Faster Diffusion Rate Research Articles

Controlled synthesis of Fe3O4 microparticles with interconnected 3D network structures for high-performance flexible solid-state asymmetric supercapacitors

The eco-friendly Fe-based oxides have attracted broad attention in supercapacitors on account of large theoretical capacities and cost-effective technologies associated with production and recycling. However, inferior conductivity and bad structural stability are still the main obstacles for its promoted application than the competition. In this work, well-designed Fe 3 O 4 microparticles with homogeneous size distribution, high crystallinity, and amorphous carbon shell have been synthesized and deposited on carbon fabric as an anode electrode via a series of feasible techniques, including anodic electrodeposition, polymerization, and annealing. The interconnected 3D network structures of electroactive materials are featured by high specific surface area and fast diffusion rate of ions. The sufacial carbon layer of Fe 3 O 4 particles, serves as the armor, which not only boosts electrical conductivity, but also maintains structural stability of the electrode during electrochemical processes. The electrochemical results show that the binder-free anode exhibits a remarkable areal capacitance of 0.95 F·cm −2 , a wide potential window of 1.2 V, and an outstanding cycling stability in 1 M KOH electrolyte (capacitance retention of 93.39 % over 8000 charge-discharge cycles). After combining with a NiCo-based cathode, 4.93 F·cm −3 volumetric capacitance, 1.8 mWh·cm −3 energy density, and 198 mW·cm −3 power density are achieved for the flexible solid-state asymmetric supercapacitor, which displays impressive cycling stability, excellent mechanical flexibility, and obvious performance advantages as compared with previously reported flexible energy storage devices. This work provides a feasible strategy to design a flexible Fe-based anode with superior conductivity and long-term stability for high-performing flexible solid-state asymmetric supercapacitor towards practical applications. • High crystallinity Fe 3 O 4 microparticles were deposited on CF via stepwise strategy. • Polypyrrole was served as carbon source and barrier material during annealing. • The 3D network structures embrace good conductivity and fast diffusion rate. • The anode exhibits large capacitance, wide potential window and good stability. • Bending test and 8000 GCD cycles demonstrate the flexibility and cycling stability.

Cobalt doped ovoid magnetite (Fe3O4) nanocomposites incrusted on sheets of reduced graphene oxide as anode for sodium-ion batteries

Fe3O4 could be a better choice as anode for sodium-ion batteries (NIBs) due to high sodium ion storage capability and abundant resource. Yet, the low conductivity and severe volume expansion during cycling have fetched large defies towards practicality. In this work, an ovoid Fe3O4/rGO and (5%, 10%) cobalt doped Fe3O4/rGO nanocomposites were synthesized through one-step hydrothermal route. Structural, morphological chemical, vibrational, and compositional analysis have been employed using X-ray diffraction, Scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The results indicate the successful substitution of cationic Co2+ ions in Fe3O4 lattice. Hence, integration of optimal cobalt doping in Fe3O4 lattice can alter the charge/discharge specific capacity as compared to undoped Fe3O4-rGO anode. Due to sufficient production of oxygen vacancies in the structure 5% Co- Fe3O4/rGO reveals the highest initial charge capacity of 434 mAh g−1 at 0.05 C and exhibits stable prolonged cycling and delivers upto 303 mAh g−1 of charge capacity during 100 cycles (with 100% of CE and 72% of remaining capacity retention)as compared to 10% Co- Fe3O4/rGO (414 mAh g−1) and Fe3O4/rGO (357 mAh g−1) nanocomposite. Moreover, the Nyquist plot reveals the rapid transfer of charge for 5% Co- Fe3O4/rGO anode due to lowest charge transfer impedance of 56.5 Ω as compared to 10% Co- Fe3O4/rGO (114.3 Ω) and pristine Fe3O4/rGO (177.8 Ω). Therefore, the presence of rGO layers and the optimum doping of Co atoms in Fe3O4 crystal can curtail volume expansion, generate more contact sites for electrode/electrolyte, deep penetration of electrolyte into the electrode and can yield superior electrochemical performance via fast Na-ion diffusion rate. Sodium-ion batteries are a promising technology for electric vehicles, the energy grid and other applications.

Controlling Li Dendritic Growth in Graphite Anodes by Potassium Electrolyte Additives for Li-Ion Batteries.

