more than 78min, which was 14 times longer than non-protective mode. Besides, the effect of heat sink on thermal conductivity enhancement was discussed

A High Quality and Quantity Hybrid Perovskite Quantum Dots (CsPbX\u3csub\u3e3\u3c/sub\u3e, X= Cl, Br and I) Powders Synthesis via Ionic Displacement

Recently, all-inorganic perovskites CsPbX3 (X= Cl, Br and I) quantum dots (QDs) have drawn great attentions because of their PL spectra tunable over the whole visible spectral region (400-700 nm) and adjustable bandgap, which revealed a promising potential on the field of photoelectronic devices, such as solar cells, LEDs and sensors. In this paper, CsPbX3 QDs and hybrid QDs, CsPbClxBr3-x and CsPbBrxI3-x were synthesized via one-step and two-step methods comparably. The optical bandgaps of CsPbCl3, CsPbBr3, and CsPbI3, were calculated as 3.08, 2.36, and 1.73eV, respectively, based on the Tauc\u27s equation and UV absorption spectra. Ionic displacement and phase transformation occurred during the mixing process were found based on the monitoring of PL spectra and HRTEM characterization. The long-term stability, dried, high quality and two-dimensional hybrid CsPbBrxI3-x QDs powders could be achieved via the two-step method. Polar solution inductions were used to wash and purify the CsPbX3 QDs, which help obtain of various compositions and well crystallize all-inorganic perovskites QDs powders

Shakedown, ratcheting and fatigue analysis of cathode coating in lithium-ion battery under steady charging-discharging process

The cyclic plasticity behaviour and failure mechanism of the cathode material in lithium-ion batteries urgently need to be understood due to the cyclic lithium-ion diffusion-induced stress during charging-discharging process. Many researches have focused on the shakedown and ratcheting responses of lithium-ion battery anode. However, the systematic investigation on the plasticity behaviour of lithium-ion battery cathode is still lacking. In this paper, the cyclic plasticity behaviour of LiNixMnyCozO2 electrode subjected to cyclic lithiation/delithiation under a constant mechanical load is investigated comprehensively. The shakedown, ratcheting and fatigue analyses of active layer are conducted using direct numerical techniques based on the Linear Matching Method framework, while coin cell electrochemical experiments are performed simultaneously to support the analysis. The effect of thickness of coating on the shakedown and ratcheting response is investigated, and the thickness is confirmed as a crucial parameter that can influence the battery performance. The strain-fatigue life curve is also obtained to effectively predict the life of active coating. Moreover, the numerical results reveal the existence of low cycle fatigue at the centre, and ratcheting mechanism on the edge of the cathode, which is consistent well with the experimental result

DDAB-assisted synthesis of iodine-rich CsPbI3 perovskite nanocrystals with improved stability in multiple environments

© 2020 The Royal Society of Chemistry. All-inorganic cesium lead halide perovskite (CsPbX3, X = Cl, Br, I) nanocrystals (NCs) have attracted considerable attention due to their tunable optical properties and high optical quantum yield. However, their stability in various environments, such as different solvents, high temperature and UV light, remains to be addressed to enable their exploitation in devices. Here, we report on the synthesis of all inorganic CsPbI3 perovskite nanocrystals capped with didodecyldimethylammonium bromide (DDAB). Monodispersed DDAB-capped CsPbI3 NCs have enhanced stability with respect to their morphological and optical properties compared to conventional oleic acid (OA)/oleylamine (OLA) capped nanocrystals. The DDAB-CsPbI3 NCs retain an optical quantum yield >80% for at least 60 days. The enhanced stability is explained by the binding of branched DDAB ligands to the NC surface, leading to the formation of a halogen-rich surface, as confirmed by X-ray photoelectron spectroscopy, with an iodine to lead atomic ratio of I : Pb = 4 : 1. These perovskites were used in light-emitting diodes (LEDs) and have a maximum external quantum efficiency (EQE) of 1.25% and a luminance of 468 cd m-2, and demonstrated improved operational performance. The enhanced stability of DDAB-CsPbI3 in the environments relevant for device processing and operation is relevant for their exploitation in optoelectronics

Cr2O3 nanoparticles boosting Cr–N–C for highly efficient electrocatalysis in acidic oxygen reduction reaction

Transition metal–nitrogen–carbon (M–N–C) catalysts have attracted significant attention for catalyzing oxygen reduction reactions (ORR). In this study, a porous Cr O @Cr–N–C catalyst with a small amount of Cr O nanoparticles loaded on the surface of Cr–N –C nanomaterials was prepared using synergistic heat treatment (SHT) method with zeolite imidazole frameworks (ZIFs) as precursors. TEM and spherical aberration-corrected TEM results demonstrated the presence of hollow morphologies, Cr O nanoparticles and atomic-level Cr distribution in Cr O @Cr–N–C. XPS, XRD and XAFS analysis indicated the coexistence of Cr O nanoparticles and Cr–N sites which were believed to act as active centers for ORR. In 0.1 M HClO , this material showed outstanding ORR catalytic activity with a half-wave potential of 0.78 V that was 40 mV higher than the traditional heat treatment derived Cr–N–C. It also revealed relatively low Tafel slope of 52.2 mV dec ; 4-electron pathway; remarkable stability and long-term durability. The improved ORR performance is mainly attributed to the synergy between Cr–N active center and Cr O nanoparticle. The SHT strategy reported here provides a new route to prepare highly efficient non-precious metal M−N–C catalysts with greater ORR activity and stability in acidic environments

