Small Decay Rate Research Articles

High Capacity and Fast Kinetics Enabled by Metal-Doping in Prussian Blue Analogue Cathodes for Sodium-Ion Batteries.

Prussian blue analogues (PBAs) have gained tremendous attention as promising low-cost electrochemically-tunable electrode materials, which can accommodate large Na+ ions with attractive specific capacity and charge-discharge kinetics. However, poor cycling stability caused by lattice strain and volume change remains to be improved. Herein, metal-doping strategy has been demonstrated in FeNiHCF, Na1.40Fe0.90Ni0.10[Fe(CN)6]0.85 ⋅ 1.3H2O, delivering a capacity as high as 148 mAh g-1 at 10 mA g-1. At an exceptionally high rate of 25.6 A g-1, a reversible capacity of ~55 mAh g-1 still can be obtained with a very small capacity decay rate of 0.02 % per cycle for 1000 cycles, considered one of the best among all metal-doped PBAs. This exhibits the stabilizing effect of Ni doping which enhances structural stability and long-term cyclability. In situ synchrotron X-ray diffraction reveals an extremely small (~1 %) change in unit cell parameters. The Ni substitution is found to increase the electronic conductivity and redox activity, especially at the low-spin (LS) Fe center due to inductive effect. This larger capacity contribution from LS Fe2+C6/Fe3+C6 redox couple is responsible for stable high-rate capability of FeNiHCF. The insight gained in this work may pave the way for the design of other high-performance electrode materials for sustainable sodium-ion batteries.

S-doped mesoporous graphene modified separator for high performance lithium-sulfur batteries

Due to their low cost, environmental friendliness and high energy density, the lithium-sulfur batteries (LSB) have been regarded as a promising alternative for the next generation of rechargeable battery systems. However, the practical application of LSB is seriously hampered by its short cycle life and high self-charge owing to the apparent shuttle effect of soluble lithium polysulfides. Using MgSO4@MgO composite as both template and dopant, template-guided S-doped mesoporous graphene (SMG) is prepared via the fluidized-bed chemical vapor deposition method. As the polypropylene (PP) modifier, SMG with high specific surface area, abundant mesoporous structures and moderate S doping content offers a wealth of physical and chemical adsorptive sites and reduced interfacial contact resistance, thereby restraining the serious shuttle effects of lithium polysulfides. Consequently, the LSB configured with mesoporous graphene (MG) as S host material and SMG as a separator modifier exhibits an enhanced electrochemical performance with a high average capacity of 955.64 mA h g−1 at 1C and a small capacity decay rate of 0.109% per cycle. Additionally, the density functional theory (DFT) calculation models have been rationally constructed and demonstrated that the doped S atoms in SMG possess higher binding energy to lithium polysulfides than that in MG, indicating that the SMG/PP separator can effectively capture soluble lithium polysulfides via chemical binding forces. This work would provide valuable insight into developing a versatile carbon-based separator modifier for LSB.

Dissipation-Driven Superradiant Phase Transition of a Two-Dimensional Bose–Einstein Condensate in a Double Cavity

Abstract We study superradiant phase transitions in a hybrid system of a two-dimensional Bose-Einstein condensate of atoms and two cavities arranged with a tilt angle. By adjusting the loss rate of cavities, we map out the phase diagram of steady states within a mean field framework. We find that when the loss rates of the two cavities are different, superradiant transitions may not occur at the same time in the two cavities. A first-order phase transition is observed between the states with only one cavity in superradiance and both in superradiance. In the case of both cavities are superradiant, a net photon current is observed flowing from the cavity with small decay rate to the one with large decay rate. The photon current shows a non-monotonic dependence on the loss rate difference, owing to the competition of photon number difference and cavity field phase difference. Our findings can be realized and detected in experiments.