Fast charging promotes Li dendrite formation and its growth on graphite anodes, which affects cell performance in Li-ion batteries (LIBs). This work reports the formation of a robust SEI layer by introducing a KPF6 inorganic additive into the electrolyte. An optimal concentration of 0.001 M KPF6 effectively inhibits the growth of Li dendrites at 2C charging rates, compared with a commercial electrolyte. Electrolytes containing a KPF6 additive are shown here to deliver dual effects to mitigate the growth of dendrites. A thin LiF-rich SEI layer is formed on graphite, which blocks the electron leakage pathways. Additionally, K+ resides at defect sites (such as particle boundaries) due to its faster diffusion rate and blocks the incoming Li+ and restricts the growth of Li dendrites. The electrolyte with optimum concentration of KPF6, i.e., 0.001 M, effectively directs Li+ transport through the thin, durable, and low resistance LiF-rich SEI layer. This has implications for fast charging through optimization of the electrode/electrolyte interphase by controlling additive concentrations.

Heteroatom doping strategy enables bi-functional electrode with superior electrochemical performance

As the fossil fuel consumption and energy shortage crisis worsen, it is urgent to develop multi-functional and cost-effective energy storage devices. However, the sluggish electrochemical kinetics of electrode materials is the major drawback which hinders their practical application. Herein, a heteroatom doped MnO2 carbon-based flexible electrode has been proposed derived from Ni2+ doping α-MnO2 by a facile hydrothermal strategy. Surprisingly, the as-prepared composite electrodes exhibit decent bi-functionally electrochemical performance both in lithium-ion batteries and aqueous supercapacitors. The superior performance of composite electrode is ascribed to high electrical conductivity, fast ionic diffusion rate, and the reduction of work function after the incorporation of Ni2+ ions based on the electrochemical kinetics analysis and density functional theory calculation. In summary, this work puts forward a facile strategy to construct high electrochemical performance electrode for lithium-ion batteries and aqueous supercapacitors.

Electrochemically Active Mn-Doped Iron Hexacyanoferrate as the Cathode Material in Sodium-Ion Batteries

In this work, for the performance enhancement of iron hexacyanoferrate, an electrochemically active Mn-doped iron hexacyanoferrate cathode is fabricated via a bottom-up approach. It is found that the pre-treatment of interstitial water and appropriate Mn doping are two keys to achieving higher capacity and higher stability. The interstitial water has a trade-off effect between the alleviation of volume expansion upon Na+ (de)intercalation and the retardation of Na-ion diffusion. The moisture-tailored iron hexacyanoferrate with appropriate Mn doping exhibits a high initial Coulombic efficiency of 94.8%, enhanced capacity and rate performance, and excellent cycling stability. These results benefit from the fact that the extraction/insertion of Na ions from/into the lattice via a solid-solution mechanism correspond to both the slight volume expansion and fast sodium diffusion rate; otherwise, the removal of interstitial water and a higher Mn content might lead to poor cycling stability due to excessive volume expansion resulting from rhombohedral to cubic phase transformation. Finally, the less demand on the control of air humidity for the fabrication of electrodes and the potential for the full cell coupled with hard carbon are also demonstrated, which shows great potential for practical applications.

Application of Fiber Biochar-MOF Matrix Composites in Electrochemical Energy Storage.

Fiber biochar–metal organic framework (MOF) composites were successfully prepared by three different biochar preparation methods, namely, the ionic liquid method, the pyrolysis method, and the direct composite method. The effects of the different preparation methods of fiber biochar on the physical and chemical properties of the biochar–MOF composites showed that the composite prepared by the ionic liquid method with the Zeolite-type imidazolate skeleton -67 (ZIF-67) composite after high temperature treatment exhibited a better microstructure. Electrochemical tests showed that it had good specific capacity, a fast charge diffusion rate, and a relatively good electrochemical performance. The maximum specific capacity of the composite was 63.54 F/g when the current density was 0.01 A/g in 1 mol/L KCl solution. This work explored the preparation methods of fiber biochar–MOF composites and their application in the electrochemical field and detailed the relationship between the preparation methods of the composites and the electrochemical properties of the electrode materials.

