Energy transfer,luminescence properties,and thermal stability of color tunable barium pyrophosphate phosphors

A series of barium pyrophosphate Ba2P2O7(BPO)phosphors doped with Ce3+or Tb3+ions is synthesized via a co-precipitation method under reducing atmosphere.The phase structures,photoluminescence(PL)properties,and thermal stabilities of the samples are characterized by using powder x-ray diffraction(PXRD)and PL spectra.The emission colors of samples can be tuned from blue(0.1544,0.0310)to green(0.2302,0.4229)by changing the doping concentrations of Tb3+under ultraviolet excitation.The energy transfer mechanism between Ce3+and Tb3+in the BPO is dipole–dipole interaction with a critical distance of 25.86°A and an energy transfer efficiency of about 85%,which are determined through the PL spectrum and the decay curve.Moreover,the Ce3+/Tb3+co-doped sample has good thermal stability for temperature quenching,and the emission intensity at 423 K is maintained at 95%measured at 298 K.The above results show that the BPO:Ce3+,Tb3+can serve as a promising candidate of green emitting phosphor for solid-state lighting.

N-doped porous carbon nanofibers sheathed pumpkin-like Si/C composites as free-standing anodes for lithium-ion batteries

Dramatic capacity fading and poor rate performance are two main obstacles that severely hamper the widespread application of the Si anode owing to its large volume variation during cycling and low intrinsic electrical conductivity.To mitigate these issues,free-standing N-doped porous carbon nanofibers sheathed pumpkin-like Si/C composites(Si/C-ZIF-8/CNFs)are designed and synthesized by electrospinning and carbonization methods,which present greatly enhanced electrochemical properties for lithium-ion battery anodes.This particular structure alleviates the volume variation,promotes the formation of stable solid electrolyte interphase(SEI)film,and improves the electrical conductivity.As a result,the as-obtained free-standing Si/C-ZIF-8/CNFs electrode delivers a high reversible capacity of 945.5 mAh g^(-1) at 0.2 A g^(-1) with a capacity retention of 64% for 150 cycles,and exhibits a reversible capacity of 538.6 mA h g^(-1) at 0.5 A g^(-1) over 500 cycles.Moreover,the full cell composed of a freestanding Si/C-ZIF-8/CNFs anode and commercial LiNi_(1/3)Co_(1/3)Mn_(1/3)O_(2)(NCM)cathode shows a capacity of 63.4 mA h g^(-1) after 100 cycles at 0.2 C,which corresponds to a capacity retention of 60%.This rational design could provide a new path for the development of high-performance Si-based anodes.

Sandwiching Sulfur into the Dents Between N,O Co-Doped Graphene Layered Blocks with Strong Physicochemical Confinements for Stable and High-Rate Li-S Batteries

The development of lithium-sulfur batteries(LSBs)is restricted by their poor cycle stability and rate performance due to the low conductivity of sulfur and severe shuttle effect.Herein,an N,O co-doped graphene layered block(NOGB)with many dents on the graphene sheets is designed as effective sulfur host for high-performance LSB s.The sulfur platelets are physically confined into the dents and closely contacted with the graphene scaffold,ensuring structural stability and high conductivity.The highly doped N and O atoms can prevent the shuttle effect of sulfur species by strong chemical adsorption.Moreover,the micropores on the graphene sheets enable fast Li^+transport through the blocks.As a result,the obtained NOGB/S composite with 76 wt%sulfur content shows a high capacity of 1413 mAh g^-1 at 0.1 C,good rate performance of 433 mAh g^-1 at 10 C,and remarkable stability with 526 mAh g^-1 at after 1000 cycles at 1 C(average decay rate:0.038%per cycle).Our design provides a comprehensive route for simultaneously improving the conductivity,ion transport kinetics,and preventing the shuttle effect in LSBs.

Earth-abundant coal-derived carbon nanotube/carbon composites as efficient bifunctional oxygen electrocatalysts for rechargeable zinc-air batteries

The exploration of active and robust electrocatalysts for both the oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)is the bottleneck to realize the commercialization of rechargeable metal-air batteries and regenerative fuel cells.Here we report facile synthesis of three-dimensional(3 D)carbon nanotube(CNT)/carbon composites using earth-abundant coal as the carbon source,hydrogen reductant and heteroatom dopant to grow CNTs.The prepared composite featuring 3 D structural merits and multiple active sites can efficiently catalyze both ORR and OER,affording high activity,fast kinetics,and long-term stability.With the additional incorporation of manganese,the developed catalyst afforded a potential difference of 0.80 V between ORR at the half wave potential and OER at a current density of 10 mA cm^(-2).The optimized sample has presented excellent OER performance within a constructed solar-powered water splitting system with continuously generating oxygen bubbles at anode.Notably,it can be further used as a durable air-electrode catalyst in constructed Zn-air battery,delivering an initial discharge/charge voltage gap of 0.73 V,a remained voltaic efficiency of 61.2%after 160 cycles and capability to power LED light for at least 80 h.This study provides an efficient approach for converting traditional energy resource i.e.coal to value-added alternative oxygen electrocatalysts in renewable energy conversion systems.