Improving the capacity of quantum dense coding with both spontaneous emission and dephasing by non-Hermitian operation

Using a non-Hermitian operation approach, we propose a scheme to improve quantum dense coding of a qubit-qubit system interacting with a zero-temperature reservoir with both spontaneous emission and dephasing. By solving the master equation of the two-qubit system, we numerically obtain the final capacity of quantum dense coding. The numerical results show explicitly that the non-Hermitian operation indeed helps to improve the non-Hermitian operation from amplitude-phase decoherence. In particular, non-Hermitian operations can protect quantum dense coding more efficiently in the case of strong decay rates than those with small decay rates.

The effect of the nozzle exit geometry on the flow characteristics of the free condensing jet

In the present study, we investigated the velocity distribution, temperature distribution and condensation characteristics of steam jet issuing from four different orifice nozzles with a Reynolds number of approximately 79,000 using the phase Doppler particle analyzer system and a K-type thermocouple. The steam jet discharged from the orifice nozzle has a wider jet width compared to pipe nozzle because of the vena-contracta which can enhance the mixing of steam jet with the ambient air. Therefore, the orifice jet showed less condensation due to its wideness, resulting in small velocity decay rate and large temperature decay rate due to momentum conservation and decreased latent heat release compared to pipe nozzle, respectively. Also, the wider jet width of the orifice jet resulted in larger velocity and temperature spread rate compared to the pipe jet. In addition, the increase in the aspect ratio of the orifice jet led to more condensation and larger velocity spread rate and temperature spread rate due to both the vena-contracta and axis-switching effect, resulting in the increase of jet entrainment.

Theoretical perspective for hydrostatic pressure responsive mechanism of room temperature phosphorescence molecules

Stimulus-responsive organic room temperature phosphorescence (RTP) materials are a class of materials that show emission property changes when subjected to diverse environmental stimuli. The change of molecular stacking modes and intermolecular interactions can result in mechanical stimulus-induced emission switching behaviour. The underlying mechanism of mechanoresponsive luminescent material is still unclear. Herein, based on density functional theory and time-dependent density functional theory calculations, the photophysical properties with response to hydrostatic pressure of RTP molecules in crystal are theoretically studied. Excited state dynamic processes are investigated by using quantum mechanics and molecular mechanics method coupled with thermal vibration correlation function method. Results show that the increase of pressure can blue-shift the RTP emissions which is mainly caused by the change of molecular conformation and the increase of bending vibration frequency. Under 2 Gpa, large spin–orbit coupling effect is determined, remarkable radiative and non-radiative decay processes are achieved. At 0.6 Gpa, a small non-radiative decay rate from T 1 to S 0 is obtained, high efficiency and long lifetime (more than 10 times the other pressures) are realised. Through further analysing the staking modes, reorganisation energies and SOC constants, relationships between molecular structures and RTP properties are determined, hydrostatic pressure responsive mechanism is revealed.

High-cooperativity cavity magnon-polariton using a high-Qdielectric resonator

The hybrid system consisting of microwave photons and ferromagnetic magnons has been studied in the context of quantum sensing and quantum manipulation of magnons. We demonstrate a strong coupling between magnons and photons in a dielectric resonator with a large dielectric constant and high quality factor. The coupling rate between magnons and photons amounts to g/2π=126 MHz, and the corresponding cooperativity reaches C=1.09×106 at cryogenic temperature. The high cooperativity is mainly due to the small internal decay rate of the resonator, which is advantageous for various quantum magnonics experiments.

Gain of a High-Impedance Cavity Coupled to Strongly Driven Semiconductor Quantum Dots

The architecture of artificial atoms coupled to superconducting cavities allows the study of light-matter interactions and intriguing phenomena such as cavity gain implying photon generation. Here, we integrate a high-impedance cavity with a double quantum dot (DQD) in GaAs/(Al,Ga)As heterostructures, achieving a considerable DQD-cavity coupling strength and a relatively small cavity decay rate. By applying a strong drive to the DQD, we realize a population inversion and observe the cavity amplitude gain in multiple regions in the measured Landau-Zener-St\"uckelberg-Majorana interference pattern. We further systematically investigate the dependence of cavity gain on the driving frequency and tunnel coupling strength of the DQD. The results show that the cavity gain is tunable, with a maximum value of approximately $1.16$ in the measured range. Our experimental results are in good agreement with theoretical simulations and may provide an opportunity to implement on-chip microwave sources or microwave amplifiers in a controllable way.

