Rational Construction of 3D Self-Supported MOF-Derived Cobalt Phosphide-Based Hollow Nanowall Arrays for Efficient Overall Water Splitting At large Current Density.

Developing efficient nonprecious bifunctional electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) in the same electrolyte with a low overpotential and large current density presents an appealing yet challenging goal for large-scale water electrolysis. Herein, a unique 3D self-branched hierarchical nanostructure composed of ultra-small cobalt phosphide (CoP) nanoparticles embedded into N, P-codoped carbon nanotubes knitted hollow nanowall arrays (CoPʘNPCNTs HNWAs) on carbon textiles (CTs) through a carbonization-phosphatization process is presented. Benefiting from the uniform protrusion distributions of CoP nanoparticles, the optimum CoPʘNPCNTs HNWAs composites with high abundant porosity exhibit superior electrocatalytic activity and excellent stability for OER in alkaline conditions, as well as for HER in both acidic and alkaline electrolytes, even under large current densities. Furthermore, the assembled CoPʘNPCNTs/CTs||CoPʘNPCNTs/CTs electrolyzer demonstrates exceptional performance, requiring an ultralow cell voltage of 1.50 V to deliver the current density of 10 mA cm-2 for overall water splitting (OWS) with favorable stability, even achieving a large current density of 200 mA cm-2 at a low cell voltage of 1.78 V. Density functional theory (DFT) calculation further reveals that all the C atoms between N and P atoms in CoPʘNPCNTs/CTs act as the most efficient active sites, significantly enhancing the electrocatalytic properties. This strategy, utilizing 2D MOF arrays as a structural and compositional material to create multifunctional composites/hybrids, opens new avenues for the exploration of highly efficient and robust non-noble-metal catalysts for energy-conversion reactions.

Ti3C2Tx MXene-embedded MnO2-based hydrophilic electrospun carbon nanofibers as a freestanding electrode for supercapacitors.

Herein, MnO2 nanoflowers are electrodeposited on a self-supported and electroconductive electrode in which 2D Ti3C2Tx nanosheets are encased in carbon nanofibers (MnO2@Ti3C2Tx/CNFs). This improves the conductivity and hydrophilicity of the MnO2 composite electrode. The asymmetric supercapacitor shows a high energy density of 46.4 W h kg-1 and a power density of 4 kW kg-1.

Fabrication of glass-based analytical devices by immobilizing nanomaterials on glass substrate with a fluorescent glue for the highly sensitive determination of mercury ions.

A facile method is reported to develop glass-based analytical devices (GADs) based on immobilizing nanomaterials on a glass substrate with fluorescent glue. The fluorescent glue was first prepared by coupling bovine serum albumin (BSA)-protected Au nanoclusters (NCs) and sugars (i.e., ascorbic acid, AA). The glue was then used to immobilize carbon dots (C-dots) on glass substrates to fabricate the portable GADs. The liquid glue-C-dots mixture and probable GADs were developed for Hg2+ detection. Under 365-nm excitation wavelength, the emission at 652 nm from the glue is gradually quenched with increasing concentrations of Hg2+. This quenching is explained in terms of the Stern-Volmer equation and is ascribed to static quenching. The fluorescent color of the glue and GADs gradually changes from pink to blue, with increasing concentrations of Hg2+. The limits of detection (LODs) for Hg2+ determination by bare eyes are 1 nM both for the glue and GADs, suggesting an uncompromised sensing capability even after immobilization. The detection sensitivity of GADs shows a significant improvement compared with the same material-based papers (5 µM). A linear relationship is observed between the total Euclidean distances (EDs) and Hg2+ concentration in the range 0-100 nM, providing the potential for Hg2+ quantification using GADs. The LOD is estimated to be 0.84 nM. To show a potentially practical application, the GADs were used to detect Hg2+ in certified reference material and lake water.

Fabrication of a LiNi0.5Mn0.4Ti0.03Mg0.03Nb0.01Mo0.03O2 cathode for low-cost long-life lithium-ion batteries.

