As one of the most promising alternatives for future energy systems, the rechargeable Zn-air battery (ZAB) has attracted extensive attention due to its extraordinarily high theoretical specific ...energy density. However, several obstacles restrict its practical application. One challenge is the sluggish kinetics of oxygen-reduction reaction (ORR) and oxygen-evolution reaction (OER) in the discharging and charging processes of ZABs. In addition, when using unifunctional ORR or OER electrocatalysts as air electrodes, like noble metal catalysts (Pt/C or Ru/IrO
2
), there are the disadvantages of high cost and poor stability. Therefore, rational design of non-noble metal bifunctional ORR/OER electrocatalysts with high activity and stability is essential for the development of ZABs. In this review, we discuss the latest developments of non-noble metal bifunctional ORR/OER electrocatalysts for ZABs. Firstly, the related reaction mechanisms of ORR and OER are introduced. Then, the latest developments of bifunctional ORR/OER materials for ZABs are discussed in detail from three aspects: (i) MOF-based catalysts, including pristine MOFs and their derivatives; (ii) metal-free-based carbon catalysts, including heteroatom-doped carbon and defective carbon; (iii) metal-based catalysts, including metal-nitrogen-carbon materials (such as metals/alloys, single-atom) and metal compound materials. Finally, some challenges and outlooks for the optimal design of bifunctional air electrodes for rechargeable ZABs with high activity and ultra-long lifetime are put forward.
The latest developments of bifunctional oxygen electrocatalysts for Zn-air batteries (ZABs) are comprehensively summarized and evaluated, laying special emphasis on the challenges, outlooks and directions of future research for the ZAB industry.
This paper studies the feature extraction and middle-level expression of Convolutional Neural Network (CNN) convolutional layer glass broken and cracked at the scene of road traffic accident. The ...image pyramid is constructed and used as the input of the CNN model, and the convolutional layer road traffic accident scene glass breakage and crack characteristics at each scale in the pyramid are extracted separately, and then the depth descriptors at different image scales are extracted. In order to improve the discriminative power of the depth descriptor, Hellinger kernel and Principal Component Analysis (PCA) are used to perform nonlinear and linear transformations. Two aggregation strategies based on depth descriptors are proposed to form a global image representation. The classification experiment of the data set shows that Hellinger kernel, PCA transformation, and two aggregation strategies are all conducive to improving the classification accuracy. In addition, the convolutional layer road traffic accident scene glass breaking and crack feature coding can obtain better classification performance than the fully connected layer feature. We conducted dynamic impact tests on plate glass and Polyvinyl Butyral- (PVB-) laminated glass under different boundary conditions and studied the crack propagation and failure process of the glass under different impact speeds. The results show that there are radial cracks and circular cracks on the glass specimens under the impact load; the glass specimens show partial damage under high-speed impact and the characteristics of glass breaking and cracks at the scene of road traffic accidents; the four-frame plate glass is supported by sharp dagger-like fragments. This paper compares the energy absorption of glass specimens under different boundary conditions. The results show that the energy absorption effect of the four-point supporting glass specimen is generally stronger than that of the four-frame supporting glass.
Positive cooperative binding, a phenomenon prevalent in biological processes, holds great appeal for the design of highly sensitive responsive molecules and materials. It has been demonstrated that ...metal–organic frameworks (MOFs) can show positive cooperative adsorption to the benefit of gas separation, but potential binding cooperativity is largely ignored in the study of sensory MOFs. Here, we report the first demonstration of positive cooperative protonation of a MOF and the relevant pH response in fluorescence and proton conduction. The MOF is built of Zr–O clusters and bipyridyl-based tetracarboxylate linkers and has excellent hydrolytic stability. It shows a unique pH response that features two synchronous abrupt turn-off and turn-on fluorescent transitions. The abrupt transitions, which afford high sensitivity to small pH fluctuations, are due to cooperative protonation of the pyridyl sites with a Hill coefficient of 1.6. The synchronous dual-emission response, which leads to visual color change, is ascribable to proton-triggered switching between (n, π*) and (π, π*) emissions. The latter emission can be quenched by electron donating anion-dependent through photoinduced electron transfer and ground-state charge transfer. Associated with cooperative protonation, the proton conductivity of the MOF is abruptly enhanced at low pH by two orders, but overhigh acid concentration is adverse because excessive anions can interrupt the conducting networks. Our work shows new perspectives of binding cooperativity in MOFs and should shed new light on the development of responsive fluorescent MOFs and proton conductive materials.