Noise Sensitivity Reduction in Low-power Multi High Gain Observers Using Low-pass Filters

Low-power multi high gain observers (LP MHGO) are proven to be effective in reducing the peaking of state estimation of nonlinear systems to an arbitrarily small magnitude. Moreover, they reduce the sensitivity of estimates to measurement noise. They also relax the numerical implementation problem of high gain observers by using gains powered up to the order of 2 instead of n. In this paper, we aim to further reduce the noise sensitivity of these observers by employing low-pass filters in the observer dynamics. The main results establish the convergence of the estimation error to zero with an arbitrarily small decay rate in the absence of noise, as well as an input to state stability feature when the noise is present. We also demonstrate in the linear case that the proposed observer improves the upper bound on the estimates. Simulation results compare the performance of the proposed observer with similar works and show the effectiveness of the proposed method.

Effect of CeO2-x-CNT/S cathode on the electrochemical performance of lithium-sulfur batteries

Despite extensive research into cerium oxide as a cathode for lithium-sulfur batteries, there are still problems with low specific capacity and high decay rate. This paper used a simple gas reduction method to prepare CeO2-x nanoparticles with more oxygen vacancies. It has been demonstrated experimentally that the presence of oxygen defects increases the electrochemical reaction rate. Using CeO2-x-CNT/S as cathode for lithium-sulfur battery not only improves the conductivity of cathode, but also restricts the movement of polysulfide. The CeO2-x-CNT/S cathode exhibits good electrochemical properties. The first discharge specific capacity of CeO2-x-CNT/S cathode is 1556.8 mAh g -1 at 0.1C. The initial discharge specific capacity is 1233.9 mAh g -1 at 0.5C, and has a small capacity decay rate after 600 cycles. It provides a new answer to the problems in lithium-sulfur batteries.

Mixed-dimensional V2CTx/Ti3C2Tx composite interlayer to boost electrochemical performance of Li-S batteries.

: A mixed-dimensional V2CTx/Ti3C2Tx composite interlayer was successfully prepared to tackle severe polysulfide (LiPS) shuttling and sluggish sulfur redox kinetics for high-performance lithium–sulfur batteries. In the unique nanoarchitecture, two-dimensional Ti3C2Tx nanosheets served as a stable skeleton with superb electronic conductivity, good mechanical strength, and high polysulfide adsorption, whereas one-dimensional V2CTx nanorods played a crucial role in chemisorbing LiPSs and catalyzing the conversion of LiPSs due to their high polarity and electrocatalysis. With the synergistic effect of V2CTx and Ti3C2Tx composite nanostructures, the cells with the mixed-dimensional V2CTx/Ti3C2Tx composite interlayer showed an impressive long-term cycling stability and small capacity decay rate of 0.062% per cycle over 600 cycles at 1 C and exhibited an outstanding rate capability of 935.3 mAh·g−1 at 2 C.

Mid-IR spectroscopy of Er3+doped low-phonon CsCdCl3and CsPbCl3crystals

The mid-IR spectroscopic properties ofEr3+doped low-phononCsCdCl3andCsPbCl3crystals grown by the Bridgman technique have been investigated. Using optical excitations at∼800nmand∼660nm, both crystals exhibited IR emissions at∼1.55,∼2.75,∼3.5, and∼4.5µmat room temperature. The mid-IR emission at 4.5 µm, originating from the4I9/2→4I11/2transition, showed a long emission lifetime of∼11.6msforEr3+dopedCsCdCl3, whereasEr3+dopedCsPbCl3exhibited a shorter lifetime of∼1.8ms. The measured emission lifetimes of the4I9/2state were nearly independent of the temperature, indicating a negligibly small nonradiative decay rate through multiphonon relaxation, as predicted by the energy-gap law for low-maximum-phonon energy hosts. The room temperature stimulated emission cross sections for the4I9/2→4I11/2transition inEr3+dopedCsCdCl3andCsPbCl3were determined to be∼0.14×10−20cm2and∼0.41×10−20cm2, respectively. The results of Judd–Ofelt analysis are presented and discussed.