Synchronous solid-state diffusion, dissolution-reprecipitation, and recrystallization leading to isotopic resetting: insights from chalcopyrite replacement by copper sulfides

Reactions among minerals occur via solid-state diffusion or fluid-induced, interface-coupled dissolution-reprecipitation (ICDR). Both mechanisms can coexist under conditions where the rates of both processes are similar, depending mainly on the nature of the mineral, temperature, and fluid composition. To clarify the synergies between these reaction mechanisms, we investigated the replacement and recrystallization reactions of chalcopyrite in the presence of a 65Cu-enriched aqueous fluid. The replacement of chalcopyrite by secondary copper sulfides follows a paragenetic sequence, whereby chalcopyrite is initially replaced by covellite, and then by digenite, with some of the digenite replacing covellite in longer duration experiments. The replacement reactions proceed via ICDR along with solid-state diffusion of 65Cu from the fluid into product minerals, with both mechanisms occurring at similar rates. Over time, chalcopyrite is completely replaced, and the secondary copper sulfides attain isotopic equilibrium with the fluid. Depending on temperature, thermal history, and fluid-mineral ratio, the reaction products may preserve kinetic or equilibrium signatures. We have identified a new geochemical process of ‘porosity-aided recrystallization’, which may result in a re-equilibration or perturbation of mineral isotopic/trace element compositions due to exchanges between the mineral and fluid facilitated by extensive micro- to nano-scale porosity created by ICDR reactions. Porosity-aided recrystallization will affect any mineral-fluid system where mass transfers via solid-state diffusion and ICDR operate at similar rates, causing rapid (days-weeks) ‘resetting’ of the original isotopic abundances and trace element contents of the affected minerals. In copper sulfides, porosity-aided recrystallization occurs at lower temperatures (<300 °C) due to fast cation diffusion rates (log10D ≈ –13.6, 300 °C), but also takes place across other mineral systems where diffusion rates are faster at high temperatures. The open-system isotopic and trace element exchanges associated with porosity-aided recrystallization could lead to erroneous petrological interpretations, especially where these markers are used as a proxy for reconstructing geological evolution.

Sorption kinetics of 1,3,5-trinitrobenzene to biochars produced at various temperatures

Sorption kinetics of organic compounds on biochars is important for understanding the retardation of mobility and bioavailability of organic compounds. Herein, sorption kinetics of 1,3,5-trinitrobenzene on biochars prepared from 200 to 700 °C was investigated to explore the sorption process. Loose partition matrix and condensed partition matrix were formed at relatively low and moderate temperatures, respectively. However, biochars produced at relatively high temperatures formed rich pore structures. Therefore, sorption equilibrium time of 1,3,5-trinitrobenzene increased with increasing preparation temperature from 200 to 350 °C due to the slower diffusion rate in the more condensed matrix, and then decreased when preparation temperature was higher than 400 °C because of the faster adsorption rate in the greater number of pores. Linear positive relationship between matrix diffusion rates of 1,3,5-trinitrobenzene on biochars prepared at 200, 250, 300, 350 °C and H/C ratios of biochars was observed, suggesting that the inhibition of partition process was caused by the condensed matrix in biochars. Linear positive relationships between adsorption rates (i.e., fast outer diffusion rate and slow pore diffusion rate) of 1,3,5-trinitrobenzene on biochars prepared at 400, 450, 550, 700 °C and graphite defects of biochars were observed, because the increase of graphite defects of biochars could promote the adsorption by increasing the quantity of fast diffusion channels and sorption sites. This study reveals the underlying mechanisms of sorption kinetics for organic compounds with relatively large size on biochars, which has potential guidance for the application of biochars and prediction of the environmental risks of organic compounds.Graphical

Constructing titanium carbide MXene/reduced graphene oxide superlattice heterostructure via electrostatic self-assembly for high-performance capacitive deionization

Capacitive deionization has attracted wide concern on accountof its high energy efficiency, low manufacturing cost and environmental friendliness. Nevertheless, the development of capacitive deionization is still impeded because of the scarcity of suitable electrode materials with superior performance. Herein, we successfully prepared the two-dimensional (2D) titanium carbide (Ti3C2Tx) MXene/ reduced graphene oxide (rGO) superlattice heterostructure by a facile electrostatic self-assembly strategy and systematically investigated its performance as capacitive deionized electrode materials. The unique 2D/2D superlattice heterostructure not only effectively alleviates the self-stacking problem of Ti3C2Tx MXene nanosheets, but also endows the heterostructure with superior conductivity and fast ion diffusion rate. As a result, the MXene/rGO superlattice heterostructure exhibits an outstanding salt (Na+) adsorption capacity (48 mg g−1) at 1.2 V significantly superior to pristine Ti3C2Tx MXene nanosheets, along with outstanding long-term cycling performance. Furthermore, the mechanism involved was elucidated through comprehensive characterizations. Therefore, this study offers a new pathway for designing high-performance electrode materials for capacitive deionization.

