Abstract ：

In carbon-based oxygen reduction reaction (ORR) catalysts, metal-free nitrogen-doped carbon-based materials generally have higher catalytic stability compared to metal catalysts with reduced catalytic activity due to the occurrence of metal agglomeration during the catalytic reaction. In this paper, a metal-free nitrogen-doped carbon-based ORR catalyst NCOH5-900 with a half-wave potential of 0.846 V and onset potential of 0.94 V was prepared using coal as the carbon source, dicyandiamide as the nitrogen source and KOH as the activator. The material has good ORR catalytic performance with half-wave potential and onset potential comparable to Pt/C catalyst with the same mass loading, with better resistance to methanol toxicity and catalytic stability. The physical and chemical properties of the prepared catalyst were controlled by adjusting the amount of nitrogen doping and activation temperature to establish the relationship between the material structure and the ORR performance. The results suggest that for the metal-free nitrogen-doped carbon-based material, the good ORR catalytic performance is attributed to the abundant edge defects, high graphitization, good mixed structure of micro/mesopores, large nitrogen content, and high ratio of pyridine to graphitic nitrogen. Finally, the catalytic mechanism of NCOH5-900 for ORR is investigated using in-situ attenuated total reflection Fourier infrared (ATRFTIR) and in-situ Raman, confirming the four-electron reduction process of O2 via a continuous dual step of two- electron transfer process.

Keyword ：

Oxygen reduction reaction Metal-free catalyst In-situ ATR-FTIR Structure-effect relationship Carbon cathodic material Coal-based carbon material

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Abstract ：

In this study, the effects of grouting sleeve anchorage defects on the seismic performance of prefabricated concrete shear walls were studied, and a fast after -damage retrofitting method has been proposed. Six specimens were investigated under cyclic loading. The parameter was the number of grouting sleeve anchorage defects, selected as 0, 2, and 4. The test was divided into two loading stages. During stage 1, the specimen was loaded until the strength dropped below 85 % of its peak strength. After stage 1, the damaged specimens were retrofitted using combined retrofitting method of steel plate and high -strength grouting material, and then subjected to loading tests in stage 2. The resulting damage characteristics, hysteretic behavior, stiffness, strength, and energy dissipation capacity were studied. The strength of the shear wall, considering anchorage defects, was calculated. The results show that anchorage defects reduce the seismic behavior of the specimens. Compared with the two defects, the strength of the shear wall with four defects did not significantly change, though the ductility coefficient and energy dissipation capacity decreased considerably. The combined steel plate -high strength grout retrofitting method could significantly improve the strength and energy dissipation and effectively restore the stiffness of prefabricated shear walls. The calculated strength of the shear wall is in good agreement with the experimental value, confirming that it is reliable and can be used to calculate the strength with anchorage defects. The proposed retrofitting method can provide a new choice for the fast damage repair of the postearthquake shear walls.

Keyword ：

Seismic performance Anchorage defects Retrofitting Prefabricated shear wall

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Abstract ：

High carrier separation efficiency and rapid surface catalytic reaction are crucial for enhancing catalytic CO2 photoreduction reaction. Herein, integrated surface decoration strategy with oxygen vacancies (Ov) and anchoring CuxO (1 < x < 2) nanodots below 10 nm is realized on Bi2MoO6 for promoting CO2 photoreduction performance. The charge interaction between Ov and anchored CuxO enables the formation of enhanced internal electric field, which provides a strong driving force for accelerating the separation of photocharge carriers on the surface of Bi2MoO6 (eta(surf) approximate to 71%). They can also cooperatively reduce the surface work function of Bi2MoO6, facilitating the migration of carrier to the surface. Meanwhile, surface-integrated Ov and CuxO nanodots allowing dual catalytic sites strengthens the adsorption and activation CO2 into *CO2 over Bi2MoO6, considerably boosting the progression of CO2 conversion process. In the absence of co-catalyst or sacrificial agent, Bi2MoO6 with Ov and CuxO nanodots achieves a photocatalytic CO generation rate of 12.75 mu mol g(-1) h(-1), a remarkable increase of over approximate to 15 times that of the original counterpart. This work provides a new idea for governing charge movement behaviors and catalytic reaction thermodynamics on the basis of synergistic improvement of electric field and active sites by coupling of the internal defects and external species.

