Free-standing and flexible polyvinyl alcohol-sodium alginate-polypyrrole electrodes based on interpenetrating network hydrogels

Flexible supercapacitors (FSCs) have attracted much attention due to their strong mechanical flexibility, wearability and portability, which greatly rely on the employed flexible electrodes. The conductive polymer hydrogels with excellent flexibility, processability and capacitive performance are one of the most promising candidates, which are still limited by their poor mechanical properties. Constructing robust interpenetrating polymer networks (IPN) is an effective approach to promote their mechanical properties. Herein, interpenetrating polyvinyl alcohol (PVA)-sodium alginate (SA)-polypyrrole (PPy) hydrogels are prepared by the freeze-thaw and in-situ polymerization method. The IPN structure composed of PVA and SA not only enhances the mechanical properties of hydrogels, but also provides substantial active sites for electrochemical reactions. Moreover, the hydrogen-bonding interaction between different components in the PVA-SA-PPy hydrogel boosts the charge/ion transfer. The optimal PVA-SA-PPy hydrogels show an elongation at break of 380 %, a tensile strength of 1.5 MPa, and a specific capacitance of 2646 mF cm-2 at 2 mA cm-2. The symmetric PVA-SA-PPy FSCs show an energy density of 96.7 μWh cm-2 at a power density of 999.9 μW cm-2, and the capacitance retention is 66.3 % after 10,000 cycles. These exceptional mechanical and electrochemical properties make the PVA-SA-PPy hydrogels a promising candidate for FSCs.

Biomimetic Mineralization Synthesis of Flower-Like Cobalt Selenide/Reduced Graphene Oxide for Improved Electrochemical Deionization

Rationally and precisely tuning the composition and structure of materials is a viable strategy to improve electrochemical deionization (EDI) performances, which yet faces enormous challenges. Herein, an eco-friendly biomimetic mineralization synthetic strategy is developed to synthesize the flower-like cobalt selenide/reduced graphene oxide (Bio-CoSe2 /rGO) composites and used as advanced sodium ion adsorption electrodes. Benefiting from the slow and controllable reaction kinetics provided by the biomimetic mineralization process, the flower-like CoSe2 is uniformly constructed in the rGO, which is endowed with robust architecture, substantial adsorption sites and rapid charge/ion transport. The Bio-CoSe2 /rGO electrode yields the maximum salt adsorption capacity and salt adsorption rate of 56.3 mg g-1 and 5.6 mg g-1 min-1 respectively, and 92.5% capacity retention after 60 cycles. These results overmatch the pristine CoSe2 and irregular granular CoSe2 /rGO synthesized by a hydrothermal method, proving the structural superiority of the Bio-CoSe2 /rGO composites. Furthermore, the in-depth adsorption kinetics study indicates the chemisorption nature of sodium ion adsorption. The structures of the Bio-CoSe2 /rGO composites after long term EDI cycles are intensively studied to unveil the mechanism behind such superior EDI performances. This study offers one effective method for constructing advanced EDI electrodes, and enriches the application of the biomimetic mineralization synthetic strategy.

Robust double-network polyvinyl alcohol-polypyrrole hydrogels as high-performance electrodes for flexible supercapacitors

The growing demands of flexible and wearable electronic devices boost the rapid development of flexible supercapacitors (FSCs). Conductive hydrogels are considered to be one type of promising electrode materials for FSCs due to their good processability and electrochemical properties. However, the poor mechanical properties of conductive hydrogels hinder their practical applications. Building robust cross-linked network structures is a feasible way to enhance their mechanical properties. Herein, the double-network polyvinyl alcohol (PVA)-polypyrrole (PPy) conductive hydrogels are synthesized by the freeze-thaw and in-situ polymerization method. The double-network structure not only enhances mechanical properties of the hydrogels, but also promotes their electrolyte ion transport. The maximum elongation at break of the optimized PVA-PPy hydrogels can reach 156.4%, and the specific capacitance is 1718.7 mF cm-2 at 0.5 mA cm-2. Furthermore, the energy densities of the symmetrical PVA-PPy FSCs are 46.7 and 13.3 μWh cm-2 at power densities of 200.0 and 2000.0 μW cm-2. Such excellent electrochemical performances and mechanical properties make the synthesized PVA-PPy hydrogels a promising candidate for FSCs.

Stabilizing non-iridium active sites by non-stoichiometric oxide for acidic water oxidation at high current density

Stabilizing active sites of non-iridium-based oxygen evolution reaction (OER) electrocatalysts is crucial, but remains a big challenge for hydrogen production by acidic water splitting. Here, we report that non-stoichiometric Ti oxides (TiOx) can safeguard the Ru sites through structural-confinement and charge-redistribution, thereby extending the catalyst lifetime in acid by 10 orders of magnitude longer compared to that of the stoichiometric one (Ru/TiO2). By exploiting the redox interaction-engaged strategy, the in situ growth of TiOx on Ti foam and the loading of Ru nanoparticles are realized in one step. The as-synthesized binder-free Ru/TiOx catalyst exhibits low OER overpotentials of 174 and 265 mV at 10 and 500 mA cm-2, respectively. Experimental characterizations and theoretical calculations confirm that TiOx stabilizes the Ru active center, enabling operation at 10 mA cm-2 for over 37 days. This work opens an avenue of using non-stoichiometric compounds as stable and active materials for energy technologies.

