Single copper sites dispersed on defective TiO2-x as a synergistic oxygen reduction reaction catalyst.

Catalysts containing isolated single atoms have attracted much interest due to their good catalytic behavior, bridging the gap between homogeneous and heterogeneous catalysts. Here, we report an efficient oxygen reduction reaction (ORR) catalyst that consists of atomically dispersed single copper sites confined by defective mixed-phased TiO2-x. This synergistic catalyst was produced by introducing Cu2+ to a metal organic framework (MOF) using the Mannich reaction, occurring between the carbonyl group in Cu(acac)2 and the amino group on the skeleton of the MOF. The embedding of single copper atoms was confirmed by atomic-resolution high-angle annular dark-field scanning transmission electron microscopy and x-ray absorption fine structure spectroscopy. Electronic structure modulation of the single copper sites coupling with oxygen vacancies was further established by electron paramagnetic resonance spectroscopy and first-principles calculations. Significantly enhanced ORR activity and stability were achieved on this special Cu single site. The promising application of this novel electrocatalyst was demonstrated in a prototype Zn-air battery. This strategy of the stabilization of single-atom active sites by optimization of the atomic and electronic structure on a mixed matrix support sheds light on the development of highly efficient electrocatalysts.

Structure Engineering of MoS2 via Simultaneous Oxygen and Phosphorus Incorporation for Improved Hydrogen Evolution.

Oxygen and phosphorus dual-doped MoS2 nanosheets (O,P-MoS2 ) with porous structure and continuous conductive network are fabricated using a one-pot NaH2 PO2 -assisted hydrothermal approach. By simply changing the precursor solution, the chemical composition and resulting structure can be effectively controlled to obtain desired properties toward the hydrogen evolution reaction (HER). Thanks to the beneficial structure and strong synergistic effects between the incorporated oxygen and phosphorus, the optimal O,P-MoS2 exhibit superior electrocatalytic performances compared with those of oxygen single-doped MoS2 nanosheets (O-MoS2 ). Specifically, a low HER onset overpotential of 150 mV with a small Tafel slope of 53 mV dec-1 , excellent conductivity, and long-term durability are achieved by the structural engineering of MoS2 via O and P co-doping, making it an efficient HER electrocatalyst for water electrocatalysis. This work provides an alternative strategy to manipulate transition metal dichalcogenides as advanced materials for electrocatalytic and related energy applications.

Tunable Redox Chemistry and Stability of Radical Intermediates in 2D Covalent Organic Frameworks for High Performance Sodium Ion Batteries.

Radicals are inevitable intermediates during the charging and discharging of organic redox electrodes. The increase of the reactivity of the radical intermediates is desirable to maximize the capacity and enhance the rate capability but is detrimental to cycling stability. Therefore, it is a great challenge to controllably balance the redox reactivity and stability of radical intermediates to optimize the electrochemical properties with a good combination of high specific capacity, excellent rate capability, and long-term cycle life. Herein, we reported the redox and tunable stability of radical intermediates in covalent organic frameworks (COFs) considered as high capacity and stable anode for sodium-ion batteries. The comprehensive characterizations combined with theoretical simulation confirmed that the redox of C-O· and α-C radical intermediates play an important role in the sodiation/desodiation process. Specifically, the stacking behavior could be feasibly tuned by the thickness of 2D COFs, essentially determining the redox reactivity and stability of the α-C radical intermediates and their contributive capacity. The modulation of reversible redox chemistry and stabilization mechanism of radical intermediates in COFs offers a novel entry to design novel high performance organic electrode materials for energy storage and conversion.

Lamellarly Stacking Porous N, P Co-Doped Mo2 C/C Nanosheets as High Performance Anode for Lithium-Ion Batteries.

Layered stacking and highly porous N, P co-doped Mo2 C/C nanosheets are prepared from a stable Mo-enhanced hydrogel. The hydrogel is formed through the ultrafast cross-linking of phosphomolybdic acid and chitosan. During the reduction of the composite hydrogel framework under inert gas protection, highly porous N and P co-doped carbon nanosheets are produced with the in situ formation of ultrafine Mo2 C nanoparticles highly distributed throughout the nanosheets which are entangled via a hierarchical lamellar infrastructure. This unique architecture of the N, P co-doped Mo2 C/C nanosheets tremendously promote the electrochemical activity and operate stability with high specific capacity and extremely stable cycling. In particular, this versatile synthetic strategy can also be extended to other polyoxometalate (such as phosphotungstic acid) to provide greater opportunities for the controlled fabrication of novel hierarchical nanostructures for next-generation high performance energy storage applications.

