Fast Na+ Kinetics and Suppressed Voltage Hysteresis Enabled by a High-Entropy Strategy for Sodium Oxide Cathodes.

O3-type layered transition metal cathodes are promising energy storage materials due to their sufficient sodium reservoir. However, sluggish sodium ions kinetics and large voltage hysteresis, which are generally associated with Na+ diffusion properties and electrochemical phase transition reversibility, drastically minimize energy density, reduce energy efficiency, and hinder further commercialization of sodium-ion batteries (SIBs). Here, this work proposes a high-entropy tailoring strategy through manipulating the electronic local environment within transition metal slabs to circumvent these issues. Experimental analysis combined with theoretical calculations verify that high-entropy metal ion mixing contributes to the improved reversibility of redox reaction and O3-P3-O3 phase transition behaviors as well as the enhanced Na+ diffusivity. Consequently, the designed O3-Na0.9Ni0.2Fe0.2Co0.2Mn0.2Ti0.15Cu0.05O2 material with high-entropy characteristic could display a negligible voltage hysteresis (<0.09 V), impressive rate capability (98.6 mAh g-1 at 10 C) and long-term cycling stability (79.4% capacity retention over 2000 cycles at 5 C). This work provides insightful guidance in mitigating the voltage hysteresis and facilitating Na+ diffusion of layered oxide cathode materials to realize high-rate and high-energy SIBs.

Covalently Bonded Ni Sites in Black Phosphorene with Electron Redistribution for Efficient Metal-Lightweighted Water Electrolysis.

The metal-lightweighted electrocatalysts for water splitting are highly desired for sustainable and economic hydrogen energy deployments, but challengeable. In this work, a low-content Ni-functionalized approach triggers the high capability of black phosphorene (BP) with hydrogen and oxygen evolution reaction (HER/OER) bifunctionality. Through a facile in situ electro-exfoliation route, the ionized Ni sites are covalently functionalized in BP nanosheets with electron redistribution and controllable metal contents. It is found that the as-fabricated Ni-BP electrocatalysts can drive the water splitting with much enhanced HER and OER activities. In 1.0 M KOH electrolyte, the optimized 1.5 wt% Ni-functionalized BP nanosheets have readily achieved low overpotentials of 136 mV for HER and 230 mV for OER at 10 mA cm-2. Moreover, the covalently bonding between Ni and P has also strengthened the catalytic stability of the Ni-functionalized BP electrocatalyst, stably delivering the overall water splitting for 50 h at 20 mA cm-2. Theoretical calculations have revealed that Ni-P covalent binding can regulate the electronic structure and optimize the reaction energy barrier to improve the catalytic activity effectively. This work confirms that Ni-functionalized BP is a suitable candidate for electrocatalytic overall water splitting, and provides effective strategies for constructing metal-lightweighted economic electrocatalysts.

Enlarging the Ni-O Bond Polarizability in a Phosphorene-Hosted Metal-Organic Framework for Boosted Water Oxidation Electrocatalysis.

The emerging lattice-oxygen oxidation mechanism (LOM) presents attractive opportunities for breaking the scaling relationship to boost oxygen evolution reaction (OER) with the direct OLattice-*O interaction. However, currently the LOM-triggering rationales are still debated, and a streamlined physicochemical paradigm is extremely desirable for the design of LOM-defined OER catalysts. Herein, a Ni metal-organic framework/black phosphorene (NiMOF/BP) heterostructure is theoretically profiled and constructed as a catalytic platform for the LOM-derived OER studies. It is found that the p-type BP host can enlarge the Ni-O bond polarizability of NiMOF through the Ni-O bond stretching and Ni valence declining synergically. Such an enlarged bond polarizability will in principle alleviate the lattice oxygen confinement to benefit the LOM pathway and OER performance. As a result, the optimized NiMOF/BP catalyst exhibits promising OER performance with a low overpotential of 260 mV at 10 mA cm-2 and long-term stability in 1 M KOH electrolyte. Both experiment and calculation results suggest the activated LOM pathway with a more balanced step barrier in the NiMOF/BP OER catalyst. This research puts forward Ni-O bond polarizability as the criterion to design LOM-scaled electrocatalysts for water oxidation.

Highly cross-linked carbon tube aerogels with enhanced elasticity and fatigue resistance.

