The Stöber method is a widely-used sol-gel route for synthesizing amorphous SiO2 colloids and conformal coatings. Recently, further enrichment of this methodology has been achieved by extending it to other materials such as TiO2 and a resorcinol–formaldehyde polymer. Nonetheless, there are still limited materials that can be synthesized by the Stöber method. Herein, by mimicking the Stöber method, we have extended the approach to metal organic frameworks (MOFs), a category of organic-inorganic hybrid materials with exceptionally customizable composition and properties. It is important to note that amorphous MOFs have demonstrated unique performances in energy storage and conversion and drug delivery applications, but achieving controllable synthesis has remained a challenge. Herein, we introduce a general synthesis route to amorphous MOFs by making use of a vapor diffusion method, which allows to precisely control the growth kinetics. Twenty-two different amorphous MOF colloids were successfully synthesized by selecting 11 metal ions and 17 organic ligands. Moreover, by introducing pre-formed core-nanoparticles (NPs), a conformal and homogeneous amorphous MOFs coating with controllable thickness can be grown on core-NPs to form core-shell colloids. The versatility of this amorphous coating technology was demonstrated by synthesizing over 100 new core-shell composites from 19 amorphous MOF shells and over 30 different core-NPs. Besides, various multifunctional nanostructures, such as conformal yolk-amorphous MOF shell, core@metal oxides, and core@carbon, can be obtained through one-step transformation of the core@amorphous MOFs. This work significantly enriches the Stöber method and introduces a platform, enabling the systematic design of colloids exhibiting different level of functionality and complexity.
Homes are becoming more intelligent due to the growth of smart sensors and devices found in typical homes. However, most of these sensors and devices function independently from one another, limiting the amount of utility and services a truly "smart" home can provide. In this demonstration, we introduce two key ideas towards more intelligent homes. First, we explore the usage of mobile drones in the home environment. Second, we propose DIA, a system that seamlessly connects to the home environment and automatically discovers and jointly utilizes smart sensors and actuators around the home to provide services that are otherwise not possible. We demonstrate three services that DIA enables.
Abstract The Stöber method is a widely-used sol-gel route for synthesizing amorphous SiO 2 colloids and conformal coatings. However, the material systems compatible with this method are still limited. Herein, we have extended the approach to metal-organic frameworks (MOFs) and coordination polymers (CPs) by mimicking the Stöber method. We introduce a general synthesis route to amorphous MOFs or CPs by making use of a base-vapor diffusion method, which allows to precisely control the growth kinetics. Twenty-four different amorphous CPs colloids were successfully synthesized by selecting 12 metal ions and 17 organic ligands. Moreover, by introducing functional nanoparticles (NPs), a conformal amorphous MOFs coating with controllable thickness can be grown on NPs to form core-shell colloids. The versatility of this amorphous coating technology was demonstrated by synthesizing over 100 core-shell composites from 20 amorphous CPs shells and over 30 different NPs. Besides, various multifunctional nanostructures, such as conformal yolk-amorphous MOF shell, core@metal oxides, and core@carbon, can be obtained through one-step transformation of the core@amorphous MOFs. This work significantly enriches the Stöber method and introduces a platform, enabling the systematic design of colloids exhibiting different level of functionality and complexity.
Cobalt ferrite (CoFe2O4) nanoparticles were prepared through an auto-combustion method. The results of XRD show that the crystallite size of CoFe2O4 nanoparticles increases from 57 to 105 nm with a slight change in lattice constant as the annealing temperature increases from 300 to 1200°C. The magnetic measurements by vibrating sample magnetometer (VSM) show that M s increases monotonously by increasing the annealing temperature from 300 to 1200°C and C hB and M s reached a maximum when annealing temperature is about 400°C due to the change of the grain size.
Abstract The key to advancing lithium‐ion battery (LIB) technology, particularly with respect to the optimization of cycling protocols, is to obtain comprehensive and in‐depth understanding of the dynamic electrochemical processes during battery operation. This work shows that pulse current (PC) charging substantially enhances the cycle stability of commercial LiNi 0.5 Mn 0.3 Co 0.2 O 2 (NMC532)/graphite LIBs. Electrochemical diagnosis unveils that pulsed current effectively mitigates the rise of battery impedance and minimizes the loss of electrode materials. Operando and ex situ Raman and X‐ray absorption spectroscopy reveal the chemical and structural changes of the negative and positive electrode materials during PC and constant current (CC) charging. Specifically, Li‐ions are more uniformly intercalated into graphite and the Ni element of NMC532 achieves a higher energy state with less Ni─O bond length variation under PC charging. Besides, PC charging suppresses the electrolyte decomposition and continuous thickening of the solid‐electrolyte‐interphase (SEI) layer on graphite anode. These findings offer mechanistic insights into Li‐ion storage in graphite and NMC532 and, more importantly, the role of PC charging in enhancing the battery cycling stability, which will be beneficial for advancing the cycling protocols for future LIBs and beyond.
Layered manganese-based oxides are promising candidates as cathode materials for sodium-ion batteries (SIBs) due to their low cost and high specific capacity. However, the Jahn-Teller distortion from high-spin Mn3+ induces detrimental lattice strain and severe structural degradation during sodiation and desodiation. Herein, lithium is introduced to partially substitute manganese ions to form distorted P'2-Na0.67Li0.05Mn0.95O2, which leads to restrained anisotropic change of Mn-O bond lengths and reinforced bond strength in the [MnO6] octahedra by mitigation of Jahn-Teller distortion and contraction of MnO2 layers. This ensures the structural stability during charge and discharge of P'2-Na0.67Li0.05Mn0.95O2 and Na+/vacancy disordering for facile Na+ diffusion in the Na layers with a low activation energy barrier of ∼0.53 eV. It exhibits a high specific capacity of 192.2 mA h g-1, good cycling stability (90.3% capacity retention after 100 cycles) and superior rate capability (118.5 mA h g-1 at 1.0 A g-1), as well as smooth charge/discharge profiles. This strategy is effective to tune the crystal structure of layered oxide cathodes for SIBs with high performance.
A well-ordered structure with high crystallinity is crucial in various applications, particularly in electrode materials for batteries. The dimensionality and connectivity of the interstitial sites, determined by the crystal structure, inherently influence Li+ ions diffusion kinetics. Niobium tungsten oxides block structures, which are built by the assembly of ReO3-type blocks of specific sizes with metal sites having well defined positions within the crystalline structure, are promising fast-charging anode materials. Structural disorder generally disrupts the regular pathways for ion and electron movement, leading to lower overall conductivity. Here, we report a new anomalous disordered Nb12WO33 structure that significantly enhances the Li-ion storage performance compared to the known monoclinic Nb12WO33 phase. The disordered Nb12WO33 phase consists of corner-shared NbO6 octahedra blocks of varied sizes, including 5x4, 4x4, and 4x3, with a disordered arrangement of the tungsten tetrahedra at the corners of the blocks, as well as distortion of the WO4 tetrahedra. This structural arrangement is found to be extremely robust during lithiation/delithiation, leading to a topotactic local structure evolution during cycling, as determined by operando X-ray diffraction and X-ray absorption spectroscopy. It leads also to accelerated Li-ion migration within the disordered phase that results in excellent fast-charging performance, namely, 62.5 % and 44.7 % capacity retention at 20 C and 80 C, respectively. This study highlights the benefits of introducing disorder into niobium tungsten oxide shear structures, through the establishment of clear structure-performance correlations, offering valuable guidelines for designing materials with targeted properties.
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