Showing papers in "Advanced Functional Materials in 2016"

Stretchable, Skin-Mountable, and Wearable Strain Sensors and Their Potential Applications: A Review

Abstract: There is a growing demand for flexible and soft electronic devices. In particular, stretchable, skin-mountable, and wearable strain sensors are needed for several potential applications including personalized health-monitoring, human motion detection, human-machine interfaces, soft robotics, and so forth. This Feature Article presents recent advancements in the development of flexible and stretchable strain sensors. The article shows that highly stretchable strain sensors are successfully being developed by new mechanisms such as disconnection between overlapped nanomaterials, crack propagation in thin films, and tunneling effect, different from traditional strain sensing mechanisms. Strain sensing performances of recently reported strain sensors are comprehensively studied and discussed, showing that appropriate choice of composite structures as well as suitable interaction between functional nanomaterials and polymers are essential for the high performance strain sensing. Next, simulation results of piezoresistivity of stretchable strain sensors by computational models are reported. Finally, potential applications of flexible strain sensors are described. This survey reveals that flexible, skin-mountable, and wearable strain sensors have potential in diverse applications while several grand challenges have to be still overcome.

CsPbX3 Quantum Dots for Lighting and Displays: Room-Temperature Synthesis, Photoluminescence Superiorities, Underlying Origins and White Light-Emitting Diodes

Abstract: Recently, Kovalenko and co-workers and Li and co-workers developed CsPbX3 (X = Cl, Br, I) inorganic perovskite quantum dots (IPQDs), which exhibited ultrahigh photoluminescence (PL) quantum yields (QYs), low-threshold lasing, and multicolor electroluminescence. However, the usual synthesis needs high temperature, inert gas protection, and localized injection operation, which are severely against applications. Moreover, the so unexpectedly high QYs are very confusing. Here, for the first time, the IPQDs' room-temperature (RT) synthesis, superior PL, underlying origins and potentials in lighting and displays are reported. The synthesis is designed according to supersaturated recrystallization (SR), which is operated at RT, within few seconds, free from inert gas and injection operation. Although formed at RT, IPQDs' PLs have QYs of 80%, 95%, 70%, and FWHMs of 35, 20, and 18 nm for red, green, and blue emissions. As to the origins, the observed 40 meV exciton binding energy, halogen self-passivation effect, and CsPbX3@X quantum-well band alignment are proposed to guarantee the excitons generation and high-rate radiative recombination at RT. Moreover, such superior optical merits endow them with promising potentials in lighting and displays, which are primarily demonstrated by the white light-emitting diodes with tunable color temperature and wide color gamut.

Hierarchical NiCo2S4 Nanowire Arrays Supported on Ni Foam: An Efficient and Durable Bifunctional Electrocatalyst for Oxygen and Hydrogen Evolution Reactions

Abstract: A recent approach for solar-to-hydrogen generation has been water electrolysis using efficient, stable, and inexpensive bifunctional electrocatalysts within strong electrolytes. Herein, the direct growth of 1D NiCo2S4 nanowire (NW) arrays on a 3D Ni foam (NF) is described. This NiCo2S4 NW/NF array functions as an efficient bifunctional electrocatalyst for overall water splitting with excellent activity and stability. The 3D-Ni foam facilitates the directional growth, exposing more active sites of the catalyst for electrochemical reactions at the electrode–electrolyte interface. The binder-free, self-made NiCo2S4 NW/NF electrode delivers a hydrogen production current density of 10 mA cm–2 at an overpotential of 260 mV for the oxygen evolution reaction and at 210 mV (versus a reversible hydrogen electrode) for the hydrogen evolution reaction in 1 m KOH. This highly active and stable bifunctional electrocatalyst enables the preparation of an alkaline water electrolyzer that could deliver 10 mA cm–2 under a cell voltage of 1.63 V. Because the nonprecious-metal NiCo2S4 NW/NF foam-based electrodes afford the vigorous and continuous evolution of both H2 and O2 at 1.68 V, generated using a solar panel, they appear to be promising water splitting devices for large-scale solar-to-hydrogen generation.

Synthesis and Characterization of 2D Molybdenum Carbide (MXene)

Abstract: Large scale synthesis and delamination of 2D Mo2CTx (where T is a surface termination group) has been achieved by selectively etching gallium from the recently discovered nanolaminated, ternary tra ...

