Synthesis of Size-Controllable NiCo2S4 Hollow Nanospheres Toward Enhanced Electrochemical Performance

Although the synthesis of novel nanostructured metal sulfides has been well established,further size-controllable optimization is still valuable to enhance their performance for various applications.Herein,a self-template method to size-controllably synthesize the hollow NiCo2S4 nanospheres is reported.Uniformly monodisperse Ni Co precursors with diameter widely ranging from 97 to 550 nm are controllably synthesized and subsequently transformed into hollow NiCo2S4 nanospheres through in situ sulfidation.Smaller nanoparticles’diameter results in the hollow NiCo2S4 nanospheres larger surface area and thinner shell thickness and hence provides much more electrochemical active sites as well as facilitate the ion and electron transfer.Consequently,the hollow NiCo2S4 nanospheres—used as the electrode materials in supercapacitors—achieve 19%enhancement of specific capacity from 484.8 to 575.1 C g-1 through lowering the 42.5%diameter of hollow NiCo2S4 nanospheres from 407 to 234 nm.Moreover,the hollow NiCo2S4 nanospheres with 234 nm diameter exhibit superior rate capacity indicated by 49%capacity retention from 1 to 50 A g-1 and excellent cycling stability(77%after 2000 cycles).Furthermore,this method is a potentially general strategy in the size-controllable synthesis of the metal sulfides hollow nanostructures and results in the remarkable electrochemical applications.

On A Collection of Cold Mountain’s Poems

Cold Mountain,whose date and name was unknown,obscured himself long in the Cuiping Mountain(also known as Cold Cave or Cold Mountain),and set up as Cold Mountain or Man of Cold Mountain.There have been a wide diversity of opinions about his age and all his born days.Principally,there are two centralized views:One holds that Cold Mountain was born in the early Tang Dynasty;the other holds that Cold Mountain was born in the middle period of the Tang Dynasty.The paper followed what had been expounded for further probes.

S1-supported Pd@CeO_(2) quasi-core@shell materials as advanced catalysts for selective hydrogenation of furfural

Bare Pd metal nanoparticles invariably suffer from poor selectivity in furfural hydrogenation by forming flat configurations,with the aromatic ring of the substrate molecules parallel to the metal surface.Herein,we put forward a promising solution by using CeO_(2)as promoters to modify Pd nanoparticles for modulating the adsorption behaviors of furfural molecules.To achieve the highly-desired ultra-small Pd@CeO_(2)core@shell nanostructure,a“constrained auto-redox”synthesis is developed,in which silicalite-1 supports play the key role of providing their surface as the landing place of PdO_(x)precursors for inhibiting the overgrowth and the deformation.To the best of our knowledge,this is one of the smallest core@shell materials obtained from aqueous synthesis.When evaluated as catalysts,Pd@CeO_(2)/S-1 gives 98.9%conversion of furfural with 94.3%selectivity for furfural alcohol in 15 h,which is much better than that of Pd/S-1(88.6%conversion with 44.3%selectively).The DFT simulation reveals a strong interaction between the defects of CeO_(2)and the oxygen atom of the–CHO group in furfural molecules,which benefits the selective hydrogenation occurred in the–CHO group rather than the furan ring.

High-efficiency PdNi single-atom alloy catalyst toward cross-coupling reaction

The preparation of Pd-based catalysts with rich electrons and a high atom dispersion rate is of great significance for improving the reactivity of cross-coupling reactions,which is a powerful tool for pharmaceutical and fine chemical synthesis.Here,we report a PdNi single-atom alloy(SAA)catalyst in which isolated Pd single atoms are anchored onto the surface of Ni nanoparticles(NPs)applied for Suzuki coupling reactions and Heck coupling reactions.The 0.1%PdNi SAA exhibits extraordinary catalytic activity(reaction rate:17,032.25 mmol h^(-1)gPd^(-1))toward the Suzuki cross-coupling reaction between 4-bromoanisole and phenylboronic acid at 80℃for 1 h.The excellent activity is supposed to attribute to the 100 percent utilization rate of Pd atoms and the highly stable surface zero-valance Pd atoms,which provides abundant sites and electrons for the adsorption and fracture of the C-X(X=Cl,Br,I)bond.Moreover,our work demonstrates the excellent application prospect of SAAs for cross-coupling reactions.

Coupling Fe and Mo single atoms on hierarchical N-doped carbon nanotubes enhances electrochemical nitrogen reduction reaction performance

Electrochemical nitrogen reduction reaction(NRR)paves a new way to cost-efficient production of ammonia,but is still challenging in the sluggish kinetics caused by hydrogen evolution reaction competition and chemical inertness of N≡N bond.Herein,we report a“dual-site”strategy for boosting NRR performance.A high-performance catalyst is successfully constructed by anchoring isolated Fe and Mo atoms on hierarchical N doped carbon nanotubes through a facile self-sacrificing template route,which exhibits a remarkably improved NH3 yield rate of 26.8μg·h^(−1)·mg with 11.8%Faradaic efficiency,which is 2.5 and 1.6 times larger than those of Fe/NC and Mo/NC.The enhancement can be attributed to the unique hierarchical structure that profits from the contact of electrode and electrolyte,thus improving the mass and electron transport.More importantly,the in situ Fourier transform infrared spectroscopy(in situ FTIR)result firmly demonstrates the crucial role of the coupling of Fe and Mo atoms,which can efficiently boost the generation and transmission of*N2Hy intermediates,leading to an accelerated reaction rate.

