Kinetic Energy Driven Superconductivity in the Electron Doped CobaltateNa_xCoO_2 · gH_2O

Within the charge-spin separation fermion-spin theory, we show that themechanism of superconductivity in the electron doped cobaltate Na_x CoO_2 · gH_2O is ascribed toits kinetic energy. The dressed fermions interact occurring directly through the kinetic energy byexchanging magnetic excitations. This interaction leads to a net attractive force between dressedfermions, then the electron Cooper pairs originating from the dressed fermion pairing state are dueto the charge-spin recombination, and their condensation reveals the superconducting ground state.The superconducting transition temperature is identical to the dressed fermion pair transitiontemperature, and is suppressed to a lower temperature due to the strong magnetic frustration. Theoptimal superconducting transition temperature occurs in the electron doping concentration δ ≈0.29, and then decreases for both underdoped and overdoped regimes, in qualitative agreement withthe experimental results.

Coupled cobalt-doped molybdenum carbide@N-doped carbon nanosheets/nanotubes supported on nickel foam as a binder-free electrode for overall water splitting

In an attempt to develop low-cost,non-noble-metal bifunctional electrocatalysts for water electrolysis in alkaline media,cobalt-doped molybdenum carbide@N-doped carbon nanosheets/nanotubes were fabricated by using C3N4 as the carbon source on a 3D porous nickel foam substrate.Benefiting from the optimized electronic structure and enhanced mass and charge transport,as well as the 3D conducting pathway,MoxCoy@N-CNSs/CNTs shows superior performance towards both the hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)in an alkaline medium.The optimal electrocatalyst is Mo2Co1@N-CNSs/CNTs,which reveals a current density of 10 mA cm^-2 at the low overpotentials of 99 mV and 300 mV for the HER and OER,respectively,and a relatively low cell voltage(1.63 V)for the overall water electrolysis.The method of optimizing the composition and nanostructure of a material provides a new avenue for the development and utilization of high-performance electrocatalysts.

Bandgap Saturation in Room Temperature Synthesized Cobalt Doped ZnS Nanoparticles

In this study,cobalt doped ZnS nanoparticles(NPs)have been synthesized by simple chemical precipitation method with six different weight percentages(0.0,0.1,0.3,0.5,0.7 and 1.0%)of cobalt content at room temperature(30°C).X-ray diffraction(XRD)patterns of the samples revealed the formation of cubic structure and calculated particle size were found to be nano-sized.Optical band gap values have been obtained from UV-Vis absorption spectra.It has also been found that energy band gap(Eg)increases with the increase in molar concentration of reactant solution and the variation of bandgap was between 5.30-6.01 eV with cobalt doping.

Synthesis and characterization of ZnS-based quantum dots to trace low concentration of ammonia

In the present work,a solution-based co-precipitation method has been adopted to synthesize pure and cobalt-doped ZnS quantum dots and characterized by XRD,SEM,TEM with EDX,FTIR and gas sensing properties.XRD analysis has shown a single phase of ZnS quantum dots having a zinc blend structure.TEM and XRD line broadening indicated that the average crystallite size in the sample is in the range of 2 to 5 nm.SEM micrographs show spherical-shaped quantum dots.FTIR studies show that cobalt has been successfully doped into the ZnS cubic lattice.EDX spectra have analyzed the elemental presence in the samples and it is evident that the spectra confirmed the presence of cobalt(Co),zinc(Zn),oxygen(O),and sulphur(S)elements only and no other impurities are observed.The ZnS-based quantum dot sensors reveal high sensitivity towards 50 ppm of ammonia vapors at an operating temperature of 70℃.Hence,ZnS-based quantum dots can be a promising and quick traceable sensor towards ammonia sensing applications with good response and recovery time.

