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This paper points out a critical issue in the study of estimating the azimuth of ground sources by using the polarization characteristics of Rayleigh waves: even if the signal quality is good, the degree of polarization of Rayleigh waves varies across different frequency bands, and the band with the strongest energy is not the one with the lowest azimuth error. A direction of arrival estimation method for ground sources based on optimally polarized Rayleigh waves using a single three-component geophone is presented in this paper. First, the reciprocal ellipse rate, flatness coefficient, and the angle between the semi-minor axes and the horizontal plane are selected as the polarization parameters of this method according to two quantitative principles. Then the frequency band range of the optimal polarization Rayleigh wave is determined by analyzing the sum of the weights of the three polarization parameters in different frequency bands. After filtering and combining with the existing surface wave analysis method, the actual data bearing estimation result with an average error of only 4.95 degrees and a standard deviation of only 1.82 degrees is obtained. It is also found that the signal-to-noise ratio approximates the exponential decay of the direction of arrival error obtained by this method.

It is challenging to hydrothermally synthesize solution-processable MoS2, as the strong van der Waals force between MoS2 nanosheets induces self-assembly of agglomerates. Here, we introduce poly(3,...

An efficient cathodic electrodeposition method is developed for coating Co-based metal-organic frameworks (Co-MOF) on carbon fiber cloth (CFC), a widely used substrate in energy fields. The use of a highly active Co metal surface enables nucleation and growth of Co-MOF in 3D rodlike crystal bundles. When used as a binder-free electrode (Co-MOF/CFC) for supercapacitors, it shows a high areal capacitance of 1784 mF cm

Iron is a promising material for cardiovascular stent applications, however, the low biodegradation rate presents a challenge. Here, a dynamic method to improve the degradation rate of iron and simultaneously deliver electrical energy that could potentially inhibit cell proliferation on the device is reported. It is realized by pairing iron with a biocompatible hydrogel cathode in a cell culture media-based electrolyte forming an iron-air battery. This system does not show cytotoxicity to human adipose-stem cells over a period of 21 days but inhibits cell proliferation. The combination of enhanced iron degradation and inhibited cell proliferation by this dynamic method suggests it might be an approach for restenosis inhibition of biodegradable stents.

Two-dimensional (2D) layered vanadium disulfide (VS2) is a promising anode material for lithium ion batteries (LIBs) due to the high theoretical capacity. However, it remains a challenge to synthesize monodispersed ultrathin VS2 nanosheets to realize the full potential. Herein, a novel solvothermal method has been developed to prepare the monodispersed bowl-shaped NH3-inserted VS2 nanosheets (VS2). The formation of such a unique structure is caused by the blocked growth of (001) or (002) crystal planes in combination with a ripening process driven by the thermodynamics. The annealing treatment in Ar/H2 creates porous monodispersed VS2 (H-VS2), which is subsequently integrated with graphene oxide to form porous monodispersed H-VS2/rGO composite coupled with a reduction process. As an anode material for LIBs, H-VS2/rGO delivers superior rate performance and longer cycle stability: a high average capacity of 868/525 mAh g−1 at a current density of 1/10 A g−1; a reversible capacity of 1177/889 mAh g−1 after 150/500 cycles at 0.2/1 A g−1. Such excellent electrochemical performance may be attributed to the increased active sites available for lithium storage, the alleviated volume variations and the shortened Li-ion diffusion induced from the porous structure with large specific surface area, as well as the protective effect from graphene nanosheets.

Freestanding flexible electrodes with high areal mass loading are required for the development of flexible high-performance lithium-ion batteries (LIBs). Currently they face the challenge of low ma...