The high price of Co and Ni restricts the development of the lithium-ion battery industry. Reducing the Ni content and eliminating Co is an effective way to lower the cost. In this work, we eliminate the Co in NCM523 cathodes by using a complex concentrated doping strategy. LiNi0.5Mn0.4Ti0.03Mg0.03Nb0.01Mo0.03O2 shows an unparalleled cost advantage with relatively high specific energy (>720 W h kg-1) and significantly improved overall performance (96% capacity retained after 1000 cycles). This report offers an important pathway to fabricate cathode materials for low-cost and long-life LIBs.

Synthesis of highly twinned ZnSe nanorods for enhancing N2 electrochemical conversion to NH3.

In this work, we report an atomistic understanding of the hydrogenation behavior of a highly twinned ZnSe nanorod (T-ZnSe) with a large density of surface atomic steps and the activation of N2 molecules adsorbed on its surface. Theoretical calculations suggest that the atomic steps are essential for the hydrogenation of T-ZnSe, which greatly enhances its catalytic activity. As a result, the T-ZnSe nanorods exhibit a significantly enhanced NH3 production rate of 13.3 µg h-1 mg-1 and faradaic efficiency of 5.83% towards the NRR compared with the pristine ZnSe nanorods. This report offers an important pathway for the development of efficient catalysts for the NRR, and a versatile anion-exchange strategy for efficiently manipulating materials' functionalities.

Cobalt-Nickel Layered Double Hydroxides on Electrospun MXene for Superior Asymmetric Supercapacitor Electrodes.

Flexible electrodes for energy storage and conversion require a micro-nanomorphology and stable structure. Herein, MXene fibers (MX-CNF) are fabricated by electrospinning, and Co-MOF nanoarrays are prepared on the fibers to form Co-MOF@MX-CNF. Hydrolysis and etching of Co-MOF@MX-CNF in the Ni2+ solution produce cobalt-nickel layered double hydroxide (CoNi-LDH). The CoNi-LDH nanoarrays on the MX-CNF substrate have a large specific surface area and abundant electrochemical active sites, thus ensuring effective exposure of the CoNi-LDH active materials to the electrolyte and efficient pseudocapacitive energy storage and fast reversible redox kinetics for enhanced charging-discharging characteristics. The CoNi-LDH@MX-CNF electrode exhibits a discharge capacity of 996 F g-1 at a current density of 1 A g-1 as well as 78.62% capacitance retention after 3,000 cycles at 10 A g-1. The asymmetric supercapacitor (ASC) comprising the CoNi-LDH@MX-CNF positive electrode and negative activated carbon electrode shows an energy density of 48.4 Wh kg-1 at a power density of 499 W kg-1 and a capacity retention of 78.9% after 3,000 cycles at a current density of 10 A g-1. Density-functional theory calculations reveal the charge density difference and partial density of states of CoNi-LDH@MX-CNF confirming the large potential of the CoNi-LDH@MX-CNF electrode in energy storage applications.

A Novel Two-Dimensional ZnSiP2 Monolayer as an Anode Material for K-Ion Batteries and NO2 Gas Sensing.

Using the crystal-structure search technique and first-principles calculation, we report a new two-dimensional semiconductor, ZnSiP2, which was found to be stable by phonon, molecular-dynamic, and elastic-moduli simulations. ZnSiP2 has an indirect band gap of 1.79 eV and exhibits an anisotropic character mechanically. Here, we investigated the ZnSiP2 monolayer as an anode material for K-ion batteries and gas sensing for the adsorption of CO, CO2, SO2, NO, NO2, and NH3 gas molecules. Our calculations show that the ZnSiP2 monolayer possesses a theoretical capacity of 517 mAh/g for K ions and an ultralow diffusion barrier of 0.12 eV. Importantly, the ZnSiP2 monolayer exhibits metallic behavior after the adsorption of the K-atom layer, which provides better conductivity in a period of the battery cycle. In addition, the results show that the ZnSiP2 monolayer is highly sensitive and selective to NO2 gas molecules.