High mass loading and additive-free prussian blue analogue based flexible electrodes for Na-ion supercapacitors

Supercapacitor electrodes often suffer from the low mass loading of active substances and the unsatisfactory ion/charge transport features due to the use of various additives. Exploring high mass loading and additive-free electrodes is of huge significance to develop advanced supercapacitors with commercial application prospects, which still remains challenging. Herein, high mass loading CoFe-prussian blue analogue (CoFe-PBA) electrodes are developed by a facile co-precipitation method using activated carbon cloth (ACC) as the flexible substrate. The homogeneous nanocube structure, large specific surface area (143.9 m2 g-1) and appropriate pore size distribution (3.4 nm) of the CoFe-PBA endow the as-prepared CoFe-PBA/ACC electrodes with low resistance and appealing ion diffusion characteristics. Typically, the high areal capacitance (1155.0 mF cm-2 at 0.5 mA cm-2) is obtained for high mass loading CoFe-PBA/ACC electrodes (9.7 mg cm-2). Furthermore, symmetrical flexible supercapacitors (FSCs) are constructed using CoFe-PBA/ACC electrodes and Na2SO4/polyving alcohol (Na2SO4/PVA) gel electrolyte, achieving superior stability (85.6% capacitance retention after 5,000 cycles), maximum energy density of 33.8 μWh cm-2 at 200.0 μW cm-2 and promising mechanical flexibility. This work is expected to offer inspirations for the development of high mass loading and additive-free electrodes for FSCs.

Ultrafast charge transfer in mixed-dimensional WO3-x nanowire/WSe2 heterostructures for attomolar-level molecular sensing

Developing efficient noble-metal-free surface-enhanced Raman scattering (SERS) substrates and unveiling the underlying mechanism is crucial for ultrasensitive molecular sensing. Herein, we report a facile synthesis of mixed-dimensional heterostructures via oxygen plasma treatments of two-dimensional (2D) materials. As a proof-of-concept, 1D/2D WO_3-x/WSe₂ heterostructures with good controllability and reproducibility are synthesized, in which 1D WO_3-x nanowire patterns are laterally arranged along the three-fold symmetric directions of 2D WSe₂. The WO_3-x/WSe₂ heterostructures exhibited high molecular sensitivity, with a limit of detection of 5 × 10^-18M and an enhancement factor of 5.0 × 10¹¹ for methylene blue molecules, even in mixed solutions. We associate the ultrasensitive performance to the efficient charge transfer induced by the unique structures of 1D WO_3-x nanowires and the effective interlayer coupling of the heterostructures. We observed a charge transfer timescale of around 1.0 picosecond via ultrafast transient spectroscopy. Our work provides an alternative strategy for the synthesis of 1D nanostructures from 2D materials and offers insights on the role of ultrafast charge transfer mechanisms in plasmon-free SERS-based molecular sensing.

Simultaneous electrical and thermal rectification in a monolayer lateral heterojunction

Efficient waste heat dissipation has become increasingly challenging as transistor size has decreased to nanometers. As governed by universal Umklapp phonon scattering, the thermal conductivity of semiconductors decreases at higher temperatures and causes heat transfer deterioration under high-power conditions. In this study, we realized simultaneous electrical and thermal rectification (TR) in a monolayer MoSe₂-WSe₂ lateral heterostructure. The atomically thin MoSe₂-WSe₂ heterojunction forms an electrical diode with a high ON/OFF ratio up to 10⁴. Meanwhile, a preferred heat dissipation channel was formed from MoSe₂ to WSe₂ in the ON state of the heterojunction diode at high bias voltage with a TR factor as high as 96%. Higher thermal conductivity was achieved at higher temperatures owing to the TR effect caused by the local temperature gradient. Furthermore, the TR factor could be regulated from maximum to zero by rotating the angle of the monolayer heterojunction interface. This result opens a path for designing novel nanoelectronic devices with enhanced thermal dissipation.

Lateral layered semiconductor multijunctions for novel electronic devices

Layered semiconductors, represented by transition metal dichalcogenides, have attached extensive attention due to their unique and tunable electrical and optical properties. In particular, lateral layered semiconductor multijunctions, including homojunctions, heterojunctions, hybrid junctions and superlattices, present a totally new degree of freedom in research on electronic devices beyond traditional materials and their structures, providing unique opportunities for the development of new structures and operation principle-based high performance devices. However, the advances in this field are limited by the precise synthesis of high-quality junctions and greatly hampered by ambiguous device performance limits. Herein, we review the recent key breakthroughs in the design, synthesis, electronic structure and property modulation of lateral semiconductor multijunctions and focus on their application-specific devices. Specifically, the synthesis methods based on different principles, such as chemical and external source-induced methods, are introduced stepwise for the controllable fabrication of semiconductor multijunctions as the basics of device application. Subsequently, their structure and property modulation are discussed, including control of their electronic structure, exciton dynamics and optical properties before the fabrication of lateral layered semiconductor multijunction devices. Precise property control will potentially result in outstanding device performances, including high-quality diodes and FETs, scalable logic and analog circuits, highly efficient optoelectronic devices, and unique electrochemical devices. Lastly, we focus on several of the most essential but unresolved debates in this field, such as the true advantages of few-layer vs. monolayer multijunctions, how sharp the interface should be for specific functional devices, and the superiority of lateral multijunctions over vertical multijunctions, highlighting the next-phase strategy to enhance the performance potential of lateral multijunction devices.

