Embedding partial sulfurization of iron-cobalt oxide nanoparticles into carbon nanofibers as an efficient electrode for the advanced asymmetric supercapacitor

In this paper,a series of partially sulfurized iron-cobalt oxide(FCOS) nanoparticles were embedded in carbon nanofibers(FCOS@CNF) via a simple electrospinning method and followed by a hydrothermal sulfurization process.The sulfurization degree of iron-cobalt oxide nanoparticles can be further controlled by tuning the hydrothermal reaction time.The self-supported FCOS@CNF samples with hierarchical nanostructure can not only effectively prevent the detaching of the FCOS nanoparticles but also provide abundant electrochemical active sites.When used as a supercapacitor electrode,the FCOS@CNF^(-1)0 electrode presents a high specific capacitance(1039 F·g^(-1)at 1 A·g^(-1)),a good rate performance(over 69.4%of capacitance retention from 1 to 15 A·g^(-1)),and a long cycle lifespan(88.3% of capacitance retention after 4000 cycles at10 A·g^(-1)).A unique(FCOS@CNF^(-1)0//F-RGO) asymmetric supercapacitor device was assembled using the FCOS@CNF^(-1)0 sample as the positive electrode and the freeze-dried reductive graphene oxide(F-RGO) as the negative electrode.The hybrid device exhibits excellent electrochemical properties,including a high specific capacity,a long cycle life(86% after5000 cycles at 10 A·g^(-1)),and a maximum energy density of 24.2 Wh·kg^(-1)@725.4 W·kg^(-1).

Coral-like cobalt selenide/carbon nanosheet arrays attached on carbon nanofibers for high-rate sodium-ion storage

Cobalt selenide(CoSe_(2))has become a promising anode material for sodium-ion batteries(SIBs)due to its stable chemical properties,environmental friendliness,and high theoretical capacity.However,the undesirable rate capacity and cycle stability of the anode materials largely limit its applications for SIBs due to the relatively low electronic conductivity and huge volume change during the Na+insertion/extraction.In this study,electrostatic spinning combined with a wet chemical method is employed to synthesize coral-like composite material(CNF@c-CoSe_(2)/C),which is composed of CoSe_(2)/carbon nanosheet arrays(CoSe_(2)/C)and carbon nanofibers(CNFs).CoSe_(2)/C nanoflakes derived from metal-organic frameworks(MOFs)with high surface area and the porous structure can inhibit the pulverization and amorphization of CoSe_(2) during charge and discharge processes,thus significantly keeping the stability of the microstructure.CNF can limit the overgrowth of nanosheets and serve as a conductive skeleton.Compared to two-dimensional CoSe_(2)/C nanoflakes and pure CoSe_(2) nanoparticles,the composite can expose more active sites and effectively accelerate the diffusion of Na+,which displays enhanced rate capability(266.5 mAh·g^(-1) at 5.0 A·g^(-1))and cycling stability(268.3 mAh·g^(-1) after 100 cycles at 1.0 A·g^(-1)).Moreover,the rational preparation strategy for metal selenide-based heterostructure material presents a new way for high-performance SIB s.

中南半岛热带森林光合碳同化的季节动态

热带森林因其生物量巨大、结构复杂和生物多样而著称。然而,关于这些森林光合作用的季节动态及其少水期间的生态适应仍知之甚少。本文利用中南半岛上跨20个纬度(2°-22°N)的自然梯度带,探讨了季节性水分条件变化对中南半岛热带森林光合作用季节动态的影响及其机理。研究结果表明,对于气候季节性明显的热带森林,不论其为常绿、落叶还是半落叶,其雨季的森林冠层光合作用(或称总初级生产总值,GPP)明显高于旱季。缺乏气候季节性的常湿热带雨林,GPP呈现“双峰”季节格局;而且,这种季节格局与太阳辐射之间有较好的对应关系。旱季或者是短干旱期内,冠层导度(Gs)有明显下降,显示出水分对气孔开度的抑制作用。然而,这种气孔开度的降低,并未导致近赤道的常湿低地雨林GPP的下降。也就是说,常湿低地雨林GPP在季节尺度上,表现为光限制而非水分限制。气候季节性明显的3个站点,不论Gs还是GPP在旱季明显低于雨季,则表现出明显的水分限制。