Efficient and Stable Bifunctional Electrocatalysts Ni/NixMy (M = P, S) for Overall Water Splitting

Abstract: Development of easy-to-make, highly active, and stable bifunctional electrocatalysts for water splitting is important for future renewable energy systems. Three-dimension (3D) porous Ni/Ni8P3 and Ni/Ni9S8 electrodes are prepared by sequential treatment of commercial Ni-foam with acid activation, followed by phosphorization or sulfurization. The resultant materials can act as self-supported bifunctional electrocatalytic electrodes for direct water splitting with excellent activity toward oxygen evolution reaction and hydrogen evolution reaction in alkaline media. Stable performance can be maintained for at least 24 h, illustrating their versatile and practical nature for clean energy generation. Furthermore, an advanced water electrolyzer through exploiting Ni/Ni8P3 as both anode and cathode is fabricated, which requires a cell voltage of 1.61 V to deliver a 10 mA cm(-2) water splitting current density in 1.0 M KOH solution. This performance is significantly better than that of the noble metal benchmark-integrated Ni/IrO2 and Ni/Pt-C electrodes. Therefore, these bifunctional electrodes have significant potential for realistic large-scale production of hydrogen as a replacement clean fuel to polluting and limited fossil-fuels.

Lightweight and Anisotropic Porous MWCNT/WPU Composites for Ultrahigh Performance Electromagnetic Interference Shielding

Abstract: Lightweight, flexible and anisotropic porous multiwalled carbon nanotube (MWCNT)/water-borne polyurethane (WPU) composites are assembled by a facile freeze-drying method. The composites contain extremely wide range of MWCNT mass ratios and show giant electromagnetic interference (EMI) shielding effectiveness (SE) which exceeds 50 or 20 dB in the X-band while the density is merely 126 or 20 mg cm−3, respectively. The relevant specific SE is up to 1148 dB cm3 g−1, greater than those of other shielding materials ever reported. The ultrahigh EMI shielding performance is attributed to the conductivity of the cell walls caused by MWCNT content, the anisotropic porous structures, and the polarization between MWCNT and WPU matrix. In addition to the enhanced electrical properties, the composites also indicate enhanced mechanical properties compared with porous WPU and CNT architectures.

Highly Conductive Optical Quality Solution-Processed Films of 2D Titanium Carbide

Abstract: MXenes comprise a new class of solution-dispersable, 2D nanomaterials formed from transition metal carbides and nitrides such as Ti3C2. Here, it is shown that 2D Ti3C2 can be assembled from aqueous solutions into optical quality, nanometer thin films that, at 6500 S cm−1, surpass the conductivity of other solution-processed 2D materials, while simultaneously transmitting >97% of visible light per-nanometer thickness. It is shown that this high conductivity is due to a metal-like free-electron density as well as a high degree of coplanar alignment of individual nanosheets achieved through spincasting. Consequently, the spincast films exhibit conductivity over a macroscopic scale that is comparable to the intrinsic conductivity of the constituent 2D sheets. Additionally, optical characterization over the ultraviolet-to-near-infrared range reveals the onset of free-electron plasma oscillations above 1130 nm. Ti3C2 is therefore a potential building block for plasmonic applications at near-infrared wavelengths and constitutes the first example of a new class of solution-processed, carbide-based 2D optoelectronic materials.

Sustainable Synthesis and Assembly of Biomass-Derived B/N Co-Doped Carbon Nanosheets with Ultrahigh Aspect Ratio for High-Performance Supercapacitors

Abstract: The practical application of graphene has still been hindered by high cost and scarcity in supply. It boosts great interest in seeking for low-cost substitute of graphene for upcoming usage where extremely physical properties are not absolutely critical. The conversion of renewable biomass offers a great opportunity for sustainable and economic fabrication of 2D carbon nanostructures. However, large-scale production of carbon nanosheets with ultrahigh aspect ratio, satisfied electronic properties, and the capability of organized assembly like graphene has been rarely reported. In this work, a facile yet efficient approach for mass production of flexible boric/nitrogen co-doped carbon nanosheets with very thin thickness of 5–8 nm and ultrahigh aspect ratio of over 6000–10 000 is demonstrated by assembling the biomass molecule in long-range order on 2D hard template and subsequent annealing. The advantage of these doped carbon nanosheets over conventional products lies in that they can be readily assembled to multilevel architectures such as freestanding flexible thin film and ultralight aerogels with better electrical properties, which exhibit exceptional capacitive performance for supercapacitor application. The recyclability of boric acid template further reduces the discharge of the waste and processing cost, rendering high cost-effectiveness and environmental benignity for scalable production.