Safety issues currently limit the development of advanced lithium‐ion batteries (LIBs) and this is exacerbated when they are misused or abused. The addition of small amounts of fillers or additives into common liquid electrolytes can greatly improve resistance to abuse without impairing electrochemical performance. This review discusses the recent progress in such abuse‐tolerant electrolytes. It covers electrolytes with shear thickening properties for tolerating mechanical abuse, electrolytes with redox shuttle additives for suppressing electrochemical abuse, and electrolytes with flame‐retardant additives for resisting thermal abuse. It aims to provide insights into the functioning of such electrolytes and the understanding of electrolyte composition‐property relationship. Future perspectives, challenges, and opportunities towards practical applications are also presented., The addition of fillers/additives into liquid electrolytes has enabled the abuse‐resistant properties towards safe lithium‐ion batteries. This review presents three types of electrolytes that can provide the protection against the commonly encountered abuses, including shear thickening electrolytes to tolerate mechanical abuse, redox shuttle additive‐based electrolytes to suppress electrochemical abuse, and flame‐retardant additive based electrolytes to resist thermal abuse.

Data in this article is associated with our research article “Bipolar Electroactive Conducting Polymers for Wireless Cell Stimulation” [1] . Primarily, the present article shows the data of PPy-pTS, PPy-DS and PPy-DS/collagen in conventional electrochemical process and bipolar electrochemical process for comprehensive supplement and comparison to help with better understanding and developing conducting polymers based bipolar electrochemistry. Secondly, the presented data of bipolar electrostimulation (BPES) protocol development constitute the complete dataset useful for modeling the bipolar electroactive conducting polymers focusing on wireless cell stimulation, which are reported in the main article. All data reported were analysed using Origin 2018b 64Bit.

Silicon-based impurities are ubiquitous in natural graphite. However, their role as a contaminant in exfoliated graphene and their influence on devices have been overlooked. Herein atomic resolution microscopy is used to highlight the existence of silicon-based contamination on various solution-processed graphene. We found these impurities are extremely persistent and thus utilising high purity graphite as a precursor is the only route to produce silicon-free graphene. These impurities are found to hamper the effective utilisation of graphene in whereby surface area is of paramount importance. When non-contaminated graphene is used to fabricate supercapacitor microelectrodes, a capacitance value closest to the predicted theoretical capacitance for graphene is obtained. We also demonstrate a versatile humidity sensor made from pure graphene oxide which achieves the highest sensitivity and the lowest limit of detection ever reported. Our findings constitute a vital milestone to achieve commercially viable and high performance graphene-based devices., Silicon-based contaminants are ubiquitous in natural graphite, and they are thus expected to be present in exfoliated graphene. Here, the authors show that such impurities play a non-negligible role in graphene-based devices, and use high-purity parent graphite to boost the performance of graphene sensors and supercapacitor microelectrodes.

Molybdenum disulfide/nitrogen-doped carbon nanocomposite can afford high capacity, good rate capability and cycling stability in lithium ion batteries owing to the synergistic effect from these two components. Structure of the material has a great impact on the performance as well. In this work, MoS2/nitrogen-doped carbon (MoS2/C) composites have been developed by manipulating the nano-featured polypyrrole templates to guide and confine their growth. They are formed via a simple hydrothermal process combined with a subsequent annealing process. The MoS2/nitrogen-doped carbon nanotubes (MoS2/CNT) composite with 76% of MoS2 exhibits an excellent performance including a high capacity of 1232 mAh g−1 at a current density of 0.1 A g−1, outstanding rate capability (947 mAh g−1 at 2 A g−1), and good cycling stability with 754 mAh g−1 retained over 1000 charge/discharge cycles at a high current density of 1 A g−1. This performance is much better than that MoS2/nitrogen-doped carbon nanoparticles (MoS2/CNP) composite. This work demonstrates the importance of introducing three-dimensional nanostructures in electrode materials to improve their electrochemical performance.

High performance supercapacitors coupled with mechanical flexibility are needed to drive flexible and wearable electronics that have anesthetic appeal and multi-functionality. Two dimensional (2D) materials have attracted attention owing to their unique physicochemical and electrochemical properties, in addition to their ability to form hetero-structures with other nanomaterials further improving mechanical and electrochemical properties. After a brief introduction of supercapacitors and 2D materials, recent progress on flexible supercapacitors using 2D materials is reviewed. Here we provide insights into the structure-property relationships of flexible electrodes, in particular free-standing films. We also present our perspectives on the development of flexible supercapacitors.