Droplet splash and spread on superhydrophobic lotus leaves: Direct regulation by tuning the chain length of surfactant

Impact and spread of droplet on superhydrophobic surface are ubiquitous in inkjet printing, pesticide spraying, paint coating, and other fields. However, due to the extremely water-repellent properties of superhydrophobic surface, droplets frequently splash or roll off, causing great waste and serious environmental problems. Thus, searching for an effective strategy to regulate the droplet splash and spread on superhydrophobic surfaces is of remarkable significance. To address the above issues, herein, we demonstrate the controllable regulation on superhydrophobic lotus leaf surface by tuning the double-chain length of surfactants. The outcomes indicate different regularities for droplet splash in a short time (~10 ms) and spread in a relatively long period (~100 s). It can be concluded that dynamic surface tension of surfactant, diffusion rate of surfactant from the bulk to the interface, and assembly disaggregation rate dominate the impact process, whereas the adsorption kinetic and effectiveness of surfactant along with the spreading driving force determine the wetting transition. Surfactant owning suitable hydrophilic and hydrophobic ratio, fast diffusion rate, and unstable assembly could inhibit droplet splash and improve spreading pronouncedly, thereby enhancing the droplet deposition on superhydrophobic surfaces. This study makes original contribution to screen suitable surfactants from the structural aspects, especially double-chain length, which has not been treated in much detail to date. Our work not only creates a big impetus in illuminating the mechanism of surfactant molecular structure on droplet deposition processes but also greatly expands the applications of surfactant in many fields.

Determining the diffusion behavior of point defects in zirconium by a multiscale modelling approach

Zr alloys are commonly used materials for in-core components of pressurized water reactors. The evolution of defects in Zr under irradiation conditions will directly contribute to the degradation of reactor components. For a better understanding of the evolution process of defects in Zr, a multiscale simulation was performed to study the diffusion behavior of radiation-induced point defects. Because the existing potentials cannot accurately describe the energy differences of stable states self-interstitial atoms (SIAs) in Zr, an embedded atom method potential that can exactly reproduce the energy difference between metastable states and ground states, and the binding energy of divacancy of Zr, was first developed by fitting a potential to point defect properties calculated by density functional theory and other basic crystal properties. Based on the constructed potential, molecular dynamics (MD) and kinetic Monte Carlo simulations were conducted to investigate the migration of point defects. We determined several frequent migration paths of SIAs by kinetic study, which is rarely reported in previous MD studies. The SIA exhibits obvious anisotropic diffusion characteristics at low temperatures (<600 K). The most frequent migration path for SIAs is the jump between the two nearest basal octahedral (BO) sites in the basal plane, which means that SIAs diffuse faster along the basal plane than along the c axis. It is found that diffusion within the basal plane tends to be two-dimensional (2D) diffusion rather than 1D diffusion, and there is a significant correlation effect for diffusion of SIAs along the basal plane. Additionally, the existence of trivacancy-SIA complex was found in the process of divacancy migration, which can inhibit divacancy migration. Monovacancies and divacancies exhibit anisotropic diffusion characteristics in the considered temperature range Divacancies have a much faster diffusion rate than monovacancies in the present MD simulation and can easily dissociate at high temperatures (>900 K). The rapid migration of the divacancies may contribute to the formation of vacancy dislocation loops. These results are meaningful to understand the evolution process of radiation-induced defects.

