Ultrafast Kinetics Research Articles

High-yield production of monolayer boron nitride nanosheets by cationic-surfactant-assisted solvothermal exfoliation for the ultrafast and selective separation of U(VI) from lanthanides

The efficient separation and recovery of uranium(VI) (U(VI)) from lanthanides is pivotal to reduce the radioactive threat of hydrometallurgical residue solution of lanthanide minerals and benefits the sustainability of U resources. Here, we develop a cationic-surfactant-assisted solvothermal exfoliation method to prepare monolayer boron nitride nanosheets (BNNSs) for the ultrafast and selective separation of U(VI) from lanthanides. With the assistance of the strong “cation–π” interaction between cationic surfactants and BN, the monolayer BNNSs were prepared. Functionalization with diamide phenanthroline (DAPhen) groups endows the pristine BNNSs, which can hardly adsorb U(VI), with outstanding U(VI) adsorption performance. Batch adsorption experiments demonstrate that the obtained DAPhen modified BNNSs (BNNSs-DAPhen) exhibited high maximum adsorption capacity and ultrafast adsorption kinetics. The adsorption process reached equilibrium less than 1 min and the maximum adsorption capacity was estimated to be 313 mg g−1 by fitting with Langmuir model. Even under high concentrations of salts and acids, BNNSs-DAPhen still maintained excellent adsorption performance owing to the strong complexing ability of DAPhen groups with U(VI). The selectivity coefficients of U(VI) toward various lanthanides including lanthanum(III), cerium(III), europium(III), gadolinium(III), ytterbium(III), and lutetium(III) were beyond 120 at a high nitric acid concentration of 5 mol L−1. This work proposed a universal strategy for the production of monolayer BNNSs and the subsequent functionalization, which might be promising in the treatment of residual solution for lanthanides hydrometallurgy and decontamination of U(VI).

Ultrafast selective adsorption of pretreatment inhibitors from lignocellulosic hydrolysate with metal-organic frameworks: Performance and adsorption mechanisms

• Four MOFs were evaluated for adsorption of furfural and four phenolic inhibitors. • MIL-140C exhibited excellent adsorption capacity and ultrafast adsorption kinetics. • MIL-140C demonstrated good reusability and high stability. • Possible adsorption mechanisms were proposed. In this work, four metal-organic frameworks materials (MOFs, MIL-140A, MIL-140C, MIL-101(Fe) and NH 2 -MIL-101(Fe) were prepared, characterized and compared for the adsorptive removal of furfural and four phenolic inhibitors. MIL-140C demonstrated the best adsorption capability among the tested MOFs. Effects of pH, ionic strength, contact time, adsorbent dosage, temperature and sugars on adsorption of inhibitors on MIL-140C were systematically investigated. Inhibitors adsorption was ultrafast within minutes and kinetic data fitted pseudo-second-order model well. The Langmuir isotherm described the adsorption process satisfactorily with maximum adsorption capacities of 222.72, 240.38, 231.48, 207.04 and 60.79 mg/g for vanillin, syringaldehyde, ferulic acid, p-coumaric acid and furfural, respectively. Thermodynamic parameters disclosed that nature of the adsorption was exothermic and spontaneous under the experimental conditions. MIL-140C demonstrated exceptional adsorption selectivity towards inhibitors even with excessive amount of xylose and glucose, as well as excellent regeneration performance after five adsorption/desorption cycles. MIL-140C also exhibited satisfactory detoxification performance after treatment of real corn stover dilute acid hydrolysate. Furthermore, analysis of underlying adsorption mechanism showed that π-π interaction, hydrophobic interaction and hydrogen bonding/metal-coordination (depending on solution pH) were involved in the adsorption of tested phenolic inhibitors, while the π-π and hydrophobic interactions contributed to the furfural adsorption. The overall results revealed that MIL-140C could hold great promise in removing phenolic and furan inhibitors from lignocellulosic hydrolysate.

