Hierarchical Li electrochemistry using alloy-type anode for high-energy-density Li metal batteries.

Exploiting thin Li metal anode is essential for high-energy-density battery, but is severely plagued by the poor processability of Li, as well as the uncontrollable Li plating/stripping behaviors and Li/electrolyte interface. Herein, a thickness/capacity-adjustable thin alloy-type Li/LiZn@Cu anode is fabricated for high-energy-density Li metal batteries. The as-formed lithophilic LiZn alloy in Li/LiZn@Cu anode can effectively regulate Li plating/stripping and stabilize the Li/electrolyte interface to deliver the hierarchical Li electrochemistry. Upon charging, the Li/LiZn@Cu anode firstly acts as Li source for homogeneous Li extraction. At the end of charging, the de-alloy of LiZn nanostructures further supplements the Li extraction, actually playing the Li compensation role in battery cycling. While upon discharging, the LiZn alloy forms just at the beginning, thereby regulating the following Li homogeneous deposition. The reversibility of such an interesting process is undoubtedly verified from the electrochemistry and in-situ XRD characterization. This work sheds light on the facile fabrication of practical Li metal anodes and useful Li compensation materials for high-energy-density Li metal batteries.

Sustainable Anionic Redox by Inhibiting Li Cross-Layer Migration in Na-Based Layered Oxide Cathodes.

The irrational utilization of an anionic electron often accompanies structural degradation with an irreversible cation migration process upon cycling in sodium-layered oxide cathodes. Moreover, the insufficient understanding of the anionic redox involved cation migration makes the design strategies of high energy density electrodes even less effective. Herein, a P3-Na0.67Li0.2Fe0.2Mn0.6O2 (P3-NLFM) cathode is proposed with the in-plane disordered Li distribution after an in-depth remolding of the Li ribbon-ordered P3-Na0.6Li0.2Mn0.8O2 (P3-NLM) layered oxide. The disordered Li sublattice in the transition metal slab of P3-NLFM leads to the dispersed |O2p orbitals, the lowered charge transfer gap, and the suppressed phase transition at high voltages. Then the enhanced Mn-O interaction and electronic stability are disclosed by the crystal orbital Hamilton population (COHP) analysis at high voltage in P3-NLFM. Furthermore, ab initio molecular dynamics (AIMD) simulation suggests the order/disorder of the transition metal layer is highly correlated with the stability of the Li sublattice. The cross-layer migration and loss of Li in P3-NLM are suppressed in P3-NLFM to enable the high reversibility upon cycling. As a result, the P3-NLFM delivers a high capacity of 163 mAh g-1 without oxygen release and an enhanced capacity retention of 81.9% (vs 42.9% in P3-NLM) after 200 cycles, which constitutes a promising approach for sustainable oxygen redox in rechargeable batteries.

Controllable Synthesis of 2D Materials by Electrochemical Exfoliation for Energy Storage and Conversion Application.

2D materials have captured much recent research interest in a broad range of areas, including electronics, biology, sensors, energy storage, and others. In particular, preparing 2D nanosheets with high quality and high yield is crucial for the important applications in energy storage and conversion. Compared with other prevailing synthetic strategies, the electrochemical exfoliation of layered starting materials is regarded as one of the most promising and convenient methods for the large-scale production of uniform 2D nanosheets. Here, recent developments in electrochemical delamination are reviewed, including protocols, categories, principles, and operating conditions. State-of-the-art methods for obtaining 2D materials with small numbers of layers-including graphene, black phosphorene, transition metal dichalcogenides and MXene-are also summarized and discussed in detail. The applications of electrochemically exfoliated 2D materials in energy storage and conversion are systematically reviewed. Drawing upon current progress, perspectives on emerging trends, existing challenges, and future research directions of electrochemical delamination are also offered.

Advanced Composite Lithium Metal Anodes with 3D Frameworks: Preloading Strategies, Interfacial Optimization, and Perspectives.

