Sub-nano metal clusters often exhibit unique and unexpected properties, which make them particularly attractive as catalysts. Herein, we report a “precursor-preselected” wet-chemistry strategy to synthesize highly dispersed Fe2 clusters that are supported on mesoporous carbon nitride (mpg-C3N4). The obtained Fe2/mpg-C3N4 sample exhibits superior catalytic performance for the epoxidation of trans-stilbene to trans-stilbene oxide, showing outstanding selectivity of 93% at high conversion of 91%. Molecular oxygen is the only oxidant and no aldehyde is used as co-reagent. Under the same condition, by contrast, iron porphyrin, single-atom Fe, and small Fe nanoparticles (ca. 3 nm) are nearly reactively inert. First-principles calculations reveal that the unique reactivity of the Fe2 clusters originates from the formation of active oxygen species. The general applicability of the synthesis approach is further demonstrated by producing other diatomic clusters like Pd2 and Ir2, which lays the foundation for discovering diatomic cluster catalysts.

High-throughput screening and optimization experiments are critical to a number of fields, including chemistry and structural and molecular biology. The separation of these two steps may introduce false negatives and a time delay between initial screening and subsequent optimization. Although a hybrid method combining both steps may address these problems, miniaturization is required to minimize sample consumption. This article reports a ''hybrid'' droplet-based microfluidic approach that combines the steps of screening and optimization into one simple experiment and uses nanoliter-sized plugs to minimize sample consumption. Many distinct reagents were sequentially introduced as Ϸ140-nl plugs into a microfluidic device and combined with a substrate and a diluting buffer. Tests were conducted in Ϸ10-nl plugs containing different concentrations of a reagent. Methods were developed to form plugs of controlled concentrations, index concentrations, and incubate thousands of plugs inexpensively and without evaporation. To validate the hybrid method and demonstrate its applicability to challenging problems, crystallization of model membrane proteins and handling of solutions of detergents and viscous precipitants were demonstrated. By using 10 l of protein solution, Ϸ1,300 crystallization trials were set up within 20 min by one researcher. This method was compatible with growth, manipulation, and extraction of high-quality crystals of membrane proteins, demonstrated by obtaining high-resolution diffraction images and solving a crystal structure. This robust method requires inexpensive equipment and supplies, should be especially suitable for use in individual laboratories, and could find applications in a number of areas that require chemical, biochemical, and biological screening and optimization.droplets ͉ plugs ͉ protein structure ͉ high-throughput ͉ miniaturization T his work reports a ''hybrid'' microfluidic approach that uses nanoliter plugs to perform screening and optimization simultaneously in the same experiment. To validate this method using a challenging problem, we demonstrate its compatibility with crystallization of membrane proteins. Small-scale screening and optimization experiments are important for biological assays, chemical screening, and protein crystallization (1-3). Screening and optimization are usually carried out sequentially. In the case of protein crystallization, random sparse matrix screening initially identifies the precipitants that may lead to crystallization. Subsequent gradient optimization establishes concentrations of these precipitants that lead to diffractionquality crystals (4). Combining screening and optimization steps into a single hybrid experiment would eliminate the need to wait for the outcome of the initial screen before carrying out subsequent optimizations. Furthermore, a hybrid experiment would reduce the false negatives (5) associated with screens performed at a single concentration. The hybrid experiment could also be more conclusive, because a single batch of the s...

Sodium-ion batteries operating at ambient temperature hold great promise for use in grid energy storage owing to their significant cost advantages. However, challenges remain in the development of suitable electrode materials to enable long lifespan and high rate capability. Here we report a sodium super-ionic conductor structured electrode, sodium vanadium titanium phosphate, which delivers a high specific capacity of 147 mA h g−1 at a rate of 0.1 C and excellent capacity retentions at high rates. A symmetric sodium-ion full cell demonstrates a superior rate capability with a specific capacity of about 49 mA h g−1 at 20 C rate and ultralong lifetime over 10,000 cycles. Furthermore, in situ synchrotron diffraction and X-ray absorption spectroscopy measurement are carried out to unravel the underlying sodium storage mechanism and charge compensation behaviour. Our results suggest the potential application of symmetric batteries for electrochemical energy storage given the superior rate capability and long cycle life.

cathode material was prepared by the sol-gel method. The material was coated with the ionic conductor Li 3 VO 4 via direct reaction with NH 4 VO 3 at 350 C. The Li 3 VO 4 coated material had a higher ordered hexagonal layered structure, and less Li + /Ni 2+ cation mixing. The surface of the coated material was composed of Li 3 VO 4 polycrystals, which were impregnated into the bulk of the active material. The surface coating protected the material from contact with CO 2 in the air, thus inhibiting the formation of an Li 2 CO 3 layer. Electrochemical studies showed that the Li 3 VO 4 surface coating improved the activation of Mn 4+ ions, resulting in a high discharge capacity. It also prohibited the growth of a solid electrolyte interface film, and facilitated the charge transfer reactions at the electrode/electrolyte interface, thus improving the rate capability and cycle stability of the material. DSC analysis of the fully charged electrode showed that the temperature of the exothermic peak increased from 205.2 C to 232.8 C, and that the amount of heat that was released was reduced from 807.5 J g À1 to 551.0 J g À1 , highlighting the improved thermal stability of the material after coating with Li 3 VO 4 .