Transient implantable medical bionics offer great promise in the field of smart controlled release and tissue regeneration. On-board energy storage is the ideal power system to drive them. In this work, a critical component of such a device, a biodegradable polymer electrolyte (silk fibroin–choline nitrate) has been developed. The efficiency of this electrolyte is demonstrated when deployed in a biodegradable thin-film magnesium battery. The battery, encapsulated in silk, offers a specific capacity of 0.06 mAh cm–2. The enzymatic degradation of the whole device occurs over 45 days in the buffered protease XIV solution. A programmed battery lifetime can be achieved using silk protection layers. This battery system provides a new avenue for an on-board biodegradable power source for next-generation transient medical bionics.

Wearable energy storage devices are of practical interest, but few have been commercially exploited. Production of electrodes with extended cycle life, as well as high energy and power densities, coupled with flexibility, remains a challenge. Herein, we have demonstrated the development of a high-performance hybrid carbon nanotube (CNT) fiber-based supercapacitor for the first time using conventional wet-spinning processes. Manganese dioxide (MnO2) nanoflakes were deposited onto the as-prepared CNT fibers by electrodeposition to form highly flexible nanocomposites fibers. As-prepared fibers were characterized by electron microscopy, electrical, mechanical, and electrochemical measurements. It was found that the specific capacitance was over 152 F g−1 (156 F cm−3), which is about 500% higher than the multi-walled carbon nanotube/MnO2 yarn-based supercapacitors. The measured energy density was 14.1 Wh kg−1 at a power density of 202 W kg−1. These values are 232% and 32% higher than the energy density and power density of MWNT/MnO2 yarn-based supercapacitor, respectively. It was found that the cyclic retention ability was more stable, revealing a 16% increase after 10 000 cycles. Such substantial enhancements of key properties of the hybrid material can be associated with the synergy of CNT and MnO2 nanoparticles in the fiber structure. The use of wet-spun hybrid CNT for fiber-based supercapacitors has been demonstrated.

Freestanding flexible electrodes with high areal mass loading are required for the development of flexible high-performance lithium-ion batteries (LIBs). Currently they face the challenge of low mass loading due to the limited concentrations attainable in processable dispersions. Here, we report a simple low-temperature hydrothermal route to fabricate flexible layered molybdenum disulfide (MoS

Conventional organic conducting polymers (CPs)-based electrical stimulation (ES) systems have been extensively explored in modulation of cell and tissue functions for biomedical applications. Bipolar electrochemistry could offer an effective pathway to modify these ES systems into a more desirable contactless mode. In this study, we present for the first time the development of a CP-based bipolar electrostimulation (BPES) system for living cells. Polypyrrole (PPy) films with different dopants have been utilised to demonstrate reversible and recoverable bipolar electrochemical activity under a low driving DC voltage (

Herein, we show properly engineered MoS2 crystals can readily form liquid crystalline dispersions in water making them ideal candidates for large-scale manufacturing processes. The guideline provided here can serve as the basis to develop practical protocols to address the long-standing goal of large-scale manufacturing of 2D materials.

The surfactant-assisted liquid-phase exfoliation of expanded graphite can produce graphene sheets in large quantities with minimal defects. However, it is difficult to completely remove the surfactant from the final product, thus affecting the electrochemical properties of the produced graphene. In this article, a novel approach to fabricate flexible graphene/polypyrrole film was developed: using surfactant cetyltrimethylammonium bromide as a template for growth of polypyrrole nanofibers (PPyNFs) instead of removal after the exfoliation process; followed by a simple filtration method. The introduction of PPyNF not only increases the electrochemical performance, but also ensures flexibility. This composite film electrode offers a capacitance up to 161 F g-1 along with a capacitance retention rate of over 80% after 5000 cycles.

