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The 3D (three-dimensional) oriented nanosheet array FeNi2P electrocatalyst grown on carbon cloth (FeNi2P/CC) is explored in this work. This unique 3D oriented nanosheet array structure can expose more catalytic active sites, promote the penetration of electrolyte solution on the catalyst surface, and facilitate the transfer of ions, thus speeding up the kinetic process of Hydrogen evolution reaction (HER) and Oxygen evolution reaction (OER). At the current densities of 10 mA/cm2 in 1 M KOH solution, the HER overpotential (71 mV) of the FeNi2P/CC self-supporting electrode is very close to that of noble metal HER catalyst of 20% Pt/C (54 mV), and its OER overpotential (210 mV) is 34% lower than that of the precious metal OER catalyst of RuO2 (318 mV), demonstrating the excellent electrocatalytic performance of the FeNi2P/CC catalyst. Moreover, the cell voltage for full water splitting (at 10 mA/cm2 current densities) of the FeNi2P/CC bifunctional electrode cell is 1.52 V, which is 3.8% lower than that of the full noble-metal electrode reference cell (RuO2 || Pt/C, 1.58 V), suggesting that this FeNi2P/CC bifunctional catalyst is likely to replace precious metals to reduce the costs in full water splitting application. According to density functional theory (DFT) calculation results, the introduction of iron atom can change the electronic structure of the Ni2P, so it can reduce the adsorption energy of hydrogen and oxygen, and facilitate the adsorption and desorption of hydrogen and oxygen on the surface of the catalyst, improving its performance of HER and OER.

TiO2 nanostructures have been one of the most explored metal oxides photocatalysts to apply for environmental remediation. However, its wide band gap results in the underutilization of sunlight for degradation of pollutants. In order to overcome this handicap, the synthesis of TiO2-based composite has brought extraordinary materials. In this study, we design and prepare TiO2/Nb2O5 heterostructures with different molar ratios by using peroxotitanium and peroxoniobium complex as precursors in aqueous solution. The TiO2 exists in the form of anatase while Nb2O5 is amorphous in the composite, leading to a special crystalline TiO2/amorphous Nb2O5 heterostructures. In particular, Nb element is also doped and Ti3+ ions are formed in the TiO2 lattice, leading to a reduced band gap. The unique TiO2/0.25Nb2O5 (Ti:Nb = 2:1) heterostructures can effectively suppress the recombination of photogenerated electrons and holes, and facilitate the charge transfer, resulting in the optimum photocatalytic performance. The nitrogen oxide removal efficiency by TiO2/0.25Nb2O5 is 77.23% in visible light, which is 3.8-folds and 7.0-folds higher than pure TiO2 and Nb2O5. Photocatalytic degradation of acetaminophen by TiO2/0.25Nb2O5 is 90.6% in visible light, which is approximately 2.5-folds higher than pure TiO2 and Nb2O5.

B atoms and cyano groups co-doped graphite carbon nitride with nitrogen vacancies (VN-BC-CN) was explored via one-step in-situ route. A series of comprehensive experiments confirmed that B atoms and cyano groups had been doped into the framework of graphite carbon nitride, forming VN-BC-CN catalyst sample with a large number of nitrogen-vacancy defects. As electron acceptors, B and cyano groups could be used as active sites for nitrogen conversion. The defect level caused by nitrogen vacancy led to red shift of the light absorption edge, which resulted in higher separation efficiency of photo-induced carriers and faster transfer rate of photo-induced electrons for the VN-BC-CN catalyst. This VN-BC-CN catalyst had good photocatalytic nitrogen fixation performance in the ultrapure water without any hole-scavengers. The nitrogen photofixation rate of VN-BC-CN (115.53 μmol g−1 h−1) was 25.5 times that of pure carbon nitride (GCN, 4.53 μmol g−1 h−1). Moreover, NH4+ generation rate hardly decreased after 10 h reaction, and the NH4+ generation rate could reach 79.56 μmol g−1 h−1 in the fifth cycle, showing the good photocatalytic stability of the VN-BC-CN catalyst.

Lithium-sulfur battery is one of the most promising candidates for next-generation energy storage systems, but the serious shuttle effect and sluggish reaction kinetics of polysulfides impair its practical applications. Herein, sulfur-deficient MoS

Lithium-oxygen batteries (LOBs) have been extensively studied as an attractive secondary battery due to their ultra-high energy density. However, its high charging voltage, poor cycle stability, and low rate performance make its practical applications very limited. Since the positive electrode is the main reaction site of LOBs, improving the structure and catalytic activity of the cathode catalyst is the key method to improve the electrochemical performance. In this work, colored titanium dioxide nanoparticles were synthesized by calcination in argon. Raman and XPS confirmed the existence of more oxygen vacancies and Ti3+ in black TiO2 than gray one. HRTEM analysis also reveals the defective layers of 2–3 nm on the TiO2 surface. Due to the high electrical conductivity and good catalytic activity promoted by oxygen vacancies and Ti3+ ions, the black TiO2-based cathodes have good electrochemical activity and enhanced cycling stability for LOBs. Compared with the gray TiO2 (4.3 V), the black TiO2 nanoparticles show a low overpotential with the charge voltage of 3.7 V. The charging voltage significantly reduced approximately 600 mV, which reduces the battery's side reactions and polarization, and thus enhances the cycling performance of the battery. When the cut-off capacity is 500 mAh g−1, it can run for 108 cycles without significant change in terminal voltage, indicating that black TiO2 is an efficient catalyst for LOBs.