Synthesis and photophysical studies on cyclometalated iridium complexes containing various monodentate phenyl-azole ancillary ligands

In this study, five cyclometalated iridium complexes containing phenyl-azole ancillary ligands were synthesized and characterized by X-ray crystallography, and their photophysical properties were studied. The reaction of [Ir(ppy)2(μ-Cl)]2 (ppy: 2-phenylpyridine) with pim (4-phenylimidazole), ptr4h (4-phenyl-4H-1,2,4-triazole), and ptr1h (1-phenyl-1H-1,2,4-triazole) ligands furnished mononuclear [Ir(ppy)2ClL] complexes (1–3; L = pim, ptr4h, ptr1h) featuring monodentate neutral N → Ir coordination. In contrast, the corresponding reaction with ptz (5-phenyl-1H-tetrazole) ligand yielded a hetero-bridged dimeric iridium complex, [Ir(ppy)2(μ-Cl)(μ-ptz)Ir(ppy)2] (4). Notably, adding dimethylsulfoxide (DMSO) solvent to complex 4 resulted in its division to [Ir(ppy)2(ptz)(DMSO)] (5) and [Ir(ppy)2Cl(DMSO)]. Complexes 1–4 exhibited blue-green phosphorescence in solution with marginal shifts in the emission wavelengths. Complex 1, having a pim ligand, exhibited a significantly higher phosphorescence quantum efficiency (ΦPL = 31%) than those of complexes 2–4 (ΦPL = 4–9%), which was attributed to the relatively small non-radiative decay rate constant in 1. Density functional theory calculations confirmed that the phosphorescence has originated from both the metal–ligand charge transfer (3MLppyCT) and the ligand-centered (3LCppy) states. An increased LC character was observed in the phosphorescence of the dinuclear complex 4.

Three-Dimensional Carbon-Catalyst As Sulfur Host for Polysulfide Regulation in Lithium-Sulfur Batteries

The ever-growing industrial society demand for limited natural resources and global energy consumption have given rise to the fast development of renewable energy storage technologies. Rechargeable batteries are considered to be indispensable for storing the supply of clean-but-intermittent energy sources, including solar and wind, in an efficiently and economically viable manner. Specifically, lithium-ion batteries (LIBs) with the reliable power capability and relatively mature storage mechanisms are commercialized in the market. However, due to shortage, high prices of lithium minerals, the physical energy density limits of innately available crystal sites, LIBs are unlikely to satisfy the need for grid-scale energy storage system in the long run. The urgent research for alternative sustainable energy storage device has led to the study of lithium-sulfur batteries (LSBs). With the new chemistries based on multi-electron conversion reaction between sulfur and lithium, LSBs are attracting great attention owing to large theoretical energy density of 2600 W h kg−1, high natural abundance and low cost of the sulfur source. Yet, despite their intriguing virtues, the fulfillment of sulfur electrochemical performance is perplexed by several intractable challenges that cause undesirable capacity fading and cycling life. Triggered by continuous round-trip diffusion in ether-based electrolyte, the shuttling effect of highly active lithium polysulfides (LiPSs) will eventually cause severe sulfur loss, electrode decomposition, and Coulombic inefficiency in LSBs. Targeting this issue, we proposed the synthesis of a novel sulfur host in cathode based on a honeycomb-like, porous nitrogen-doped carbon network consisting of MoC with three-dimensional architecture as sulfur host to suppress the shuttling behavior of LiPSs. Benefiting from the interconnected carbon with strong physical adsorption and MoC planes as catalytic sites for acceleration of redox kinetics. We demonstrated experimentally here that this sulfur reservior could realize the improved cell performance with high electronic conductivity, excellent sulfur chemisorption, high rate capacity with 1316 at 0.1 C, 646mAh g-1 at 3C, and long cycling stability with a small capacity decay rate.