Highly efficient and selective Hg(II) removal from water by thiol-functionalized MOF-808: Kinetic and mechanism study

Mercury pollution poses a serious threat to the ecological environment and public health due to its high toxicity and persistence, but there is still a lack of rapid and effective Hg(II) removal technology, especially emergency response of Hg(II) leakage. Herein, an effective metal-organic framework adsorbent, MOF-808-SH, was fabricated by grafting thioglycollic acid on MOF-808 for Hg(II) removal. The MOF-808-SH demonstrated high adsorption capacity of 977.5 mg/g, impressively ultrafast adsorption kinetics (C0 = 10 mg/L, removal > 99 % in 10 s) with a rate constant k of 36.89 g mg−1 min−1, which is dozens of times faster than that of ever reported Hg(II) adsorbents. Batch experiments show that MOF-808-SH exhibits high selectivity toward Hg(II) with a distribution coefficient Kd as high as 5.0×106 mL/g. Moreover, MOF-808-SH exhibits excellent recyclability with a negligible loss of capacity after 6 adsorption-regeneration cycles. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectrometry (XPS) unveil that the –SH groups in MOF-808-SH are the key adsorption sites, and specific inner-sphere coordination with Hg(II) is responsible for the high selectivity. In addition, large surface area, well-developed porous structures and high –SH loading of MOF-808-SH reasonably explains ultrafast kinetics and high adsorption capacity for Hg(II). This study indicates the potential of MOF-808-SH to remove Hg(II) from wastewater.

Elucidating molecular mechanisms of two-dimensional chemical reactions

Elucidating molecular mechanisms of two-dimensional chemical reactions

"Water-in-Sugar" Electrolytes Enable Ultrafast and Stable Electrochemical Naked Proton Storage.

Proton is an ideal charge carrier for rechargeable batteries due to its small ionic radius, ultrafast diffusion kinetics and wide availability. However, in commonly used acid electrolytes, the co-interaction of polarized water and proton (namely hydronium) with electrode materials often causes electrode structural distortions. The hydronium adsorption on electrode surfaces also facilitates hydrogen evolution as an unwanted side reaction. Here, a "water-in-sugar" electrolyte with high concentration of glucose dissolved in acid to enable the naked proton intercalation, as well as an extended 3.9V working potential window, is shown. A glucose-derived organic thin film is formed on electrode surface upon cycling. Molecular dynamics simulations reveal the significant decrease of free water in bulk electrolytes, while density functional theory calculations indicate that glucose preferentially binds to the electrode surface which can inhibit water adsorption. The scarcity of free water and the protective organic film work in synergy to suppress water interactions with the electrode surface, which enables the naked proton (de)intercalation. The "water-in-sugar" electrolyte significantly enhances a MoO3 electrode for stable cycling over 100000 times. This facile electrolyte approach opens new avenues to aqueous electrochemistry and energy storage devices.

Peroxymonosulfate activation by Fe3O4-MnO2/CNT nanohybrid electroactive filter towards ultrafast micropollutants decontamination: Performance and mechanism

Electrocatalytic peroxymonosulfate (PMS) activation is a promising advanced oxidation process for the degradation of micropollutants. Herein, we developed an electroactive carbon nanotube (CNT) filter functionalized with Fe3O4-MnO2 hybrid (Fe3O4-MnO2/CNT) to activate PMS towards ultrafast degradation of sulfamethoxazole (SMX). SMX was completely degraded via a single-pass through the nanohybrid filter (τ < 2 s). The ultrafast degradation kinetics were maintained across a wide pH range (from 3.0 to 8.0), in complicated matrices (e.g., tap water, lake water, WWTP effluent and pharmaceutical wastewater), and for the degradation of various persistent micropollutants. Compared with a conventional batch reactor, the flow-through operation provides an 9.2-fold higher SMX degradation kinetics by virtue of the convection-enhanced mass transport (1.47 vs. 0.16 min−1). The efficient redox cycle of Fe2+/Fe3+ and Mn2+/Mn4+ facilitate the PMS activation to generate SO4•– under electric field. Meanwhile, the ketonic groups on the CNT provide active sites for the generation of 1O2. Both experimental and theoretical results revealed the superior activity of nanohybrid filter associated with the synergistic effects among Fe, Mn, CNT and electric field. Therefore, the electrocatalytic filter based PMS activation system provides a green strategy for the remediation of micropollutants in a sustainable manner.