Lithium (Li) metal is regarded as the most promising anode candidate for next-generation rechargeable storage systems due to its impeccable capacity and the lowest electrochemical potential. Nevertheless, the irregular dendritic Li, unstable interface, and infinite volume change, which are the intrinsic drawbacks rooted in Li metal, give a seriously negative effect on the practical commercialization for Li metal batteries. Among the numerous optimization strategies, designing a 3D framework with high specific surface area and sufficient space is a convincing way out to ameliorate the above issues. Due to the Li-free property of the 3D framework, a Li preloading process is necessary before the 3D framework that matches with the electrolyte and cathode. How to achieve homogeneous integration with Li and 3D framework is essential to determine the electrochemical performance of Li metal anode. Herein, this review overviews the recent general fabrication methods of 3D framework-based composite Li metal anode, including electrodeposition, molten Li infusion, and pressure-derived fabrication, with the focus on the underlying mechanism, design criteria, and interfacial optimization. These results can give specific perspectives for future Li metal batteries with thin thickness, low N/P ratio, lean electrolyte, and high energy density (>350 Wh Kg-1 ).

Slight compositional variation-induced structural disorder-to-order transition enables fast Na+ storage in layered transition metal oxides.

The omnipresent Na+/vacancy orderings change substantially with the composition that inevitably actuate the ionic diffusion in rechargeable batteries. Therefore, it may hold the key to the electrode design with high rate capability. Herein, the influence of Na+/vacancy ordering on Na+ mobility is demonstrated firstly through a comparative investigation in P2-Na2/3Ni1/3Mn2/3O2 and P2-Na2/3Ni0.3Mn0.7O2. The large zigzag Na+/vacancy intralayer ordering is found to accelerate Na+ migration in P2-type Na2/3Ni1/3Mn2/3O2. By theoretical simulations, it is revealed that the Na+ ordering enables the P2-type Na2/3Ni1/3Mn2/3O2 with higher diffusivities and lower activation energies of 200 meV with respect to the P3 one. The quantifying diffusional analysis further prove that the higher probability of the concerted Na+ ionic diffusion occurs in P2-type Na2/3Ni1/3Mn2/3O2 due to the appropriate ratio of high energy ordered Na ions (Naf) occupation. As a result, the interplay between the Na+/vacancy ordering and Na+ kinetic is well understood in P2-type layered cathodes.

Sustainable LiCoO2 by collective glide of CoO6 slabs upon charge/discharge.

SignificanceTraditional views indicate that the well-known layered LiCoO2 cathode delivers a typical solid-solution reaction upon delithiation. The problem is that "solid solution" is a vague concept, and the phase transition remains ambiguous. Here, we reveal a mechanism with the collective and quasi-continuous glide of CoO6 slabs in layered LiCoO2 through combining in situ XRD and ex situ STEM characterizations. Such a delithiation mechanism does not involve the nucleation-and-growth-type delithiation process and represents a completely different manner from the conventional two-phase or solid solution-phase transition processes. The lessons provide a different insight into understanding the working mechanism of layered oxide materials.

Accelerated Ionic and Charge Transfer through Atomic Interfacial Electric Fields for Superior Sodium Storage.

Atomic interfacial electric fields hold great potential for boosting ionic and charge transfer and accelerating electrochemical reaction kinetics. Here, built-in electric fields within the heterostructure are created by electrostatic assembly of unilamellar titano-niobate/graphene (reduced graphene oxide) nanosheets as building blocks. Scanning Kelvin probe microscopy confirms the existence of built-in electric fields by detecting the unbalanced surface potential of disparate nanosheets in the heterostructure, which facilitates ion and electron transfer, thus enabling an excellent reversible sodium storage capacity of 245 mAh g-1 at 0.05 A g-1. Theoretical analysis also confirms that the electric field can enhance the electric conductivity and facilitate electron transfer at the atomic interface. Moreover, in situ TEM observations confirm the homogeneous intercalation of sodium ions and very small volume expansion of the hybrid materials. As a result, a highly stable lifetime of 3000 cycles is achieved with capacity retention of 98.8%. This work attests the importance of accelerating ionic and charge transfer through atomic interfacial electric field for superior sodium storage.