Competing reduction induced homogeneous oxygen doping to unlock MoS2 basal planes for faster polysulfides conversion

The parasitic polysulfides shuttle effect greatly hinders the practical application of lithium sulfur batteries, and this issue can be addressed by promoting polysulfides conversion with catalytic materials such as MoS2. However, the catalytic activity of MoS2 mainly relies on edge sites, but is limited by inert basal planes. We herein report a novel, facile, ethylene glycol enabled competing reduction strategy to dope MoS2 homogeneously with oxygen atoms so that its inert basal planes can be unlocked. Ethylene glycol works as a reducing agent and competes with thiourea to react with ammonium molybdate, leading to insufficient sulfuration of Mo, and consequent formation of O-MoS2. Our theoretical and experimental investigations indicate that the homogeneously distributed O dopants can create abundant adsorption/catalytic sites in the MoS2 basal planes, enlarge the inter-plane distance to promote ion transport, and thus enhance the catalytic conversion of polysulfides. The oxygen doped MoS2 (O-MoS2) is supported on carbon nanosheets (CNS) and the composite (O-MoS2/CNS) is employed to modify the separator of Li–S battery. It gives the battery an initial discharge capacity of 1537 mAh g−1 at 0.2 C, and the battery retains a discharge capacity of 545 mAh g−1 after ultra-long 2000 cycles at 1 C, corresponding to a very small cyclic decay rate of 0.0237%. Even under a raising sulfur loading of 8.2 mg cm−2, the Li-S battery also delivers a high discharge capacity (554 mAh g−1) with outstanding cycle stability (84.6% capacity retention) after 100 cycles at 0.5 C. Our work provides a novel, facile approach to fabricate highly catalytically active oxygen-doped MoS2 for advanced Li–S batteries.

Interface behavior and removal mechanisms of human pathogenic viruses in anaerobic membrane bioreactor (AnMBR)

Effective removal of human pathogenic viruses is an indispensable yet rarely studied aspect for sustainable treatment of domestic wastewater by anaerobic membrane bioreactor (AnMBR). In this study, the interface behaviors and removal mechanisms of norovirus genogroup I (GI), genogroup II (GII), and rotavirus A from domestic wastewater was systematically investigated in a one-stage AnMBR. On average, norovirus GI, GII and rotavirus were reduced by 4.64, 5.00, and 2.31 logs, respectively. Viruses tended to be transferred to larger-sized suspended solids from sewage influent to the mixed liquor, and the weight-specific concentration of the virus in >100 μm particles of the mixed liquor was significantly higher than that of sewage, indicating a particle scale-dependent affinity with the virus. In-series membrane filtration test showed the main contribution of the membrane retention, which was dominated by the bio-cake layer and the pristine membrane, while the membrane and associated pore foulants can retain viruses in a filtration resistance-efficient way. An unsteady-state mass balance model revealed that free viruses in the bulk liquid of AnMBR were minimally attached to the cake layer but mainly retained by the membrane and pore foulants (>99%). In addition, despite the small virus decay rates in the mixed liquor, the associated contribution increased with run time due to the prolonged sludge retention time. These insights into virus behaviors and removal mechanisms may provide novel regulation strategies for enhanced virus removal by AnMBR.