Atomic Fe-N4 /C in Flexible Carbon Fiber Membrane as Binder-Free Air Cathode for Zn-Air Batteries with Stable Cycling over 1000 h

Noble-metal-free, durable, and high-efficiency electrocatalysts for oxygen reduction and evolution reaction (ORR/OER) are vital for rechargeable Zn-air batteries (ZABs). Herein, a flexible and free-standing carbon fiber membrane immobilized with atomically dispersed Fe-N₄ /C catalysts (Fe/SNCFs-NH₃ ) is synthesized and used as air cathode for ZABs. The intertwined fibers with hierarchical nanopores facilitate the gas transportation, electrolyte infiltration and electron transfer. The large specific surface area exposes a high concentration of Fe-N₄ /C sites embedded in the carbon matrix. Modulation of local atomic configurations by sulfur doping in Fe/SNCFs-NH₃ catalyst leads to excellent ORR and enhanced OER activities. The as-synthesized Fe/SNCFs-NH₃ catalyst demonstrates a positive half-wave potential of 0.89 V and a small Tafel slope of 70.82 mV dec^-1 , outperforming the commercial Pt/C (0.86 V/94.74 mV dec^-1 ) and most reported M-N_x /C (M = Fe, Co, Ni) catalysts. Experimental characterizations and theoretical calculations uncover the crucial role of S doping in regulating ORR and OER activities. The liquid-state ZABs with Fe/SNCFs-NH₃ catalyst as air cathode deliver a large peak power density of 255.84 mW cm^-2 and long-term cycle durability over 1000 h. Solid-state ZAB shows stable cycling at various flat/bent/flat states, demonstrating great prospects in flexible electronic device applications.

Mo2C-MoO2 Heterostructure Quantum Dots for Enhanced Electrocatalytic Nitrogen Reduction to Ammonia

The electrocatalytic nitrogen reduction reaction (NRR) has been regarded as a promising strategy for producing ammonia (NH₃) at ambient conditions. However, the development of the NRR is severely hindered by the difficult adsorption and activation of N₂ on the catalyst surface and the competitive hydrogen evolution reaction (HER) due to the lack of efficient NRR electrocatalysts. Herein, Mo₂C-MoO₂ heterostructure quantum dots embedded in reduced graphene oxide (RGO) are proposed as efficient catalysts for the electrocatalytic NRR. The ultrasmall size of the quantum dot is beneficial for exposing the active sites for the NRR, and the synergetic effect of Mo₂C and MoO₂ can promote N₂ adsorption and activation and suppress the competitive HER simultaneously. As a result, a well-balanced NRR performance is achieved with a high NH₃ yield rate of 13.94 ± 0.39 μg h^-1 mg^-1 at -0.15 V vs RHE and a high Faradaic efficiency of 12.72 ± 0.58% at -0.1 V vs RHE. Density functional theory (DFT) calculations reveal that the Mo₂C (001) surface has a strong N₂ adsorption energy of -1.47 eV with the side-on configuration, and the N≡N bond length is elongated to 1.254 Å, indicating the enhanced N₂ adsorption and activation on the Mo₂C surface. On the other hand, the low ΔG_H* for HER over the MoO₂ (-111) surface demonstrates the impeded HER process for MoO₂. This work may provide effective catalyst-design strategies for enhancing the electrocatalytic NRR performance of Mo-based materials.

A Highly Sensitive Electrochemical Glucose Sensor Based on Room Temperature Exfoliated Graphite-Derived Film Decorated with Dendritic Copper

An ultrasensitive enzyme-free glucose sensor was facilely prepared by electrodepositing three-dimensional dendritic Cu on a room temperature exfoliated graphite-derived film (RTEG-F). An excellent electrocatalytic performance was demonstrated for glucose by using Cu/RTEG-F as an electrode. In terms of the high conductivity of RTEG-F and the good catalytic activity of the dendritic Cu structures, the sensor demonstrates high sensitivities of 23.237 mA/mM/cm², R² = 0.990, and 10.098 mA/mM/cm², R² = 0.999, corresponding to the concentration of glucose ranging from 0.025 mM to 1.0 mM and 1.0 mM to 2.7 mM, respectively, and the detection limit is 0.68 μM. In addition, the Cu/RTEG-F electrode demonstrates excellent anti-interference to interfering species and a high stability. Our work provides a new idea for the preparation of high-performance electrochemical enzyme-free glucose sensor.

Graphitic carbon nitride (g-C3N4) alleviates cadmium-induced phytotoxicity to rice (Oryza sativa L.)