Molecular-Scale Manipulation of Layer Sequence in Heteroassembled Nanosheet Films toward Oxygen Evolution Electrocatalysts.

Flocculation or restacking of different kinds of two-dimensional (2D) nanosheets into heterostructure nanocomposites is of interest for the development of high-performance electrode materials and catalysts. However, lacking a molecular-scale control on the layer sequence hinders enhancement of electrochemical activity. Herein, we conducted electrostatic layer-by-layer (LbL) assembly, employing oxide nanosheets (e.g., MnO2, RuO2.1, reduced graphene oxide (rGO)) and layered double hydroxide (LDH) nanosheets (e.g., NiFe-based LDH) to explore a series of mono- and bilayer films with various combinations of nanosheets and sequences toward oxygen evolution reaction (OER). The highest OER activity was attained in bilayer films of electrically conductive RuO2.1 nanosheets underlying catalytically active NiFe LDH nanosheets with mixed octahedral/tetrahedral coordination (NiFe LDHTd/Oh). At an overpotential of 300 mV, the RuO2.1/NiFe LDHTd/Oh film exhibited an electrochemical surface area (ECSA) normalized current density of 2.51 mA cm-2ECSA and a mass activity of 3610 A g-1, which was, respectively, 2 and 5 times higher than that of flocculated RuO2.1/NiFe LDHTd/Oh aggregates with a random appearance of a surface layer. First-principles density functional theory calculations and COMSOL Multiphysics simulations further revealed that the improved catalytic performance was ascribed to a substantial electronic coupling effect in the heterostructure, in which electrons are transferred from exposed NiFe LDHTd/Oh nanosheets to underneath RuO2.1. The study provides insight into the rational control and manipulation of redox-active surface layers and conductive underlying layers in heteroassembled nanosheet films at molecular-scale precision for efficient electrocatalysis.

Heterostructured Pd/Ti/Pd Thin Films as Highly Efficient Catalysts for Methanol and Formic Acid Oxidation.

Finding a highly efficient catalyst for proton exchange membrane fuel cells is still the subject of extensive research. This article describes heterostructured Pd/Ti/Pd bimetallic thin films prepared using a strain-release technology as electrocatalysts for fuel cells. With their particular structure, these materials exhibit intriguing electrocatalytic activity toward the oxidation of both methanol and formic acid, yielding current densities of 0.17 and 0.56 A mg-1Pd, much superior to that of the commercial Pd black catalyst. Moreover, the Pd/Ti/Pd thin films display a low onset oxidation potential and extremely high current retention in both acidic and alkaline media. The carbon monoxide poisoning resistance is also significantly enhanced, thus contributing to ultrahigh stability in the long-term electrocatalytic processes. Their encouraging performance implies that such composites could be potential materials for energy conversion in the fuel cell field.

Tunable Doping of Rhenium and Vanadium into Transition Metal Dichalcogenides for Two-Dimensional Electronics.

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) with unique electrical properties are fascinating materials used for future electronics. However, the strong Fermi level pinning effect at the interface of TMDCs and metal electrodes always leads to high contact resistance, which seriously hinders their application in 2D electronics. One effective way to overcome this is to use metallic TMDCs or transferred metal electrodes as van der Waals (vdW) contacts. Alternatively, using highly conductive doped TMDCs will have a profound impact on the contact engineering of 2D electronics. Here, a novel chemical vapor deposition (CVD) using mixed molten salts is established for vapor-liquid-solid growth of high-quality rhenium (Re) and vanadium (V) doped TMDC monolayers with high controllability and reproducibility. A tunable semiconductor to metal transition is observed in the Re- and V-doped TMDCs. Electrical conductivity increases up to a factor of 108 in the degenerate V-doped WS2 and WSe2 . Using V-doped WSe2 as vdW contact, the on-state current and on/off ratio of WSe2 -based field-effect transistors have been substantially improved (from ≈10-8 to 10-5 A; ≈104 to 108 ), compared to metal contacts. Future studies on lateral contacts and interconnects using doped TMDCs will pave the way for 2D integrated circuits and flexible electronics.