Transition metal oxides have shown an extraordinary potential for lithium-storage capability to date. However, it remains enormous challenge to gain high capacities, good rate performance and cyclability due to their inferior conductivity. To address this issue, oxygen vacancies (VOs) implanted ultrathin WO3 nanorods (the diameter around 5 nm and the length less than 100 nm) composed with reduced graphene oxide (namely WO3-x/rGO), were synthesized by proposing a logical design. For the sake of better showing the outcome of such configuration, holy nanosheets of pure WO3 anode were proposed to compare with nanorods WO3-x/rGO one in terms of electrochemical properties, and they were obtained via annealing H2WO4/rGO precursor in air and argon atmosphere with the same annealing ramp, respectively. By contrast, both electron paramagnetic resonance and X-ray photoelectron spectroscopic characterizations demonstrate the existence of VOs in WO3-x/rGO composite. The generation of VOs together with the reserve of rGO, the conductivity of WO3-x/rGO anode is distinctly enhanced, which is then verified by the compared electrochemical performance in this work. It is clearly shown that the WO3-x/rGO nanocomposite displays a capacity of 745 mAh g−1 at a current density of 0.1 A g−1 after 200 cycles and excellent cycling stability up to 1000 cycles with capacity of 428 mAh g−1 at 1 A g−1. These findings exhibit that nanorods WO3-x/rGO nanocomposite is a promising candidate for high-performance Li-ion battery anode.

We present a precipitation-strengthening strategy to produce a strong and ductile alloy at a broad range of temperatures., High-entropy alloys (HEAs), as an emerging class of materials, have pointed a pathway in developing alloys with interesting property combinations. Although they are not exempted from the strength-ductility trade-off, they present a standing chance in overcoming this challenge. Here, we report results for a precipitation-strengthening strategy, by tuning composition to design a CoNiV-based face-centered cubic/B2 duplex HEA. This alloy sustains ultrahigh gigapascal-level tensile yield strengths and excellent ductility from cryogenic to elevated temperatures. The highest specific yield strength (~150.2 MPa·cm3/g) among reported ductile HEAs is obtained. The ability of the alloy presented here to sustain this excellent strength-ductility synergy over a wide temperature range is aided by multiple deformation mechanisms i.e., twins, stacking faults, dynamic strain aging, and dynamic recrystallization. Our results open the avenue for designing precipitation-strengthened lightweight HEAs with advanced strength-ductility combinations over a wide service temperature range.

The 3D (three-dimensional) oriented nanosheet array FeNi

Ruthenium (Ru) single atoms were decorated on the surface of the graphitic carbon nitride (g-C3N4) successfully in this work. By varieties of characterization, the existence of Ru single atoms and the defects (cyano groups) caused in the process of synthesis have been confirmed. The catalyst decorated by Ru atoms (Ru-CCN-0.05) had better absorption capacity and a wider absorption range of light than the catalyst with no Ru atoms loading on (Ru-CCN-0). Without the help of hole-scavengers, the rate of photocatalytic nitrogen fixation of Ru-CCN-0.05 in ultra-pure water was 2.26 mg L−1 gcat −1 h−1, 1.5 times that of bare g-C3N4.

TiO

B atoms and cyano groups co-doped graphite carbon nitride with nitrogen vacancies (VN-BC-CN) was explored via one-step in-situ route. A series of comprehensive experiments confirmed that B atoms and cyano groups had been doped into the framework of graphite carbon nitride, forming VN-BC-CN catalyst sample with a large number of nitrogen-vacancy defects. As electron acceptors, B and cyano groups could be used as active sites for nitrogen conversion. The defect level caused by nitrogen vacancy led to red shift of the light absorption edge, which resulted in higher separation efficiency of photo-induced carriers and faster transfer rate of photo-induced electrons for the VN-BC-CN catalyst. This VN-BC-CN catalyst had good photocatalytic nitrogen fixation performance in the ultrapure water without any hole-scavengers. The nitrogen photofixation rate of VN-BC-CN (115.53 μmol g

The genetic improvement of nitrogen use efficiency (NUE) of crops is vital for grain productivity and sustainable agriculture. However, the regulatory mechanism of NUE remains largely elusive. Here, we report that the rice Grain number, plant height, and heading date7 (Ghd7) gene genetically acts upstream of ABC1 REPRESSOR1 (ARE1), a negative regulator of NUE, to positively regulate nitrogen utilization. As a transcriptional repressor, Ghd7 directly binds to two Evening Element-like motifs in the promoter and intron 1 of ARE1, likely in a cooperative manner, to repress its expression. Ghd7 and ARE1 display diurnal expression patterns in an inverse oscillation manner, mirroring a regulatory scheme based on these two loci. Analysis of a panel of 2656 rice varieties suggests that the elite alleles of Ghd7 and ARE1 have undergone diversifying selection during breeding. Moreover, the allelic distribution of Ghd7 and ARE1 is associated with the soil nitrogen deposition rate in East Asia and South Asia. Remarkably, the combination of the Ghd7 and ARE1 elite alleles substantially improves NUE and yield performance under nitrogen-limiting conditions. Collectively, these results define a Ghd7-ARE1-based regulatory mechanism of nitrogen utilization, providing useful targets for genetic improvement of rice NUE.

