Multifunctional thermal management materials with highly efficient electromagnetic wave (EMW) absorption performance are urgently required to tackle the heat dissipation and electromagnetic ...interference issues of high integrated electronics. However, the high thermal conductivity (λ) and outstanding EMW absorption performance are often incompatible with each other in a single material. Herein, a through‐thickness arrayed NiCo2O4/graphene oxide/carbon fibers (NiCO@CFs) elastomer with integrated functionalities of high thermal conductivity, highly efficient EMW absorption, and excellent compressibility is reported. The NiCO@CFs elastomer realizes a high out‐of‐plane thermal conductivity of 15.55 W m−1 K−1, due to the through‐thickness vertically aligned CFs framework. Moreover, the unique horizontal segregated magnetic network effectively reduces the electrical contact between the CFs, which significantly enhances impedance matching of NiCO@CFs elastomer. As a result, the vertically arrayed NiCO@CFs elastomer synchronously exhibits ultrabroad effective absorption bandwidth of 8.25 GHz (9.75–18 GHz) at a thickness of 2.4 mm, good impedance matching, and a minimum reflection loss (RLmin) of −55.15 dB. Given these outstanding findings, the multifunctional arrayed NiCO@CFs elastomer opens an avenue for applications in EMW absorption and thermal management. This strategy of constructing thermal/electrical/mechanical pathways provides a promising way for the high‐performance multifunctional materials in electronic devices.
A novel strategy of constructing a through‐thickness array pathway segregated by horizontal magnetic network is proposed to reconcile the conflict between high thermal conductivity and high electromagnetic wave absorption performance within one material. Such an original strategy avoids trade‐off between the functional components and maximizing the performance of multifunctions.
Metal‐based materials with exceptional intrinsic conductivity own excellent electromagnetic interference (EMI) shielding performance. However, high density, corrosion susceptibility, and poor ...flexibility of the metal severely restrict their further applications in the areas of aircraft/aerospace, portable and wearable smart electronics. Herein, a lightweight, flexible, and anticorrosive silver nanowire wrapped carbon hybrid sponge (Ag@C) is fabricated and employed as ultrahigh efficiency EMI shielding material. The interconnected Ag@C hybrid sponges provide an effective way for electron transport, leading to a remarkable conductivity of 363.1 S m−1 and superb EMI shielding effectiveness of around 70.1 dB in the frequency range of 8.2–18 GHz, while the density is as low as 0.00382 g cm−3, which are among the best performances for electrically conductive sponges/aerogels/foams by far. More importantly, the Ag@C sponge surprisingly exhibits super‐hydrophobicity and strong corrosion resistance. In addition, the hybrid sponges possess excellent mechanical resilience even with a large strain (90% reversible compressibility) and an outstanding cycling stability, which is far better than the bare metallic aerogels, such as silver nanowire aerogels and copper nanowire foams. This strategy provides a facile methodology to fabricate lightweight, flexible, and anticorrosive metal‐based sponge for highly efficient EMI shielding applications.
Anticorrosive, ultralightweight, and flexible silver nanowire wrapped with carbon hybrid sponge is designed and employed as electromagnetic interference (EMI) shielding material with ultrahigh efficiency. The interconnected hybrid sponge shows superb EMI shielding effectiveness of 70.1 dB, while the density is as low as 0.00382 g cm−3, which are among the best performances for electrically conductive sponges/aerogels/foams by far.
Porous materials that can undergo pore‐structure adjustment to better accommodate specific molecules are ideal for separation and purification. Here, we report a stable microporous metal‐organic ...framework, JNU‐1, featuring one‐dimensional diamond‐shaped channels with a high density of open metal sites arranged on the surface for the cooperative binding of acetylene. Together with its framework flexibility and appropriate pore geometry, JNU‐1 exhibits an induced‐fit behavior for acetylene. The specific binding sites and continuous framework adaptation upon increased acetylene pressure are validated by molecular modeling and in situ X‐ray diffraction study. This unique induced‐fit behavior endows JNU‐1 with an unprecedented increase in the acetylene binding affinity (adsorption enthalpy: up to 47.6 kJ mol−1 at ca. 2.0 mmol g−1 loading).
