A cost-efficient and stable oxygen evolution electrocatalyst is essential for improving energy storage and conversion efficiencies. Herein, 2D nanosheets with randomly cross-linked CoNi layered ...double hydroxide （LDH） and small CoO nanocrystals were designed and synthesized via in situ reduction and interface- directed assembly in air. The formation of CoNi LDH/CoO nanosheets was attributed to the strong extrusion of hydrated metal-oxide clusters driven by the interfacial tension. The obtained loose and porous nanosheets exhibited low crystallinity due to the presence of numerous defects. Owing to the orbital hybridization between metal 3d and O 2p orbitals, and electron transfer between metal atoms through Ni-O-Co, a number of Co and Ni atoms in the CoNi LDH present a high ＋3 valency. These unique characteristics result in a high density of oxygen evolution reaction （OER） active sites, improving the affinity between OH- and catalyst, and resulting in a large accessible surface area and permeable channels for ion adsorption and transport. Therefore, the resulting nanosheets exhibited high catalytic activity towards the OER. The CoNi LDH/CoO featured a low onset potential of 1.48 V in alkaline medium, and required an overpotential of only 300 mV at a current density of 10 mA.cm-2, while displaying good stability in accelerated durability tests.
High-performance elastic supercapacitors represent a promising kind of energy storage devices that can be employed in soft robotics and wearable electronics. The development of novel functional ...materials as supercapacitor electrode is still tremendously challenging. In the present work, the conductive polyvinyl alcohol–graphene oxide–polypyrrole (PVA–GO–PPy) composite hydrogels are fabricated through in situ polymerization of pyrrole in the presence of PVA and GO and subsequent freeze-thawing. Owing to the unique porous layered-wrinkle network and functional component of PVA–GO–PPy composite hydrogels, the as-prepared hydrogels exhibit lightweight, elasticity, compressibility, formability and softness. Furthermore, the mechanically robust and microstructured PVA–GO–PPy composite hydrogels are used to construct an elastic symmetric solid-state supercapacitor with good electrochemical performance. The device exhibits long-term compression/recovery elasticity under 50% strain, and even the volumetric capacitance retention is still about 81% when the strain is up to 80%. The excellent compression/recovery elasticity and good mechanical integrity of the high-performance supercapacitor based on PVA–GO–PPy composite hydrogel open up new opportunities for next-generation electronic devices in the practical application.
SUMMARY
At the beginning of 2018, President Trump started taking protective tariff measures against products from China in a sequence of events which started a ‘trade war’ between the United States ...and China. As the value of trade flows affected on both sides rose to a significant amount, this episode will become an interesting research object in the future. A thorough analysis of many outcomes of interest is at this point in time – and even will be in the next few years – impossible due to a lack of data which will only become available at a later point. However, as is customary with historical preferential liberalizations in trade agreements and potentially the opposite of it through Brexit, it is possible to gauge consequences of this ‘trade war’ or ‘trade dispute’ when focusing on the stocks of listed companies around related tariff-change announcements or implementations by the United States and China in the relevant time span. This paper proposes such an analysis and finds, very much consistent with the rumours from business, that the associated protectionist tariffs appear to have done to a large extent the opposite of what was intended: they hurt domestic firms in targeted and also other, untargeted sectors of an acting country, and they affect third countries and territories which are not even party to the ‘trade war’ or ‘dispute’.
Developing cost-efficient electrocatalysts for oxygen evolution is vital for the viability of H2 energy generated via electrolytic water. Engineering favorable defects on the electrocatalysts to ...provide accessible active sites can boost the sluggish reaction thermodynamics or kinetics. Herein, Col_xS nanosheets were designed and grown on reduced graphene oxide （rGO） by controlling the successive two-step hydrothermal reaction. A belt-like cobalt-based precursor was first formed with the assistance of ammonia and rGO, which were then sulfurized into Col_xS by L-cysteine at a higher hydrothermal temperature. Because of the non-stoichiometric defects and ultrathin sheet-like structure, additional cobalt vacancies （V~o） were formed/exposed on the catalyst surface, which expedited the charge diffusion and increased the electroactive surface in contact with the electrolyte. The resulting Col_xS/rGO hybrids exhibited an overpotential as low as 310 mV at 10 mA.cm-2 in an alkaline electrolyte for the oxygen evolution reaction （OER）. Density functional theory calculations indicated that the Vco on the Col_xS/rGO hybrid functioned as catalytic sites for enhanced OER. They also reduced the energy barrier for the transformation of intermediate oxygenated species, promoting the OER thermodynamics.
Along with the unceasing growth of worldwide economic and the associated issues on resources, energy and environment, clean energy generating technologies that are based on recyclable materials, if ...possible, may become the future trend of development. Here, we report the design of a cheap, lightweight, and recyclable single-electrode triboelectric nanogenerator (TENG) that utilizes waste paper as the triboelectric material. Under the current strategy, we successfully developed green energy machines without vastly increasing the mining of various critical minerals around the world. The as-designed TENG could not only collect and convert mechanical energy into electricity with sound efficiency, but also has the merit for continuous reuse and quick construction. The maximum output power density is as high as 171 mW·m
−2
at a resistance of 130 MΩ and could be integrated into a book for monitoring reading actions, thus providing a new approach to the low-cost, green and sustainable self-powered electronic systems.