Stress-dissipated conductive polymer binders for high-stability silicon anode in lithium-ion batteries

Silicon-based anodes with high theoretical capacity have intriguing potential applications for high energy density lithium-ion batteries(LIBs),while suffer from immense volumetric change and brittle solidstate electrolyte interface that causes collapse of electrodes.Here,a stress-dissipated conductive polymer binder(polyaniline with citric acid,PC)is developed to enhance the mechanical electrochemical performance between Si nanoparticles(SiNPs)and binders.Benefiting from the stable triangle network node of citric acid and a considerable distributed of hydroxyl groups,the PC binder can effectively dissipate the stress from SiNPs,thus providing an excellent cyclic stability of Si anodes.Both experimental results and theoretical calculation demonstrate the enhanced adhesion between binders and SiNPs could bond the particles tightly to form a robust electrode.The as-fabricated Si anode exhibits outstanding structural stability upon long-term cycles that exhibit a highly reversible capability of 1021 mA·h·g^(-1)over 500 cycles at a current density of 0.5 C(1 C¼4200mA·g^(-1)).Evidently,this stressdissipated binder design will provide a promising route to achieve long-life Si-based LIBs.

From high-yield Ti3AlCN ceramics to high-quality Ti3CNTx MXenes through eliminating Al segregation

Ti3CNTx MXenes with unique electrical conductivity can be widely applied for supercapacitors and electromagnetic shielding.However,its relatively low-yield quaternary nitrogen-containing Ti3AlCN ce ramics precursor(less than 50%),due to the inevitable Al segregation during the synthesizing process,significantly hindered its widely commercial applications.Herein,we employed the controllable AlNoversaturation precursor strategy to precisely tune the phase transition point of quaternary Ti3AlCN ceramics to obtain high-yield Ti3 AlCN precursor for the purpose of high conductivity Ti3 CNTx MXenes.Combined energy dispersive X-ray spectrometer(XRD)with X-ray photoelectron spectroscopy(XPS)characterizations,the yield of the quaternary nitrogen-containing Ti3 AlCN ceramics was evidently proved to be up to 70%,which is 1.4 times than that of previously reported works.Such relatively highyield quaternary Ti3AlCN is mainly ascribed to the elimination of Al segregation.Based on it,we further developed accordion-like two-dimensional(2D)MXene via hydrofluoric acid etch and vacuum freezedry.This novel accordion-like 2D Ti3CNTx MXene possesses high electrochemical capacitive properties(209 F/g).Therefore,this controllable AlN-oversaturation precursor strategy will pave a way to exploit costly high-yield MAX ceramics precursor for high conductivity MXenes and also play a powerful role in promoting their practical applications including electrical and magnetic engineering fields.

Boosting the energy density of aqueous MXene-based supercapacitor by integrating 3D conducting polymer hydrogel cathode

The wide-spread proliferation of aqueous MXene-based supercapacitor has been largely shadowed by the limited cell potential window(typically in the range of 0-0.6 V).To address this baffling issue,designing asymmetric supercapacitor(ASC)is proposed as a rational strategy to enlarge the potential window(thus energy density)of individual cell in aqueous electrolytes.To this date,however,it still remains a great challenge to develop easy fabricating,3D nanostructured,and pseudocapacitive cathode materials that can perfectly match with MXene anodematerials.In this work,we propose a supramolecular strategy to construct conducting polymer hydrogel(CPH)with highly interconnected 3D nanostructures and large pseudocapacitance,which can finely match with 2D Ti_(3)C_(2)T_(x).The as-assembled CPH//Ti_(3)C_(2)T_(x) ASCwith CPH cathode and MXene anode can operate in a broadened potential window of 1.15 V in aqueous PVA/H_(2)SO_(4) gel electrolyte with remarkably improved energy density of 16.6μWh/cm^(2)(nine times higher than that of symmetric MXene supercapacitor).Additionally,this ASC exhibits outstanding cyclic stability with no trackable performance decay over 30,000 galvanostatic charge and discharge cycles.It is demonstrated in this work that employing positive CPH electrode is a feasible yet promising strategy to enhance the potential window and energy density of aqueous MXene supercapacitors.

敦煌语言文学资料的独特价值

1900年敦煌莫高窟藏经洞打开以后,数量多达7万余件的古代写本重现于世,其中包括大量古代文学和语言学资料,多数都是首次面世。研究这些崭新的资料,足以改写中国文学史,并极大地推进汉语史研究的进展。下面简要地介绍敦煌文学、语言学研究的成绩及其意义。

Optimal Grading Policies in the Online Acquisition of Used Products

Although online reverse commerce(recommerce)is convenient and efficient,it is not without caveats.It limits recommerce firms’flexibility to offer personalized prices and may cause mismatched grading between the firms and sellers of used products.This study examines a recommerce firm’s decision on grading criteria and prices.We find that the firm’s optimal policy exhibits two distinctly different patterns depending on the trade value of the product.We demonstrate that sellers’overestimate and underestimate errors have qualitatively different effects on firm profitability,and the effects crucially rely on the type of optimal policy.These findings can apprise firms on how to preset sorting criteria and prices as well as reduce grading errors.