Bifunctional Nickel Phosphide Nanocatalysts Supported on Carbon Fiber Paper for Highly Efficient and Stable Overall Water Splitting

Abstract: Self-supported electrodes comprising carbon fiber paper (CP) integrated with bifunctional nickel phosphide (Ni-P) electrocatalysts are fabricated by electrodeposition of Ni on functionalized CP, followed by a convenient one-step phosphorization treatment in phosphorus vapor at 500 °C. The as-fabricated CP@Ni-P electrode exhibits excellent electrocatalytic performance toward hydrogen evolution in both acidic and alkaline solutions, with only small overpotentials of 162 and 250 mV, respectively, attaining a cathodic current density of 100 mA cm−2. Furthermore, the CP@Ni-P electrode also exhibits superior catalytic performance toward oxygen evolution reaction (OER). An exceptionally high OER current of 50.4 mA cm−2 is achieved at an overpotential of 0.3 V in 1.0 m KOH. The electrode can sustain 10 mA cm−2 for 180 h with only negligible degradation, showing outstanding durability. Detailed microstructural and compositional studies reveal that upon OER in alkaline solution the surface Ni-P is transformed to NiO covered with a thin Ni(OH)x layer, forming a Ni-P/NiO/Ni(OH)x heterojunction, which presumably enhances the electrocatalytic performance for OER. Given the well-defined bifunctionality, a full alkaline electrolyzer is constructed using two identical CP@Ni-P electrodes as cathode and anode, respectively, which can realize overall water splitting with efficiency as high as 91.0% at 10 mA cm−2 for 100 h.

Physical Mechanisms behind the Field-Cycling Behavior of HfO2-Based Ferroelectric Capacitors

Abstract: Novel hafnium oxide (HfO2)-based ferroelectrics reveal full scalability and complementary metal oxide semiconductor integratability compared to perovskite-based ferroelectrics that are currently used in nonvolatile ferroelectric random access memories (FeRAMs). Within the lifetime of the device, two main regimes of wake-up and fatigue can be identified. Up to now, the mechanisms behind these two device stages have not been revealed. Thus, the main scope of this study is an identification of the root cause for the increase of the remnant polarization during the wake-up phase and subsequent polarization degradation with further cycling. Combining the comprehensive ferroelectric switching current experiments, Preisach density analysis, and transmission electron microscopy (TEM) study with compact and Technology Computer Aided Design (TCAD) modeling, it has been found out that during the wake-up of the device no new defects are generated but the existing defects redistribute within the device. Furthermore, vacancy diffusion has been identified as the main cause for the phase transformation and consequent increase of the remnant polarization. Utilizing trap density spectroscopy for examining defect evolution with cycling of the device together with modeling of the degradation results in an understanding of the main mechanisms behind the evolution of the ferroelectric response.

High-Performance Epoxy Nanocomposites Reinforced with Three-Dimensional Carbon Nanotube Sponge for Electromagnetic Interference Shielding

Abstract: Light-weight and high-performance electromagnetic interference (EMI)-shielding epoxy nanocomposites are prepared by an infiltration method using a 3D carbon nanotube (CNT) sponge as the 3D reinforcement and conducting framework. The preformed, highly porous, and electrically conducting framework acts as a highway for electron transport and can resist a high external loading to protect the epoxy nanocomposite. Consequently, a remarkable conductivity of 148 S m−1 and an outstanding EMI shielding effectiveness of around 33 dB in the X-band are achieved for the epoxy nanocomposite with 0.66 wt% of CNT sponge, which is higher than that achieved for epoxy nanocomposites with 20 wt% of conventional CNTs. More importantly, the CNT sponge provides a dual advantage over conventional CNTs in its prominent reinforcement and toughening of the epoxy composite. Only 0.66 wt% of CNT sponge significantly increases the flexural and tensile strengths by 102% and 64%, respectively, as compared to those of neat epoxy. Moreover, the nanocomposite shows a 250% increase in tensile toughness and a 97% increase in elongation at break. These results indicate that CNT sponge is an ideal functional component for mechanically strong and high-performance EMI-shielding nanocomposites.