In the present study, graphitic carbon nitride (g-C₃N₄) was synthesized in a tube furnace and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR). Different concentrations (0-200 mg/L) of g-C₃N₄ were prepared in nutrient solution amended with or without 20 mg/L CdCl₂ for the greenhouse study. Rice seedlings were exposed to g-C₃N₄ and Cd for 20 days. Our results suggest that 200 mg/L g-C₃N₄ significantly increased the fresh weight and root and shoot length as compared with the control, and notably alleviated Cd-induced toxicity. The addition of 200 mg/L g-C₃N₄ significantly reduced the root and shoot Cd content by approximately 14% and 23%, respectively. In addition, 200 mg/L g-C₃N₄ significantly elevated the nitrogen content and decreased C/N ration in rice shoots; most importantly, it alleviated Cd-induced nitrogen reduction. Our findings demonstrated the potential of g-C₃N₄ in regulating plant growth and minimizing the Cd-induced phytotoxicity, and shed light on providing a new strategy to maintain heavy metal contamination in agriculture using a low-cost and environmental friendly NMs.

Ultralight Flexible Electrodes of Nitrogen-Doped Carbon Macrotube Sponges for High-Performance Supercapacitors

Light-weight and flexible supercapacitors with outstanding electrochemical performances are strongly desired in portable and wearable electronics. Here, ultralight nitrogen-doped carbon macrotube (N-CMT) sponges with 3D interconnected macroporous structures are fabricated and used as substrate to grow nickel ferrite (NiFe₂ O₄ ) nanoparticles by vapor diffusion-precipitation and in situ growth. This process effectively suppresses the agglomeration of NiFe₂ O₄ , enabling good interfacial contact between N-CMT sponges and NiFe₂ O₄ . More remarkably, the as-synthesized NiFe₂ O₄ /N-CMT composite sponges can be directly used as electrodes without additional processing that could cause agglomeration and reduction of active sites. Benefiting from the tubular structure and the synergetic effect of NiFe₂ O₄ and N-CMT, the NiFe₂ O₄ /N-CMT-2 exhibits a high specific capacitance of 715.4 F g^-1 at a current density of 1 A g^-1 , and 508.3 F g^-1 at 10 A g^-1 , with 90.9% of capacitance retention after 50 000 cycles at 1 A g^-1 in an alkaline electrolyte. Furthermore, flexible supercapacitors are fabricated, yielding areal specific capacitances of 1397.4 and 1041.2 mF cm^-2 at 0.5 and 8 mA cm^-2 , respectively. They also exhibit exceptional cycling performance with capacitance retention of 92.9% at 1 mA cm^-2 after 10 000 cycles under bending. This work paves a new way to develop flexible, light-weight, and high-performance energy storage devices.

Defect Engineering of van der Waals Solids for Electrocatalytic Hydrogen Evolution

Van der Waals solids with tunable band gaps and interfacial properties have been regarded as a class of promising active materials for electrocatalytic hydrogen evolution reaction (HER). However, due to the anisotropic features, their basal planes are usually electrochemically inert, only a few unsaturated edge atoms could serve as active centers to actuate H₂ generation. Hence, material utilization and productivity efficiency are insufficient for practical applications. Recently, diverse defects have been confirmed to enable tailoring atomic configurations and electronic properties of van der Waals solids, thus triggering their superior catalytic activity of in-plane atoms while introducing high amount of new active sites. In this minireview, we summarize the state-of-the-art progress of defect engineering in van der Waals solids for HER, focusing in particular on their advantages in material modification and corresponding catalytic mechanisms. We also propose the challenges and perspectives of these catalytic materials in terms of both experimental synthesis and fundamental understanding of the defect structures.

[Analysis on the use of radiation protective equipment for the accompanying examinees]

Objective: To investigate the situation of wearing protective equipment in the process of X-ray radiation examination (including DR and CT) in a 3A general hospital, so as to provide technical basis and solutions for better reducing the radiation dose of accompanying patients. Methods: From November 1, 2018 to June 30, 2019, the accompanying examinee 6 who had to stay in the examination room during the radiology examination (X-ray and CT examination) of a 3A general hospital from June 1, 2018 to June 30, 2019 was selected 535 people were divided into three groups according to whether they were reminded and instructed to wear protective equipment: group A was not reminded (group A) , group B was reminded to wear protective equipment, and group C was reminded and instructed to wear protective equipment (Group C) . Results: The wearing rates of protective equipment of the three groups were 35.0% (744/2126) , 85.2% (1858/2181) and 91.0% (2028/228) , and the complete wearing rates were 15.0% (319/2126) , 54.8% (1195/2181) and 88.0% (1960/228) , respectively. 4% (1450/3060) , 28.6% (876/3060) , 24.0% (734/3060) , respectively. 523 patients refused to wear protective equipment. The main reasons were emotion (33.8%, 177/523) and time (32.5%, 170/523) . Conclusion: The intervention of radiation workers can effectively improve the correct wearing rate of protective equipment and reduce the radiation exposure of accompanying people.

Regulatory mechanism of TGF-β1/SGK1 pathway in tubulointerstitial fibrosis of diabetic nephropathy

OBJECTIVE

The aim of this study was to clarify the potential function of transforming growth factor-β1/serum/glucocorticoid-regulated kinase 1 (TGF-β1/SGK1) pathway in diabetic nephropathy-induced tubulointerstitial fibrosis.

MATERIALS AND METHODS

Type 2 diabetes mellitus (T2DM) model was successfully established in rats by high-sucrose-high-fat diet combined with streptozotocin (STZ) induction. Subsequently, blood glucose level, renal function and pathological changes in kidneys of T2DM and control rats were evaluated. Western blot and quantitative Real Time-Polymerase Chain Reaction (qRT-PCR) were conducted to determine the protein and mRNA expression levels of TGF-β1, SGK1, fibronectin (FN) and α-smooth muscle actin (α-SMA) in rat kidney tissues, respectively.