Spectroscopic study of Er-doped Ga2Ge5S13 glass for mid-IR laser applications

We present mid-IR spectroscopic characterization of the low-phonon chalcogenide glass, Ga2Ge5S13 (GGS) doped with Er3+ ions. Under the excitation at ∼800 nm, Er3+:GGS exhibited broad mid-IR emission bands centered at ∼2.7, ∼3.5, and ∼4.5 µm at room temperature. The emission lifetime of the 4I9/2 level of Er3+ ions in GGS glass was found to be millisecond-long at room temperature. The measured fluorescence lifetimes were nearly independent of temperature, indicating negligibly small nonradiative decay rate for the 4I9/2 state, as can be expected for a low-maximum-phonon energy host. The transition line-strengths, radiative lifetimes, fluorescence branching ratios were calculated by using the Judd-Ofelt method. The peak stimulated emission cross-section of the 4I9/2 → 4I11/2 transition of Er3+ ion was determined to be ∼0.10×10−20 cm2 at room temperature.

Modulating the temporal dynamics of nonlinear ultrafast plasmon resonances

Surface plasmon-induced nonlinear optical resonances have shown immense potential in advanced optical imaging and nonlinear photonic devices. However, the ultrashort lifetime of these intense nonlinear fields inhibits their effective use in the vast applications of quantum plasmonics. Here, we propose enhancement in the lifetime of fast decaying second harmonic (SH) plasmon mode through a weak and pure resonant interaction with a two-level quantum emitter (QE). We compute the time evolution of SH response under a two-coupled oscillator model, in which we examine the interaction of short-lived SH mode supported by Au nanoparticle (AuNP) with long-lived dark mode (DM) or QE systems. To analyze the effect of spectral and temporal properties of DM and QE on the SH field, we evaluate the lifetime enhancement factor as a function of coupling strength and tuned resonant frequencies. The results show that tiny object like QE with sharp spectral bandwidth, small decay rate, and large oscillating strength is more efficient to control and probe the temporal dynamics of the SH field, as compared to DM which have a wide spectral bandwidth. Also, we control the lifetime of the SH mode after the natural decay time of the fundamental mode (FM), which distinguishes SH mode irrespective of its spatial convolution with elementary modes. Our proposed AuNP-QE coupled plasmonic system supporting nonlinear signal with enhanced temporal character paves its way for designing efficient on-chip nonlinear optical devices and can be a powerful tool in ultrahigh resolution nonlinear optical imaging.

A transient model for charge and mass transfer through anion exchange membranes in vanadium redox flow batteries

Vanadium redox flow batteries (VRFBs) with anion exchange membranes (AEMs) exhibit a high columbic efficiency and slow capacity decay due to the reduced crossover rate of vanadium ions. Modeling of this promising type of flow battery is challenging because of the difficulty in the description of charge and mass transfer through AEMs. In this work, we propose a transient model for VRFBs with AEM, which incorporates the ion selective adsorption to overcome the inaccurate description of ion distributions in AEM, and improves the transport coefficients to avoid their changes with different electrolytes, thereby introducing AEM parameters such as porosity and fixed charges into the description of charge and mass transfer. It shows that the simulation results of ion selective adsorption are highly consistent with the experiment; the effects of AEM parameters on transport processes and battery performance are well captured. Interestingly, it is found that the current density in AEM is carried by both H+ and HSO4− ions, and the proportion of H+ ions is quite large. At high current densities, an increase in AEM porosity greatly improve the voltage efficiency while maintaining a high coulombic efficiency. Meanwhile, small capacity decay rate can be obtained by adjusting fixed concentration.

Поляритонный резонанс в автомодуляции асимметричного состояния сверхизлучающего лазера

Based on the numerical solution to the semiclassical Maxwell-Bloch equations in a one-dimensional model of a superradiant laser with a low-Q symmetric Fabry-Perot cavity, a comparative analysis of the spectrum of polariton modes of the linearized problem and the discrete spectrum of the of quasi-monochromatic generation with weak self-modulation under the condition of strong spontaneous mirror symmetry breaking of the counterpropagating electromagnetic waves, population inversion and polarization of an active medium is carried out. It is shown that the main frequencies of resonant self-modulation of a steady asymmetric superradiant phase state are close to the frequencies of polariton modes that are calculated in the linearized problem for the average level of the population inversion taken from the nonlinear problem and have small decay rates.