Design, synthesis, and antitumor evaluation of quinoline-imidazole derivatives.

A series of compounds bearing quinoline-imidazole (8a-e, 9a-e, 10a-e, 11a-e, and 12a-e) not reported previously were designed and synthesized. The target compounds were evaluated for antitumor activity against A549, PC-3, HepG2, and MCF-7 cells by the MTT method, with NVP-BEZ235 being the positive control. Most compounds showed moderate activity and compound 12a showed the best activity against HepG2, A549, and PC-3 cells, with half-maximal inhibitory concentration (IC50 ) values of 2.42 ± 1.02 µM, 6.29 ± 0.99 µM, and 5.11 ± 1.00 µM, respectively, which was equal to NVP-BEZ235 (0.54 ± 0.13 µM, 0.36 ± 0.06 µM, 0.20 ± 0.01 µM). Besides, the IC50 value of 12a against the cell line WI-38 (human fetal lung fibroblasts) was 32.8 ± 1.23 µM, indicating that the target compounds were selective for cancer cells. So, 11a and 12a were evaluated against PI3Kα and mTOR to find out if the compounds acted through the PI3K-Akt-mTOR signal transduction pathway. The inhibition ratios to PI3Kα and mTOR were slightly lower than that of NVP-BEZ235, suggesting there may be some other mechanisms of action. The structure-activity relationships and docking study of 11a and 12a revealed that the latter was superior. Moreover, the target compounds showed better in vitro anticancer activity when the C-6 of the quinoline ring was replaced by a bromine atom.

Multistimuli-Responsive, Moldable Supramolecular Hydrogels Cross-Linked by Ultrafast Complexation of Metal Ions and Biopolymers.

A new type of multistimuli-responsive hydrogels cross-linked by metal ions and biopolymers is reported. By mixing the biopolymer chitosan (CS) with a variety of metal ions at the appropriate pH values, we obtained a series of transparent and stable hydrogels within a few seconds through supramolecular complexation. In particular, the CS-Ag hydrogel was chosen as the model and the gelation mechanism was revealed by various measurements. It was found that the facile association of Ag(+) ions with amino and hydroxy groups in CS chains promoted rapid gel-network formation. Interestingly, the CS-Ag hydrogel exhibits sharp phase transitions in response to multiple external stimuli, including pH value, chemical redox reactions, cations, anions, and neutral species. Furthermore, this soft matter showed a remarkable moldability to form shape-persistent, free-standing objects by a fast in situ gelation procedure.

Redox of Dual-Radical Intermediates in a Methylene-Linked Covalent Triazine Framework for High-Performance Lithium-Ion Batteries.

Covalent triazine frameworks (CTFs) are promising electrodes for rechargeable batteries due to their adjustable structures, rich redox sites, and tunable porosity. However, the CTFs usually exhibit inferior electrochemical stability because of the inactivation of the unstable radical intermediates. Here, a methylene-linked CTF has been synthesized and evaluated as a cathode for rechargeable lithium-ion batteries. Electron paramagnetic resonance (EPR) and in situ Raman characterizations demonstrated that the redox activity and reversibility of α-C and triazine radical intermediates are essentially important for the charging/discharging process, which have been efficiently stabilized by the synergetic π conjugation and hindrance effect caused by the adjacent rigid triazine rings and benzene rings in the unique CTF-p framework. Additionally, the methylene groups provided extra redox-active sites. As a result, high capacity and cycling stability were achieved. This work inspires the rational modulation of the radical intermediates to enhance the electrochemical performance of organic electrode materials for the next-generation energy storage devices.

A Co-Doped Nanorod-like RuO2 Electrocatalyst with Abundant Oxygen Vacancies for Acidic Water Oxidation.