Bifunctional Porous NiFe/NiCo2O4/Ni Foam Electrodes with Triple Hierarchy and Double Synergies for Efficient Whole Cell Water Splitting

Abstract: A 3D hierarchical porous catalyst architecture based on earth abundant metals Ni, Fe, and Co has been fabricated through a facile hydrothermal and electrodeposition method for efficient oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The electrode is comprised of three levels of porous structures including the bottom supermacroporous Ni foam (≈500 μm) substrate, the intermediate layer of vertically aligned macroporous NiCo2O4 nanoflakes (≈500 nm), and the topmost NiFe(oxy)hydroxide mesoporous nanosheets (≈5 nm). This hierarchical architecture is binder-free and beneficial for exposing catalytic active sites, enhancing mass transport and accelerating dissipation of gases generated during water electrolysis. Serving as an anode catalyst, the designed hierarchical electrode displays excellent OER catalytic activity with an overpotential of 340 mV to achieve a high current density of 1200 mA cm−2. Serving as a cathode catalyst, the catalyst exhibits excellent performance toward HER with a moderate overpotential of 105 mV to deliver a current density of 10 mA cm−2. Serving as both anode and cathode catalysts in a two-electrode water electrolysis system, the designed electrode only requires a potential of 1.67 V to deliver a current density of 10 mA cm−2 and exhibits excellent durability in prolonged bulk alkaline water electrolysis.

Electrochemical Intercalation of Potassium into Graphite

Abstract: Exceptional cycling performance of graphite anode in K-ion batteries is demonstrated with a reversible capacity of 246 mAh g–1 and 89% retention of the initial capacity after 200 cycles. Although the graphite anode experiences huge volume change and worse kinetics during K intercalation/deintercalation, the cycling stability delivered in K-ion batteries is comparable to that of Li-ion batteries using the same graphite anode. The combination of excellent electrochemical performance, the abundance and wide availability of K in earth's crust, and the well-developed technology of the graphite anode make the K-ion battery very attractive for offering a low cost battery chemistry for large-scale energy storage applications.

High-Quality Whispering-Gallery-Mode Lasing from Cesium Lead Halide Perovskite Nanoplatelets

Abstract: Semiconductor micro/nano-cavities with high quality factor (Q) and small modal volume provide critical platforms for exploring strong light-matter interactions and quantum optics, enabling further development of coherent and quantum photonic devices. Constrained by exciton binding energy and thermal fluctuation, only a handful of wide-band semiconductors such as ZnO and GaN have stable excitons at room temperature. Metal halide perovskite with cubic lattice and well-controlled exciton may provide solutions. In this work, high-quality single-crystalline cesium lead halide CsPbX3 (X = Cl, Br, I) whispering-gallery-mode (WGM) microcavities are synthesized by vapor-phase van der Waals epitaxy method. The as-grown perovskites show strong emission and stable exciton at room temperature over the whole visible spectra range. By varying the halide composition, multi-color (400–700 nm).WGM excitonic lasing is achieved at room temperature with low threshold (~ 2.0 μJ cm−2) and high spectra coherence (~0.14–0.15 nm). The results advocate the promise of inorganic perovskites towards development of optoelectronic devices and strong light-matter coupling in quantum optics.

In Situ Bond Modulation of Graphitic Carbon Nitride to Construct p–n Homojunctions for Enhanced Photocatalytic Hydrogen Production

Abstract: Graphitic carbon nitride (g-C3N4) has recently emerged as an attractive photocatalyst for solar energy conversion. However, the photocatalytic activities of g-C3N4 remain moderate because of the insufficient solar-light absorption and the fast electron–hole recombination. Here, defect-modified g-C3N4 (DCN) photocatalysts, which are easily prepared under mild conditions and show much extended light absorption with band gaps decreased from 2.75 to 2.00 eV, are reported. More importantly, cyano terminal CN groups, acting as electron acceptors, are introduced into the DCN sheet edge, which endows the DCN with both n- and p-type conductivities, consequently giving rise to the generation of p–n homojunctions. This homojunction structure is demonstrated to be highly efficient in charge transfer and separation, and results in a fivefold enhanced photocatalytic H2 evolution activity. The findings deepen the understanding on the defect-related issues of g-C3N4-based materials. Additionally, the ability to build homojunction structures by the defect-induced self-functionalization presents a promising strategy to realize precise band engineering of g-C3N4 and related polymer semiconductors for more efficient solar energy conversion applications.