Simulations of the Ultra-Fast Kinetics in Ni-Si-C Ternary Systems under Laser Irradiation.

We present a method for the simulation of the kinetic evolution in the sub µs timescale for composite materials containing regions occupied by alloys, compounds, and mixtures belonging to the Ni-Si-C ternary system. Pulsed laser irradiation (pulses of the order of 100 ns) promotes this evolution. The simulation approach is formulated in the framework of the phase-field theory and it consists of a system of coupled non-linear partial differential equations (PDEs), which considers as variables the following fields: the laser electro-magnetic field, the temperature, the phase-field and the material (Ni, Si, C, C clusters and Ni-silicides) densities. The model integrates a large set of materials and reaction parameters which could also self-consistently depend on the model variables. A parameter calibration is also proposed, specifically suited for the wavelength of a widely used class of excimer lasers (λ = 308 nm). The model is implemented on a proprietary laser annealing technology computer-aided design (TCAD) tool based on the finite element method (FEM). This integration allows, in principle, numerical solutions in systems of any dimension. Here we discuss the complex simulation trend in the one-dimensional case, considering as a starting state, thin films on 4H-SiC substrates, i.e., a configuration reproducing a technologically relevant case study. Simulations as a function of the laser energy density show an articulated scenario, also induced by the variables’ dependency of the materials’ parameters, for the non-melting, partial-melting and full-melting process conditions. The simulation results are validated by post-process experimental analyses of the microstructure and composition of the irradiated samples.

Metallic V5S8 microparticles with tunnel-like structure for high-rate and stable zinc-ion energy storage

Rechargeable aqueous zinc-ion batteries (AZIBs) are tremendously competitive in terms of cost-economy and safe-operation. However, their development is significantly hampered by the lack of stable cathode materials allowing robust zinc-ion diffusion. Herein, it is firstly reported that a facile synthesis V5S8 with tunnel-like crystal structure, even in micron-size form, can be investigated as a superior intercalated cathode material for AZIBs, which delievers a high capacity of 240 mAh g−1 at 0.1 A g−1 and a record capacity retention of 94% (182 mAh g−1) after 1000 cycles at a high current density of 10 A g−1. Density functional theory (DFT) calculations show that V5S8 has a strong metallic characteristic and an optimal zinc-ion diffusion path with a low hopping energy barrier, boosting the distinctly fast transport capability of both electrons and ions. Consequently, an unprecedented rate capacity retention of 80.75% was obtained when the current density underwent a hundred-fold change, and the ultrafast ion migration kinetics along with desirable pseudocapacitive behaviors were further confirmed. Moreover, using in-situ synchrotron X-ray diffraction, ex-situ X-ray photoelectron spectroscopy, and DFT calculations, this study provides significant insight into the reaction mechanism of the V5S8 cathode with self-adaptive multistage ion storage.

Ultrafast Kinetics Investigation of a Fluorinated-Benzothiadiazole Polymer with an Increased Excited State Transition Dipole Moment Applied in Organic Solar Cells

Ultrafast Kinetics Investigation of a Fluorinated-Benzothiadiazole Polymer with an Increased Excited State Transition Dipole Moment Applied in Organic Solar Cells

Machine-learning model selection and parameter estimation from kinetic data of complex first-order reaction systems.

