Phase-engineering modulation of Mn-based oxide cathode for constructing super-stable sodium storage

The Mn-based oxide cathode with enriched crystal phase structure and component diversity can provide the excellent chemistry structure for Na-ion batteries.Nevertheless,the broad application prospect is obstructed by the sluggish Na^(+)kinetics and the phase transitions upon cycling.Herein,we establish the thermodynamically stable phase diagram of various Mn-based oxide composites precisely controlled by sodium content tailoring strategy coupling with co-doping and solid-state reaction.The chemical environment of the P2/P'3 and P2/P3 biphasic composites indicate that the charge compensation mechanism stems from the cooperative contribution of anions and cations.Benefiting from the no phase transition to scavenge the structure strain,P2/P'3 electrode can deliver long cycling stability(capacity retention of 73.8%after 1000 cycles at 10 C)and outstanding rate properties(the discharge capacity of 84.08 mA h g^(-1)at 20 C)than P2/P3 electrode.Furthermore,the DFT calculation demonstrates that the introducing novel P'3 phase can significantly regulate the Na^(+)reaction dynamics and modify the local electron configuration of Mn.The effective phase engineering can provide a reference for designing other high-performance electrode materials for Na-ion batteries.

A general synthetic strategy to monolayer graphene

The emergence and establishment of new techniques for material fabrication are of fundamental importance in the development of materials science. Thus, we herein report a general synthetic strategy for the preparation of monolayer graphene. This novel synthetic method is based on the direct solid-state pyrolytic conversion of a sodium carboxylate, such as sodium gluconate or sodium citrate, into monolayer graphene in the presence of Na2CO3. In addition, gram-scale quantities of the graphene product can be readily prepared in several minutes. Analysis using Raman spectroscopy and atomic force microscopy clearly demonstrates that the pyrolytic graphene is composed of a monolayer with an average thickness of - 0.50 nm. Thus, the present pyrolytic conversion can overcome the issue of the low monolayer contents （i.e., 1 wt.%-12 wt.%） obtained using exfoliation methods in addition to the low yields of chemical vapor deposition methods. We expect that this novel technique may be suitable for application in the preparation of monolayer graphene materials for batteries, supercapacitors, catalysts, and sensors.

The way to improve the energy density of supercapacitors:Progress and perspective

Compared with other energy storage devices, supercapacitors have superior qualities,including a long cycling life,fast charge/discharge processes,and a high safety rating.The practical use of supercapacitor devices is hindered by their low energy density.Here,we briefly review the factors that influence the energy density of supercapacitors.Furthermore,possible pathways for enhancing the energy density via improving capacitance and working voltage are discussed. In particular,we offer our perspective on the most exciting developments regarding high-energy-density supercapacitors, with an emphasis on future trends.We conclude by discussing the various types of supercapacitors and highlight crucial tasks for achieving a high energy density.

Hierarchical flower-like spinel manganese-based oxide nanosheets for high-performance lithium ion battery

Hierarchical flower-structured two-dimensional(2 D)nanosheet is favorable for electrochemical reactions.The unique structure not only exposes the maximized active sites and shortens ion/electron diffusion channels,but also inhibits the structural strain during cycling processes.Herein,we report the hierarchical flower-like pure spinel manganese-based oxide nanosheets synthesized via a template-orientated strategy.The oriented template is fabricated by decomposition of carbonate obtained from"bubble reaction",via an alcoholassisted hydrothermal process.The resultant spinel manganese-based oxide nanosheets simultaneously possess excellent rate capability and cycling stability.The high-voltage LiNi0.5Mn1.5O4(LNMO-HF)has a uniform phase distribution without the common impurity phase LixNi1-xO2 and NixO.Besides,the LNMO-HF delivers high discharge capacity of142.6 mA h g-with specific energy density of 660.7 W h kg 1 at 1 C under 55℃.More importantly,the template-orientated strategy can be extended to the synthesis of LiMn2 O4(LMO),which can achieve 88.12%capacity retention after 1000 cycles.

Bifunctional catalysts of Co3O4@GCN tubular nanostructured （TNS） hybrids for oxygen and hydrogen evolution reactions

Catalysts for oxygen and hydrogen evolution reactions （OER/HER） are at the heart of renewable green energy sources such as water splitting. Although incredible efforts have been made to develop efficient catalysts for OER and HER, great challenges still remain in the development of bifunctional catalysts. Here, we report a novel hybrid of Co3O4 embedded in tubular nanostructures of graphitic carbon nitride （GCN） and synthesized through a facile, large-scale chemical method at low temperature. Strong synergistic effects between Co3O4 and GCN resulted in excellent performance as a bifunctional catalyst for OER and HER. The high surface area, unique tubular nanostructure, and composition of the hybrid made all redox sites easily available for catalysis and provided faster ionic and electronic conduction. The Co3O4@GCN tubular nanostructured （TNS） hybrid exhibited the lowest overpotential （0.12 V） and excellent current density （147 mA/cm^2） in OER, better than benchmarks IrO2 and RuO2, and with superior durability in alkaline media. Furthermore, the Co3O4@GCN TNS hybrid demonstrated excellent performance in HER, with a much lower onset and overpotential, and a stable current density. It is expected that the Co3O4@GCN TNS hybrid developed in this study will be an attractive alternative to noble metals catalysts in large scale water splitting and fuel cells.