Keyword ：

build-in electric field oxygen vacancies Bi2MoO6 CuxO nanodots CO2 reduction

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Structural assessment of buried energy pipelines is often hindered by the abundance of external vibrations resulting in nebulous noises. Effective and secure nondestructive approaches need to be devised to efficiently reduce noise in multidimensional magnetic anomaly signals collected from a pipeline. This study focuses on the mechanism by which a measured source signal can be broken down into low- and high-frequency constituents known as intrinsic mode functions (IMFs). By doing so, a well-defined set of instantaneous frequencies is obtained utilizing improved complete ensemble empirical mode decomposition (ICEEMDAN) algorithms. These IMFs contain useful structural evidence across multiple scales that can be extracted for effective identification of the defect location. To accomplish this objective, first, the signal gradients are calculated using dual-density complex wavelet transform to diminish the influence of the geomagnetic field. The multiscale variance fusion (MVF) algorithm is then adopted to quantize the fluctuations occurring in each individual IMF. The output signals generated by computing the variances provide sufficient information about the location and severity of the pipeline defects. Numerical simulations for a buried pipeline model have been presented to validate the authenticity of the proposed technique. Indoor laboratory implantation on a pipeline test sample with prefabricated defects justifies the effectiveness of the ICEEMDAN-MVF model, to localize hidden structural flaws in energy pipelines without physical contact and even in more complex environments with multiple sources of magnetic interference.

Keyword ：

empirical mode decomposition damage diagnosis intrinsic mode functions pipeline flaw detection Structural health monitoring

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Abstract ：

V -based alloy membranes have huge potential for hydrogen separation and purification due to their higher hydrogen permeability, but suffer from hydrogen embrittlement. To address this matter, Pd and Fe have been chosen as alloying additions in V -based membranes to inhibit hydrogen embrittlement and maintain high hydrogen permeation performance based on the lattice -matching strategy. The phase structure, composition, microstructure and hydrogen permeation properties of V -Pd -Fe ternary alloy are investigated systematically, and the V -Fe and V -Pd binary alloys are presented for comparison. The results show that the prepared V -Pd -Fe ternary can match almost perfectly with pure V in lattice constants. Attributing to the lattice -matching strategy, the V -Pd -Fe ternary alloy exhibits more excellent hydrogen permeable properties than that of V -Fe and V -Pd binary alloys. The reduction of hydrogen embrittlement is ascribed to the lower hydrogen solubility that induced by the lattice distortion and electronegativity of Fe and Pd. Meanwhile, the manipulated lattice constant that parallel to pure V maintains high hydrogen permeation performance. Additionally, the designed ternary V 87.8 Pd 8 Fe 4.2 alloy exhibits exceptional long-term hydrogen permeation stability at 573 and 623 K, and hydrogen flux gradually decreases at 673 and 723 K is observed due to the interdiffusion between Pd film and V 87.8 Pd 8 Fe 4.2 substrate and defects in the Pd coating. This study offers new scenario and method for optimized hydrogen permeable properties and restrains hydrogen embrittlement in the alloy membrane.

Keyword ：

Hydrogen solubility First -principles calculation Hydrogen permeable membrane Hydrogen embrittlement Vanadium alloy

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Devising exceptional S-scheme heterojunction photocatalysts utilized in annihilating pharmaceuticals and chromium contamination is significant for addressing the problem of global water pollution. In this work, a chemically bonded Mn0.5Cd0.5S/BiOBr S-scheme heterostructure with oxygen vacancies is ingeniously developed through a facile in-situ solvothermal synthesis. The designed Mn0.5Cd0.5S/BiOBr heterojunction exhibits eminently reinforced photo-activity for destruction of tetracycline hydrochloride and Cr(VI) as compared with its individual components. This substantial photo-redox performance amelioration is benefitted from the creation of an intense internal electric field (IEF) via supplying powerful driving force and migration highway by interfacial chemical bond to foster the S-scheme electron/hole disintegration. More intriguingly, the IEF at the hetero-interface drives the fast consumption of the photo-induced holes in Mn0.5Cd0.5S by the photoelectrons from BiOBr, profoundly boosting the enrichment of active photo-carriers and sparing the photo-corrosion of Mn0.5Cd0.5S. Furthermore, Mn0.5Cd0.5S/BiOBr with exceptional anti-interference property can work efficiently in real water matrices. Multiple uses of the recycled Mn0·5Cd0·5S/BiOBr evidence its prominent robustness and stability. This achievement indicates the vast potential of chemically bonded S-scheme photosystems with structural defects in the design of photo-responsive materials for effective wastewater treatment. © 2024 Central South University.

Keyword ：

Wastewater treatment Water pollution Chromium compounds Electric fields Bismuth compounds Heterojunctions Oxygen vacancies Manganese compounds Disintegration Corrosion