Sn@Graphene composites as anode materials in Lithium-ion batteries have attracted intensive interest due to the inherent high capacity. On the other side, the high atomic ratio (Li4.4Sn) induces the pulverization of the electrode with cycling. Thus, suppressing pulverization by designing the structure of the materials is an essential key for improving cyclability. Applying the nanotechnologies such as electrospinning, soft/hard nano template strategy, surface modification, multi-step chemical vapor deposition (CVD), and so on has demonstrated the huge advantage on this aspect. These strategies are generally used for homogeneous dispersing Sn nanomaterials in graphene matrix or constructing the voids in the inner of the materials to obtain the mechanical buffer effect. Unfortunately, these processes induce huge energy consumption and complicated operation. To solve the issue, new nanotechnology for the composites by the bottom-up strategy (Organic Molecule Confinement Reaction (OMCR)) was shown in this report. A 3D organic nanoframes was synthesized as a graphene precursor by low energy nano emulsification and photopolymerization. SnO2 nanoparticles@3D organic nanoframes as the composites precursor were in-situ formed in the hydrothermal reaction. After the redox process by the calcination, the Sn nanoparticles with nanovoids (~100 nm, uniform size) were homogeneously dispersed in a Two-Dimensional Laminar Matrix of graphene nanosheets (2DLMG) by the in-situ patterning and confinement effect from the 3D organic nanoframes. The pulverization and crack of the composites were effectively suppressed, which was proved by the electrochemical testing. The Sn nanoparticles@2DLMG not delivered just the high cyclability during 200 cycles, but also firstly achieved a high specific capacity (539 mAh g−1) at the low loading Sn (19.58 wt%).

Bramble-like NaVMoO6/C nanofibers with remarkable lithium-storage property are fabricated via a simple electrospinning method. The NaVMoO6 nanoparticles with average size of 84 nm are uniformly embedded into the carbon nanofibers at loading of 77.2 wt%. The unique architecture of the resulting nanocomposite has great advantages like enhanced surface-to-volume ratio, reduced ion transport lengths and strengthened electron transfer along the longitudinal direction. As a new-type anode for lithium-ion batteries (LIBs), NaVMoO6/C composite demonstrates a stable capacity of 1013 and 682 mAh g−1 at the current density of 0.1 and 1 A g−1, respectively. Furthermore, the structure evolution mechanism during the first discharge process is carefully researched by ex-situ X-ray diffraction and X-ray photoelectron spectroscopy. It is found that the NaVMoO6 crystals begin to change after being embedded with a few equivalent Li+ when discharging to 2.2 V. With the continuous intercalation of Li+ ions, the main crystal form of the electrode is V2O5 at the potential of about 2.0 V. At low potential (≈ 1.2 V vs. Li/Li+), the formed V2O5 is transformed into LiVO2. In addition, the volume expansion of the NaVMoO6 particles is alleviated due to the confining effect of carbon nanofibers. Consequently, NaVMoO6/C nanofibers demonstrate a high reversible capacity even at high rate.

Lithium metal batteries (LMBs) are favored due to their high energy densities. However, how to inhibit the growth of Li dendrites, slow down the volume expansion and realize the reversible utilization of Li anode are still big challenges for the practical feasibility. Herein, a pre-lithiated edge-enriched ultra-thin MoS2 embedded carbon nanofiber (PCNF/MoS2) framework was prepared as a protective layer to stablize Li metal anode, Mo and Li2S was in situ formed on the surface of Li foil by a facile spontaneous chemical reaction of MoS2 and Li. Among them, Mo significantly reduces the overvoltage of the Li nucleation, achieves homogeneous Li plating/stripping, guides Li deposition in the cavity of three-dimensional (3D) framework, and thus inhibits the Li dendrites growth. More importantly, Li2S, as an effective additive, facilitates uniform and robust solid electrolyte interface (SEI) formation with excellent chemical stability and high ionic conductivity, which successfully realizes stable Li anode. Thereafter, the PCNF/MoS2-Li composite anode exhibits excellent long cycle life over 750 h at 1 mA cm−2 with a capacity of 1 mAh cm−2 in the symmetrical cell. In addition, when the PCNF/MoS2-Li composite anodes were paired with LiFePO4 and LiNi0.8Co0.1Mn0.1O2 cathodes, the batteries delivered improved cycling stability and rate performance, providing a promising new avenue to achieve pratical LMBs.