Formation and Optical Properties of ZnO:ZnFe_(2)O_(4) Superlattice Microwires

Pure ZnO hexagonal microwires and Fe(Ⅲ)-doped ZnO microwires(MWs)with a novel rectangular cross section were synthesized in a confined chamber by a convenient one-step thermal evaporation method.An oriented attachment mechanism is consistent with a vapor-solid growth process.Photoluminescence(PL)and Raman spectroscopy of the Fe(Ⅲ)-doped ZnO MWs and in situ spectral mappings indicate a quasi-periodic distribution of Fe(Ⅲ)along a one-dimensional(1-D)superlattice ZnO:ZnFe_(2)O_(4) wire,while PL mapping shows the presence of optical multicavities and related multimodes.The PL spectra at room temperature show weak near-edge doublets(376 nm and 383 nm)and a broad band(450-650 nm)composed of strong discrete lines,due to a 1-D photonic crystal structure.Such a 1-D coupled optical cavity material may find many applications in future photonic and spintronic devices.

Assembly-promoted photocatalysis:Three-dimensional assembly of CdS_(x)Se_(1-x)(x=0-1) quantum dots into nanospheres with enhanced photocatalytic performance

In this paper,through an emulsion-based bottom-up self-assembly method,monodisperse CdS_(x)Se_(1-x)(x=0-1)quantum dots(QDs)with tailoring compositions have been three-dimensionally assembled into spherical architectures in sub-micrometer sizes.UVeVis absorption measurements revealed the enhanced light harvesting abilities of the assembled CdS_(x)Se_(1-x) spheres relative to their constituting QDs.HRTEM characterizations over the CdS_(x)Se_(1-x) assemblies suggested the existence of localized oriented adjoining of the CdS_(x)Se_(1-x) QDs and the resulting nano-twin structures that are favorable for photogenerated electron-hole separation.The quenching of photoluminescence and the improvement in IPCE after the assembly of CdS_(x)Se_(1-x) QDs provided a clue to the likely suppressed electron-hole recombination brought about by the unique architectures and interfaces derived from self-assembly.The above findings were coincided with the remarkably improved H2 evolution activities observed for the wellassembled CdS_(x)Se_(1-x) nanospheres in photocatalytic water splitting,underpinning the importance of the alternative strategy to design advanced semiconductor photocatalysts based on architectural engineering.

Scalable and general synthesis of spinel manganese- based cathodes with hierarchical yolk-shell structure and superior lithium storage properties

Hierarchical yolk-shell structured cathodes with controllable composition are potentially attractive materials for the fabrication of lithium-ion batteries, but they are difficult to synthesize. In this work, we present a simple, scalable, and general morphology-inheritance strategy to synthesize spinel manganese cathodes with a hierarchical yolk-shell structure. Starting from uniform Mn carbonate spheres prepared by an ultrafast and scalable microwave-assisted method, we show that the subsequent sintering results in the formation of Mn203 precursors with a yolk-shell structure, which can be effectively transferred to spinel manganese cathodes via simple impregnation and solid-state reaction. Owing to the simple and scalable nature of the present strategy, materials prepared through this approach have great potential as cathodes of lithium-ion batteries, where they can lead to high specific capacity, outstanding cyclability, and superior rate capability. In particular, both LiMn204 and LiNi05Mn1504 with hierarchical yolk-shell structure achieved nearly theoretical capacity, without any apparent decay after 100 cycles at I C. Moreover, 80% of the initial discharge capacities of both samples can be maintained for up to 500 cycles at a high rate of 10 C.

Constructing Cation Vacancy Defects on NiFe-LDH Nanosheets for Efficient Oxygen Evolution Reaction

Active site exposure and intrinsic catalytic performance are considered important aspects of oxygen evolution reaction catalyst design.In this work,the coordination capacity of tributylphosphine is utilized to construct cationic vacancy defects on NiFe-LDH nanosheets.As-prepared defective NiFe-LDH nanosheets show not only the optimization of the exposure ability of the active site but also the intrinsic catalytic capacity is improved by construction of cationic vacancy defect to tune local electronic structure.The x-ray photoelectron spectroscopy results revealed that after reconstruction of the prepared d-NiFe-LDH,high-valence Ni and Fe can stably appear on the surface of the material.The presence of high-valence Ni and Fe is considered to be the main reason to improve the intrinsic catalytic capacity of catalysts.Finally,d-NiFe-LDH nanosheets show excellent catalytic performance(η_(10)=243 mV)and remarkable long-term stability.