基于应力场的锂离子电池正极多尺度失效研究

Lithium-ion batteries are widely used as energy storage and dynamic power, while the capacity life of battery is one of the key factors affecting its further application. The electrochemical-mechanical multi-field coupling effect of the lithium-ion batteries during the cyclic charging and discharging process cause the damage accumulation for the electrode materials, thereby deteriorates the mechanical stability of the electrode materials, leading to multi-scale damage to the electrode materials, ultimately declining the battery life. In this study, the multi-scale failure behavior of LiNixCoyMnzO2 (NCM) cathode materials were summarized through our previous research, and the experimental and simulation analysis method for studying the damage of electrode material are introduced systematically, to provide reference for selecting damage analysis methods at different scales. In addition, the failure mechanisms of NCM cathode materials at the scale of active particles and electrode coating were studied in-depth based on combination of experimental and simulated analysis, including electrochemical experimental of lithium-ion batteries, extended finite element method (XFEM), linear matching method (LMM) framework. The research work provides important guidance for the mechanism analysis of multi-scale failure behavior and microstructure modification of electrode materials

Numerical analysis of the cyclic mechanical damage of Li-ion battery electrode and experimental validation

Evidences have accumulated that the cyclic diffusion-induced stress within lithiation-delithiation process will result in the cyclically evolutive mechanical damage of battery electrode, which adversely affects the mechanical integrity as well as the performance of the Li-ion battery. In this work, the mechanical degradation of electrode under electrochemical-mechanical condition is innovatively evaluated as a fatigue damage process, governed by the interaction between diffusion behaviour and stress generation, and accumulated fatigue damage affected stress–strain response. Structural configuration of a layered electrode plate is modeled in finite element software ABAQUS and a set of user subroutines are developed to implement the proposed fatigue evaluation approach for battery electrode. The constructed approach is proved to be able to simulate multifarious categories of fatigue damage accumulation trends of battery electrode. The strategy to correlate the electrochemistry represented damage with mechanical fatigue damage are proposed. Experimental performance tests are conducted to parameterize the fatigue damage model within the assessment approach for electrode material LiNi0.5Mn0.3Co0.2O2 (NMC532). After parameterization, further circulating charging-discharging experiments and fatigue damage simulations with respect to different C-rate conditions are carried out to study the applicability of the proposed evaluation model as well as the assumption between electrochemical and mechanical deterioration. It is observed that the electrode surface adhering to electrolyte is more prone to fracture in the cycling operation. The present research work shows that it is available to apply the fatigue damage method to study the gradually mechanical failure of battery electrode under electrochemical-mechanical condition

Enhanced electrocatalytic oxygen reduction reaction for Fe-N4-C by the incorporation of Co nanoparticles

Oxygen reduction reaction (ORR) catalytic activity can be improved by means of enhancing the synergy between transition metals. In this work, a novel porous Fe-N4-C nanostructure containing uniformly dispersed Co nanoparticles (CoNPs) is prepared by an assisted thermal loading method. The as-prepared Co@Fe-N-C catalyst shows enhanced ORR activity with a half-wave potential (E1/2) of 0.92 V vs. RHE, which is much higher than those of the direct pyrolysis CoNP-free sample Fe-N-C (E1/2 = 0.85 V) and Pt/C (E1/2 = 0.90 V) in alkaline media. It exhibits remarkable stability with only a 10 mV decrease in E1/2 after 10 000 cycles and an outstanding long-term durability with 85% current remaining after 60 000 s. In acidic media, this catalyst exhibits catalytic activity with an E1/2 of 0.79 V, comparable to Pt/C (E1/2 = 0.82 V). X-ray absorption fine spectroscopy analysis revealed the presence of active centres of Fe-N4. Density functional theory calculations confirmed the strong synergy between CoNPs and Fe-N4 sites, providing a lower overpotential and beneficial electronic structure and a local coordination environment for the ORR. The incorporation of CoNPs on the surface of Fe-N4-C nanomaterials plays a key role in enhancing the ORR catalytic activity and stability, providing a new route to prepare efficient Pt-free ORR catalysts

The diffusion induced stress and cracking behaviour of primary particle for Li-ion battery electrode

Mechanical fracture is commonly regarded as one of key ingredients affecting the reliability of Li-ion battery electrode. In order to avoid the rapid mechanical collapse of electrode, attempts have been made to work on obtaining the accurate critical fracture condition for electrode particle with initial cracks under diffusion-induced stress produced in Li-ion intercalation and deintercalation process. However, considering the integrated fracture process on pristine particle, it is crucial to assess crack initiation phase in fracture analysis so as to obtain the comprehensive failure margins of three-dimensional primary particle. This paper evaluates the diffusion induced stress for NCM primary particle morphology under lithiation-delithiation condition, where the coevolving process of diffusion and stress generation is implemented with both diffusion driven approach and chemical potential driven approach by developing finite element subroutines. Based on the coupled diffusion-stress analyses, crack onset and growth of ternary cathode particle are studied by using ABAQUS extended finite element method (XFEM) with appropriate mesh density and verified by experimental observation. The integrated crack initiation and fracture margins with various current densities and particle dimensions are plotted. The innovative equations to acquire critical particle dimension for crack initiation and fracture under applied electrochemical load are established, which are significant for evaluating particle status. Associating the critical failure diagram with the size distribution of particles in NCM electrode samples, the failure proportion is presented for electrode in microscale. The impact of diffusion on active material property is also investigated comprehensively in stress evolution and fracture analysis