RESULTS

Blood glucose (BG), glycosylated hemoglobin (GHb), serum creatinine (Scr) and blood urea nitrogen (BUN) in T2DM rats were significantly higher than those of control rats (p<0.05). The morphology of glomeruli and renal tubules in rats of control group were normal. In contrast, T2DM rats showed significant lesions in glomeruli, renal tubules, and renal interstitium. Furthermore, the relative expression levels of TGF-β1, SGK1, FN, and α-SMA in kidney tissues of T2DM rats were remarkably higher than those of controls (p<0.05).

CONCLUSIONS

The TGF-β1/SGK1 pathway is closely related to tubulointerstitial fibrosis in T2DM rats.

Pore structure regulation of hard carbon: Towards fast and high-capacity sodium-ion storage

Hard carbon is regarded as one of the most promising anode material for sodium-ion batteries in virtue of the low cost and stable framework. However, the correlation between pore structures of hard carbon and sodium-ion storage is still ambiguous. In this work, based on precise control of pore-size distribution, the capacity, ion diffusion, and initial Coulombic efficiency were improved. Meanwhile, the relationship between pore structure and capacity was investigated. Our result indicates that the micropores hinder ion diffusion and hardly ever accommodate Na⁺ ions, while mesopores facilitate Na⁺ ion intercalation. Hard carbon with negligible micropores and abundant mesopores delivers a maximum capacity of 283.7 mAh g^-1 at 20 mA g^-1, which is 83% higher than that of micropore-rich one. Even after 320 cycles at 200 mA g^-1, the capacity still remains 189.4 mAh g^-1.

Advanced Materials for Sodium-Ion Capacitors with Superior Energy-Power Properties: Progress and Perspectives

Developing electrochemical energy storage devices with high energy-power densities, long cycling life, as well as low cost is of great significance. Sodium-ion capacitors (NICs), with Na⁺ as carriers, are composed of a high capacity battery-type electrode and a high rate capacitive electrode. However, unlike their lithium-ion analogues, the research on NICs is still in its infancy. Rational material designs still need to be developed to meet the increasing requirements for NICs with superior energy-power performance and low cost. In the past few years, various materials have been explored to develop NICs with the merits of superior electrochemical performance, low cost, good stability, and environmental friendliness. Here, the material design strategies for sodium-ion capacitors are summarized, with focus on cathode materials, anode materials, and electrolytes. The challenges and opportunities ahead for the future research on materials for NICs are also proposed.

MoS2/carbon composites prepared by ball-milling and pyrolysis for the high-rate and stable anode of lithium ion capacitors

Lithium ion capacitors (LICs), bridging the advantages of batteries and electrochemical capacitors, are regarded as one of the most promising energy storage devices. Nevertheless, it is always limited by the anodes that accompany with low capacity and poor rate performance. Here, we develop a versatile and scalable method including ball-milling and pyrolysis to synthesize exfoliated MoS₂ supported by N-doped carbon matrix derived from chitosan, which is encapsulated by pitch-derived carbon shells (MoS₂/CP). Because the carbon matrix with high nitrogen content can improve the electron conductivity, the robust carbon shells can suppress the volume expansion during cycles, and the sufficient exfoliation of lamellar MoS₂ can reduce the ions transfer paths, the MoS₂/CP electrode delivers high specific capacity (530 mA h g^-1 at 100 mA g^-1), remarkable rate capability (230 mA h g^-1 at 10 A g^-1) and superior cycle performance (73% retention after 250 cycles). Thereby, the LICs, composed of MoS₂/CP as the anode and commercial activated carbon (21 KS) as the cathode, exhibit high power density of 35.81 kW kg^-1 at 19.86 W h kg^-1 and high energy density of 87.74 W h kg^-1 at 0.253 kW kg^-1.

Electrochemically triggered degradation of silicon membranes for smart on-demand transient electronic devices

Transient electronics is an emerging technology that enables unique functional transformation or the physical disappearance of electronic devices, and is attracting increasing attention for potential applications in data secured hardware as an ultimate solution against data breaches. Developing smart triggered degradation modalities of silicon (Si) remain the key challenge to achieve advanced non-recoverable on-demand transient electronics. Here, we present a novel electrochemically triggered transience mechanism of Si by lithiation, allowing complete and controllable destruction of Si devices. The depth and microstructure of the lithiation-affected zone over time is investigated in detail and the results suggest a few hours of lithiation is sufficient to create microcracks and significantly promote lithium penetration. Finite element models are proposed to confirm the mechanism. Electrochemically triggered degradation of thin film Si ribbons and Si integrated circuit chips with metal-oxide-semiconductor field-effect transistors from a commercial 0.35 micrometer complementary metal-oxide-semiconductor technology node is performed to demonstrate the potential applications for commercial electronics. This work opens new opportunities for versatile triggered transience of Si-based devices for critical secured information systems and green consumer electronics.