Dealing with a system of first-order reactions is a recurrent issue in chemometrics, especially in the analysis of data obtained by spectroscopic methods applied on complex biological systems. We argue that global multiexponential fitting, the still common way to solve such problems, has serious weaknesses compared to contemporary methods of sparse modeling. Combining the advantages of group lasso and elastic net-the statistical methods proven to be very powerful in other areas-we created an optimization problem tunable from very sparse to very dense distribution over a large pre-defined grid of time constants, fitting both simulated and experimental multiwavelength spectroscopic data with high computational efficiency. We found that the optimal values of the tuning hyperparameters can be selected by a machine-learning algorithm based on a Bayesian optimization procedure, utilizing widely used or novel versions of cross-validation. The derived algorithm accurately recovered the true sparse kinetic parameters of an extremely complex simulated model of the bacteriorhodopsin photocycle, as well as the wide peak of hypothetical distributed kinetics in the presence of different noise levels. It also performed well in the analysis of the ultrafast experimental fluorescence kinetics data detected on the coenzyme FAD in a very wide logarithmic time window. We conclude that the primary application of the presented algorithms-implemented in available software-covers a wide area of studies on light-induced physical, chemical, and biological processes carried out with different spectroscopic methods. The demand for this kind of analysis is expected to soar due to the emerging ultrafast multidimensional infrared and electronic spectroscopic techniques that provide very large and complex datasets. In addition, simulations based on our methods could help in designing the technical parameters of future experiments for the verification of particular hypothetical models.

Investigation of Ultrafast Carrier Dynamics in InGaN/GaN‐Based Nanostructures Using Femtosecond Pump–Probe Absorption Spectroscopy

GaN‐based optoelectronic devices including light‐emitting diodes and lasers realized with quantum‐confined nanostructures, revolutionized the solid‐state lighting. Excited‐state ultrafast nonlinear dynamics of these nanostructures are crucial in determining the device performance in terms of luminescence efficacy, emission spectra, wall‐plug efficiency, turn‐on delay, lasing threshold current, and modulation bandwidth. Therefore, understanding the carrier and photon dynamics of these nanostructures is of utmost importance. A comparative investigation of ultrafast nonlinear carrier‐photon dynamics of 2D, 1D, and 0D InGaN/GaN nanostructures is carried out. Femtosecond pump–probe absorption spectroscopy is used uniformly herein to obtain the wavelength‐dependent ultrafast kinetics of these nanostructures, with a temporal resolution of ≈50 fs. Carrier thermalization and relaxation processes of all the samples are studied both experimentally and theoretically. Distinguished phenomena, such as fast carrier trapping and subsequent detrapping of the carriers from sub‐bandgap defect states are observed. Real‐time monitoring of quantum confined Stark effect, enhanced radiative recombination, and diffusion‐limited carrier kinetics are manifested. Carrier capture and recombination time constants are calculated theoretically, considering quantum properties. Theoretical values are in good agreement with the experimental observations. In addition, transient absorption spectroscopy is used to investigate and decouple the surface and the bulk properties of GaN surfaces.

Ultrafast kinetics and high capacity for Stable Sodium Storage enabled by Fe3Se4/ZnSe heterostructure engineering

The development of advanced sodium-ion batteries is hindered by the low sluggish kinetics and electrochemical performance. In this work, heterostructure-decorated core-shell Fe3Se4/ZnSe@carbon (Fe3Se4/ZnSe@C) nanospheres were designed to boost the kinetics. The electrochemical and structural study results demonstrate that hetero-interfaces between Fe3Se4 and ZnSe not only propel fast transport of charges but also effectively enhance the reaction kinetics. The carbon shell enables to improve the electronic conductivity and maintains the structural stability of the active materials. In addition, the electrochemical mechanism is also investigated via the in-situ X-ray diffraction technique. When the resulted Fe3Se4/ZnSe@C composite material is employed as the anode materials of sodium-ion batteries, it shows ultrafast charging-discharging kinetics and outstanding cycling stability with a high capacity retention of 473.8 mAh g−1 after 300 cycles at a large current density of 5 A g−1. This work offers a strategy of enhancing reaction kinetics as well as a synthetic route for high-performance anode materials for sodium storage.

