Nano-Au-decorated hierarchical porous cobalt sulfide derived from ZIF-67 toward optimized oxygen evolution catalysis:Important roles of microstructures and electronic modulation

Enhancing both the number of active sites available and the intrinsic activity of Co-based electrocatalysts simultaneously is a desirable goal.Herein,a ZIF-67-derived hierarchical porous cobalt sulfide decorated by Au nanoparticles(NPs)(denoted as HP-Au@CoxSy@ZIF-67)hybrid is synthesized by low-temperature sulfuration treatment.The well-defined macroporous-mesoporous-microporous structure is obtained based on the combination of polystyrene spheres,as-formed CoxSy nanosheets,and ZIF-67 frameworks.This novel three-dimensional hierarchical structure significantly enlarges the three-phase interfaces,accelerating the mass transfer and exposing the active centers for oxygen evolution reaction.The electronic structure of Co is modulated by Au through charge transfer,and a series of experiments,together with theoretical analysis,is performed to ascertain the electronic modulation of Co by Au.Meanwhile,HP-Au@CoxSy@ZIF-67 catalysts with different amounts of Au were synthesized,wherein Au and NaBH4 reductant result in an interesting“competition effect”to regulate the relative ratio of Co^(2+)/Co^(3+),and moderate Au assists the electrochemical performance to reach the highest value.Consequently,the optimized HP-Au@CoxSy@ZIF-67 exhibits a low overpotential of 340 mV at 10 mA cm^(-2)and a Tafel slope of 42 mV dec-1 for OER in 0.1 M aqueous KOH,enabling efficient water splitting and Zn-air battery performance.The work here highlights the pivotal roles of both microstructural and electronic modulation in enhancing electrocatalytic activity and presents a feasible strategy for designing and optimizing advanced electrocatalysts.

柔性锌-空气电池进展与展望

近年来,人们越来越关注柔性可穿戴电子设备。柔性锌-空气电池由于有较高的理论能量密度以及对像人体一样不均匀表面的适应能力,有望成为下一代电子产品的电源。在柔性锌-空气电池研究领域,人们已经取得了较好的研究进展,各种柔性锌-空气电池的制备方法已被报道。本文阐述了近年来柔性锌-空气电池的主要成就以及面临的困难,特别是关注凝胶电解质、金属阳极以及柔性空气阴极对柔性锌-空气电池电化学性能的影响,最后讨论了柔性锌-空气电池面临的主要挑战与发展前景。

由超拍电子伏特加速器产生的超高能伽马射线气泡

We report the detection of aγ-ray bubble spanning at least 100deg2 in ultra-high energy(UHE)up to a few PeV in the direction of the star-forming region Cygnus X,implying the presence super PeVatron(s)accelerating protons to at least 10 PeV.A log-parabola form with the photon indexΓ(E)=(2.71±0.02)+(0.11±0.02)×log10(E/10 TeV)is found fitting the gamma-ray energy spectrum of the bubble well.UHE sources,“hot spots”correlated with very massive molecular clouds,and a quasi-spherical amorphousγ-ray emitter with a sharp central brightening are observed in the bubble.In the core of~0.5°,spatially associating with a region containing massive OB association(Cygnus OB2)and a microquasar(Cygnus X-3),as well as previously reported multi-TeV sources,an enhanced concentration of UHEγ-rays is observed with 2 photons at energies above 1 PeV.The general feature of the bubble,the morphology,and the energy spectrum,are reasonably reproduced by the assumption of a particle accelerator in the core,continuously injecting protons into the ambient medium.

New thermoelectric semiconductors Pb_(5)Sb_(12+x)Bi_(6-x)Se_(32) with ultralow thermal conductivity

Five new semiconductors Pb_(5)Sb_(12+x)Bi_(6-x)Se_(32)(x=0,1,2,3,and 4)have been synthesized for the first time,which adopt pavonite-type structure and crystallize in monoclinic C2/m space group.The crystal structure is composed of two different types of polyhedral slabs.Slab-I is a galena-like structure motif that forms with[MSe_(6)](M=Pb,Sb,and Bi)octahedra and slab-Ⅱcontains one octahedral[MSe_(6)]block and paired squared pyramids[MSe_(5)].Pb_(5)Sb_(12+x)Bi_(6-x)Se_(32)exhibits n-type semiconductor behaviors and the remarkable Seebeck coefficient from-64.1μV K^(-1)for x=0 sample to-242μV K^(-1)forx=4 sample at 300 K.Moreover,the Pb_(5)Sb_(12)Bi_(6)Se_(32)has the highest carrier concentration of 1.35×10^(20)cm^(-3)in pavonite-type materials.The complex compositions,mixed occupancies of the cations,and quasi-two-dimensional structure lead to the low lattice thermal conduc-tivity(κ_(lat))less than 0.48 W m^(-1)K^(-1)from 300 to 723 K,at which Pb_(5)Sb_(16)Bi_(2)Se_(32)especially shows the ultralow value of 0.25 W m^(-1)K^(-1).As a result,the thermoelectric figure of merit,ZT~0.34 at 723 K,is obtained for the intrinsic Pb_(5)Sb_(12)Bi_(6)Se_(32).