Tailoring surface capacitance of Ti3C2Tx-PANI@CNTs nanoarchitecture for tunable energy storage and high-performance micro-supercapacitor

Transition metal carbide or nitride (MXenes), as a novel family of two-dimensional materials, exhibit huge potential for electrochemical energy storage thanks to their excellent electrical conductivity, fast ion diffusion rate, high electrochemical activity and good hydrophilicity. However, the electrochemical properties of MXenes tend to be deteriorated due to the self-restacking phenomenon. Herein, by self-assembly, a unique three-dimensional (3D) Ti3C2Tx-PANI@CNTs (TPCs) nanoarchitecture was constructed. Through optimizing structures, the surface capacitance of TPCs can be tailored to tune energy storage. The optimal specific capacitance up to 431.9 F/g was achieved under 1 A/g. Further, the TPCs nanoarchitectures were prepared into self-standing films with excellent mechanical properties and micro-supercapacitors (MSCs) in various shapes were manufactured based on the film. The MSCs demonstrate competitive energy storage capacities, obtaining an areal capacitance of 78.2 mF/cm2 and energy density of up to 2.72 μWh/cm2, still maintain excellent performance under harsh bending. The strategy for constructing 3D nanoarchitectures and further manufacturing MSCs can inspire the design of novel electrode materials and devices to advance the development in the field of energy storage.

Seignette salt induced defects in Zr-MOFs for boosted Pb(Ⅱ) adsorption: universal strategy and mechanism insight

Within this work, a green and facile approach was proposed to modulate NH2-UiO-66 for purpose of obtaining SS-NH2-UiO-66-X (“X” implied the dosage of used SS) using seignette salt (SS). The generation of abundant vacancies with the formation of hierarchical pores boosted their sorption performance for lead (Pb(II)), which strengthened the mass transfer of Pb(II) in SS-NH2-UiO-66-X interior. Particularly, the optimal SS-NH2-UiO-66-5 exhibited good adsorption capacity toward Pb(II) (186.14 mg g−1) and fast diffusion rate (32.1 mg g−1·min0.5) at 25 °C and initial pH = 5.46, which were about 34.2 and 66.9 times higher than those of the pristine NH2-UiO-66, respectively. SS-NH2-UiO-66-5 could selectively capture the Pb(II) from simulated wastewater containing different co-existing ions. The mechanism was proposed that the defect sites played a significant role in boosting the Pb(II) capture performance, which was further affirmed by X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectra (XPS). The density functional theory calculations (DFT calculations) illustrated that the hierarchical pores and rich vacancies enhanced the Pb(II) mobility toward the adsorption active sites and reduced the adsorption energy between SS-NH2-UiO-66-X and Pb(II). This defect engineering approach could be introduced to modulate other Zr-MOFs like MOF-801, UiO-66 and MOF-808, which presented a general strategy to fabricate defective Zr-MOFs for the boosted adsorption performance toward pollutants removal from wastewater.

Niche and interspecific associations of Pseudoanabaena limnetica – Exploring the influencing factors of its succession stage

In aquatic ecosystems, the dynamics of ecological parameters play an important role in community organization. To understand the changes in the phytoplankton community structure in karstic reservoirs, the Hongfeng reservoir in Guizhou plateau was monitored monthly from 2016 to 2019. The results showed that the dominant organisms in phytoplankton comprised five phyla and twelve species during 4 years, among which the proportion of abundance of Pseudoanabaena limnetica begin to rise in 2018 and reached 46.57% in 2019 (the highest during the study period). The niche breadth (0.259–0.925) and overlap value (0–0.991) of P. limnetica have an obvious seasonal trend and are significantly affected by environmental factors such as water temperature, nutrients, and interspecific competition. This is primarily reflected in the high adaptability of the dominant species to changes in the N:P concentration ratio in water. Variance Partitioning Analysis (VPN) results show that the diffusion degree of P. limnetica is the result of the interaction between internal (i.e. interspecific competition, with a contribution rate of 13.4%) and external (i.e. environmental factors, with a contribution rate of 86.6%). The greater the external influence, the higher the diffusion degree. The results of niche-based theories and neutral-based theories showed that the stable community structure (variance rate (VR > 1)) and the excessive fast diffusion rate of dominant species (migration rate (m = 0.84)) may lead to the risk of P. limnetica and other toxic filamentous cyanobacteria blooms. The results provide basic data for the study of early warnings regarding phytoplankton community succession and cyanobacteria blooms in large reservoirs in the karst areas.