Implanting Ru nanoclusters into N-doped graphene for efficient alkaline hydrogen evolution

Electrocatalytic hydrogen evolution reaction (HER) in alkaline media is important for low-cost hydrogen production in industry. Developing catalysts with ultrafast water dissociation kinetics and decent activity are main challenges for alkaline HER. Here, we report a two-step pyrolysis method to construct Ru nanoclusters uniformly deposited on nitrogen-doped graphene for efficient alkaline HER. The catalyst shows an exceptional intrinsic activity with a low overpotential of 25.9 mV at 10 mA cm−2 and a low Tafel slope of 32.6 mV dec−1 in alkaline media. Density functional theory calculations indicate that the Ru-based nanoclusters exhibit good ability for water dissociation, giving rise to the superior hydrogen evolution activity. This work shines fresh light on fabricating highly efficient catalysts for alkaline HER, as well as provides a deep insight on the reaction mechanism of Ru-based catalysts under alkaline conditions.

(Invited) Tuning Interlayer Exciton Energetics in Twisted and Stacked Materials

Using time-space resolved ultrafast microscopy on individual 2D crystal grains, we show how long-range interlayer electronic coupling can be selectively enhanced either by applying an E-field or by twisting the layer stacking orientation. In both cases, transient interlayer exciton states form and drive the optoelectronic material response. Considering first twisted bilayer graphene (tBLG), we discovered how stacking-angle tunable absorption resonances form a strongly-bound exciton state as a consequence of the symmetrized rehybridization of the interlayer 2p orbitals.[1] Using two-photon photoluminescence and intraband-transient absorption microscopies, we have recently imaged the photoemission and exciton dynamics from single-grains of tBLG. After resonant excitation, our results suggest the formation of strongly-bound (up to 690 meV), metastable interlayer exciton states. Our observation of resonant PL emission from twisted bilayer graphene materials in Fig. 1a is best explained by the theoretically predicted coexistence of strongly-bound interlayer excitons and metallic graphene continuum states. We show how stacking angle -tunable interlayer excitons states may permit new photocurrent extraction routes from quasi-stable interlayer excitons.Unlike stacked graphene, semiconducting 2D transition metal dichalcogenides (TMDCs) have diffuse interlayer d-orbital overlap. To enhance interlayer electronic coupling in TMDCs, we apply an interlayer directed E-field, inducing electron-hole dissociation [2]. Time-resolved photocurrents show that stacked WSe2 devices can have both IQE >50% and fast (<60 ps) picosecond electron escape times. Our ultrafast photocurrent rates kinetics give the same E-field-dependent electronic escape and dissociation rates seen from optical ultrafast microscopy. To confirm the fast electronic escape rates, we show the ratio of the electronic rates accurately matches our overall WSe2 device IQE in the limit of zero Auger recombination. Collectively, we show how optical and photocurrent-based ultrafast microscopies together provide an analytical extraction of the photocurrent-generating ultrafast dynamics in both TMDCs and tBLG van der Waals stacked materials.

Tuning the intermediate reaction barriers by a CuPd catalyst to improve the selectivity of CO2 electroreduction to C2 products