Structural evolution of mesoporous graphene/LiNi_(1/3)Co_(1/3)Mn_(1/3)O_(2) composite cathode for Li-ion battery

Layered LiMO_(2)(M=Ni,Co,and Mn) is a type of promising cathode materials for high energy density and high work voltage lithium-ion batteries.However,the poor rate performance and low power density hinder its further applications.The capacity fade is related to the structural transformation in the layered LiMO_(2).In this work,the structural changes of bi-material cathode composed of mesoporous graphene and layered LiNi_(1/3)Co_(1/3)Mn_(1/3)O_(2)(NCM) were studied via in situ X-ray diffraction(XRD).During different C-rate charge-discharge test at the voltage range of 2.5-4.1 V,the composite cathode of NCM-graphene(NCM-G) reveals better rate performances than pure NCM cathode.The NCM-G composite electrode displays a higher rate capability of 76.7 mAh·g^(-1) at 5 C rate,compared to the pure NCM cathode of 69.8 mAh·g^(-1)discharge capacity.The in situ XRD results indicate that a reversible phase transition from hexagonal H1 to hexagonal H2 occurs in layered NCM material during 1 C chargedischarge process.With the current increasing to 2 C/5 C,the structure of layered NCM material for both electrodes reveals few changes during charge and discharge processes,which indicates the less utilization of NCM component at high C-rates.Hence,the improved rate performance for bi-material electrode is attributed to the highly conductive mesoporous graphene and the synergistic effect of mesoporous graphene and NCM material.

Recovery of iron from copper slag via modified roasting in CO-CO2 mixed gas and magnetic separation

A novel technology,modified roasting in CO-CO2 mixed gas and magnetic separation,was presented to recover iron from copper slag.The effects of various parameters such as dosage of flux(CaO),gas flowrate of CO and CO2,roasting temperature,roasting time,particle size of modified slag and magnetic flux density on the oxidized modification and magnetic separation were investigated by comparison of the X-ray diffraction patterns and iron recovery ratio.The optimum conditions for recovering iron by oxidizing roasting and magnetic separation are as follows:calcium oxide content of 25 wt.%,mixed gas flow rates of CO2 and CO of 180 and 20 mL/min,oxidizing roasting at 1323 K for 2 h,grinding the modified slag to 38.5-25.0μm and magnetic separation at 170 mT.The mineralogical and microstructural characteristics of modified slag revealed that the iron-bearing minerals in the copper slag were oxidized,the generated magnetite grew into large particles,and the silicate in copper slag was combined with calcium oxide to form calcium silicate.Finally,the iron-bearing concentrate with an iron grade of 54.79%and iron recovery ratio of 80.14%was effectively obtained.

A new energy landscape paving heuristic for satellite module layouts

卫星舱布局问题是一种带性能约束的三维布局优化问题,已经被证明具有NP难度。通过采用拟物策略和罚函数方法,我们将该问题转化为一个不带约束的优化问题。势能曲面变平法(energy landscape paving,ELP)是一个经典的基于蒙特卡洛的全局优化算法,已被成功应用于许多优化问题。ELP能够通过在复杂的势能曲面随机行走来搜索低能构形。然而,当ELP陷入又窄又深的势能曲面山谷时,它很难逃离。通过提出ELP方法中直方图函数的一种新的更新机制,我们获得了一种改进的势能曲面变平法。通过将带局部搜索的梯度法融入改进的ELP方法,为卫星舱布局问题提出了一种新的全局搜索方法 n ELP。本文测试了来自文献的两个有代表性的算例。计算结果显示,n ELP是求解带性能约束的卫星舱布局问题的有效算法。