Preparation of MnCo2O4@Ni(OH)2 Core–Shell Flowers for Asymmetric Supercapacitor Materials with Ultrahigh Specific Capacitance

Abstract: Supercapacitors have attracted much interest in the past decades owing to their important applications, but most of them are focused on solitary or simple metal oxides. Here, a novel supercapacitor electrode composed of multicomponent MnCo2O4@Ni(OH)2 belt-based core–shell nanoflowers is reported by a facile and cost-effective method. This hybrid electrode exhibits a significantly enhanced specific capacitance. An asymmetric supercapacitor based on this unique hybrid nanoflowers as anode and an activated carbon film as cathode demonstrates high energy density, high power density, and long cycling lifespan.

Mechanistic Insights on Ternary Ni2−xCoxP for Hydrogen Evolution and Their Hybrids with Graphene as Highly Efficient and Robust Catalysts for Overall Water Splitting

Abstract: Searching the high-efficient, stable, and earth-abundant electrocatalysts to replace the precious noble metals holds the promise for practical utilizations of hydrogen and oxygen evolution reactions (HER and OER). Here, a series of highly active and robust Co-doped nickel phosphides (Ni2−xCoxP) catalysts and their hybrids with reduced graphene oxide (rGO) are developed as bifunctional catalysts for both HER and OER. The Co-doping in Ni2P and their hybridization with rGO effectively regulate the catalytic activity of the surface active sites, accelerate the charge transfer, and boost their superior catalytic activity. Density functional theory calculations show that the Co-doped catalysts deliver the moderate trapping of atomic hydrogen and facile desorption of the generated H2 due to the H-poisoned surface active sites of Ni2−xCoxP under the real catalytic process. Electrochemical measurements reveal the high HER efficiency and durability of the NiCoP/rGO hybrids in electrolytes with pH 0–14. Coupled with the remarkable and robust OER activity of the NiCoP/rGO hybrids, the practical utilization of the NiCoP/rGO‖NiCoP/rGO for overall water splitting yields a catalytic current density of 10 mA cm−2 at 1.59 V over 75 h without an obvious degradation and Faradic efficiency of ≈100% in a two-electrode configuration and 1.0 m KOH.

Modulation of Hypoxia in Solid Tumor Microenvironment with MnO2 Nanoparticles to Enhance Photodynamic Therapy

Abstract: Hypoxia not only promotes tumor metastasis but also strengthens tumor resistance to therapies that demand the involvement of oxygen, such as radiation therapy and photodynamic therapy (PDT). Herein, taking advantage of the high reactivity of manganese dioxide (MnO2) nanoparticles toward endogenous hydrogen peroxide (H2O2) within the tumor microenvironment to generate O2, multifunctional chlorine e6 (Ce6) loaded MnO2 nanoparticles with surface polyethylene glycol (PEG) modification (Ce6@MnO2-PEG) are formulated to achieve enhanced tumor-specific PDT. In vitro studies under an oxygen-deficient atmosphere uncover that Ce6@MnO2-PEG nanoparticles could effectively enhance the efficacy of light-induced PDT due to the increased intracellular O2 level benefited from the reaction between MnO2 and H2O2, the latter of which is produced by cancer cells under the hypoxic condition. Owing to the efficient tumor homing of Ce6@MnO2-PEG nanoparticles upon intravenous injection as revealed by T1-weighted magnetic resonance imaging, the intratumoral hypoxia is alleviated to a great extent. Thus, in vivo PDT with Ce6@MnO2-PEG nanoparticles even at a largely reduced dose offers remarkably improved therapeutic efficacy in inhibiting tumor growth compared to free Ce6. The results highlight the promise of modulating unfavorable tumor microenvironment with nanotechnology to overcome current limitations of cancer therapies.

Large-Area Compliant, Low-Cost, and Versatile Pressure-Sensing Platform Based on Microcrack-Designed Carbon Black@Polyurethane Sponge for Human–Machine Interfacing

Abstract: It is a challenge to manufacture pressure-sensing materials that possess flexibility, high sensitivity, large-area compliance, and capability to detect both tiny and large motions for the development of artificial intelligence products. Herein, a very simple and low-cost approach is proposed to fabricate versatile pressure sensors based on microcrack-designed carbon black (CB)@polyurethane (PU) sponges via natural polymer-mediated water-based layer-by-layer assembly. These sensors are capable of satisfying the requirements of ultrasmall as well as large motion monitoring. The versatility of these sensors benefits from two aspects: microcrack junction sensing mechanism for tiny motion detecting (91 Pa pressure, 0.2% strain) inspired by the spider sensory system and compressive contact of CB@PU conductive backbones for large motion monitoring (16.4 kPa pressure, 60% strain). Furthermore, these sensors exhibit excellent flexibility, fast response times (<20 ms), as well as good reproducibility over 50 000 cycles. This study also demonstrates the versatility of these sensors for various applications, ranging from speech recognition, health monitoring, bodily motion detection to artificial electronic skin. The desirable comprehensive performance of our sensors, which is comparable to the recently reported pressure-sensing devices, together with their significant advantages of low-cost, easy fabrication, especially versatility, makes them attractive in the future of artificial intelligence.