The lithium-sulfur (Li-S) batteries involve intricate electrochemical processes containing the formation and conversion of polysulfides, in which the shuttle effect and slow reaction kinetics impair its practical performance. Exploring new electrocatalyst with strong catalytic ability can greatly accelerate the conversion of polysulfides in Li-S batteries. Herein, BiOI/carbon fibers (BiOI/CFs) core–shell composite has been prepared by a facile electrospinning combined with solvothermal method and used as a promising electrocatalyst. The BiOI nanosheets are cross-linked to form a porous three-dimensional network on the surface of carbon fibers. This architecture not only has the advantage of large aspect ratio, but also has a high specific surface area, which provides abundant active sites and ensures high electron/ion transfer for the electrocatalysis of lithium polysulfides. As expected, BiOI/CFs electrode presents a superior bidirectional oxidation–reduction ability for polysulfides. The first-principles calculations also prove the strong interaction between BiOI and polysulfides. Due to these advantages, BiOI/CFs can effectively inhibit the shuttle effect of polysulfides, and possesses excellent electrochemical performance in Li-S batteries. The specific capacity of the BiOI/CFs-S electrode is stable at 1020 mAh g−1 after 200 cycles at 0.2C and 598 mAh g−1 after 1000 cycles at 5C. This work provides new insights for the development of high-performance electrocatalysts for polysulfide conversion.

NiS2 nanoparticle electrocatalysts grown on sulfur and nitrogen co-doped reduced graphene oxide (NiS2/S,N-rGO) were explored. Since the hybrid catalyst of NiS2/S,N-rGO had a large surface area and high conductivity, it demonstrated outstanding electrocatalytic properties. This NiS2/S,N-rGO hybrid electrocatalyst required only 95 mV overvoltage to reach the current density of 10 mA cm−2 in hydrogen evolution reaction (HER) in acidic solution. In addition, the 5000 cycles test experiment showed the excellent HER electrochemical stability of the NiS2/S,N-rGO catalyst. This work also provided new strategies for increasing the catalytic activity of non-precious metal electrocatalysts.

ZnCo2O4/ZnO/carbon nanotubes (ZZCO/CNTs) nanocomposite is fabricated via a facile and rapid strategy of microwave-irradiation process followed by annealing. The nanocomposites are composed of ZnCo2O4/ZnO (ZZCO) nanocrystals (~ 5 nm) coated on the surfaces of carbon nanotubes, and the introduction of carbon nanotubes can greatly improve the conductivity and stability of the hybrid material and effectively prevent the aggregation of ZZCO nanoparticles. When considered as an anode material for lithium-ion batteries, the as-synthesized ZZCO/CNTs nanocomposite exhibits a high-reversible specific capacity of around 1440 mAh g−1 at the current density of 100 mA g−1, excellent cycling stability up to 200 cycles at a high current density of 500 mA g−1 and superior rate performance.

Core-shell structure of ultrathin MoS2 nanosheets attached on carbon microspheres (C@MoS2) are synthesized through a simple and rapid L-cysteine-assisted hydrothermal procedure. When used as a promising anode for lithium ion battery, the as-synthesized C@MoS2 core-shell microspheres electrodes exhibit high capacity (1333 mAh g−1 of the first cycle and 753 mAh g−1 after 50 cycles at 0.2 A g−1), excellent rate capability (a reversible capacity of 850 mAh g−1 when the current density returns from 1600 to initial 100 mA g−1), and long cycling stability (a reversible capacity of 737 mAh g−1 after 200 cycles at a much higher current density of 1 A g−1). The superior electrochemical performances of C@MoS2 core-shell microstructures should be attributed to the purposely designed unique structures, in which the ultrathin 2D MoS2 nanosheets provide more lithium storage sites and shorter Li-ion diffusion length, and the micron-sized carbon microspheres maintain the structural integrity and improve the conductivity of active materials.

Lithium-oxygen (Li-O2) battery is regarded as one of the potential energy storage system due to the ultra-high theoretical energy density and environmental friendliness. However, the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) severely limited the discharge/charge efficiency. Herein, the single-atom Ru anchored N-doped reduced graphene oxide nanosheets (Ru-N/rGO) was fabricated via a simple impregnation method. When employed as cathode for Li-O2 battery, the Ru-N/rGO delivers a higher discharge capacity, a lower overpotential and better rate performance in comparison with pure N-rGO without Ru atoms. Based on the in situ DEMS, the e-/O2 ratio of Ru-N/rGO (2.08) is close to the theoretical value for the desired O2 reduction to Li2O2 (2.00), suggesting the discharged product is mainly Li2O2. The density functional theory simulations reveal that the Ru single atoms offer high catalytic activity for OER and ORR. This work gives insight for the application of single atoms in advanced rechargeable Li-O2 batteries.

A novel PANI/Ni2P hybrid electrocatalyst with enhanced performance in hydrogen evolution reaction was explored. The current densities of the PANI/Ni2P hybrid electrocatalyst could achieve 10 mA cm−2 under much lower overpotential of 83 mV with a small Tafel slope of 69 mV dec−1. This was due to the fact that nitrogen atoms in polyaniline had more isolated electrons, which could capture protons from hydrated ions to form protonated amino groups, thus accelerating the kinetics process of hydrogen evolution. Moreover, the current densities of the PANI/Ni2P hybrid electrocatalysts was only slightly attenuated after 5000 cycles, showing good stability and application potential of the PANI/Ni2P hybrid electrocatalysts. The effect of the thickness of the polyaniline layer on the performance of the PANI/Ni2P hybrid catalyst was fully discussed. This work also provided a new strategy to increase the catalytic activity of non-noble metal catalysts.