Tailored pores: A flexible microporous metal‐organic framework (MOF) physisorbent, JNU‐1, exhibits an induced‐fit behavior for acetylene. This unique behavior endows JNU‐1 with an unprecedented increase in the acetylene binding affinity (adsorption enthalpy: up to 47.6 kJ mol−1 at ca. 2.0 mmol g−1 loading), which enables a remarkable selectivity towards acetylene over other gas molecules including carbon dioxide.
Dicarboxylic acids (DCAs) are highly value-added chemicals and intermediates extensively applied in various fields of the chemical industry. Transformation of the renewable and abundant biomass and ...its derivatives is viewed as a promising and sustainable process for DCA production, thus being paid considerable attention. The present Review provides a summary of recent achievements in the development of catalytic systems for synthesis of DCAs, including oxalic acid, malonic acid, tartronic acid, maleic acid, fumaric acid, succinic acid, adipic acid, glucaric acid, 2,5-furandicarboxylic acid, and terephthalic acid from biomass derivatives in thermocatalytic routes. The performances of catalytic systems are assessed in aspects of reactivity, selectivity toward each DCA, reusability, and operating conditions. The involved reaction pathways and mechanisms are discussed to offer deep insights into DCA formations from biomass derivatives.
The Shockley-Queisser limit for solar cell efficiency can be overcome if hot carriers can be harvested before they thermalize. Recently, carrier cooling time up to 100 picoseconds was observed in ...hybrid perovskites, but it is unclear whether these long-lived hot carriers can migrate long distance for efficient collection. We report direct visualization of hot-carrier migration in methylammonium lead iodide (CH₃NH₃PbI₃) thin films by ultrafast transient absorption microscopy, demonstrating three distinct transport regimes. Quasiballistic transport was observed to correlate with excess kinetic energy, resulting in up to 230 nanometers transport distance that could overcome grain boundaries. The nonequilibrium transport persisted over tens of picoseconds and ~600 nanometers before reaching the diffusive transport limit. These results suggest potential applications of hot-carrier devices based on hybrid perovskites.
•Multiple technical indicators were generated as input variables.•Long short-term memory (LSTM) performance was improved by AdaBoost based feature selection.•Predicting out-of-sample stock index ...futures price in Chinese market.
Stock index futures allows stock investors to manage different kinds of risk. This paper combines the AdaBoost feature selection and deep learning model for predicting stock index futures prices. In particular, a hybrid model is proposed in which the sklearn wrapped AdaBoost regressor is used for feature selection and the two-layer long short-term memory-based predictor is constructed. Performance metrics consistently show that the proposed model outperforms other popular prediction models such as random forest, multi-layer perception, gated recurrent unit, deep belief network and stacked denoising autoencoder.
The effect of dispersion state of graphene on mechanical properties of graphene/epoxy composites was investigated. The graphene sheets were exfoliated from graphite oxide (GO) via thermal reduction ...(thermally reduced GO, RGO). Different dispersions of RGO sheets were prepared with and without ball mill mixing. It was found that the composites with highly dispersed RGO showed higher glass transition temperature (Tg) and strength than those with poorly dispersed RGO, although no significant differences in both the tensile and flexural moduli are caused by the different dispersion levels. In particular, the Tg was increased by nearly 11°C with the addition of 0.2wt.% well dispersed RGO to epoxy. As expected, the highly dispersed RGO also produced one or two orders of magnitude higher electrical conductivity than the corresponding poorly dispersed RGO. Furthermore, an improved quasi-static fracture toughness (KIC) was measured in the case of good dispersion. The poorly and highly dispersed RGO at 0.2wt.% loading resulted in about 24% and 52% improvement in KIC of cured epoxy thermosets, respectively. RGO sheets were observed to bridge the micro-crack and debond/delaminate during fracture process due to the poor filler/matrix and filler/filler interface, which should be the key elements of the toughening effect.