Nitrogen and boron doped carbon layer coated multiwall carbon nanotubes as high performance anode materials for lithium ion batteries.

Lithium ion batteries (LIBs) are at present widely used as energy storage and conversion device in our daily life. However, due to the limited power density, the application of LIBs is still restricted in some areas such as commercial vehicles or heavy-duty trucks. An effective strategy to solve this problem is to increase energy density through the development of battery materials. At the same time, a stable long cycling battery is a great demand of environmental protection and industry. Herein we present our new materials, nitrogen and boron doped carbon layer coated multiwall carbon nanotubes (NBC@MWCNTs), which can be used as anodes for LIBs. The electrochemical results demonstrate that the designed NBC@MWCNTs electrode possesses high stable capacity over an ultra-long cycling lifespan (5000 cycles) and superior rate capability even at very high current density (67.5 A g-1). Such impressive lithium storage properties could be ascribed to the synergistic coupling effect of the distinctive structural features, the reduced diffusion length of lithium ions, more active sites generated by doped atoms for lithium storage, as well as the enhancement of the electrode structural integrity. Taken together, these results indicate that the N, B-doped carbon@MWCNTs materials may have great potential for applications in next-generation high performance rechargeable batteries.

CoNiFe Layered Double Hydroxide/RuO2.1 Nanosheet Superlattice as Carbon-Free Electrocatalysts for Water Splitting and Li-O2 Batteries.

Efficient electrocatalysts are highly demanded for oxygen evolution reaction (OER) in water splitting and metal-air batteries. Here, superlattice structured materials composed of CoNiFe layered double hydroxide (LDH)/ruthenium oxide nanosheets are synthesized as carbon-free electrocatalysts for OER. The positively charged CoNiFe LDH and negatively charged RuO2.1 are alternately stacked at the molecular level into superlattice-like hybrids by electrostatic interaction upon mixing their dispersions under suitable conditions. Such heterostructured composites are found to act as effective catalysts toward OER of water splitting with a small overpotential of 281 mV and Tafel plot of 48.9 mV/decade. Such composites also serve as efficient carbon-free cathode catalysts for aprotic Li-O2 batteries with remarkable higher specific capacities and lower overvoltages than RuO2 nanoparticles. The superior performance may be attributed to the peculiar superlattice structure, resulting in strong interfacial electronic coupling, better electrical conductivity, and the suppression of side reactions caused by traditional carbon-based materials. Furthermore, potential difference between RuO2.1 and CoNiFe LDH nanosheets is observed directly by scanning Kelvin probe microscopy, indicating that electrostatic fields might be induced in the superlattice structures to benefit the transport of electrons and charged ions as well as the catalytic process.

On/Off Boundary of Photocatalytic Activity between Single- and Bilayer MoS2.

Molecularly thin two-dimensional (2D) semiconductors are emerging as photocatalysts owing to their layer-number-dependent quantum effects and high charge separation efficiency. However, the correlation among the dimensionality, crystallinity, and photocatalytic activity of such 2D nanomaterials remains unclear. Herein, a Ag photoreduction technique coupled with microscopic analyses is employed to spatially resolve the photocatalytic activity of MoS2 as a model catalyst. Interestingly, we find that only monolayer (1L)-MoS2 is active for a Ag photoreduction reaction. The photocatalytic activity of 1L-MoS2 is enhanced by a built-in electrical field originated from the MoS2/SiO2 interface, instead of by the specific surface structure and quantum electronic state of 1L-MoS2. Furthermore, we observe photocatalytic active sites to be geometrically distributed on triangular 1L-MoS2 crystals, wherein the Ag particles are preferentially deposited on the outermost zigzag edges and defective inner parts of the triangular grains. The degradation of photocatalytic activity and electron mobility with the formation of Mo(VI) species indicates that the species inhibit the in-plane diffusion of the photogenerated electrons to the reductive sites. The monolayer-selectivity, activation, and inactivation mechanisms, unveiled in this work, will offer future directions in designing 2D nanophotocatalysts.