MXene nanofibers confining MnOx nanoparticles: a flexible anode for high-speed lithium ion storage networks.

The electron and ion conductivities of anode materials such as MnOx affect critically the properties of anodes in Li-ion batteries. Herein, a three-dimensional (3D) nanofiber network (MnOx-MXene/CNFs) for high-speed electron and ion transport with a MnOx surface anchored and embedded inside is designed via electrospinning manganese ion-modified MXene nanosheets and subsequent carbonization. Ion transport analysis reveals improved Li+ transport on the MnOx-MXene/CNF electrode and first-principles density functional theory (DFT) calculation elucidates the Li+ adsorption and storage mechanism. The surface-anchored MnOx nanoparticles form extremely strong bonds with the nanofibers, and the internally embedded MnOx nanoparticles, due to the fiber confinement effect, ensure the structural stability during charging and discharging, achieving the so-called dual stabilization strategies for cyclic fluctuation. By electrospinning, self-restacking of MXene flakes can be prevented, thereby giving rise to a larger surface area and more accessible active sites on the flexible anode. Benefiting from the 3D network with excellent conductivity and stability, at high current densities, the MnOx-MXene/CNF anode exhibits outstanding electrochemical characteristics. Even after 2000 cycles, a reversible capacity of 1098 mA h g-1 can be obtained at 2 A g-1 with only 0.007208% decay rate. The MnOx-MXene/CNF anode also shows a significant rate performance such as 1268 mA h g-1 at 2 A g-1 and 1137 mA h g-1 at 5 A g-1 corresponding to an area specific capacity of 2.536 mA h cm-2 at 4 mA cm-2 and 2.274 mA h cm-2 at 10 mA cm-2, respectively. The results indicate that the MnOx-MXene/CNF anode has excellent Li-ion storage properties and great commercial potential.

Double perovskite microcrystals-based white light-emitting diodes without reabsorption of multiphase phosphors.

Here, Tb3+ ions are incorporated into Cs2Ag0.6Na0.4InCl6:Bi double perovskite microcrystals via a re-crystallization method. Tb3+ ions doping not only makes the white light spectrum adjustable, but also maintains the high photoluminescence quantum yield (PLQY). The optimal value of PLQY is 95%. These are comparable to the current highest values. Noteworthy is that, intrinsic emission of Tb3+ ions is attributed to the effective energy transfer from the trapped exciton state of the double perovskite host to Tb3+ ions. Finally, mixing 30% Tb3+ alloyed Cs2Ag0.6Na0.4InCl6:Bi and Cs2NaInCl6:10%Sb phosphors, a series of double-perovskite-based white light-emitting diodes (WLEDs) are prepared. The color coordinates of the best WLEDs are (0.34, 0.32), the lumen efficiency is 42 lm/W, and the color rendering index is 94.3. It is worth mentioning here that there is no blue light loss caused by energy reabsorption between the two phosphors, because the excitation wavelengths of the two phosphors are concentrated in the ultraviolet band. This work provides a new strategy for preparing high-performance WLED.

TiN@C nanocages as multifunctional sulfur hosts for superior lithium-sulfur batteries.

The lithium polysulfide (LiPS) shuttle effect and low redox kinetics are the key problems that hinder performance improvement and prevent achieving the commercial requirements for lithium-sulfur batteries (LSBs), and the reasonable construction of sulfur hosts is one effective strategy to relieve the polysulfide shuttle effect and improve redox kinetics. Herein, N-doped carbon nanocages decorated with homogeneously dispersed TiN nanoparticles (TiN@C NCs) as multifunctional sulfur hosts are designed for superior LSBs. Carbon nanocages provide space to mitigate volume expansion and provide additional physical adsorption to trap the LiPSs. Polar TiN nanoparticles not only exhibit the chemisorption capacity for LiPSs, but also catalyze and promote the conversion of long-chain LiPSs to Li2S2/Li2S in the reduction process as well as the decomposition of Li2S in the oxidation reaction, which significantly boosts electron/ion transport and decreases the potential barrier. Therefore, the S/TiN@C NC cathode has an excellent electrochemical capacity of 1485.7 mA h g-1 at 0.1 C. In particular, the cathode demonstrates high capacity reversibility after 500 cycles at 3 C with a retention of about 73.1%, which is equivalent to a slow capacity decay rate of 0.053% per cycle.