Carbon aerogels are elastic, mechanically robust and fatigue resistant and are known for their promising applications in the fields of soft robotics, pressure sensors etc. However, these aerogels are generally fragile and/or easily deformable, which limits their applications. Here, we report a synthesis strategy for fabricating highly compressible and fatigue-resistant aerogels by assembling interconnected carbon tubes. The carbon tube aerogels demonstrate near-zero Poisson's ratio, exhibit a maximum strength over 20 MPa and a completely recoverable strain up to 99%. They show high fatigue resistance (less than 1.5% permanent degradation after 1000 cycles at 99% strain) and are thermally stable up to 2500 °C in an Ar atmosphere. Additionally, they possess tunable conductivity and electromagnetic shielding. The combined mechanical and multi-functional properties offer an attractive material for the use in harsh environments.

Elimination of Chirality in Three-Dimensionally Confined Open-Access Microcavities.

The emergent optical activity (OA) caused by anisotropic light emitter in microcavities is an important physical mechanism discovered recently, which leads to Rashba-Dresselhaus photonic spin-orbit (SO) coupling. In this study, we report a sharp contrast of the roles of the emergent OA in free and confined cavity photons, by observing the optical chirality in a planar-planar microcavity and its elimination in a concave-planar microcavity, evidenced by polarization-resolved white-light spectroscopy, which agrees well with the theoretical predictions based on the degenerate perturbation theory. Moreover, we theoretically predict that a slight phase gradient in real space can partially restore the effect of the emergent OA in confined cavity photons. The results are significant additions to the field of cavity spinoptronics and provide a novel method for manipulating photonic SO coupling in confined optical systems.

Hierarchical SiC-Graphene Composite Aerogel-Supported Ni-Mo-S Nanosheets for Efficient pH-Universal Electrocatalytic Hydrogen Evolution.

MoS2 exhibits good prospects in electrocatalytic hydrogen evolution. Whereas, the electrocatalytic property of MoS2 is restrained by its insufficient active sites, low electrical conductivity, and slow water dissociation processes. Herein, an aerogel composed of silicon carbide (SiC) and graphene (SiCnw-RGO) was constructed by growing SiC nanowires (SiCnw) in the graphene aerogel (RGO) via the CVD method, and then Ni-Mo-S nanosheets were hydrothermally synthesized on the SiCnw-RGO composite aerogel to develop an efficient pH-universal electrocatalyst. Ni-Mo-S nanosheets supported on SiCnw-RGO (Ni-Mo-S@SiCnw-RGO) exhibit an interesting hierarchical three-dimensional interconnected structure of composite aerogel. The optimal Ni-Mo-S@SiCnw-RGO electrocatalyst exhibits excellent catalytic performance with low Tafel slopes of 60 mV/dec under acidic conditions and 90 mV/dec under alkaline conditions. Density functional theory calculations demonstrate a composite catalyst exhibits advantageous hydrogen adsorption free energy and water dissociation energy barrier. This study provides a reference to design an efficient hierarchical aerogel electrocatalyst.

Interlayer-Expanded MoS2 Nanoflowers Vertically Aligned on MXene@Dual-Phased TiO2 as High-Performance Anode for Sodium-Ion Batteries.

As a promising energy-storage and conversion anode material for high-power sodium-ion batteries operated at room temperature, the practical application of layered molybdenum disulfide (MoS2) is hindered by volumetric expansion during cycling. To address this issue, a rational design of MoS2 with enlarged lattice spacing aligned vertically on hierarchically porous Ti3C2Tx MXene nanosheets with partially oxidized rutile and anatase dual-phased TiO2 (MoS2@MXene@D-TiO2) composites via one-step hydrothermal method without following anneal process is reported. This unique "plane-to-surface" structure accomplishes hindering MoS2 from aggregating and restacking, enabling sufficient electrode/electrolyte interaction simultaneously. Meanwhile, the heterogeneous structure among dual-phased TiO2, MoS2, and MXene could constitute a built-in electric field, promoting high Na+ transportation. As a result, the as-constructed 3D MoS2@MXene@D-TiO2 heterostructure delivers admirable high-rate reversible capacity (359.6 mAh g-1 up to 5 A g-1) at room temperature, excellent cycling stability (about 200 mAh g-1) at a low temperature of -30 °C, and superior electrochemical performance in Na+ full batteries by coupling with a Na3V2(PO4)3 cathode. This ingenious design is clean and facile to inspire the potential of advanced low-dimensional heterogeneous structure electrode materials in the application of high-performance sodium-ion batteries.

High Annealing Stability of InAlZnO Nanofiber Field-Effect Transistors with Improved Morphology by Al Doping.