Orthorhombic V2O5 nanowires were successfully synthesized via a hydrothermal method. A cellconfiguration system was built utilizing V2O5 as the cathode and 1 M Mg(ClO4)2 electrolyte within acetonitrile, together with MgxMo6S8 (x ≈ 2) as the anode to investigate the structural evolution and oxidation state and local structural changes of V2O5. The V2O5 nanowires deliver an initial discharge/charge capacity of 103 mAh g-1 /110 mAh g-1 and the highest discharge capacity of 130 mAh g-1 in the 6 th cycle at C/20 rate in the cell-configuration system. In operando synchrotron diffraction and in operando X-ray absorption spectroscopy together with ex situ Raman and X-ray photoelectron spectroscopy reveal the reversibility of magnesium insertion/extraction and provide the information on the crystal structure evolution and changes of the oxidation states during cycling.

The continuous phase transformation to spinel LiMn 2 O 4 seriously hinders the electrochemical properties of Li-excess layered oxides in lithium ion batteries. Herein, we prepared a heterostructured Li-excess layered cathode material consisting of a Li(Li 0.18 Ni 0.15 Co 0.15 Mn 0.52 )O 2 active material in conjunction with a surface Li 4 M 5 O 12 spinel and a Li 2 O-LiBO 2 -Li 3 BO 3 glass coating layer. The material showed improved electrochemical kinetic properties with respect to its pristine counterpart because the Li 2 O-LiBO 2 -Li 3 BO 3 glass layer not only improved the ionic conductivity of the material but also depressed the side reactions of the electrode with the electrolyte. In addition, the surface Li 4 M 5 O 12 spinel constantly grew inwards the bulk of the material during long term charge-discharge cycling instead of the conventional LiMn 2 O 4 transformation for the pristine Li(Li 0.18 Ni 0.15 Co 0.15 Mn 0.52 )O 2 . As a result, the heterostructured cathode material showed overall improved electrochemicalperformance. An initial discharge capacity of 258.8 mAh g -1 was obtained at the 0.2 C rate with remarkable capacity retention of 92.2 % after 100 cycles. Moreover, the material showed excellent rate capacity delivering a high discharge capacity of 130.4 mAh g -1 and 100.4 mAh g -1 at the 10 C and 20 C rates, respectively. Differential scanning calorimetry showed that the exothermic temperature of the fully charged electrode was elevated to 324.2 o C with little thermal release of 232.5 J g -1 demonstrating good thermal safety of the material.

In the past decade, isolated single atoms have been successfully dispersed on various substrates, with their potential applications being intensively investigated in different reactions. While the essential target of research in single-atom catalysis is the precise synthesis of stable single-atom catalysts (SACs) with clear configurations and impressive catalytic performance, theoretical investigations have also played important roles in identifying active sites, revealing catalytic mechanisms, and establishing structure–activity relationships. Nevertheless, special attention should still be paid in theoretical works to the particularity of SACs. In this Perspective, we will summarize the theoretical progress made on the understanding of the rich phenomena in single-atom catalysis. We focus on the determination of local structures of SACs via comparison between experiments and simulations, the discovery of distinctive catalytic mechanisms induced by multiadsorption, synergetic effects, and dynamic evolutions, to name a few, the proposal of criteria for theoretically designing SACs, and the extension of original concepts of single-atom catalysis. We hope that this Perspective will inspire more in-depth thinking on future theoretical studies of SACs.

An electrochemical detection method was introduced for aqueous droplet analysis in oil phase of microfluidic devices. This method is based on the electrochemical signal difference between aqueous and oil. Applying a low alternating current (AC) voltage to a couple of Au microelectrodes, this method can offer size information and ion concentration range from 0.02 mmol/L to 1 mol/L of tens of picoliter to nanoliter aqueous droplets. Alternatively, applying a relative high AC voltage (18 Vpp) at a frequency of 1 kHz leads to electroporation of yeast cells encapsulated into picoliter droplets. We believe that this simple technique is useful for a number of aqueous droplet-based chemical and biological analyses as well as cell electroporation.