Free-standing and flexible battery electrodes are highly pursued due to its good electrochemical performance and transformation ability. Two-dimensional materials such as transition metal dichalcogenides (TMDs) and graphene with large surface area and good mechanical properties provide a good solution for this problem. The high lithium storage of MoS2 is attractive for achieving high capacity while the high conductivity of graphene is of favorable for good rate capability. The excellent mechanical properties of graphene are able to form a stable structure contributing to long cycle life, flexibility and get rid of substrates [1, 2]. A self-assembly process was developed to produce MoS2/ reduced graphene oxide (MG) hydrogel films in this work. Making use of the ordered structure existed in liquid crystalline graphene oxide (LCGO) dispersion [3], a layer structure with small MoS2 nanosheets sandwiched between large LCGO nanosheets could be easily obtained by simply mixing their dispersion together. A heating process at 70 ℃ was used to accelerate the self-assembly process. The unique layer structure turned into a three-dimensional porous structure during the self-assembly process and preserved after freeze-drying, which could effectively increase the surface area of active materials for high performance. This work develops a simple, straightforward and cost-effective method to fabricate self-assembled, layer-by-layer, free-standing porous MG hydrogel films. The structure displayed excellent electrochemical properties as a lithium-ion battery electrode [4]: a high discharge capacity of 800 mAh g-1 at a current density of 100 mA g-1; and an excellent cycling stability with slightly increased capacity (112.5%) after 500 cycles at a current density of 400 mA g-1. Such enhancement can be ascribed to the synergistic effect between these two components and gradual perfection of the ordered structure. This approach enables the exploitation of the LC order of GO sheets to organize and align 2D MoS2 in-between GO sheets, which may provide a new avenue for the development of 3D porous flexible composite electrode materials with high performance using the unique LCGO. References: [1]. N. A. Kumar, M. A. Dar, R. Gul and J. B. Baek, Materials Today, 2015, 18, 286-298. [2]. M. Yang, S. Ko, J. S. Im and B. G. Choi, Journal of Power Sources, 2015, 288, 76-81. [3]. R. Jalili, S. H. Aboutalebi, D. Esrafilzadeh, K. Konstantinov, J. M. Razal, S. E. Moulton and G. G. Wallace, Materials Horizons, 2014, 1, 87-91. [4]. Y. Chao, R. Jalili, Y. Ge, C. Wang, T. Zheng, K. Shu and G. G. Wallace, Advanced Functional Materials, 2017, 27, 1700234.

Molybdenum sulfide/graphene composites are promising anode materials for lithium-ion batteries (LIBs). In this work, MoSx /graphene composite film with an ideal 3D porous structure is developed via a facile and straightforward electrochemical route. The MoSx nanoparticles are uniformly anchored on the graphene nanosheets that are randomly arranged, resulting in MoSx /graphene composites with well-developed porous structure. Benefiting from such structure and the synergistic effect from two components, this material shows a high specific capacity over 1200 mA h g-1 , an excellent rate performance, and superior cycling stability. The dominating pseudocapacitive behavior in Li storage contributes to the outstanding rate capacity. Importantly, this kind of novel material can be easily produced as 3D microelectrodes for microscaled LIBs that are highly demanded for autonomous microelectronic systems.

Flexible freestanding electrodes are highly desired to realize wearable/flexible batteries as required for the design and production of flexible electronic devices. Here, the excellent electrochemical performance and inherent flexibility of atomically thin 2D MoS2 along with the self-assembly properties of liquid crystalline graphene oxide (LCGO) dispersion are exploited to fabricate a porous anode for high-performance lithium ion batteries. Flexible, free-standing MoS2-reduced graphene oxide (MG) film with a 3D porous structure is fabricated via a facile spontaneous self-assembly process and subsequent freeze-drying. This is the first report of a one-pot self-assembly, gelation, and subsequent reduction of MoS2/LCGO composite to form a flexible, high performance electrode for charge storage. The gelation process occurs directly in the mixed dispersion of MoS2 and LCGO nanosheets at a low temperature (70 °C) and normal atmosphere (1 atm). The MG film with 75 wt% of MoS2 exhibits a high reversible capacity of 800 mAh g-1 at a current density of 100 mA g-1. It also demonstrates excellent rate capability, and excellent cycling stability with no capacity drop over 500 charge/discharge cycles at a current density of 400 mA g-1.