Active and highly stable electrocatalysts for oxygen evolution reaction (OER) in acidic media are currently in high demand as a cleaner alternative to the combustion of fossil fuels. Herein, we report a Co-doped nanorod-like RuO2 electrocatalyst with an abundance of oxygen vacancies achieved through the facile, one-step annealing of a Ru-exchanged ZIF-67 derivative. The compound exhibits ultra-high OER performance in acidic media, with a low overpotential of 169 mV at 10 mA cm-2 while maintaining excellent activity, even when exposed to a 50-h galvanostatic stability test at a constant current of 10 mA cm-2. The dramatic enhancement in OER performance is mainly attributed to the abundance of oxygen vacancies and modulated electronic structure of the Co-doped RuO2 that rely on a vacancy-related lattice oxygen oxidation mechanism (LOM) rather than adsorbate evolution reaction mechanism (AEM), as revealed and supported by experimental characterizations as well as density functional theory (DFT) calculations.

A novel Mn/Co dual nanoparticle decorated hierarchical carbon structure derived from a biopolymer hydrogel as a highly efficient electro-catalyst for the oxygen reduction reaction.

A Mn/Co dual nanoparticle-decorated hierarchical carbon structure was derived from a Zn/Mn/Co/chitosan composite hydrogel. This strategy critically relied on the formation of a supramolecularly crosslinked hydrogel that allowed the efficient and homogeneous incorporation of highly active Mn/Co species onto the surface of hierarchical carbon structures. The resultant electrocatalyst outperformed Pt/C toward the oxygen reduction reaction in 0.1 M KOH electrolytes.

Self-supported nickel iron oxide nanospindles with high hydrophilicity for efficient oxygen evolution.

Engineering nanoarray structures with favorable hydrophilicity is proposed to unlock the electrocatalysis of NiFe2O4 for the oxygen evolution reaction (OER). The resulting electrode, consisting of NiFe2O4 nanospindles directly grown on FeNi3 foam, features enlarged active surface area, high hydrophilicity and increased electronic conductivity, which achieves superior OER activity and remarkable durability.

Hybrid digital holographic imaging system for three-dimensional dense particle field measurement.

To apply digital holography to the measurement of three-dimensional dense particle fields in large facilities, we have developed a hybrid digital holographic particle-imaging system. The technique combines the advantages of off-axis (side) scattering in suppressing speckle noise and on-axis (in-line) recording in lowering the digital sensor resolution requirement. A camera lens is attached to the digital sensor to compensate for the weak object wave from side scattering over a large recording distance. A simple numerical reconstruction algorithm is developed for holograms recorded with a lens without requiring complex and impractical mathematical corrections. We analyze the effect of image sensor resolution and off-axis angle on system performance and quantify the particle positioning accuracy of the system. The holographic system is successfully applied to the study of inertial particle clustering in isotropic turbulence.

A new ether-based electrolyte for lithium sulfur batteries using a S@pPAN cathode.

A new electrolyte composed of 4 M LiFSI in dibutyl ether (DBE) is proposed for Li-S batteries. Dissolution of lithium polysulfides is definitely inhibited by DBE. More impressively, the electrolyte ensures a high Coulombic efficiency for Li deposition/stripping (∼99.2%) without dendrite growth. Enhanced cycling stability is demonstrated when coupled with a sulfurized poly(acrylonitrile) (S@pPAN) cathode. This electrolyte offers new insight into electrolyte design for high performance Li-S batteries.

Synergistic Effects of C/α-MoC and Ag for Efficient Oxygen Reduction Reaction.

It remains challenging to prepare highly active and stable catalysts from earth-abundant elements for the oxygen reduction reaction (ORR). Herein we report a facile method to synthesize cost-effective heterogeneous C/α-MoC/Ag electrocatalysts. Rotating disc electrode (RDE) experiments revealed that the obtained C/α-MoC/Ag exhibited much superior catalytic performance for ORR than that of C/Ag, C/α-MoC, or even the conventional Pt/C. First-principles calculations indicated that the enhanced activity could be attributed to the efficient synergistic effects between Ag and α-MoC/C by which the energy barrier for O2 dissociation has been substantially reduced. Furthermore, Li-air and Al-air cells were assembled to demonstrate the unprecedented electrochemical performance of C/α-MoC/Ag nanocomposites surpassing the Pt/C. Thus experimental results and theoretical calculations together showed that the heterogeneous C/α-MoC/Ag nanocomposites are a promising alternative to platinum for applications in industrial metal-air batteries.

Biopolymer-chitosan based supramolecular hydrogels as solid state electrolytes for electrochemical energy storage.