Urchin-Like CoSe2 as a High-Performance Anode Material for Sodium-Ion Batteries

Abstract: Urchin-like CoSe2 assembled by nanorods has been synthesized via simple solvothermal route and has been first applied as an anode material for sodium-ion batteries (SIBs) with ether-based electrolytes. The CoSe2 delivers excellent sodiation and desodiation properties when using 1 m NaCF3SO3 in diethyleneglycol dimethylether as an electrolyte and cycling between 0.5 and 3.0 V. A high discharge capacity of 0.410 Ah g−1 is obtained at 1 A g−1 after 1800 cycles, corresponding to a capacity retention of 98.6% calculated from the 30th cycle. Even at an ultrahigh rate of 50 A g−1, the capacity still maintains 0.097 Ah g−1. The reaction mechanism of the as-prepared CoSe2 is also investigated. The results demonstrate that at discharged 1.56 V, insertion reaction occurs, while two conversion reactions take place at the second and third plateaus around 0.98 and 0.65 V. During the charge process, Co first reacts with Na2Se to form NaxCoSe2 and then turns back to CoSe2. In addition to Na/CoSe2 half cells, Na3V2(PO4)3/CoSe2 full cell with excessive amount of Na3V2(PO4)3 has been studied. The full cell exhibits a reversible capacity of 0.380 Ah g−1. This work definitely enriches the possibilities for anode materials for SIBs with high performance.

Anode-Free Rechargeable Lithium Metal Batteries

Abstract: Anode-free rechargeable lithium (Li) batteries (AFLBs) are phenomenal energy storage systems due to their significantly increased energy density and reduced cost relative to Li-ion batteries, as well as ease of assembly because of the absence of an active (reactive) anode material. However, significant challenges, including Li dendrite growth and low cycling Coulombic efficiency (CE), have prevented their practical implementation. Here, an anode-free rechargeable lithium battery based on a Cu||LiFePO4 cell structure with an extremely high CE (>99.8%) is reported for the first time. This results from the utilization of both an exceptionally stable electrolyte and optimized charge/discharge protocols, which minimize the corrosion of the in situly formed Li metal anode.

Overall Water Splitting Catalyzed Efficiently by an Ultrathin Nanosheet-Built, Hollow Ni3S2-Based Electrocatalyst

Abstract: Making highly efficient catalysts for an overall ​water splitting reaction is vitally important to bring solar/electrical-to-hydrogen energy conversion processes into reality. Herein, the synthesis of ultrathin nanosheet-based, hollow MoOx/Ni3S2 composite microsphere catalysts on nickel foam, using ammonium molybdate as a precursor and the triblock copolymer pluronic P123 as a structure-directing agent is reported. It is also shown that the resulting materials can serve as bifunctional, non-noble metal electrocatalysts with high activity and stability for the hydrogen evolution reaction (HER) as well as the oxygen evolution reaction (OER). Thanks to their unique structural features, the materials give an impressive water-splitting current density of 10 mA cm−2 at ≈1.45 V with remarkable durability for >100 h when used as catalysts both at the cathode and the anode sides of an alkaline electrolyzer. This performance for an overall water splitting reaction is better than even those obtained with an electrolyzer consisting of noble metal-based Pt/C and IrOx/C catalytic couple—the benchmark catalysts for HER and OER, respectively.