A rapid reduction of Au(I→0) strategy for the colorimetric detection and discrimination of proteins.

A gold nanoparticle (AuNP)-based sensing strategy based on rapid reduction of Au(I→0) is proposed. As a proof-of-concept study, the proposed sensing principle is designed for simultaneous and colorimetric detection and discrimination of multiple proteins. In the presence of H2O2, the target proteins could reduce Au(I) (i.e. HAuCl2) to AuNPs with different sizes, shapes and dispersion/aggregation states, thus resulting in rapidly colorimetric identification of different proteins. The optical response (i.e. color) of AuNPs is found to be characteristic of a given protein. The color response patterns are characteristic for each protein and can be quantitatively differentiated by statistical techniques. The sensor array is capable of discriminating proteins at concentrations as low as 0.1 µg/mL with high accuracy. A linear relationship was observed between the total Euclidean distances and protein concentration, providing the potential for protein quantification using this sensor array. The limit of detection (LOD) for catalase (Cat) is 0.08 µg/mL. The good linear range (from 0 to 8 µg/mL) has been used for the quantitative assay of Cat. To show a potentially practical application, this method was used to detect and discriminate proteins in human urine and tear samples. Graphical abstract We report a facile gold nanoparticle (AuNP)-based sensing strategy, that is, "a rapid reduction of Au(I) to Au(0) nanoparticles with different sizes and shapes by analytes that having certain reducing capabilities, resulting in different colours." The proposed sensing principle is designed for simultaneous, colorimetric detection and discrimination of multiple proteins.

Hierarchical crumpled NiMn2O4@MXene composites for high rate ion transport electrochemical supercapacitors.

MXenes have received great attention due to their excellent features such as metal-like electronic conductivity, hydrophilic surface groups, and high volumetric capacitance. However, many performances of MXenes are still unsatisfactory due to their low energy density and easy horizontal stacking. In this work, an NiMn2O4@MXene composite with a crumpled surface was fabricated by a hydrothermal method and a developed dip-coating method. The maximum specific capacitance of the electrode is about 1.52 times that of NiMn2O4. Besides, it delivers a retention rate of 93.3% after 4000 cycles due to the increased transport of ions and electrons by the crumpled surface. An asymmetrical device based on the crumpled NiMn2O4@MXene composite and AC was also assembled, which shows an ultra-high energy density. This work provides an effective strategy to solve the vertical stacking problem of MXenes, which can open new avenues for large-scale applications of MXenes in energy storage.

Template-free synthesis of ordered ZnO@ZnS core-shell arrays for high performance supercapacitors.

In this article, ordered ZnO@ZnS core-shell structures have been produced on a stainless mesh by a two-step approach without using a template. ZnO nanorods fabricated by a chemical vapor method are transferred into a 50 ml autoclave for a second stage ion-exchange reaction followed by heating at 120 °C for 4-16 h. The ZnO core is prepared as the conducting channel and ZnS as the active material. Such unique architecture exhibits remarkable electrochemical performance with high capacitance and desirable cycle life. When evaluating as the electrode for supercapacitors, the ZnO@ZnS core-shell structure delivers a high specific capacitance of 603.8 F g-1 at a current density of 2 A g-1, with 9.4% capacitance loss after cycling 3000 times. The fabrication strategy presented here is simple and cost-effective, which can open new avenues for large-scale applications of the novel materials in energy storage.

Hierarchical, porous CuS microspheres integrated with carbon nanotubes for high-performance supercapacitors.