Nanosized anode materials have been shown to be successful in addressing the problems of metal oxide anodes during electrochemical reactions. However, issues with low Coulombic efficiencies and poor cyclability of nanostructured metal oxide anodes still need to be resolved. Ultrafine CuCo 2 O 4 nanoparticles of 6∼9 nm uniformly anchored on graphene have been synthesized. CuCo 2 O 4 /graphene (CuCo 2 O 4 /G) composites show superior lithium-storage performances. A high reversible capacity of 1040 mAh g −1 is achieved at 0.1 C after 80 cycles, and can retain 211 mAh g −1 at a current density of 2 C. Furthermore, the lithiation process of CuCo 2 O 4 /G was recorded by TEM. It suggests the Li + diffuse through an individual CuCo 2 O 4 nanoparticle consists of three stages: (1) the insertion of Li + without crystalline structure change, (2) the nanoparticle’s crystalline lattice collapses, and (3) nanograins grow and reform from the collapsed nanoparticle. The lithium conversion resulting in the formation of a network of many ultrafine nanograins (2 nm) embedded in the Li 2 O matrix; also these ultrafine nanograins are confined in a layer of crystal, which is beneficial for the improved electrochemical performance. The macroscopic electrochemical performance of CuCo 2 O 4 /G was further correlated with the microcosmic in situ TEM results.

CoFe2O4 quantum dots/N-doped graphene (CoFe2O4 QDs/N-G) composites have been successfully fabricated through a facile strategy involving a hydrothermal process and subsequent calcination at high temperature. Uniform nanoparticles with high density are homogeneously anchored on the surfaces of graphene sheets. The CoFe2O4 QDs with a distribution within 4–12 nm can be observed clearly, and there is no apparent aggregation of CoFe2O4 QDs on the graphene nanosheets. The CoFe2O4 QDs/N-G obtained as an anode material for LIBs presents an initial discharge capacity of 1616 mAh g−1 and maintains a reversible capacity of 1223 mAh g−1 after 90 cycles at a current of 100 mA g−1. The gradual capacity increase with cycling results primarily from the formation of Co3+ during the electrochemical process. After being cycled at various rates for 90 cycles, the capacity can recover to 1239 mAh g−1 when the current is switched to 100 mA g−1. This superior lithium-storage performance can be attributed to the quantum and size effects of CoFe2O4 quantum dots and the excellent electrochemical properties of N-doped graphene.

A carbon nanotube/polyaniline/graphene (MWCNT–PANI–G) composite as sulfur host has been prepared by a simple self-assembly approach with potential application for lithium–sulfur (Li–S) batteries. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were used to investigate the microstructures and morphology of the as-prepared samples. It is demonstrated that the sulfur can be evenly impregnated into the MWCNT–PANI–G composite with strong chemical bonding. The resultant S@MWCNT–PANI–G composite with a sulfur content of 68 wt% shows excellent electrochemical performance as cathode for Li–S batteries. It delivers a high initial discharge capacity up to 1290 mA h g−1, good capacity retention of 784 mA h g−1 after 100 cycles of charge/discharge at the current density of 330 mA g−1, and good rate capability of 663 mA h g−1 and 548 mA h g−1 at 1.65 and 3.3 A g−1, respectively. The remarkable electrochemical performances are mainly attributed to the unique architecture of MWCNT–PANI–G with an enhanced electronic and ionic conductivity. Furthermore, this special architecture can provide strong physical and chemical confinement to the active materials and the soluble lithium polysulphides. Therefore, our study demonstrates a facile and low-cost approach to fabricate cathode materials for high-performance Li–S batteries.

Three-dimensional (3D) porous carbon-coated ZnFe2O4 nanospheres/N-doped graphene aerogels (ZnFe2O4@C/N-G) have been synthesized via a facile hydrothermal method. The obtained ZnFe2O4@C hierarchical nanospheres with a size distribution of 150–210 nm are uniformly encapsulated within the graphene aerogels matrix. The ZnFe2O4@C/N-G composites as anode materials for Li-ion batteries demonstrate a high initial discharge capacity of ~1176 mA h g−1 with an initial coulombic efficiency of ~71.1% at a rate of 100 mA g−1. Moreover, a significantly enhanced reversible capacity of 952 mA h g−1 is retained after 100 cycles. After being cycled at various rates for 100 cycles, the capacity can reincrease to 955 mA h g−1 when the specific current returns back to 100 mA g−1. The improved electrochemical performance is attributed to the unique architectures of the carbon layer (~2 to 4 nm) and 3D porous N-doped graphene aerogels.

All solid-state composite polymer electrolyte (CPE) is considered to be the key to solving the high safety and long life of solid Li metal batteries (LMBs), but there are few CPEs that can suppress the side reactions of the cathode and achieve dendrite-free plating simultaneously. Here, a sandwiched structure CPE (SCPE) is prepared through a layer-by-layer coating process. Oxidation resistant polyacrylonitrile (PAN) and reduction resistant polyethylene oxide (PEO) are used to contact with cathode and anode respectively to protect “polymer-in-ceramic” (PIC)-CPE in SCPE. In which, PAN-CPE contacts with LiNi0.8Mn0.1Co0.1O2 (NCM811) to form a stable interface, and PEO-CPE contacts with lithium (Li) to avoid reduction, thus ensuring high-voltage tolerance. More importantly, the synergistic effect of different CPEs in SCPE significantly facilitates high Li ion conductivity, wide electrochemical window, strong mechanical property and stable electrolyte/electrode interface. As a result, the Li symmetric cell using SCPE can be cycled over 500 h without voltage hysteresis. The NCM811/Li battery assembled with SCPE exhibits excellent cycle stability (88% after 500 cycles), and high Coulombic efficiency (over 99.2% after 500 cycles). This work proposes an approach to develop a low-cost, safe, and promising CPE to achieve high safety LMBs.