Two-Dimensional Bimetallic Zn/Fe-Metal-Organic Framework (MOF)-Derived Porous Carbon Nanosheets with a High Density of Single/Paired Fe Atoms as High-Performance Oxygen Reduction Catalysts.

Developing efficient non-precious-metal catalysts to accelerate the sluggish oxygen reduction reaction (ORR) is highly desired but remains a great challenge. Herein, using 2D bimetallic Zn/Fe-MOF as the precursor and g-C3N4 as the nitrogen source and stabilizer, porous carbon nanosheets doped with large amounts of single/paired Fe atoms (3.89 wt %) and N (10.28 wt %) are successfully prepared. It is found that the addition of g-C3N4 plays a key role in achieving a high loading of Fe single/paired atoms, and the 2D nanosheet structure gives the materials a high surface area and highly porous structure, resulting in outstanding ORR catalytic activity in both alkaline and acidic solutions. Our optimal sample achieved half-wave potentials in alkaline and acid media of up to 0.86 and 0.79 V (vs reversible hydrogen electrode (RHE)), respectively, values 20 mV higher than a commercial Pt/C catalyst in an alkaline medium and only 60 mV lower than Pt/C in an acidic medium. Moreover, its ORR durability was superior to that of commercial Pt/C in both electrolytes. We found that almost all the doped Fe in the sample existed as single or paired atoms coordinated with N. This work may provide an effective strategy for preparing high-performance catalysts bearing single/paired atoms by using MOFs as precursors.

2D Layered Double Hydroxide Nanosheets and Their Derivatives Toward Efficient Oxygen Evolution Reaction.

Layered double hydroxides (LDHs) have attracted tremendous research interest in widely spreading applications. Most notably, transition-metal-bearing LDHs are expected to serve as highly active electrocatalysts for oxygen evolution reaction (OER) due to their layered structure combined with versatile compositions. Furthermore, reducing the thickness of platelet LDH crystals to nanometer or even molecular scale via cleavage or delamination provides an important clue to enhance the activity. In this review, recent progresses on rational design of LDH nanosheets are reviewed, including direct synthesis via traditional coprecipitation, homogeneous precipitation, and newly developed topochemical oxidation as well as chemical exfoliation of parent LDH crystals. In addition, diverse strategies are introduced to modulate their electrochemical activity by tuning the composition of host metal cations and intercalated counter-anions, and incorporating dopants, cavities, and single atoms. In particular, hybridizing LDHs with conductive components or in situ growing them on conductive substrates to produce freestanding electrodes can further enhance their intrinsic catalytic activity. A brief discussion on future research directions and prospects is also summarized.

All solid-state lithium-oxygen batteries with MOF-derived nickel cobaltate nanoflake arrays as high-performance oxygen cathodes.

Solid-state Li1+xAlxGe2-x(PO4)3 electrolytes with high ionic conductivity were prepared and successfully applied in lithium-oxygen batteries (LOBs). Combined with MOF-derived NiCo2O4 cathodes, the solid-state LOBs deliver a high discharge capacity and good rate performance. Moreover, enabled by such a bifunctional cathode, the as-assembled solid-state LOBs show enhanced reversibility and long-term cycling stability over 90 cycles.

Graphene-Activated Optoplasmonic Nanomembrane Cavities for Photodegradation Detection.

Graphene, with its excellent chemical stability, biocompatibility, and capability of electric field enhancement, has a great potential in optical and optoelectronic applications with superior performances by integrating with conventional optical and plasmonic devices. Here, we design and demonstrate graphene-activated optoplasmonic cavities based on rolled-up nanomembranes, which are employed for in situ monitoring the photodegradation dynamics of organic dye molecules on the molecular level in real time. The presence of the graphene layer significantly enhances the electric field of hybrid optoplasmonic modes at the cavity surface, enabling a highly sensitive surface detection. The degradation of rhodamine 6G molecules on the graphene-activated sensor surface is triggered by localized laser irradiation and monitored by measuring the optical resonance shift. Our demonstration paves the way for real-time, high-precision analysis of photodegradation by resonance-based optical sensors, which promises the comprehensive understanding of degradation mechanism and exploration of effective photocatalysts.