Boosting the Activity and Stability with Dual-Metal-N Couplings for Li–O_(2)Battery

Electrocatalysts with high efficiency are crucial for improving the storage capacity and electrochemical stability of lithium–oxygen batteries(LOBs).In this work,through a facile hydrothermal method,cobalt–nitrogen-doped carbon nanocubes(Co–N/C),the calcination products of zeolitic imidazolate framework(ZIF–67)are encapsulated by ultrathin C–MoS_(2) nanosheets to obtain Co–N/C@C–MoS_(2) composites which are used as host materials for the oxygen cathode.The synergistic effect between Co–N_(x) active sites and Mo–N coupling centers effectively promotes the formation and decomposition of Li_(2)O_(2) during repeated discharge and charge process.The mesoporous C–MoS_(2) nanosheets with delicately designed morphology facilitate charge transfer and account for improved reaction kinetics and more importantly,suppressed side reactions between the carbon materials and the electrolyte.The oxygen cathode with the Co–N/C@C–MoS_(2)host shows a high initial discharge specific capacity of 21197 mAh g^(-1)and a long operation life of 332 cycles.Theoretical calculation provides in-depth explanation for the reaction mechanism and offers insights for the rational design of electrocatalysts for LOBs.

Alloying cobalt with ruthenium in nitrogen doped graphene layers for developing highly active hydrogen evolution electrocatalysts in alkaline media

Subject Code:B01With the support by the National Natural Science Foundation of China,a creative study by the research group led by Prof.Chen Qianwang(陈乾旺)from the University of Science and Technology of China and High Magnetic Field Laboratory,Hefei Institutes of Physical Science,Chinese Academy of

Noble-metal-free catalyst with enhanced hydrogen evolution reaction activity based on granulated Co-doped Ni-Mo phosphide nanorod arrays

The development of noble-metal-free electrocatalysts for water splitting is indispensable for the efficient production of hydrogen fuel.Herein,a Co-doped Ni-Mo phosphide nanorod arrays fabricated on porous Ni foam was shown to be an efficient binder-free electrocatalyst for water splitting.This catalyst featured exceptional activity,exhibiting an overpotential of 29 mV at a current density of 10 mA·cm−2 for the hydrogen evolution reaction,whereas the corresponding precatalyst exhibited an overpotential of 314 mV at a current density of 50 mA·cm^−2 for the oxygen evolution reaction.The achieved electrocatalytic performance provided access to a simple water splitting system,affording a current density of 10 mA·cm^−2 at 1.47 V in 1 M KOH electrolyte.Density functional theory results indicated that Co doping and phosphorization were responsible for the high electrocatalytic performance.Thus,this work paves the way for the development of novel noble-metal-free electrocatalysts for practical H2 production via water splitting.

Promotional effect of cobalt doping on catalytic performance of cryptomelane-type manganese oxide in toluene oxidation

The cryptomelane-type manganese oxide (OMS-2)-supported Co (x Co/OMS-2;x=5,10,and15 wt.%) catalysts were prepared via a pre-incorporation route.The as-prepared materials were used as catalysts for catalytic oxidation of toluene (2000 ppmV).Physical and chemical properties of the catalysts were measured using the X-ray diffraction (XRD),Fourier transform infrared spectroscopic (FT-IR),scanning electron microscopic (SEM),X-ray photoelectron spectroscopy (XPS),and hydrogen temperature-programmed reduction (H_(2)-TPR)techniques.Among all of the catalysts,10Co/OMS-2 performed the best,with the T90%,specific reaction rate at 245℃,and turnover frequency at 245℃ (TOFCo) being 245℃,1.23×10^(-3)moltoluene/(gcat·sec),and 11.58×10^(-3)sec-1for toluene oxidation at a space velocity of 60,000mL/(g·hr),respectively.The excellent catalytic performance of 10Co/OMS-2 were due to more oxygen vacancies,enhanced redox ability and oxygen mobility,and strong synergistic effect between Co species and OMS-2 support.Moreover,in the presence of poisoning gases CO_(2),SO_(2)or NH_(3),the activity of 10Co/OMS-2 decreased for the carbonate,sulfate and ammonia species covered the active sites and oxygen vacancies,respectively.After the activation treatment,the catalytic activity was partly recovered.The good low-temperature reducibility of 10Co/OMS-2 could also facilitate the redox process accompanied by the consecutive electron transfer between the adsorbed O_(2)and the cobalt or manganese ions.In the oxidation process of toluene,the benzoic and aldehydic intermediates werefirst generated,which were further oxidized to the benzoate intermediate that were eventually converted into H_(2)O and CO_(2).