Highly efficient nonuniform finite difference method for three-dimensional electrically stimulated liquid crystal photonic devices

Liquid crystal(LC)photonic devices have attracted intensive attention in recent decades,due to the merits of tunability,cost-effectiveness,and high efficiency.However,the precise and efficient simulation of large-scale three-dimensional electrically stimulated LC photonic devices remains challenging and resource consuming.Here we report a straightforward nonuniform finite difference method(NFDM)for efficiently simulating largescale LC photonic devices by employing a spatially nonuniform mesh grid.

碳纳米管提升氧化亚硅负极稳定性的起源

高容量的SiO (SO)合金基材料是最有希望的下一代锂离子电池负极之一.使用碳纳米管(CNTs)导电添加剂,虽然可以有效地解决SO较差的循环寿命这一难题,然而除了动力学因素之外,其它潜在的作用机理目前仍不明确.在本工作中,一系列的测试结果表明CNTs可以使电极在循环后依然维持完整的导电网络,确保均匀的电化学反应.CNTs也使得电极局部的体积膨胀得到了抑制,从而避免了固态电解质界面的不断生长,活性材料从集流体剥离,甚至析锂.得益于CNTs的上述作用, SO-CNTs负极在0.5 C (1 C=1600 mA g^(-1))下可以稳定循环200次,其容量保持率为96.2%. CNTs的作用机理也进一步地在商业化的SO/石墨复合负极(SO650-CNTs, 1 C=650 mA g^(-1))中得到了验证,SO650-CNTs在1 C下循环400次后容量保持率为80.6%.本工作为导电添加剂的作用机理提出了新的见解,并将有助于加速合金类负极的商业化进程.

LHAASO解密宇宙线起源

宇宙线是星际空间中以接近光速高速运动的带电粒子,它在星际介质中是与磁场和冷气体同样重要的成分,在星际化学过程和恒星形成过程中也扮演着重要的角色,是宇宙不可或缺的重要组成部分[1].高能宇宙线还是连接微观粒子和宏观宇宙的桥梁,与宇宙天体中的极端物理过程相联系,是近年来新兴的交叉学科——粒子天体物理的重要组成部分.然而,宇宙线的起源依然未知.

Main Mechanism for Generating Overpressure in the Paleogene Source Rock Series of the Chezhen Depression,Bohai Bay Basin, China

The Chezhen depression,located in the south of Bohai Bay Basin,is an oil-producing basin in China. The third and fourth members of the Shahejie Formation(E(s3) and E(s4)) are the main source rock series in the Chezhen depression. Widespread overpressures occurred in the E(s3) and E(s4) from the depths of approximately 2 000 to 4 600 m,with the maximum pressure coefficient of 1.98 from drillstem tests(DST). Among the sonic,resistivity and density logs,sonic-log is the only reliable pressure indicator and can be used to predict the pore pressure with Eaton's method. All the overpressured mudstones in the source rock series have higher acoustic traveltimes compared with normally pressured mudstones at a given depth. The overpressured mudstones in the E(s3) and E(s4) units are characterized by a normal geothermal gradient,high average density values up to 2.5 g/cm^3,strong present-day hydrocarbon generation capability,abundant mature organic matter and high contents of residual hydrocarbons estimated by the Rock-Eval S1 values and chloroform-soluble bitumen "A" values. All suggest that the dominant mechanism for overpressure in the mudstones of source rock series in the Chezhen depression is hydrocarbon generation. A comparison between the matrix porosity of the normally pressured sandstones and overpressured sandstones,the quantitative evaluation of porosity loss caused by compaction and the conventional thin section inspection demonstrate that the sandstones in the Chezhen depression were normally compacted. The high contents of hydrocarbons in the overpressured reservoirs prove that the overpressure in the sandstones of the source rock series was caused by pressure transmission from the source rocks.

Cobalt and nitrogen codoped porous carbon as superior bifunctional electrocatalyst for oxygen reduction and hydrogen evolution reaction in alkaline medium

Cobalt and nitrogen codoped carbon materials(Co-N-C) were fabricated by pyrolysis of the mixture of poly(4-vinylpyridine) and cobalt chloride using SiO_2 nanoparticles as hard template, which were the first transition metal/nitrogen-codoped carbon bifunctional electrocatalyst derived from noncarbonizable polymer for ORR and HER. The as-made Co-N-C possessed hierarchical pore structure and high specific surface area, achieving excellent electrocatalytic performances for ORR and HER. Its ORR catalytic performances were comparable to those of Pt/C catalyst and its HER catalytic performances were superior to those of most doped carbon catalysts in KOH electrolyte. Moreover, its bifunctional electrocatalytic performances for ORR and HER were better than those of most bifunctional doped carbon catalysts in alkaline electrolyte.