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It is still an enormous challenge to regulate microstructure of pure carbonaceous electromagnetic (EM) wave absorbents in order to gain superior wideband microwave absorption (MA) with environmentally adaptive ability. Herein, the novel pure cellulose-derived graphite carbon materials (CGC) with abundant defects were fabricated via the self-assembly strategy combined with simple carbonization for the first time. The EM and MA performance of as-prepared CGC with different carbonization temperatures were studied in detail. The minimum reflection loss of CGC was up to- 46.2 dB (over 99.99% MA) at only 1.42 mm, and the maximum effective absorption bandwidth (EABmax, max , RL <- 10 dB) was as wide as 6.32 GHz. The greatly improved MA of pure carbon materials outperformed those of many previously reported carbon-based composite absorbents with tedious preparation process. The excellent MA property was attributed to the optimal synergy of good impedance matching and satisfactory EM attenuation capability. Besides, the CGC still retains a strong and broadband MA ability in the simulated real harsh environmental conditions (acid rain/alkaline solution, salt spray and strong UV exposure). Hence, the CGC is believed to be a very promising candidate as high-efficiency EM wave absorbents with wide frequency and excellent environmental adaptability for practical application. (c) 2024 The Authors. Published by Elsevier B.V. on behalf of The Chinese Ceramic Society. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Keyword ：

Microwave absorption Impedance matching Environment adaptability Graphitic carbon Cellulose Polarization

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BaO-CaO-Al2O3 aluminate impregnants, the source for producing Ba for Ba-W cathodes, play an indispensable role in the cathode performance. Possessing the high thermionic emission property and low melting point is a huge challenge for the aluminate impregnants of Ba-W cathodes. Here, a 'kill two birds with one stone' strategy is designed to simultaneously reduce the melting points and increase the thermionic emission capability. A novel BaO-CaO-Al2O3-BaF2 quaternary aluminate impregnant was obtained and the addition of BaF2 decreases the viscosity and melting point of the aluminate impregnants. When the content of BaF2 reaches 0.15 mol, the emission current density of Ba-W cathode impregnated with quaternary aluminate impregnant can reach 15.89 A cm−2 at 1100°Cb, which is 1.11 times higher than that of the without BaF2. In contrast, the continuous rise of BaF2 leads to the decreased emission current density due to the formation of a glassy phase. It is found that the introduction of BaF2 led to the formation of a new skeletal structure in the quaternary aluminate impregnant – [AlO3F], which coexists with [AlOn] (n = 4, 5, 6) to reduce the melting point. Theoretical calculations confirm that introducing fluorine triggers the number of point defects and barium compound in impregnant to gain electron convert to the metastable Baδ+ (0 © 2024

Keyword ：

Barium compounds Sodium Aluminate Thermionic cathodes Aluminum oxide Point defects Alumina Fluorine compounds Thermionic emission

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Abstract ：

Lead sulfide quantum dots (PbS QDs) show great potential application in near infrared range, and incorporation of PbS QDs into all solid glass matrix improves both their chemical and thermal stabilities as well as the shaping ability. However, the incorporation of PbS QDs into all solid glass matrix makes it difficult to modify their surface, resulting in the relatively low absolute photoluminescence quantum yield (PL QY) caused by the surface defects. Here, PbS QDs with tunable photoluminescence band in near-infrared range in silicate glasses were prepared by melting-quenching method. By addition of chloride and forming PbClx shell around PbS QDs in glass, defects induced by surficial lead ions of above PbS QDs can be effectively passivated, reducing subsequent trapping of photo-generated electrons accordingly. PL QY of PbS QDs inbuilt glasses is enhanced eventually and achieved as high as 49.3%. Furthermore, thermo- and photo-stabilities of PbS QDs in glass are greatly improved compared with those without surface chlorine passivation. These high performance PbS QDs embedded glasses with excellent stability show significant potential in light-emitting diodes, lasers and fiber amplifiers in nearinfrared range.

Keyword ：

PbS QDs Glass Quantum yield Chloride surface passivation

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Mixing material such as fibers into concrete is an effective method to change the brittle behavior of concrete. To reduce the internal defects of concrete and improve the mechanical performance and crack resistance of concrete, this study proposed the design concept of multiscale modified concrete. To further investigate the feasibility of the design concept, the two-stage test method is adopted to study the performance of multiscale modified concrete. First, carbon nanotubes (CNT) and CaCO3 whiskers were mixed into concrete, and the optimum contents of CNT and CaCO3 whiskers were determined by uniaxial compression test. Subsequently, based on the optimum contents of CNT and CaCO3 whiskers, polyvinyl alcohol fibers (PVAF), steel fibers (SF), and rubber particles (RP) were further mixed into concrete, and the uniaxial compression test and scanning electron microscopy (SEM) test were completed. From the test results, the influence of materials contents on the mechanical performance of concrete was analyzed, an accurate and reasonable compressive stress-strain model was established, and the comprehensive toughness evaluation index of concrete considering the multiple factors influence was presented. The comprehensive toughness evaluation results show that the multiscale modified concrete has outstanding compressive strength and toughness when the contents of CNT, CaCO3 whiskers, PVAF, SF, and RP are 0.6%, 6.0%, 0.075%, 1.0%, and 0%, respectively. The SEM results revealed that adding materials of various sizes into concrete can hinder the growth of cracks and improve the cracking pattern of concrete.

Keyword ：

Concrete Stress-strain curve Mechanical performance Multiscale Toughness

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