In2O3 nanofibers usually suffer a high off-current and consequent low on/off current ratio, as well as a large negative threshold voltage (Vth). Furthermore, regarding Zn doped binary-cation In2O3 nanofibers, severe thermal diffusion of Zn elements can result in deteriorated electrical performance when annealed at high temperature. Here, we applied an electrospinning technique to obtain ternary-cation IAZO nanofibers with controllable Vth and chemical stoichiometry. The presence of the Al element in IAZO nanofibers can lead to more superior microstructure with improved uniformity, lower surface defect, and superior metal-oxide-metal lattice at high annealing temperature. Consequently, our Al-doped ternary-cation IAZO devices exhibited an improved on/off current ratio of 107 and a high electron mobility of ∼10 cm2 V-1 s-1. Moreover, the electron mobility can be increased to 30 cm2 V-1 s-1 in our low-voltage operated FETs with high-k AlOx as the dielectric layer, which can be envisioned to exhibit vast implications for high-performance transparent electronics.

Modulating electrical and photoelectrical properties of one-step electrospun one-dimensional SnO2 arrays.

One-dimensional nanostructured SnO2 has attracted intense research interest due to its advantageous properties, including a large surface-to-volume ratio, high optical transparency and typical n-type properties. However, how to fabricate high-performance and multifunctional electronic devices based on 1D nanostructured SnO2 via low-cost and efficient preparation techniques is still a huge challenge. In this work, a low-cost, one-step electrospun technology was employed to synthesize the SnO2 nanofiber (NF) and nanotube (NT) arrays. The electrical and photoelectrical parameters of SnO2 NTs-based devices were effectively controlled through simple changes to the amount of Sn in the precursor solution. The optimal 0.2 SnO2 NTs-based field effect transistors (FETs) with 0.2 g SnCl2*4H2O per 5 ml in the precursor solution exhibit a high saturation current (∼9 × 10-5 A) and a large on/off ratio exceeding 2.4 × 106. Additionally, 0.2 SnO2 NTs-based FET also exhibit a narrowband deep-UV photodetectivity (240-320 nm), including an ultra-high photocurrent of 307 µA, a high photosensitivity of 2003, responsibility of 214 A W-1 and detectivity of 2.19 × 1013 Jones. Furthermore, the SnO2 NTs-based transparent photodetectors were as well be integrated with fluorine-doped tin oxide glass and demonstrated a high optical transparency and photosensitivity (∼199). All these results elucidate the significant advantages of these electrospun SnO2 NTs for next-generation multifunctional electronics and transparent photonics.

Fabricating hierarchical micro and nano structures on implantable Co-Cr-Mo alloy for tissue engineering by one-step laser ablation.

Surface texturing is one of the effective strategies to improve bioactivity of implantable materials. In this study, hierarchical micro and nano structure (HMN) were fabricated on Co-Cr-Mo alloy substrate by a movable picosecond laser irradiation. Respectively, microgrooves with nano ripples and islands were produced on Co-Cr-Mo alloy by low and high laser power density. X-ray diffraction apparatus (XRD) phase analysis illustrated that substrate was in the phase of γ- face-centered cubic structure (FCC) before laser treatment, while it was in ε-hexagonal closest packing structure (HCP) phase dominant after laser treatment. Cell adhesion and proliferation studies showed that the HMN surface exhibits enhanced adhesion of MC3TC-E1 osteoblast and promoted cell activity. Analyzing of the morphology of osteoblast cells indicated cells were in high ratio of elongation on the HMN surface, while they mainly kept in round shape on the polished surface. Results indicated the formation of hierarchical structure on Co-Cr-Mo alloy was able to improve biological performances, suggesting the potential application in cobalt based orthopedic implants.

Helium Ion Microscope Fabrication Causing Changes in the Structure and Mechanical Behavior of Silicon Micropillars.

Silicon is used as a prominent case to demonstrate the dramatic effects of helium ion microscope nanofabrication. Structurally, a submicrometer Si pillar can turn completely amorphous at He+ doses typically used for micromachining, forming nanobubbles at higher doses. In terms of mechanical properties, the flow stress decreases markedly with increasing dosage, and the softened amorphous Si exhibits spread-out plastic flow.

Extreme chemical sensitivity of nonlinear conductivity in charge-ordered LuFe(2)O(4).

Nonlinear transport behaviors are crucial for applications in electronic technology. At the nonlinear critical turning point, the nonequilibrium states cause rich physics responses to environment. The corresponding study in this field is crucial for physics and industry application. Here nonlinear conductivity in charge-ordered (CO) LuFe(2)O(4 )has been demonstrated. Remarkable resistivity switching behavior was observed and the gas-sensing property can be reversibly tuned by a small alternation of partial pressure and/or chemical components of the environment. These facts allow us to use LuFe(2)O(4) materials as a sensitive chemical gas sensor in technological applications. Careful analysis of the gas sensing process in LuFe(2)O(4) suggests a novel sensing mechanism in sharp contrast with that discussed for the conventional gas sensors which depend fundamentally on surface chemical reactions.