Diffusion coefficient analysis of aluminum electrolysis spent cathode as anode material for lithium-ion battery

The aluminum electrolysis spent cathode (SC) was treated by hydrothermal method and used as anode material for lithium-ion battery. The purified SC material shows excellent electrochemical performance. In order to understand the diffusion behavior of Li+ in the SC electrode, the diffusion coefficient of Li+ in the SC electrode was systematically analyzed by galvanostatic intermittent titration technique (GITT), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The results show that the diffusion coefficient ( $${D}_{{\text{Li}}^{+}}$$ ) of Li+ in SC electrode is calculated by CV is 2.2292 × 10−11 cm2 s−1, and the ranges calculated by GITT and EIS are 4.2286 × 10−13 − 2.9667 × 10−10 cm2 s−1, 4.05 × 10−13 − 3.87 × 10−12 cm2 s−1, respectively. SC electrode exhibits better Li+ diffusion kinetics compared to commercial graphite (CG). In addition, the full cell of LiNi0.5Co0.2Mn0.3O2/SC also shows excellent cycle performance. After 80 cycles at 1 °C (1 °C = 172 mA g−1), the specific discharge capacity of LiNi0.5Co0.2Mn0.3O2/SC full-cell can reach 94.7 mAh g−1, and the capacity retention can reach 98.13%. The fast lithium-ion diffusion rate and high discharge capacity provide a feasible direction for the high value utilization of aluminum electrolysis spent cathode.

Lithium ion sieve modified three-dimensional graphene electrode for selective extraction of lithium by capacitive deionization

Faced with the strong demand of clean energy, development of lithium source is becoming exceedingly vital. Spinel-type manganese oxide (λ-MnO2) is a typical lithium ion sieve material. Herein, the conductive three-dimensional (3D) lithium ion sieve electrode material was fabricated by in-situ growth of λ-MnO2 on 3D reduced graphene oxide (3D-rGO) matrix for Li extraction by capacitive deionization (CDI). The λ-MnO2 modified rGO (λ-MnO2/rGO) retained the 3D network structure with uniform distribution of λ-MnO2 nanosheets on rGO. Electrochemical characterization demonstrated its high conductivity and fast lithium ion diffusion rate. By adjusting the rGO concentration, λ-MnO2 activity was improved significantly. With λ-MnO2/rGO as a positive electrode (activated carbon as negative electrode), the corresponding CDI system was successfully applied for the selective extraction of Li+. The final rGO content in the λ-MnO2/rGO was attained by thermogravity analysis. With the appropriate rGO content (15.5%), the obtained λ-MnO2/rGO electrode achieved the optimal Li+ adsorption amount. The corresponding λ-MnO2/rGO-based CDI cell showed good selectivity and high cycle stability. When applied to the extraction of lithium from synthetic salt lake brine, the electrode also obtained high Li+ adsorption amount with good selectivity.

Electrical properties of NbN/NbN x /NbN Josephson junctions

In this work, we report the electrical properties of NbN internally shunted Josephson junctions with NbN x barriers. Cross-sectional scanning transmission electron microscopy analysis shows that all layers have the same cubic structure; NbN/NbN x /NbN trilayers were epitaxially grown on MgO substrates. The resistivity of the NbN x films could be varied in the range of 1–104 mΩ cm by controlling both the N2 partial pressure and the deposition time during reactive sputtering. The temperature dependence of the critical current density (J c) and characteristic voltage (I c R n) of the junctions with different barrier resistivities were measured for various barrier thicknesses. For the 10 nm-thick NbN x layer with resistivities of 73.44, 385.72, and 711 mΩ cm, the coherence length of the barrier was determined to be 5.55 ± 0.07, 4.88 ± 0.06, and 1.40 ± 0.13 nm, respectively, corresponding to carrier diffusion rates of 2.741 ± 0.004, 1.211 ± 0.002, and 0.008 ± 0.001 cm2 s−1, respectively. Thus, the reduction in barrier resistivity leads to a larger coherence length and a faster diffusion rate, which will further increase the J c and I c R n of the junction. By adjusting the barrier resistivity and thickness, the J c of the junction can be easily tuned over more than four orders of magnitude, and an I c R n value of 0.97 ± 0.07 mV was obtained at 10 K. The results indicate that the all-NbN self-shunt junction is a promising candidate in high-speed and high-temperature applications.