Direct synthesis of large-area Al-doped graphene by chemical vapor deposition:Advancing the substitutionally doped graphene family

Graphene doping continues to gather momentum because it enables graphene properties to be tuned,thereby affording new properties to,improve the performance of,and expand the application potential of graphene.Graphene can be chemically doped using various methods such as surface functionalization,hybrid composites(e.g.,nanoparticle decoration),and substitution doping,wherein C atoms are replaced by foreign ones in the graphene lattice.Theoretical works have predicted that graphene could be substitutionally doped by aluminum(Al)atoms,which could hold promise for exciting applications,including hydrogen storage and evolution,and supercapacitors.Other theoretical predictions suggest that Al substitutionally doped graphene(AIG)could serve as a material for gas sensors and the catalytic decomposition of undesirable materials.However,fabricating Al substitutionally doped graphene has proven challenging until now.Herein,we demonstrate how controlled-flow chemical vapor deposition(CVD)implementing a simple solid precursor can yield high-quality and large-area monolayer AIG,and this synthesis is unequivocally confirmed using various characterization methods including local electron energy-loss spectroscopy(EELS).Detailed high-resolution transmission electron microscopy(HRTEM)shows numerous bonding configurations between the Al atoms and the graphene lattice,some of which are not theoretically predicted.Furthermore,the produced AIG shows a CO_(2) capturability superior to those of other substitutionally doped graphenes.

Modeling the effect of water vaporization and salt precipitation on reservoir properties due to carbon dioxide sequestration in a depleted gas reservoir

Vaporization of water during both gas reservoir development and CO2 geological sequestration in saline formations can cause salt precipitation with rapid loss of formation porosity and permeability.Water vaporization and precipitation of halite around a single well from stage production to CO2 injection are studied to investigate the effect on reservoir properties in a gas reservoir.This paper identifies and quantifies post-flood dry zones and permeability changes in depleted gas reservoir after CO2 exposure with the comparison in gas production period by performing the numerical simulation with the compositional simulator.Simulation results indicate that water vaporization and salt precipitation occur during gas production,and can be intensified by CO2 injection.Dry supercritical CO2 injection vaporizes the brine promoting brine concentration and halite precipitation.The simulation indicates a drying area with a radius of 78 m around wellbore after CO2 injection.Porosity reduces with the most scope of 58%,and permeability can be decreased by up to 93.9%due to salt precipitation.And the injectivity is damaged by 99.77%at the end of injection period based on maximum permeability reduction.Moreover,six factors are investigated to conduct the influence analysis,showing that higher salinity brine,higher injection rate,higher irreducible water saturation,lower initial permeability,higher temperature and with capillary flow are conditions enhancing the salt precipitation due to dry CO2 injection.

Liquid crystal-based optical aptasensor for the sensitive and selective detection of Gram-negative bacteria

The sensitive and differential detection of Gram-negative bacteria is essential in food processing,environmental monitoring,and the daily chemical industry.Herein,we propose and validate a liquid crystal(LC)-based aptasensor for the ultrasensitive detection of Escherichia coli(E.coli),a model of Gram-negative bacteria.The nematic liquid crystal of 4-cyano-4’-pentylbiphenyl(5 CB) molecules can be orderly or disorderly arranged at the LC-aqueous interface via different stimuli,causing changes in optical texture due to birefringence.Bright schlieren texture is observed when a mixture solution of aptamer and hexadecyl trimethyl ammonium bromide(CTAB) is dripped onto the segmented LC films on a copper mesh.The specific binding of aptamers with target bacteria biomarkers liberates the CTAB molecules,which then self-assemble at the LC-aqueous interface to induce the vertical alignment of LCs.An optical transition from bright to dark is therefore achieved via the LC molecular orientation and serves as an aptasensor.Given the prominent affinity and specificity of the aptamer,the established sensitive and selective E.coli assay shows an ultralow detection limit of 27 cfu/mL.The prepared aptasensor can also be applied for the sensitive and selective determination of E.coli in fruit juice,soft drink,and cosmetic products,and shows great promise for the on-site detection of Gram-negative bacteria with high sensitivity and specificity for environmental monitoring,food safety assessment,and household chemical inspection.

LHAASO and Galactic cosmic rays

Cosmic rays(CRs)are relativistic charged particles in the interstellar medium(ISM).They are mainly protons(hydrogen nuclei)with about 10%fraction of helium nuclei and smaller abundances of heavier elements.CRs are an important component in ISM.In our galaxy,the energy density of CRs is similar to that of the magnetic fields and interstellar radiation fields(ISRFs).CRs also determine the ionization rate and heating of gas in the dense core of molecular clouds,thus playing a leading role in the astro-chemistry processes therein and controling the star-forming processes.More than a century has passed since Hess discovered the extra-terrestrial origin of CRs(in 1912),yet the origin of CRs still remains as a mystery.