The microscopic mechanism of solid-solid phase transitions is a long-standing fundamental issue in materials science. Here we directly report the experimental evidence of the existence of an intermediate liquid during the solid-solid phase transition in a bulk Pd43Cu27Ni10P20 alloy by in situ high temperature high energy X-ray diffraction, combined with the differential scanning calorimetry at slow heating rates down to 5 K/min. We elucidate that this intermediate liquid is attributed to the melting of the low-melting-point crystalline phases, rather than induced by the elastic stress energy along the interface proposed in literatures. This could also be a general feature in multicomponent alloys if a low-melting-point crystalline phase is formed together with other crystalline phases during heating. All results obtained here are scientifically sound and provide new insight into the phase transition theory, which will trigger more studies on the microscopic mechanism of solid-solid phase transition via an intermediate liquid.

One-dimensional zinc molybdate (ZnMoO4) nanotubes with excellent sodium-storage performance are controllably and delicately prepared by a facile electrospinning method. The as-prepared nanotubes are systematically characterized. The charge-discharge cycling curves, cyclic voltammetry and rate performance further reveal the electrochemical properties of the samples when used as the new Sodium-ion batteries (SIBs) anode material. In the charge-discharge process, the initial discharge capacity of the electrode is 548 mAh g−1, and remains a reversible capacity of about 190 mAh g−1 after 500 cycles at the current density of 100 mA g−1. ZnMoO4 nanotubes also deliver an excellent rate capability. In addition, the sodium-storage reaction mechanism of ZnMoO4 nanotubes is revealed via ex-situ XRD and TEM analysis. The results suggest the transformation of ZnMoO4 to Zn and NaMoO4 at the potential of ∼1.0 V during the first discharge, which is subsequently converted to Zn and Mo nanograins of 3–5 nm with the deepening of the discharge. This study provides an in-depth understanding of the electrochemical mechanism of molybdates-type anode materials.

White TiO2 (W-TiO2), gray TiO2 (G-TiO2) and black TiO2 (B-TiO2) have been prepared through simple annealing process in different atmospheres. The oxygen vacancy content in the TiO2 samples and the relationship between oxygen vacancy and photocatalytic performance have been studied by comprehensive analyses. The XRD peaks slightly move to a low angle and the Raman strongest peak shifts positively owing to oxygen vacancy and Ti3+. The energy bandgap of G-TiO2 and B-TiO2 is tuned from 3.10 to 3.02 and 1.99 eV. The content of oxygen vacancy is 1%, 4.8% and 7.8% for W-TiO2, G-TiO2 and B-TiO2, respectively. The efficiency of NO removal is stable at 34%, 38% and 45%, and the decomposition rate of Rhodamine B under visible light is 75%, 83% and 89% for W-TiO2, G-TiO2 and B-TiO2, respectively. The results are significant for the design of high-performance photocatalytic materials in the field of solar energy conversion.

After Xiamen VSC-HVDC Project is put into operation, it can improve the power supply capacity and reliability of Xiamen Power Grid.But at the same time,it also brings new problems to the operation of the power grid, among which the short-circuit current problem is particularly prominent.In the preliminary analysis of power grid operation, using the short- circuit current program (PSD-SCCP) commonly used in domestic power grid simulation analysis to calculate to be found that:VSC-HVDC will provide a large short-circuit current when the AC grid is short-circuited, causing the short-circuit current levels of multiple 220kV busbars of the Xiamen Power Grid to approach or exceed 50kA, which brings greater pressure on the adjustment and arrangement of the grid operation mode.Therefore, it is necessary to study the true level of the impact of Xiamen VSC-HVDC on the short-circuit current of the AC grid based on the actual control logic of the Xiamen VSC-HVDC project, in order to propose more accurate short-circuit current suppression measures to achieve bipolar operation of Xiamen VSC-HVDC.

In this paper, a short-circuit current suppression method based on the adjustment of low-voltage current limiting strategy is proposed, which can suppress the output current of VSC-HVDC system during the fault by adjusting the low-voltage current limiting setting value of the VSC-HVDC control system, so as to achieve the purpose of suppressing the short-circuit current level in the converter station.