Electrochemical CO2 reduction is a promising strategy for the utilization of CO2 and intermittent excess electricity. Cu is the only single metal catalyst that can electrochemically convert CO2 into multicarbon products. However, Cu exhibits an unfavorable activity and selectivity for the generation of C2 products because of the insufficient amount of CO* provided for the C-C coupling. Based on the strong CO2 adsorption and ultrafast reaction kinetics of CO* formation on Pd, an intimate CuPd(100) interface was designed to lower the intermediate reaction barriers and improve the efficiency of C2 product formation. Density functional theory (DFT) calculations showed that the CuPd(100) interface enhanced the CO2 adsorption and decreased the CO2* hydrogenation energy barrier, which was beneficial for the C-C coupling. The potential-determining step (PDS) barrier of CO2 to C2 products on the CuPd(100) interface was 0.61 eV, which was lower than that on Cu(100) (0.72 eV). Encouraged by the DFT calculation results, the CuPd(100) interface catalyst was prepared by a facile chemical solution method and characterized by transmission electron microscopy. CO2 temperature-programmed desorption and gas sensor experiments further confirmed the enhancement of the CO2 adsorption and CO2* hydrogenation ability of the CuPd(100) interface catalyst. Specifically, the obtained CuPd(100) interface catalyst exhibited a C2 Faradaic efficiency of 50.3% ± 1.2% at −1.4 VRHE in 0.1 M KHCO3, which was 2.1 times higher than that of the Cu catalyst (23.6% ± 1.5%). This study provides the basis for the rational design of Cu-based electrocatalysts for the generation of multicarbon products by fine-tuning the intermediate reaction barriers.

Ultrafast capacitive deionization using rice husk activated carbon electrodes

Capacitive deionization (CDI) has attracted much attention as a promising desalination technology, since inexpensive carbon electrodes can be employed at a large scale. In this work, rice husk activated carbon (RHAC) was utilized to obtain electrodes for desalination. The RHAC materials were synthesized using different carbonization temperatures. After their physicochemical and electrochemical characterization, it was observed that the electrodes produced with the RHAC obtained at lower carbonization temperatures (450 or 650 °C) provided better desalination performance with a salt removal capacity of 15.5 mg g−1 (1.2 V and C0 = 600 mg L-1). However, the most remarkable feature of the RHAC electrodes was their ultrafast kinetics. To the best of our knowledge, here we report the fastest electrosorption rates observed for carbon electrodes applied for CDI (10.52 mg g−1 min−1). From a simultaneous analysis considering the electrosorption/desorption kinetics and the electrosorption capacity, the RHAC carbonized at 600 °C displayed an outstanding value of 5.2 g of salt removed per gram of electrode per day. Importantly, the electrodes remained stable even up to 80 electrosorption/desorption cycles, with both the kinetics and the electrosorption capacities remaining close to the initial values.

Greener route for the removal of toxic heavy metals and synthesis of 14-aryl-14H dibenzo[a,j] xanthene using a novel and efficient Ag-Mg bimetallic MOF as a recyclable heterogeneous nanocatalyst

Removing of heavy metal ions from aqueous solutions has become a serious challenge from both biological and environmental viewpoints. Recently, metal-organic frameworks (MOF) including two metal ions in its framework have been enhanced as promising structure in the capture of various hazardous and toxic substances. Herein, Ag-Mg-MOF were synthesized through a one-step approach using solvothermal technique. Then, the as-synthesized Bimetallic MOFs were characterized by TEM, SEM, EDS, XRD, FTIR and N2 adsorption. The as-synthesized Ag-Mg-MOF samples were used for heavy metal removal. The results showed that the adsorption of cadmium, lead and Cupper ions on MOF was improved by the pH increasing. The experimental data were examined through Freundlich and Langmuir models. The fabricated Ag-Mg MOFs exhibit enhanced decontaminant performance toward Cu2+, Cd2+and Pb2 ions in terms of high adsorption capacities, Pb2+ (350 mg/g)> Cd2+ (270 mg/g)> Cu2+ (202 mg/g), and ultrafast kinetics compared to the monometallic Mg-MOF. FT-IR spectra of adsorbed pyridine methods and non-aqueous potentiometric titration were used for measuring surface acidity of the prepared MOF. It was observed that the surface acidity and the catalytic activity were increased in bimetallic MOF compared to monometallic MOF. The catalytic results of the formation of free solvent 14-aryl-14-Hdibenzo[a,j]xanthene compound by Ag-Mg MOF showed a high yield at a lower time. Also, the prepared MOF catalysts still preserved their initial catalytic activity even after the 4th run. The results of this work demonstrate that the novel Ag-Mg MOFs nanocatalysts have great potential for applications in environmental protection, especially in heavy metal ions removal present in wastewaters and in the synthesis of pharmacologically and biologically active compound.