Steam Selective Etching: A Strategy to Effectively Enhance the Flexibility and Suppress the Volume Change of Carbonized Paper-Supported Electrodes

Paper-supported electrodes with high flexibility have attracted much attention in flexible Li-ion batteries. However, they are restricted by the heavy inactive paper substrate and large volume change during the lithiation-delithiation process, which will lead to low capacity and poor rate capability and cyclability. Converting the paper substrate to carbon fiber by carbonization can substantially eliminate the "dead mass", but it becomes very brittle. This study reports a water-steam selective etching strategy that successfully addresses these problems. With the help of steam etching, pores are created, and transition-metal oxides are embedded into the fiber. These effectively accommodate the volume change and enhances the kinetics of ion and electron transport. The pores release the mechanical stress from bending, ensuring the sufficient bendability of carbonized paper. Benefiting from these merits, the steam-etched samples show high flexibility and possess outstanding electrochemical performance, including ultra-high capacity and superior cycling stability with capacity retention over 100% after 1500 cycles at 2 A g^-1. Furthermore, a flexible Li-ion full battery using the steam-etched Fe₂O₃@CNF anode and LiFePO₄/steam-etched CNF cathode delivers a high capacity of 623 mAh g^-1 at 100 mA g^-1 and stable electrochemical performances under the bent state, holding great promise for next-generation wearable devices.

Sulfur-Doped Reduced Graphene Oxide for Enhanced Sodium Ion Pseudocapacitance

Sodium-ion capacitors (NICs) are considered an important candidate for large-scale energy storage in virtue of their superior energy-power properties, as well as availability of rich Na+ reserves. To fabricate high-performance NIC electrode material, a hydrothermal method was proposed to synthesize sulfur-doped reduced graphene oxide (SG), which exhibited unique layered structures and showed excellent electrochemical properties with 116 F/g capacitance at 1 A/g as the cathode of NICs from 1.6 V to 4.2 V. At the power-energy density over 5000 W/kg, the SG demonstrated over 100 Wh/kg energy density after 3500 cycles, which indicated its efficient durability and superior power-energy properties. The addition of a sulfur source in the hydrothermal process led to the higher specific surface area and more abundant micropores of SG when compared with those of reduced graphene oxide (rGO), thus SG exhibited much better electrochemical properties than those shown by rGO. Partially substituting surface oxygen-containing groups of rGO with sulfur-containing groups also facilitated the enhanced sodium-ion storage ability of SG by introducing sufficient pseudocapacitance.

Coupled ultrasonication-milling synthesis of hierarchically porous carbon for high-performance supercapacitor

Activated carbon (AC) based supercapacitors exhibit intrinsic advantages in energy storage. Traditional two-step synthesis (carbonization and activation) of AC faces difficulties in precisely regulating its pore-size distribution and thoroughly removing residual impurities like silicon oxide. This paper reports a novel coupled ultrasonication-milling (CUM) process for the preparation of hierarchically porous carbon (HPC) using corn cobs as the carbon resource. The as-obtained HPC is of a large surface area (2288 m² g^-1) with a high mesopore ratio of ∼44.6%. When tested in a three-electrode system, the HPC exhibits a high specific capacitance of 465 F g^-1 at 0.5 Ag^-1, 2.7 times higher than that (170 F g^-1) of the commercial AC (YP-50F). In the two-electrode test system, the HPC device exhibits a specific capacitance of 135 F g^-1 at 1 A g^-1, twice higher than that (68 F g^-1) of YP-50F. The above excellent energy-storage properties are resulted from the CUM process which efficiently removes the impurities and modulates the mesopore/micropore structures of the AC samples derived from the agricultural resides of corn cobs. The CUM process is an efficient method to prepare high-performance biomass-derived AC materials.

Locally Induced Spin States on Graphene by Chemical Attachment of Boron Atoms

Pristine graphene is known to be nonmagnetic due to its π-conjugated electron system. However, we find that localized magnetic moments can be generated by chemically attaching boron atoms to the graphene sheets. Such spin-polarized states are evidenced by the spin-split of the density of states (DOS) peaks near the Fermi level in scanning tunneling spectroscopy (STS). In the vicinity of several coadsorbed boron atoms, the Coulomb repulsion between multiple spins leads to antiferromagnetic coupling for the induced spin states in the graphene lattice, manifesting itself as an increment of spin-down state at specific regions. Experimental observations and interpretations are rationalized by extensive density functional theory (DFT) simulations.

High Areal Capacity Li-Ion Storage of Binder-Free Metal Vanadate/Carbon Hybrid Anode by Ion-Exchange Reaction

Storing more energy in a limited device area is very challenging but crucial for the applications of flexible and wearable electronics. Metal vanadates have been regarded as a fascinating group of materials in many areas, especially in lithium-ion storage. However, there has not been a versatile strategy to synthesize flexible metal vanadate hybrid nanostructures as binder-free anodes for Li-ion batteries so far. A convenient and versatile synthesis of M_x V_y O_x+2.5y @carbon cloth (M = Mn, Co, Ni, Cu) composites is proposed here based on a two-step hydrothermal route. As-synthesized products demonstrate hierarchical proliferous structure, ranging from nanoparticles (0D), and nanobelts (1D) to a 3D interconnected network. The metal vanadate/carbon hybrid nanostructures exhibit excellent lithium storage capability, with a high areal specific capacity up to 5.9 mAh cm^-2 (which equals to 1676.8 mAh g^-1 ) at a current density of 200 mA g^-1 . Moreover, the nature of good flexibility, mixed valence states, and ultrahigh mass loading density (over 3.5 mg cm^-2 ) all guarantee their great potential in compact energy storage for future wearable devices and other related applications.