Solid-state composite polymer electrolytes (CPEs) are promising for solving the safety problem of lithium metal batteries. However, the CPEs with comparable thickness (10 μm), improved ion conductivities and excellent mechanical strength are great challenges. In the present study, ultrathin (9.6 μm), flexible, mechanically strong, and sandwiched structure solid-state electrolytes (SSEs) are fabricated by a tape casting process, involving the 75 wt % LLTO/PVDF-CPE (LLTO-75) layer designed as intermediate layer sandwiched by two 15 wt % LLTO/PVDF-CPE (LLTO-15) layers. The LLTO-15 is a soft, stable layer on upper and lower sides that could create excellent interfacial contact with electrodes, and LLTO-75 possesses physical rigidity that could inhibit the Li dendrites growth. The balancing between the excellent interfacial contact of LLTO-15 and the inhibition of lithium dendrites growth of LLTO-75 gives sandwiched SSE a high ionic conductivity (4.7 × 10-4 S cm-1) at room temperature, an excellent mechanical strength (7.2 MPa), and uniform Li plating/stripping. When coupled with LiFePO4 and Li metal, the battery assembled with sandwiched SSE maintains 91.7% of its capacity and 99.7% of the Coulombic efficiency, after 1000 cycles. Our study suggests that the proposed sandwiched structure SSE is one of the alternatives for high performance solid-state LMBs.

A three-dimensional CoFe2O4 nanowire array on carbon cloth was fabricated with a hydrothermal method together with a post-annealing treatment. As a binder-free and flexible anode material for LIBs, it showed an improved electrochemical performance with high cycling stability and excellent rate capability. It exhibited an initial discharge capacity of 1615 mAh g−1 and retained a reversible capacity of about 1204 mAh g−1 after 200 cycles at a specific current of 500 mA g−1. The high capacity, outstanding rate performance and cycling stability can be attributed to the special configuration of hierarchal porous CoFe2O4 nanowires on carbon cloth, which possess many advantages like short diffusion length, easy strain relaxation and fast electron transport. Moreover, the integrated CoFe2O4 nanowires/carbon cloth electrode shows high flexibility and high areal capacity (2.41 mAh cm−2), which makes it suitable for use as a binder-free anode to build flexible LIBs.

Hierarchal three-dimensional (3D) CoO nanowire arrays have been directly grown on flexible carbon cloth substrate via a hydrothermal method, which can be used as a binder-free flexible anode for lithium ion battery (LIBs). These porous CoO nanowire arrays give rise to large surface area and space for efficient buffering of the volume change during electrochemical lithiation. The integrated hierarchal electrodes possess many advantages by directly building 3D nanostructures on conductive substrate, such as short diffusion length, easy strain relaxation and fast electron transport. Thus, the CoO nanowire arrays show an improved lithium-storage performance with high cycling stability and good rate capacity. It exhibits an initial discharge capacity of 1730 mAh g −1 and retains a reversible gravimetric capacity of about 1300 mAh g −1 after 90 cycles at a current density of 100 mA g −1 . Moreover, the integrated CoO nanowires/carbon cloth electrode shows high flexibility and high areal capacity (1.95 mAh cm −2 ), which can be directly used as an anode to build flexible LIBs.

Transition-metal selenides have attracted extensive concern as one of the alternatives for sodium-ion batteries (SIBs) anodes due to their high theoretical capacities, good cycling stability and environmental benignity. However, the application of metal selenides is restricted by severe volume variation and sluggish kinetics during cyclings, which cause capacity fading induced by the pulverization and aggregation of the electrode materials. Herein, the FeSe2@C microspheres assembled with FeSe2 nanoparticles cotaed by carbon layers are fabricated using a hydrothermal method and the subsequent annealing treatment. When served as anodes for SIBs, the FeSe2@C electrodes exhibit excellent electrochemical performances. A high reversible capacity of 461 mA h g−1 is retained after 100 cycles at 50 mA g−1. Even at high rate of 1000 mA g−1, a long-term cycling capacity of 428 mA h g−1 is achieved after 1000 cycles. The kinetic analyses confirm that the superior sodium storage performances of FeSe2@C composites are mainly attributed to the pseudocapacitive contribution facilitated by the unique nano-micro hierarchical structure.

Transition metal sulfides are regarded as a type of high-performance anode materials for lithium ion batteries (LIBs). However, their electrochemical process and lithium-storage mechanism are complicated and remain controversial. This work is intended to give the direct observation on the electrochemical behavior and find out the lithium-storage mechanism of molybdenum disulfide (MoS2) using in situ transmission electron microscopy (TEM). We find that single-crystalline MoS2 nanosheets convert to Mo nanograins (~2 nm) embedded in Li2S matrix after the first full lithiation. After the delithiation, the Mo nanograins and Li2S transform to a large number of lamellar MoS2 nanocrystals. The discharge-charge cycling of MoS2 in LIBs is found to be a fully reversible conversion between MoS2 and Mo/Li2S rather than the electrochemical conversion between S and Li2S proposed by many researchers. The in situ real-time characterization results give direct evidence and profound insights into the lithium-storage mechanism of MoS2 as anode in LIBs.

The realization of antipulverization electrode structures, especially using low-carbon-content anode materials, is crucial for developing high-energy and long-life lithium-ion batteries (LIBs); however, this technology remains challenging. This study shows that SnO2 triple-shelled hollow superstructures (TSHSs) with a low carbon content (4.83%) constructed by layer-by-layer assembly of various nanostructure units can withstand a huge volume expansion of ≈231.8% and deliver a high reversible capacity of 1099 mAh g-1 even after 1450 cycles. These values represent the best comprehensive performance in SnO2 -based anodes to date. Mechanics simulations and in situ transmission electron microscopy suggest that the TSHSs enable a self-synergistic structure-preservation behavior upon lithiation/delithiation, protecting the superstructures from collapse and guaranteeing the electrode structural integrity during long-term cycling. Specifically, the outer shells during lithiation processes are fully lithiated, preventing the overlithiation and the collapse of the inner shells; in turn, in delithiation processes, the underlithiated inner shells work as robust cores to support the huge volume contraction of the outer shells; meanwhile, the middle shells with abundant pores offer sufficient space to accommodate the volume change from the outer shell during both lithiation and delithiation. This study opens a new avenue in the development of high-performance LIBs for practical energy applications.