Design of amine-functionalized layered double oxide nanosheets with efficient CO2 capture capacities from ambient air, ultrafast kinetics, and promising stability

Recently, the Innovation Team of Energy-Water-Air (ITEWA) from Shanghai Jiao Tong University has carried out researches on direct air capture of CO2. A new family of amine functionalized DAC adsorbent was reported by impregnating branched polyethyleneimine onto mixed metal oxide nanosheets, which exhibits excellent CO2 adsorption capacity (2.27 mmol/g) and kinetics (1.1 mmol/g∙h) under 400 ppm CO2 as well as good thermal stability and hydrothermal stability with almost no performance degradation after 20 adsorption cycles (DOI: 10.1039/D0TA05079B). On this basis, a three-step steam-assisted temperature vacuum swing adsorption (S-TVSA) cycle was designed for DAC (DOI: 10.1016/j.rser.2020.110651). Simulation results show that the S-TVSA cycle could capture CO2 at a rate of 4.45 mol/kg·day. By using novel adsorbents with better adsorption capacities and kinetics, the capture rate can be further increased by 280% and the energy consumption reduced to 32.8%.

Boosting ultrafast Li storage kinetics of conductive Nb-doped TiO2 functional layer coated on LiMn2O4

Interface engineering of LiMn2O4 (LMO) is a promising strategy to enhance the lithium storage capability and cycling stability of cathode materials in Li-ion batteries (LIBs). This is because the strategy prevents structural degradation; however, Li storage kinetics remains unsatisfactory, resulting in poor ultrafast cycling performance. Therefore, we fabricated an Nb-doped TiO2 (NTO) functional layer as a conductive passivation layer on the LMO surface by horizontal ultrasonic spray pyrolysis deposition. The NTO functional layer suppressed the volume expansion of LMO and exhibited high electrical and ionic conductivity, which resulted in improved structural stability of LMO (related to cycling stability) and increased electron/ion transfer rate (related to ultrafast cycling performance). In the TiO2 structure, Ti4+ ions were replaced by Nb5+ ions, which possess high electrical conductivity and a wide c-axis as a Li-ion diffusion route. As a result, the NTO-coated LMO cathode material showed an outstanding specific capacity of 112.7 mAh/g with a remarkable capacity retention of 96.2% after 100 cycles at a current density of 1 C and excellent ultrafast cycling capacity and stability of 70.0 mAh/g after 500 cycles at a current density of 10 C.

Ultra-fast and efficient calcium co-intercalation host enabled by hierarchically 3D porous carbon nanotemplates

As promising candidates for next-generation batteries, calcium-ion batteries (CIBs) have attracted significant attention because of the lower cost and improved environmental friendliness of Ca metal relative to those of Li and their potential to deliver higher energy densities. However, their practical application has been limited by the lack of an appropriate electrode that can induce fast Ca co-intercalation/deintercalation reactions while providing longer cycle life. In this study, we report bacterial cellulose (BC) with a highly graphitic-like ordered structure as a new and efficient co-intercalation host for multivalent Ca ions. The free-standing BC electrode with unique 3D porous morphology possessed ultra-fast co-intercalation kinetics, much faster than that for a commercial graphite electrode. In addition, we addressed the controversial issue of whether Ca co-intercalation truly occurs in the graphitic layer. It is demonstrated that the co-intercalation is directly dependent on the degree of carbon crystallinity by using various BC electrodes with different crystallinities at regular intervals. Finally, the effect of the ordering of the carbon stacking layer on the co-intercalation chemistry was electrochemically investigated.