Carbon nanotubes (CNTs) incorporated porous 3-dimensional (3D) CuS microspheres have been successfully synthesized via a simple refluxing method assisted by PVP. The composites are composed of flower-shaped CuS secondary microspheres, which in turn are assembled with primary nanosheets of 15-30 nm in thickness and fully integrated with CNT. The composites possess a large specific surface area of 189.6 m(2) g(-1) and a high conductivity of 0.471 S cm(-1). As electrode materials for supercapacitors, the nanocomposites show excellent cyclability and rate capability and deliver an average reversible capacitance as high as 1960 F g(-1) at a current density of 10 mA cm(-2) over 10000 cycles. The high electrochemical performance can be attributed to the synergistic effect of CNTs and the unique microstructure of CuS. The CNTs serve as not only a conductive agent to accelerate the transfer of electrons in the composites, but also as a buffer matrix to restrain the volume change and stabilize the electrode structure during the charge/discharge process. The porous structure of CuS also helps to stabilize the electrode structure and facilitates the transport for electrons.

Hierarchical Core/Shell NiCo2O4@NiCo2O4 Nanocactus Arrays with Dual-functionalities for High Performance Supercapacitors and Li-ion Batteries.

We report the synthesis of three dimensional (3D) NiCo2O4@NiCo2O4 nanocactus arrays grown directly on a Ni current collector using a facile solution method followed by electrodeposition. They possess a unique 3D hierarchical core-shell structure with large surface area and dual-functionalities that can serve as electrodes for both supercapacitors (SCs) and lithium-ion batteries (LIBs). As the SC electrode, they deliver a remarkable specific capacitance of 1264 F g(-1) at a current density of 2 A g(-1) and ~93.4% of capacitance retention after 5000 cycles at 2 A g(-1). When used as the anode for LIBs, a high reversible capacity of 925 mA h g(-1) is achieved at a rate of 120 mA g(-1) with excellent cyclic stability and rate capability. The ameliorating features of the NiCo2O4 core/shell structure grown directly on highly conductive Ni foam, such as hierarchical mesopores, numerous hairy needles and a large surface area, are responsible for the fast electron/ion transfer and large active sites which commonly contribute to the excellent electrochemical performance of both the SC and LIB electrodes.

Mesoporous ZnCo2O4 nanoflakes grown on nickel foam as electrodes for high performance supercapacitors.

ZnCo2O4 nanoflakes, as electrodes for supercapacitors, are grown on a cellular nickel foam using a cost-effective hydrothermal procedure. The mesoporous ZnCo2O4 nanoflakes have large electroactive surface areas with strong adhesion to the Ni foam, allowing fast ion and electron transport. The nanoarchitecture electrodes deliver an excellent specific capacitance of 1220 F g(-1) at a current density of 2 A g(-1) in a 2 M KOH aqueous solution and a long-term cyclic stability of 94.2% capacitance retention after 5000 cycles. The fabrication strategy is facile, cost-effective, and can offer great promise for large-scale supercapacitor applications.

Facile synthesis of graphene-like copper oxide nanofilms with enhanced electrochemical and photocatalytic properties in energy and environmental applications.

Novel graphene-like CuO nanofilms are grown on a copper foam substrate by in situ anodization for multifunctional applications as supercapacitor electrodes and photocatalysts for the degradation of dye pollutants. The as-prepared CuO consists of interconnected, highly crystalline, conductive CuO nanosheets with hierarchical open mesopores and a large surface area. The CuO nanofilms supported on a copper foam are employed as freestanding, binder-free electrodes for supercapacitors, which exhibit wonderful electrochemical performance with a large specific capacitance (919 F g(-1) at 1 A g(-1)), an excellent cycling stability (7% capacitance loss after 5000 cycles), and a good rate capability (748 F g(-1) at 30 A g(-1)). The porous CuO nanofilms also demonstrate excellent photocatalytic activities for degradation of methylene blue, with a degradation rate 99% much higher than 54% of the commercial CuO powders after 60 min. This excellent energy storage and photocatalytic performance of the graphene-like CuO nanofilms can open a new avenue for large-scale applications in energy and environmental fields.