A Novel Optical Thermometry Strategy Based on Diverse Thermal Response from Two Intervalence Charge Transfer States

Abstract: In this work, a novel thermometry strategy based on the diversity in thermal quenching behavior of two intervalence charge transfer (IVCT) states in oxide crystals is proposed, which provides a promising route to design self-referencing optical temperature sensing material with superior temperature sensitivity and signal discriminability. Following this strategy, uniform Tb3+/Pr3+:NaGd(MoO4)2 micro-octahedrons are directionally synthesized. Originated from the diverse thermal responses between Tb3+-Mo6+ and Pr3+-Mo6+ IVCT states, fluorescence intensity ratio of Pr3+ to Tb3+ in this material displays excellent temperature sensing property in a temperature range from 303 to 483 K. The maximum absolute and relative sensitivity reaches as high as 0.097 K−1 and 2.05% K−1, respectively, being much higher than those of the previously reported optical thermometric materials. Excellent temperature sensing features are also demonstrated in the other Tb3+/Pr3+ codoped oxide crystals having d0 electron configured transition metal ions (Ti4+, V5+, Mo6+, or W6+), such as scheelite NaLu(MoO4)2 and NaLu(WO4)2, and monazite LaVO4 and perovskite La2Ti3O9, evidencing the universal validity of the proposed strategy. This work exploits an effective pathway for developing new optical temperature sensing materials with high performance.

Amorphous FeOOH Quantum Dots Assembled Mesoporous Film Anchored on Graphene Nanosheets with Superior Electrochemical Performance for Supercapacitors

Abstract: Previous research on iron oxides/hydroxides has focused on the crystalline rather than the amorphous phase, despite that the latter could have superior electrochemical activity due to the disordered structure. In this work, a simple and scalable synthesis route is developed to prepare amorphous FeOOH quantum dots (QDs) and FeOOH QDs/graphene hybrid nanosheets. The hybrid nanosheets possess a unique heterostructure, comprising a continuous mesoporous FeOOH nanofilm tightly anchored on the graphene surface. The amorphous FeOOH/graphene hybrid nanosheets exhibit superior pseudocapacitive performance, which largely outperforms the crystalline iron oxides/hydroxides-based materials. In the voltage range between −0.8 and 0 V versus Ag/AgCl, the amorphous FeOOH/graphene composite electrode exhibits a large specific capacitance of about 365 F g−1, outstanding cycle performance (89.7% capacitance retention after 20 000 cycles), and excellent rate capability (189 F g−1 at a current density of 128 A g−1). When the lower cutoff voltage is extended to −1.0 and −1.25 V, the specific capacitance of the amorphous FeOOH/graphene composite electrode can be increased to 403 and 1243 F g−1, respectively, which, however, compromises the rate capability and cycle performance. This work brings new opportunities to design high-performance electrode materials for supercapacitors, especially for amorphous oxides/hydroxides-based materials.

All‐Inorganic Perovskite Nanocrystals for High‐Efficiency Light Emitting Diodes: Dual‐Phase CsPbBr3‐CsPb2Br5 Composites

Abstract: A dual-phase all-inorganic composite CsPbBr3-CsPb2Br5 is developed and applied as the emitting layer in LEDs, which exhibited a maximum luminance of 3853 cd m–2, with current density (CE) of ≈8.98 cd A–1 and external quantum efficiency (EQE) of ≈2.21%, respectively. The parasite of secondary phase CsPb2Br5 nanoparticles on the cubic CsPbBr3 nanocrystals could enhance the current efficiency by reducing diffusion length of excitons on one side, and decrease the trap density in the band gap on the other side. In addition, the introduction of CsPb2Br5 nanoparticles could increase the ionic conductivity by reducing the barrier against the electronic and ionic transport, and improve emission lifetime by decreasing nonradiative energy transfer to the trap states via controlling the trap density. The dual-phase all-inorganic CsPbBr3-CsPb2Br5 composite nanocrystals present a new route of perovskite material for advanced light emission applications.

Atomically Thin Boron Nitride: Unique Properties and Applications

Abstract: Atomically thin boron nitride (BN) is an important 2D nanomaterial, with many properties distinct from graphene. In this feature article, these unique properties and associated applications, often not feasible with graphene, are outlined. The article starts with characterization and identification of atomically thin BN. It is followed by demonstrating their strong oxidation resistance at high temperatures and applications in protecting metals from oxidation and corrosion. As flat insulators, BN nanosheets are ideal dielectric substrates for surface enhanced Raman spectroscopy (SERS) and electronic devices based on 2D heterostructures. The light emission of BN nanosheets in the deep ultraviolet (DUV) and ultraviolet (UV) regions is also included for its scientific and technological importance. The last part is dedicated to synthesis, characterization, and optical properties of BN nanoribbons, a special form of nanosheets.