Synthesis and photocatalytic activity of mesoporous g-C3N4/MoS2 hybrid catalysts

The key to solving environmental and energy issues through photocatalytic technology requires highly efficient, stable and eco-friendly photocatalysts. Graphitic carbon nitride (g-C₃N₄) is one of the most promising candidates except for its limited photoactivity. In this work, a facile and scalable one-step method is developed to fabricate an efficient heterostructural g-C₃N₄ photocatalyst in situ coupled with MoS₂. The strong coupling effect between the MoS₂ nanosheets and g-C₃N₄ scaffold, numerous mesopores and enlarged specific surface area helped form an effective heterojunction. As such, the photocatalytic activity of the g-C₃N₄/MoS₂ is more than three times higher than that of the pure g-C₃N₄ in the degradation of RhB under visible light irradiation. Improvement of g-C₃N₄/MoS₂ photocatalytic performance is mainly ascribed to the effective suppression of the recombination of charge carriers.

Ectopic Cartilage Formation Induced by Mesenchymal Stem Cells on Porous Gelatin-Chondroitin-Hyaluronate Scaffold Containing Microspheres Loaded with TGF-β1

The study aimed to produce a novel porous gelatin-chondroitin-hyaluronate scaffold in combination with a controlled release of TGF-β1 and to evaluate its potentials in ectopic cartilage formation. The gelatin-chondroitin-hyaluronate scaffold was developed to mimic the natural extra cellular matrix of cartilage. Gelatin microspheres loaded with TGF-β1 (MS-TGFβ1) showed a fast cytokine release at initial phase (37.4%) and the ultimate accumulated release was 83.1% by day 18. Then MS-TGFβ1 were incorporated into scaffold. The MSCs seeded on scaffold with or without MS-TGFβ1 were incubated in vitro or implanted subcutaneously in nude mice. In vitro study showed that, compared to the scaffold, the scaffold/MS-TGFβ1 significantly augmented the proliferation of MSCs and GAG synthesis. Three weeks postoperatively histology observation showed that in MSCs/scaffold/MS-TGFβ1 implantation group, cells of newly formed ectopic cartilage were located within typical lacunae and demonstrated morphological characteristics of chondrocytes. Six weeks later the ectopic cartilage grew more and islands of cartilage were observed. The matrix was extensively metachromatic by safranin-O/Fast green staining. Immunohistochemical staining also indicated ectopic cartilage was intensely stained for type II collagen. Instead, in the MSCs/scaffold implantation group, no cartilage-like tissue formed and matrix showed negative or weak positive staining. The percentage of positive staining area was significantly larger in MSCs/scaffold/MS-TGFβ1 group (p<0.05) at each time point. The results indicated that the novel gelatin-chondroitin-hyaluronate scaffold with MS-TGFβ1 could induce the chondral differentiation of MSCs to form cartilage and might serve as a new way to repair cartilage defects.

Flexible C–Mo2C fiber film with self-fused junctions as a long cyclability anode material for sodium-ion battery

Fiber junctions were fused by introducing MoO₂, that eliminates the contact resistance at fiber junctions, and significantly improves the cyclability.

Efficient photocatalysis with graphene oxide/Ag/Ag2S–TiO2 nanocomposites under visible light irradiation

The photocatalytic reaction efficiency of GO/Ag/Ag₂S–TiO₂ nanorod arrays is 600% higher than that of a pure TiO₂ sample under visible light.

Low-temperature Synthesis of Heterostructures of Transition Metal Dichalcogenide Alloys (WxMo1-xS2) and Graphene with Superior Catalytic Performance for Hydrogen Evolution

Large-area (∼cm²) films of vertical heterostructures formed by alternating graphene and transition-metal dichalcogenide (TMD) alloys are obtained by wet chemical routes followed by a thermal treatment at low temperature. In particular, we synthesized stacked graphene and W_xMo_1-xS₂ alloy phases that were used as hydrogen evolution catalysts. We observed a Tafel slope of 38.7 mV dec^-1 and 96 mV onset potential (at current density of 10 mA cm^-2) when the heterostructure alloy was annealed at 300 °C. These results indicate that heterostructures formed by graphene and W_0.4Mo_0.6S₂ alloys are far more efficient than WS₂ and MoS₂ by at least a factor of 2, and they are superior compared to other reported TMD systems. This strategy offers a cheap and low temperature synthesis alternative able to replace Pt in the hydrogen evolution reaction (HER). Furthermore, the catalytic activity of the alloy is stable over time, i.e., the catalytic activity does not experience a significant change even after 1000 cycles. Using density functional theory calculations, we found that this enhanced hydrogen evolution in the W_xMo_1-xS₂ alloys is mainly due to the lower energy barrier created by a favorable overlap of the d-orbitals from the transition metals and the s-orbitals of H₂; with the lowest energy barrier occurring for the W_0.4Mo_0.6S₂ alloy. Thus, it is now possible to further improve the performance of the "inert" TMD basal plane via metal alloying, in addition to the previously reported strategies such as creation of point defects, vacancies and edges. The synthesis of graphene/W_0.4Mo_0.6S₂ produced at relatively low temperatures is scalable and could be used as an effective low cost Pt-free catalyst.