CuO–Cu 2 O/graphene composite has been successfully prepared by the combination of a microwave-assisted process and subsequent annealing. X-ray diffraction and electron microscopy reveals that copper oxide nanospheres with a size of 120–200 nm are uniformly anchored on graphene nanosheets. The copper oxide nanospheres are composed of numerous CuO and Cu 2 O nanocrystals of ∼10 nm. These nanospheres are hollow and the thickness of the shells is around 50–70 nm. The CuO–Cu 2 O/graphene composite shows a highly reversible capacity and excellent rate performance as anode for Li-ion battery. The reversible capacity of the composite retains 487 mA h g −1 after 60 cycles at 200 mA g −1 . Even when cycled at various rate (200, 500, 1000, 2000, 5000 mA g −1 ) for 60 cycles, the capacity can recover to 520 mA h g −1 at the current of 200 mA g −1 . The enhanced electrochemical performances are ascribed to the hollow spherical architectures, excellent conductivity of graphene sheets, and possible synergistic effects between CuO, Cu 2 O and graphene that enhance the intrinsic properties of each component.

Two kinds of graphene–sulfur composites with 50 wt% of sulfur are prepared using hydrothermal method and thermal mixing, respectively. Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectra mapping show that sulfur nanocrystals with size of ∼5 nm dispersed on graphene sheets homogeneously for the sample prepared by hydrothermal method (NanoS@G). While for the thermal mixed graphene–sulfur composite (S–G mixture), sulfur shows larger and uneven size (50–200 nm). X-ray Photoelectron Spectra (XPS) reveals the strong chemical bonding between the sulfur nanocrystals and graphene. Comparing with the S–G mixture, the NanoS@G composite shows highly improved electrochemical performance as cathode for lithium–sulfur (Li–S) battery. The NanoS@G composite delivers an initial capacity of 1400 mAh g −1 with the sulfur utilization of 83.7% at a current density of 335 mA g −1 . The capacity keeps above 720 mAh g −1 over 100 cycles. The strong adherence of the sulfur nanocrystals on graphene immobilizes sulfur and polysulfides species and suppressed the “shuttle effect”, resulting higher coulombic efficiency and better capacity retention. Electrochemical impedance also suggests that the strong bonding enabled rapid electronic/ionic transport and improved electrochemical kinetics, therefore good rate capability is obtained. These results demonstrate that the NanoS@G composite is a very promising candidate for high-performance Li–S batteries.

Novel α-Bi2O3 nanosheets have been successfully synthesized by graphite oxide (GO)-assisted sonochemical route and subsequent calcining treatment. The morphology of the final products can be controlled by tuning GO nanosheets in the synthesis process. Porous and nanosheet-covered α-Bi2O3 microrods have also been obtained, and the growth mechanism has been discussed. Scanning electron microscopy and transmission electron microscopy analyses reveal that the α-Bi2O3 nanosheets are 10–20 nm in thickness with suppressed growth along the [2 1 −4] direction. Owing to the unique structure, the α-Bi2O3 nanosheets show broader optical absorption and narrower band gap (2.25 eV) as compared to other two forms of α-Bi2O3 (~2.8 eV). Photocatalytic experiments demonstrated that the α-Bi2O3 nanosheets exhibited excellent activity much higher than the porous and nanosheet-covered α-Bi2O3 microrods in degrading organic pollutants under visible light. This study opens up a new route for the preparation of α-Bi2O3 nanosheets with superior photocatalytic performance.

A family of mixed transition–metal oxides (MTMOs) has great potential for applications as anodes for lithium ion batteries (LIBs). However, the reaction mechanism of MTMOs anodes during lithiation/delithiation is remain unclear. Here, the lithiation/delithiation processes of ZnFe2O4 nanoparticles are observed dynamically using in situ transmission electron microscopy (TEM). Our results suggest that during the first lithiation process the ZnFe2O4 nanoparticles undergo a conversion process and generate a composite structure of 1–3 nm Fe and Zn nanograins within Li2O matrix. During the delithiation process, volume contraction and the conversion of Zn and Fe take place with the disappearance of Li2O, followed by the complete conversion to Fe2O3 and ZnO not the original phase ZnFe2O4. The following cycles are dominated by the full reversible phase conversion between Zn, Fe and ZnO, Fe2O3. The Fe valence evolution during cycles evidenced by electron energy–loss spectroscopy (EELS) techniques also exhibit the reversible conversion between Fe and Fe2O3 after the first lithiation, agreeing well with the in situ TEM results. Such in situ TEM observations provide valuable phenomenological insights into electrochemical reaction of MTMOs, which may help to optimize the composition of anode materials for further improved electrochemical performance.