Optimization of N-Substituted Oseltamivir Derivatives as Potent Inhibitors of Group-1 and -2 Influenza A Neuraminidases, Including a Drug-Resistant Variant.

On the basis of our earlier discovery of N1-selective inhibitors, the 150-cavity of influenza virus neuraminidases (NAs) could be further exploited to yield more potent oseltamivir derivatives. Among the synthesized compounds, 15b and 15c were exceptionally active against both group-1 and -2 NAs. Especially for 09N1, N2, N6, and N9 subtypes, they showed 6.80-12.47 and 1.20-3.94 times greater activity than oseltamivir carboxylate (OSC). They also showed greater inhibitory activity than OSC toward H274Y and E119V variant. In cellular assays, they exhibited greater potency than OSC toward H5N1, H5N2, H5N6, and H5N8 viruses. 15b demonstrated high metabolic stability, low cytotoxicity in vitro, and low acute toxicity in mice. Computational modeling and molecular dynamics studies provided insights into the role of R group of 15b in improving potency toward group-1 and -2 NAs. We believe the successful exploitation of the 150-cavity of NAs represents an important breakthrough in the development of more potent anti-influenza agents.

In Situ Generation of Plasmonic Nanoparticles for Manipulating Photon-Plasmon Coupling in Microtube Cavities.

In situ generation of silver nanoparticles for selective coupling between localized plasmonic resonances and whispering-gallery modes (WGMs) is investigated by spatially resolved laser dewetting on microtube cavities. The size and morphology of the silver nanoparticles are changed by adjusting the laser power and irradiation time, which in turn effectively tune the photon-plasmon coupling strength. Depending on the relative position of the plasmonic nanoparticles spot and resonant field distribution of WGMs, selective coupling between the localized surface plasmon resonances (LSPRs) and WGMs is experimentally demonstrated. Moreover, by creating multiple plasmonic-nanoparticle spots on the microtube cavity, the field distribution of optical axial modes is freely tuned due to multicoupling between LSPRs and WGMs. The multicoupling mechanism is theoretically investigated by a modified quasipotential model based on perturbation theory. This work provides an in situ fabrication of plasmonic nanoparticles on three-dimensional microtube cavities for manipulating photon-plasmon coupling which is of interest for optical tuning abilities and enhanced light-matter interactions.

The discovery of novel diarylpyri(mi)dine derivatives with high level activity against a wide variety of HIV-1 strains as well as against HIV-2.

By means of structure-based molecular hybridization strategy, a series of novel diarylpyri(mi)dine derivatives targeting the entrance channel of HIV-1 reverse transcriptase (RT) were designed, synthesized and evaluated as potent non-nucleoside reverse transcriptase inhibitors (NNRTIs). Encouragingly, all the tested compounds showed good activities against wild-type (WT) HIV-1 (IIIB) with EC50 in the range of 1.36 nM-29 nM, which is much better than those of nevirapine (NVP, EC50 = 125.42 nM) and azidothymidine (AZT, EC50 = 11.36 nM). Remarkably, these compounds also displayed effective activity against the most of the single and double-mutated HIV-1 strains with low EC50 values, which is comparable to the control drugs. Besides, these compounds were also exhibited favorable enzymatic inhibitory activity. Moreover, preliminary structure-activity relationships (SARs) and molecular modeling study were investigated and discussed in detail. Unexpectedly, four diarylpyrimidines yielded moderate anti-HIV-2 activities. To our knowledge, this is rarely reported that diarylpyrimidine-based NNRTIs have potent activity against both HIV-1 and HIV-2 in cell culture.