Doping two-dimensional materials: ultra-sensitive sensors, band gap tuning and ferromagnetic monolayers

The successful isolation of graphene from graphite in 2004 opened up new avenues to study two-dimensional (2D) systems from layered materials. Since then, research on 2D materials, including graphene, hexagonal-BN (h-BN), transition metal dichalcogenides (TMDs) and black phosphorous, has been extensive, thus leading to various possible applications in the fields of optoelectronics, biomedicine, spintronics, electrochemistry, energy storage and catalysis. However, certain barriers still need to be overcome when dealing with real applications, such as graphene's lack of a bandgap, restricting its use in semiconductor electronics. In this context, a possible solution is to tailor the electronic and optical properties of 2D materials by introducing defects or elemental doping. Although defects play a major role in modifying materials properties, the fact that we call them "defects" might have a negative impact. There has been a long debate on whether structurally perfect materials are equally relevant for modifying the properties and for applications. In this focus article, we clarify that although extra large amounts of defects could be detrimental to the materials properties, well-designed defects might lead to unprecedented properties and interesting applications that pristine materials do not have. Given the relatively short history of research on doped 2D layered materials, our objective is to answer and clarify the following fundamental questions: why does nanomaterial doping offer improved physico-chemical properties? What new applications arise from doping? And what are the current challenges along this line?

Ultrasensitive Pressure Detection of Few-Layer MoS2

Ultrasensitive pressure sensors are constructed with few-layer MoS₂ films. As-designed Fabry-Perot (F-P) sensors exhibit nearly synchronous pressure-deflection responses with a very high sensitivity (89.3 nm Pa^-1 ), which is three orders of magnitude higher than those of conventional diaphragm materials (e.g., silica, silver films). This kind of F-P sensor may open up new avenues for 2D materials in biomedical and environmental applications.

Noble-Metal-Free Hybrid Membranes for Highly Efficient Hydrogen Evolution

Free-standing and flexible WS₂ /WO_2.9 /C hybrid membranes are synthesized and used as catalytic electrodes for electrochemical hydrogen evolution, exhibiting a high and stable catalytic activity. By virtue of the synergetic effect, a low onset overpotential of 20 mV and a Tafel slope of 36 mV dec^-1 are achieved.

Three-dimensional reduced graphene oxide powder for efficient microwave absorption in the S-band (2–4 GHz)

Three-dimensional reduced graphene oxide (3D-rGO) powders are synthesized and demonstrate remarkably enhanced microwave absorption in the S-band (2–4 GHz).

Carbon Nanotube-Silicon Nanowire Heterojunction Solar Cells with Gas-Dependent Photovoltaic Performances and Their Application in Self-Powered NO2 Detecting

A multifunctional device combining photovoltaic conversion and toxic gas sensitivity is reported. In this device, carbon nanotube (CNT) membranes are used to cover onto silicon nanowire (SiNW) arrays to form heterojunction. The porous structure and large specific surface area in the heterojunction structure are both benefits for gas adsorption. In virtue of these merits, gas doping is a feasible method to improve cell's performance and the device can also work as a self-powered gas sensor beyond a solar cell. It shows a significant improvement in cell efficiency (more than 200 times) after NO2 molecules doping (device working as a solar cell) and a fast, reversible response property for NO2 detection (device working as a gas sensor). Such multifunctional CNT-SiNW structure can be expected to open a new avenue for developing self-powered, efficient toxic gas-sensing devices in the future.

Ultrasensitive molecular sensor using N-doped graphene through enhanced Raman scattering

As a novel and efficient surface analysis technique, graphene-enhanced Raman scattering (GERS) has attracted increasing research attention in recent years. In particular, chemically doped graphene exhibits improved GERS effects when compared with pristine graphene for certain dyes, and it can be used to efficiently detect trace amounts of molecules. However, the GERS mechanism remains an open question. We present a comprehensive study on the GERS effect of pristine graphene and nitrogen-doped graphene. By controlling nitrogen doping, the Fermi level (E F) of graphene shifts, and if this shift aligns with the lowest unoccupied molecular orbital (LUMO) of a molecule, charge transfer is enhanced, thus significantly amplifying the molecule's vibrational Raman modes. We confirmed these findings using different organic fluorescent molecules: rhodamine B, crystal violet, and methylene blue. The Raman signals from these dye molecules can be detected even for concentrations as low as 10(-11) M, thus providing outstanding molecular sensing capabilities. To explain our results, these nitrogen-doped graphene-molecule systems were modeled using dispersion-corrected density functional theory. Furthermore, we demonstrated that it is possible to determine the gaps between the highest occupied and the lowest unoccupied molecular orbitals (HOMO-LUMO) of different molecules when different laser excitations are used. Our simulated Raman spectra of the molecules also suggest that the measured Raman shifts come from the dyes that have an extra electron. This work demonstrates that nitrogen-doped graphene has enormous potential as a substrate when detecting low concentrations of molecules and could also allow for an effective identification of their HOMO-LUMO gaps.