In winter cities, outdoor seasons are highly valued due to the long cold winter. By improving the outdoor thermal environment during marginal seasons, outdoor seasons may be extended. Therefore, ...outdoor thermal comfort and adaptive behaviors during marginal seasons should be considered. Three representative residential public open spaces in Harbin, a typical winter city, were selected to conduct an empirical study. Meteorological measurements and rudimentary questionnaires were administered and observations were conducted to explore outdoor thermal comfort and adaptive behaviors. Three important conclusions were obtained from the survey. The result from the questionnaire surveys showed that users of public spaces generally believed that “warm” was comfortable during the spring marginal season of the winter cities. The 90% thermal acceptable physiologically equivalent temperature (PET) range, which was calculated using meteorological measurements and questionnaire results, was more than 10.2 °C for this time period in the winter cities. This threshold value was much lower than that of temperate and subtropical zones, indicating that the outdoor thermal comfort of users in the winter cities had regional characteristics. Moreover, users engaged in static vs. dynamic activities showed different sensitivities to thermal environments. The users’ location selection showed a strong dependence on microclimate rather than on the activity-supported facilities; when microclimate conditions changed, users made accommodations by moving to sunny areas or performing other adaptive behaviors, and thus, space utilization changed. These findings can inform thermal comfort-oriented planning and design from the perspectives of microclimate regulations, site planning, and activities in the residential public open spaces of winter cities.
The effects of non-isothermal aging treatment on strength and corrosion behavior of Alsingle bond Znsingle bond Mgsingle bond Cu alloy have been investigated by hardness and electrical conductivity, ...tensile testing, intergranular corrosion (IGC) testing, potentiodynamic polarization combined with optical microscopy (OM) and transmission electron microscopy (TEM). The combination of excellent mechanical properties and satisfactory corrosion resistance can be acquired by adjusting the key parameters of non-isothermal aging. The differences of strength and corrosion resistance are explained on the basis of the microstructure evolution of intra-grain and grain boundary precipitates.
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► Nano-ZnO modified PVDF membrane reached 100% water flux recovery. ► The initial flux of modified membrane maintained stable in the long-term operation. ► Moderate modification ...almost doubled the water permeability. ► Modified internal pores might render enhanced anti-irreversible fouling property.
Irreversible membrane fouling is harmful for long-term operation of filtration. In this study, a novel anti-irreversible fouling polyvinylidene fluoride (PVDF) membrane was successfully fabricated using the wet phase separation methods. Nano-ZnO, with different dosages ranging from 6.7% to 26.7% (percentage of PVDF weight), was blended as an additive into the membrane matrix for the modification of the internal surfaces of membrane pores. A series of tests, such as filtration experiments, contact angle measurements, scanning electron microscope (SEM)/energy dispersive X-ray spectrometer (EDS) analyses and mechanical tests, were performed to characterize the modified membranes. The multi-cycle filtration experiments showed that the modified PVDF membranes demonstrated significant anti-irreversible fouling property. All the modified membranes achieved almost 100% water flux recovery after physical cleaning, whereas the raw membrane only reached 78% recovery. This promotion might be related to the increase of membrane hydrophilicity. The implantation of nano-ZnO into membrane inner surface (i.e., pore wall), as indicated by SEM/EDS tests, might be responsible for the enhancement of anti-irreversible fouling property. The water permeability of the modified membrane almost doubled by adding 6.7% nano-ZnO which was determined as the optimum dosage (within the dosage range in this study) for PVDF membrane modification. Additionally, the mechanical strength was found reinforced for modified membranes, which should also benefit the filtration application.
The Zn(
ii
) MOF with a tripyridinium-based hexacarboxylate shows direct color change on exposure to small primary amines and UV-assisted color response on exposure to small alcohols. The reversible, ...group-specific and size-selective chemochromic/chemophotochromic behaviours are ascribed to spontaneous/photoinduced guest-to-host electron transfer within the unique confined space furnished with electron-deficient sites.