A biopolymer-chitosan based Supramolecular Hydrogel type solid state Electrolyte (SHE) is prepared via a simple and fast cross-linking between chitosan and Li+/Ag+. The obtained SHE itself shows high thermal stability and excellent flexible and mouldable properties. When integrated in an asymmetric supercapacitor with MnO2 as the positive electrode and active carbon as the negative electrode, it can survive more than 10 000 cycles with the areal capacity of 10 mF cm-2 at the 1.8 mA cm-2 current density.

Supramolecular hydrogel directed self-assembly of C- and N-doped hollow CuO as high-performance anode materials for Li-ion batteries.

A novel hollow-structured CuO derived from chitosan-coated Cu/Cu2O composite hollow spheres was mass produced via a supramolecular hydrogel templating method and homogeneously co-doped with C and N. Evaluation of the as-produced co-doped CuO hollow spheres as anode materials for Li ion batteries showed that they had superior electrochemical properties.

Low-Cost and Novel Si-Based Gel for Li-Ion Batteries.

Si-based nanostructure composites have been intensively investigated as anode materials for next-generation lithium-ion batteries because of their ultra-high-energy storage capacity. However, it is still a great challenge to fabricate a perfect structure satisfying all the requirements of good electrical conductivity, robust matrix for buffering large volume expansion, and intact linkage of Si particles upon long-term cycling. Here, we report a novel design of Si-based multicomponent three-dimensional (3D) networks in which the Si core is capped with phytic acid shell layers through a facile high-energy ball-milling method. By mixing the functional Si with graphene oxide and functionalized carbon nanotube, we successfully obtained a homogeneous and conductive rigid silicon-based gel through complexation. Interestingly, this Si-based gel with a fancy 3D cross-linking structure could be writable and printable. In particular, this Si-based gel composite delivers a moderate specific capacity of 2711 mA h g-1 at a current density of 420 mA g-1 and retained a competitive discharge capacity of more than 800.00 mA h g-1 at the current density of 420 mA g-1 after 700 cycles. We provide a new method to fabricate durable Si-based anode material for next-generation high-performance lithium-ion batteries.

Highly durable organic electrode for sodium-ion batteries via a stabilized α-C radical intermediate.

It is a challenge to prepare organic electrodes for sodium-ion batteries with long cycle life and high capacity. The highly reactive radical intermediates generated during the sodiation/desodiation process could be a critical issue because of undesired side reactions. Here we present durable electrodes with a stabilized α-C radical intermediate. Through the resonance effect as well as steric effects, the excessive reactivity of the unpaired electron is successfully suppressed, thus developing an electrode with stable cycling for over 2,000 cycles with 96.8% capacity retention. In addition, the α-radical demonstrates reversible transformation between three states: C=C; α-C·radical; and α-C- anion. Such transformation provides additional Na+ storage equal to more than 0.83 Na+ insertion per α-C radical for the electrodes. The strategy of intermediate radical stabilization could be enlightening in the design of organic electrodes with enhanced cycling life and energy storage capability.

A high performance O2 selective membrane based on CAU-1-NH2@polydopamine and the PMMA polymer for Li-air batteries.

A novel mixed matrix membrane (MMM) was prepared by incorporating polydopamine-coated metal organic framework (MOF) crystals of CAU-1-NH2 into a PMMA (polymethylmethacrylate) matrix. The MMM possesses the advantages of high O2 permeability, high capability of carbon dioxide capture, and excellent hydrophobic behavior. The MMM was assembled in the Li-air batteries which displayed promising electrochemical performance in the real ambient air with 30% relative humidity.

Facile synthesis of spinel CuCo2O4 nanocrystals as high-performance cathode catalysts for rechargeable Li-air batteries.

CuCo2O4 nanoparticles have been synthesized by a simple and low-cost urea combustion method and characterized as bifunctional catalysts for non-aqueous Li-air batteries. The resulting CuCo2O4 catalyst has been demonstrated to effectively reduce the charge-discharge polarization of Li-air batteries in a simulated air environment (80% Ar : 20% O2).

A highly permeable mixed matrix membrane containing CAU-1-NH2 for H2 and CO2 separation.

A thin and compact mixed matrix membrane containing CAU-1-NH2 and the poly(methyl methacrylate) polymer has been originally synthesized. The as-prepared membrane exhibits high permeability of H2 and excellent H2/CO2 selectivity.