Enhanced electrochemical performance of CoNiS_(x)@Ti_(3)C_(2)T_(x)electrode material through in-situ doping of cobalt element

The composite electrode of CoNiS_(x)and Ti_(3)C_(2)T_(x)MXene was successfully prepared using a onestep hydrothermal method under the in-situ doping of the cobalt element.The effects of in-situ doping of the cobalt element on the micromorphology and electrochemical performance of the electrodes were investigated.After insitu doping of the cobalt element,NiS with a needle-like structure was converted into a CoNiS_(x)with petal-like structure.The petal-like CoNiS_(x)with a rough surface was very dense and evenly wrapped on the surface and interlamination of Ti_(3)C_(2)T_(x),which helped increase the specific surface area and pore volume of the electrode.Under the identical test conditions,CoNiS_(x)@Ti_(3)C_(2)T_(x)had a higher specific capacitance and capacitance retention than NiS@Ti_(3)C_(2)T_(x).This result indicated that the in-situ doping of the cobalt element promoted the electrochemical performance of the electrode.The energy density of the CoNiS_(x)@Ti_(3)C_(2)T_(x)/nickel foam(NF)//activated carbon(AC)/NF asymmetric supercapacitor device was 59.20 Wh·kg^(–1)at a power density of 826.73 W·kg^(–1),which was much higher than that of NiS@Ti_(3)C_(2)T_(x)/NF//AC/NF.Three CoNiS_(x)@Ti_(3)C_(2)T_(x)/NF//AC/NF in series were able to illuminate the light emitting diode lamp for about 10 min,which was higher than the 5 min of three NiS@Ti_(3)C_(2)T_(x)/NF//AC/NF in series under the same condition.The CoNiS_(x)@Ti_(3)C_(2)T_(x)/NF//AC/NF with high energy density had better application potential in energy storage than the NiS@Ti_(3)C_(2)T_(x)/NF//AC/NF.

Carbon polyhedra encapsulated Si derived from Co-Mo bimetal MOFs as anode materials for lithium-ion batteries

Silicon(Si)holds promise as an anode material for lithium-ion batteries(LIBs)as it is widely avail-able and characterized by high specific capacity and suitable working potential.However,the relatively low electrical conductivity of Si and the significantly high extent of volume expansion realized dur-ing lithiation hinder its practical application.We prepared N-doped carbon polyhedral micro cage en-capsulated Si nanoparticles derived from Co-Mo bimetal metal-organic framework(MOFs)(denoted as Si/CoMo@NCP)and explored their lithium storage performance as anode materials to address these prob-lems.The Si/CoMo@NCP anode exhibited a high reversible lithium storage capacity(1013 mAh g^(−1)at 0.5 A g^(−1)after 100 cycles),stable cycle performance(745 mAh g^(−1)at 1 A g^(−1)after 400 cycles),and excellent rate performance(723 mAh g^(−1)at 2 A g^(−1)).Also,the constructed the full-cell NCM 811//Si/CoMo@NCP exhibited well reversible capacity.The excellent electrochemical performances of Si/CoMo@NCP were at-tributed to two unique properties.The encapsulation of NCP with doped nitrogen and porous structural carbon improves the electrical conductivity and cycling stability of the molecules.The introductions of metallic cobalt and its oxides help to improve the rate capability and lithiation capacity of the materials following multi-electron reaction mechanisms.