The MOF provides unique confined space furnished with electron acceptor sites, and exposure to amines/alcohols causes specific and size-selective direct/UV-assisted color change owing to spontaneous/photoinduced electron transfer.
One of the biggest challenges for the practical application of forward osmosis (FO) is lack of high-performance FO membranes. In this study, a novel thin film nanocomposite (TFNC) FO membrane was ...fabricated based on a layered double hydroxide nanoparticles (LDH-NPs) blended ultrafiltration substrate. The influence of the LDH-NPs addition on the physicochemical properties of the ultrafiltration substrate and the resultant FO membrane was systematically investigated. The addition of LDH-NPs endowed the ultrafiltration substrate with increased porosity, surface hydrophilicity, surface pore diameter, mechanical strength and thermal stability. Consequently, all the resultant TFNC FO membranes obtained increased water permeability as compared with pristine FO membrane. Specifically, the TFNC membrane with a 2wt% LDH-NPs dosage exhibited a water flux of 18.1Lm−2h−1 (~42.5% higher than that of the pristine FO membrane) with little compromise in reverse salt flux. Moreover, this membrane reached a higher water flux of 26.9Lm−2h−1 when 2M NaCl was used as draw solution. The water-flux increase could be attributed to the decrease of the structural parameter (S value) of the LDH-NPs blended ultrafiltration substrate. The loaded LDH-NPs facilitated the development of a considerable amount of finger-liked macrovoids, which decreased the support layer tortuosity thus favoring the inhibition of internal concentration polarization. As a result, a moderate water flux was obtained. To the best of our knowledge, this is the first reported TFNC membrane using LDH-NPs blended substrates for FO applications.
A novel thin film nanocomposite forward osmosis membrane based on layered double hydroxide nanoparticles blended polysulfone substrate was fabricated and investigated.
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•Thin film FO membrane with LDH-NPs blended PSf substrate was fabricated.•The addition of LDH-NPs endowed the PSf substrate with increased properties.•The water flux was increased from 12.7 to 18.1Lm−2h−1 by the addition of LDH-NPs.•This contribution represents the first application of LDH-NPs in FO membranes.
Inverse synthetic aperture radar (ISAR) can only provide two-dimensional (2-D) images to represent the target's scattering projection on the corresponding imaging planes. However, as the echo of the ...target from different observation angles can be achieved simultaneously, the radar network can provide 3-D scattering information about the target. In this article, a novel 3-D scattering image reconstruction method is proposed based on the radar network and compressed sensing (CS). First, the general signal model and the reconstruction conditions of the radar network 3-D reconstruction are given. Then, the 3-D scattering distribution reconstruction model is built in a CS framework, which can reconstruct the positions and coefficients of scattering centers simultaneously. Moreover, the sparse structure with three layers in radar network 3-D reconstruction is defined and a fast 3-D reconstruction algorithm is proposed. To the end, the numerical simulations under noise scenarios and the principle prototype experiments on real data are shown to demonstrate the validity of the proposed method.
Due to its great relevance to environmental, biological, and chemical processes, the precise detection of pH or acidic/basic species is an ongoing and imperative need. In this context, pH-sensitive ...luminescent systems are highly desired. We reported a three-dimensional Zn(II) MOF synthesized from a bipyridyl-tetracarboxylic ligand and composed of 4-fold interpenetrated diamond frameworks. Because the steric hindrance in the ligand prevents metal coordination with the pyridyl group, the MOF features free basic N sites accessible to the small H
ions, which renders pH responsivity. The aqueous dispersion exhibits an abrupt, high-contrast, and reversible on-off fluorescence transition in the narrow pH range of 5.4-6.2. The sensitive bistable system can be used for the precise monitoring of pH within the range and for use as a pH-triggered optical switch. The responsive mechanism through pyridyl protonation is collaboratively supported by data fitting, absorption spectra, and molecular orbital calculations. In particular, spectral and theoretical analyses reveal the destruction of n → π* transitions and the appearance of intramolecular charge-transfer transitions upon pyridyl protonation. Moreover, by virtue of the pH-responsive fluorescence, the MOF shows appealing sensing performance for the detection of 3-nitropropionic acid, a major mycotoxin in moldy sugar cane.
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