Ultralight cellulose fiber/thermally reduced graphene oxide (CF/RGO) hybrid aerogel with super-elasticity and excellent electromagnetic interference (EMI) shielding capability was fabricated through ...lyophilization and carbonization process. CF/RGO aerogel with 5 mm thickness exhibits high EMI shielding effectiveness (SE) of ∼47.8 dB after annealing at 1000 °C with 5% hydrogen-argon mixture atmosphere. The superior SE is mainly ascribed to the cellular structure and good electrical conductivity of aerogel. The density of CF/RGO aerogel is as low as 2.83 mg/cm3, leading to ultrahigh specific shielding effectiveness (up to 33780 dB cm2/g). The volume/shape of obtained monolithic carbon material can be preserved very well after thermal treatment. The effects of RGO content and annealing conditions on EMI shielding and mechanical properties were investigated. Moreover, the hybrid aerogel possesses excellent mechanical resilience even with large strain (80% reversible compressibility) and outstanding cycling stability. In addition, adjustable EMI shielding capability could be realized by simple mechanical compression. These results demonstrate a promising and facile approach to fabricate low-cost and volume-preserving porous carbon material with superior and tunable EMI shielding performance for potential applications in aerospace and wearable electronic devices.
Display omitted
•A daily climate policy uncertainty index was constructed for China.•Analyze the effects of climate policy uncertainty and coal price on carbon price.•Coal price is the main shock ...transmitter.•Climate policy uncertainty and carbon price are mostly net shock receivers.
This paper applies the time-varying parameters vector autoregression (TVP-VAR) model to investigate the dynamic effects of climate policy uncertainty and coal price on carbon price in China. Based on news from China's mainstream newspapers and websites, a tailor-made climate policy uncertainty index is constructed. The VAR-BEKK-GARCH model is utilized as robustness check. The results indicate that both the climate policy uncertainty and coal price have significant time-varying effects on the carbon price. Additional dynamic connectedness analysis reveals that coal price is the main shock transmitter while climate policy uncertainty and carbon price are mostly net shock receivers.
Side‐chain engineering has been an effective strategy in tuning electronic energy levels, intermolecular interaction, and aggregation morphology of organic photovoltaic materials, which is very ...important for improving the power conversion efficiency (PCE) of organic solar cells (OSCs). In this work, two D–A copolymers, PBQ5 and PBQ6, are designed and synthesized based on bithienyl‐benzodithiophene (BDTT) as the donor (D) unit, difluoroquinoxaline (DFQ) with different side chains as the acceptor (A) unit, and thiophene as the π‐bridges. PBQ6 with two alkyl‐substituted fluorothiophene side chains on the DFQ units possesses redshifted absorption, stronger intermolecular interaction, and higher hole mobility than PBQ5 with two alkyl side chains on the DFQ units. The blend film of the PBQ6 donor with the Y6 acceptor shows higher and balanced hole/electron mobilities, less charge carrier recombination, and more favorable aggregation morphology. Therefore, the OSC based on PBQ6:Y6 achieves a PCE as high as 17.62% with a high fill factor of 77.91%, which is significantly higher than the PCE (15.55%) of the PBQ5:Y6‐based OSC. The PCE of 17.62% is by far one of the highest efficiencies for the binary OSCs with polymer donor and Y6 acceptor.
Two D–A copolymers, PBQ5 and PBQ6, are designed and synthesized based on difluoroquinoxaline (DFQ) units with different side chains. The organic solar cell (OSC) based on PBQ6 as donor and Y6 as acceptor achieves a high power conversion efficiency of 17.62%, which is one of the highest efficiencies for binary OSCs with a polymer donor and Y6 acceptor.