Metal-organic framework derived cobalt phosphide nanoparticles encapsulated within hierarchical hollow carbon superstructure for stable sodium storage

Metal-organic framework (MOF) derivatives with controllable morphology, porosity, and high specific area are considered as potential anodes for sodium-ion batteries (SIBs). However, the poor conductivity and sluggish diffusion kinetics of Na+ of MOF-derived materials result in rapid capacity decline and inferior rate capability. Herein, a hierarchical hollow superstructure composed of CoP nanoparticles anchored on the N-doped carbon polyhedral frameworks with the epitaxial growth of carbon nanotubes (CoP@N-HP/CT), is prepared by MOF coating, and subsequent carbonization − oxidation − phosphorization strategy. Owing to the elaborate hierarchical hollow superstructure, the CoP@N-HP/CT composites achieve long cycling stability (over 2500 cycles), and good rate capability as SIBs anodes. The remarkable electrochemical performance of the CoP@N-HP/CT hybrids is attributed to their high capacitive contribution and fast sodium ion diffusion rate. Furthermore, the sodium storage behaviors of the CoP@N-HP/CT are revealed by ex-situ X-ray photoelectron spectroscopy and transmission electron microscope techniques. Thus, the well-designed hierarchical hollow CoP@N-HP/CT superstructure gives an insight into the superior anodes for sodium storage.

A mathematical model for understanding nanoparticle biodistribution after intratumoral injection in cancer tumors

To exploit the benefits of a multifunctional nanomaterial as theranostics, drug carriers, and adjuvant therapeutics, tissue parameters affecting in-vivo transport, intratumoral diffusion, need to be understood properly. Literature has reported different regions of tumor such as necrotic core, viable tumor which are surrounded by healthy tissue. Transvascular exchange of the fluid and solute plays a crucial role in nanoparticle retention in the tumors. Modeling fluid and solute transport phenomenon in tissue considering in-vivo tumor architecture is essential. In this study, the influence of necrotic core presence, transvascular transport, nanoparticle size, and vascular normalization have been investigated to better understand the nanoparticle distribution in tumors. A three-dimensional numerical model has been developed to study the interstitial fluid flow and nanoparticle distribution in tumors considering the reported in-vivo scenario. The effects of nanoparticle size, intratumoral single-site, and multi-site injection methods, and vascular normalization on the distribution were investigated. In-silico investigations were carried out with respective parameters of tumor and healthy tissues using finite element based COMSOL Multiphysics 5.6® software. Interstitial fluid pressure, velocity, and nanoparticle concentration in interstitial space were predicted by solving the developed models. It was found that the interstitial fluid pressure is elevated and uniform throughout the tumor region, inhibiting the convective transport of the nanoparticles. Post-injection distribution patterns of nanoparticles revealed that the smaller nanoparticles show faster diffusion and rapid clearance from the tissues, while larger particles are retained for longer periods. The multi-site infusion method is more efficacious than the single-site method, gives better distribution patterns in the tumor. Vascular normalization does not affect the distribution of larger particles while it has shown a profound effect on the 10 nm particle distribution. Considering necrotic core and transvascular transport is inevitable in modeling to replicate the in-vivo scenario in in-silico investigations. Based on the results obtained, it is found that very fine particles of the size 10 nm will lead to lower therapeutic concentrations due to vascular clearance, despite faster diffusion rates. Particle sizes larger than 30 nm will not diffuse into the tumor due to lower diffusion coefficients and retained at the injected site. This study proposes 15 nm–30 nm as the suitable size for hyperthermia considerations.

Effect of Sn doping concentration on the oxidation of Al-containing MAX phase (Ti3AlC2) combining simulation with experiment

Sn doping is usually adopted to prepare Ti3AlC2 in mass production because it can reduce the synthesis temperature while increasing the phase purity. However, excessive Sn doping usually deteriorates the oxidation resistance of Ti3AlC2. Therefore, an appropriate Sn doping concentration is a vital issue. In this work, the effect of Sn doping concentration on the oxidation behavior of Ti3AlC2 was systematically investigated by combining theoretical calculations and experimental methods. Density function theory calculations suggest that the oxygen adsorption mechanisms for the (001) surface of Ti3AlC2 with and without Sn doping are similar, and Ti-O bonds are always preferentially formed. The molecular dynamics simulation further indicates that Al atoms have a faster diffusion rate during the oxidation process. Therefore, a continuous Al2O3 layer can form rapidly at high temperature. Nevertheless, when the Sn doping concentration exceeds 10 mol%, the continuity of the Al2O3 layer is destroyed, thereby impairing the oxidation resistance of Ti3AlC2. Furthermore, oxidation experiments verify the above results. The oxidation mechanisms of Ti3AlC2 with different Sn doping concentrations are also proposed.