Energy harvesting and power transmission is a significant challenge for the self-powered technologies towards mobile electronic devices. Here, we propose a hybridized energy harvester to complement ...each other’s strengths for simultaneously scavenging multiple types of energy and then wirelessly transmit the power. The harvester consists of electromagnetic-triboelectric nanogenerator units for collecting rotational energy and a commercial water-proof flexible solar cell. At a rotation rate of 500 rpm, the output current of electromagnetic-triboelectric nanogenerator units can reach about 630 mA through energy management. Moreover, the power harvested by hybridized energy harvester can be wirelessly transmitted up to a distance of about 100 cm in real time to charge mobile phone, anemometer, and hygrometer based on self-resonant coils. The hybridized energy harvester with wireless power transmission has potential applications in large-scale energy collection, long-distance wireless power transmission and sustainably driving mobile electronic devices.
This paper addresses the question of how to model the process of abnormal returns on individual stocks. It postulates a framework, where abnormal returns are generated by a process which features two ...autoregressive components, one stock-specific and one related to network effects. This process deviates from customary ones in that the parameters are specific to each stock/firm, that the autoregressive process is explicitly modelled instead of using cumulative abnormal returns over a pre-specified window, and that network effects are present. Abandoning either one of those deviations is rejected by data on Chinese stocks in 2018 and 2019, an episode which is significant for an abnormal stock-market returns analysis, as it was characterized by numerous tariff-setting events related to the “trade war” between the USA and China.
Surface electromyography (sEMG) signals can reflect the body motion information and are widely used in military, medical rehabilitation, industrial production. The lower limb motion classification ...mainly includes feature extraction and classification model establishment. Firstly, we proposed a feature extraction method based on the wavelet packet transform (WPT) and principal component analysis (PCA). We used the wavelet packet method to decompose the sEMG signals of three muscles in the lower limb and got the 24-dimensional eigenvector. To reduce the calculation and improve the speed of the classification model, we used the PCA method to reduce the dimension of the feature vector and got the 3-dimensional eigenvector. Then, we proposed a method based on the scale unscented Kalman filter (SUKF) and neural network (NN) for lower limb motion classification. Through the scale correction unscented transform (SCUT) could optimize the neural network weight and improve lower limb motion classification accuracy. Finally, the experimental results showed that the average accuracy was 93.7%. Compared with the backpropagation neural network (BPNN) and wavelet neural network (WNN), this method could improve the accuracy and reliability of the lower limb motion classification.
A magnetically functionalized Fe
O
@ZIF-67 metal-organic framework (MOF) was prepared by electrostatic self-assembly using magnetic Fe
O
nanoparticles as the core and ZIF-67 as the shell. The ...composite was characterized by electron microscopy, X-ray diffraction, Fourier- transform infrared spectroscopy, and Brunauer-Emmett-Teller measurements. Magnetic solid-phase extraction (MSPE) was performed on five flavonoids from
using Fe
O
@ZIF-67 as an adsorbent. The developed MSPE method was combined with high-performance liquid chromatography-ultraviolet detection to preconcentrate and separate five flavonoids (rutin, quercitrin, kaempferol-3-O-α-L-rhamnoside, quercetin, and kaempferol) from
. The factors affecting the extraction, such as the amount of Fe
O
@ZIF-67 adsorbent, salt ion concentration in the sample solution, vortex time, type and amount of desorbing solvent, concentration of formic acid to acidify the desorbing solvent, and acetonitrile ratio, were optimized. The developed method showed good linearity over the concentration range of 1.09-70.0 μg∙mL
for the five flavonoids, with R
values between 0.9901 and 0.9945. The limits of detection and average recoveries for the five flavonoids were in the ranges of 39.5-56.2 ng∙mL
and 92.2-100.7%, respectively. The method presented herein is simple, efficient, and sensitive; it can be used for enrichment analysis of the five flavonoids in
.
We focused on the quasi-projective synchronization (QPS) and finite-time synchronization (FNTS) for a class of fractional-order memristive complex-valued delay neural networks (FOMCVDNNs). Rather ...than decomposing the complex-valued system into its real and imaginary components, we adopted a more streamlined approach by introducing a lemma associated with the complex-valued sign function. This innovative technique enabled us to design a simpler discontinuous controller. Then, based on the finite-time Lemma, measurable selection theorem, Lyapunov function theory, properties of the Mittag-Leffler function, and the fractional-order Razumikhin theorem, various substantial results were derived using a novel hybrid control scheme. In conclusion, we presented numerical simulations to illustrate the practical effectiveness of our theoretical findings.
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