Template‐Based Engineering of Carbon‐Doped Co3O4 Hollow Nanofibers as Anode Materials for Lithium‐Ion Batteries

Abstract: Co3O4 anode materials exhibit poor conductivity and a large volume change, rendering controlling of their nanostructure essential to optimize their lithium storage performance. Carbon-doped Co3O4 hollow nanofibers (C-doped Co3O4 HNFs), for the first time are synthesized using bifunctional polymeric nanofibers as template and carbon source. Compared with undoped Co3O4 HNFs and solid Co3O4 NFs, C-doped Co3O4 HNFs feature a remarkably high specific capacity, excellent cycling stability, and superior rate capacity as anode materials for lithium-ion batteries. The superior performance of C-doped Co3O4 HNFs electrodes can be attributed to their structural features, which confer enhanced electron transportation and Li+ ion diffusion due to C-doping, and tolerance for volume change due to the 1D hollow structure. Density functional theory calculations provide a good explanation of the observed enhanced conductivity in C-doped Co3O4 HNFs.

Cobalt‐Doping in Molybdenum‐Carbide Nanowires Toward Efficient Electrocatalytic Hydrogen Evolution

Abstract: Efficient hydrogen evolution reaction (HER) over noble-metal-free electrocatalysts provides one of the most promising pathways to face the energy crisis Herein, facile cobalt-doping based on Co-modified MoOx–amine precursors is developed to optimize the electrochemical HER over Mo2C nanowires The effective Co-doping into Mo2C crystal structure increases the electron density around Fermi level, resulting in the reduced strength of Mo–H for facilitated HER kinetics As expected, the Co-Mo2C nanowires with an optimal Co/Mo ratio of 0020 display a low overpotential (η10 = 140 and 118 mV for reaching a current density of –10 mA cm−2; η100 = 200 and 195 mV for reaching a current density of –100 mA cm−2), a small Tafel slope (39 and 44 mV dec−1), and a low onset overpotential (40 and 25 mV) in 05 m H2SO4 and 10 m KOH, respectively This work highlights a feasible strategy to explore efficient electrocatalysts via engineering on composition and nanostructure

High-Strength and High-Toughness Double-Cross-Linked Cellulose Hydrogels: A New Strategy Using Sequential Chemical and Physical Cross-Linking

Abstract: Polysaccharide-based hydrogels have multiple advantages because of their inherent biocompatibility, biodegradability, and non-toxicic properties. The feasibility of using polysaccharide-based hydrogels could be improved if they could simultaneously fulfill the mechanical property and cell compatibility requirements for practical applications. Herein, the construction of double-cross-linked (DC) cellulose hydrogels is described using sequential chemical and physical cross-linking, resulting in DC cellulose hydrogels that are mechanically superior to single-cross-linked cellulose hydrogels. The formation and spatial distribution of chemically cross-linked domains and physically cross-linked domains within the DC cellulose hydrogels are demonstrated. The molar ratio of epichlorohydrin to anhydroglucose units of cellulose and the concentration of the aqueous ethanol solution are two critical parameters for obtaining mechanically strong and tough DC cellulose hydrogels. The mechanical properties of the DC cellulose hydrogels under loading-unloading cycles are described using compression and tension models. The possible toughening mechanism of double-cross-linking is discussed.

Ternary Metal Phosphide with Triple-Layered Structure as a Low-Cost and Efficient Electrocatalyst for Bifunctional Water Splitting

Abstract: Development of low-cost, high-performance, and bifunctional electrocatalysts for water splitting is essential for renewable and clean energy technologies. Although binary phosphides are inexpensive, their performance is not as good as noble metals. Adding a third metal element to binary phosphides (Ni-P, Co-P) provides the opportunity to tune their crystalline and electronic structures and thus their electrocatalytic properties. Here, ternary phosphide (NiCoP) films with different nickel to cobalt ratios via an electrodeposition technique are synthesized. The films have a triple-layered and hierarchical morphology, consisting of nanosheets in the bottom layer, ≈90–120 nm nanospheres in the middle layer, and larger spherical particles on the top layer. The ternary phosphides exhibit versatile activities that are strongly dependent on the Ni/Co ratios and Ni0.51Co0.49P film is found to have the best electrocatalytic activities for both hydrogen evolution reactions and oxygen evolution reactions. The high performance of the ternary phosphide film is attributed to enhanced electric conductivity so that reaction kinetics is accelerated, enlarged surface area due to the hierarchical and three-layered morphology, and increased local electric dipole so that the energy barrier for the water splitting reaction is lowered.