Porous LiFePO_(4)/NiP Composite Nanospheres as the Cathode Materials in Rechargeable Lithium Ion Batteries

We report the synthesis of porous LiFePO4/NiP composite nanospheres and their application in rechargeable lithium-ion batteries.A simple one-step spraying technique was developed to prepare LiFePO_(4)/NiP composite nanospheres with an electrical conductivity 10^(3)-10^(4) times that of bulk particles of LiFePO_(4).Electrochemical measurements show that LiFePO_(4) nanospheres with a uniform loading of 0.86 wt%1.50 wt%NiP exhibit high discharge capacity,good cycling reversibility,and low apparent activation energies.The superior electrode performance of the as-prepared composite nanospheres results from the greatly enhanced electrical conductivity and porous structure of the materials.

Rational design of nitrogen doped hierarchical porous carbon for optimized zinc-ion hybrid supercapacitors

Aqueous rechargeable zinc-ion hybrid supercapacitors are considered to be a promising candidate for large-scale energy storage devices owing to their high safety,long life,and low price.In this paper,a nitrogen doped hierarchical porous carbon is evaluated as the cathode for aqueous rechargeable zinc-ion hybrid supercapacitors.Benefiting from the synergistic merits of excellent structural features of N-HPC and tiny zinc dendrite of Zn anode in ZnSO4 electrolyte,the zinc-ion hybrid supercapacitor exhibits excellent energy storage performance including high capacity of 136.8 mAh·g^−1 at 0.1·Ag^−1,high energy density of 191 Wh·kg^−1,large power density of 3,633.4 W·kg^−1,and satisfactory cycling stability of up to 5,000 cycles with a capacity retention of 90.9%.This work presents a new prospect of developing high-performance aqueous rechargeable zinc ion energy storage devices.

Ni_(1-x)Pt_(x) (x=00.08) Films as the Photocathode of Dye-Sensitized Solar Cells with High Effi ciency

Films of Ni_(1-x)Pt_(x)(x=0,0.02,0.04,0.06,and 0.08)have been prepared on fluorine-doped tin oxide-coated(FTO)glass substrates by a chemical plating method and used as the photocathode for dye-sensitized solar cells(DSCs).The Ni_(0.94)Pt_(0.06 )film consisted of nanoparticles with a size of 46 nm and a Pt loading of 5.13μg/cm^(2).The Ni_(0.94)Pt_(0.06) photocathode exhibited high catalytic performance toward triiodide reduction,high light refl ectance,and low charge-transfer resistance.The DSC assembled with the Ni_(0.94)Pt_(0.06) photocathode gave a short-circuit photocurrent density(Jsc)of 16.79 mA/cm^(2),an open-circuit photovoltage(Voc)of 736 mV,and a fi ll factor(FF)of 66.4%,corresponding to an overall conversion effi ciency of 8.21%under standard AM 1.5 irradiation(100 mW/cm^(2)),which is higher than that for the DSC with a pure Pt photocathode obtained by conventional thermal decomposition.Furthermore,the DSC based on the Ni0.94Pt0.06 photocathode showed good stability.The results indicate that Ni0.94Pt0.06 fi lms are promising low-cost and high-performance photocathodes for use in DSCs.

Mg micro/nanoscale materials with sphere-like morphologies:Size-controlled synthesis and characterization

Mg micro/nanoscale materials with sphere-like morphologies are prepared via a vapor-transport deposition process. The structure and morphology of the asprepared products are characterized by powder X-ray diffraction and scanning electron microscopy. Vapor-liquid-solid mechanism is proposed to explain the formation of Mg micro/nanospheres on the basis of the experimental results.

Design of layered-stacking graphene assemblies as advanced electrodes for supercapacitors

Graphene is a competitive electrode material for supercapacitors due to its unique two-dimensional structure,large surface area,high conductivity,and good physicochemical stability.However,random agglomeration and restacking of graphene sheets result in a reduced surface area and a loose structure with low density,which severely restricts the application for high gravimetric/volumetric energy density devices.Rational design of the layered-stacking structure of graphene assemblies can effectively prevent the restacking of graphene sheets,construct efficient ion transport channels,and improve spatial utilization,demonstrating the huge potential for developing advanced electrode materials.Herein,from the aspect of improving the electrochemical kinetics through designing efficient electron and ion transport paths,we first highlight the advantages of layered-stacking graphene assemblies,describe some common routes for preparing graphene building units,and then summarize the novel methods to design layered-stacking structures.A comprehensive review of the typical structure including nanocarbon pillared graphene,porous graphene blocks,and graphene ribbon films is provided with a focus on the mechanisms behind the performance improvements.Finally,critical challenges and some general ideas for future development are proposed,which may open up new opportunities for material chemistry and device innovation.

Visible-light-driven external-photocatalyst-free alkylative carboxylation of alkenes with CO_(2)

Herein,we report a novel protocol for visible-light-driven alkylative carboxylation of alkenes with CO_(2) in the absence of external photocatalyst.Under the irradiation of visible light,a variety of 4-alkyl-1,4-dihydropyridines(alkyl-DHPs)serve as not only alkyl radical precursors but also photoexcited reductants probably with the potential to reduce benzyl radicals.Several styrenes and acrylates are applicable in this reaction to give structurally diverse carboxylic acids in good to excellent yields.These reactions feature mild reaction conditions(1 atm of CO_(2),room temperature,visible light,photocatalyst-and transition metalfree),good functional group tolerance,easy scalability,as well as high regio-,and chemo-selectivity.Mechanistic investigations provide evidence that alkyl radical,benzyl radical and carbanion might be involved in this reaction,providing a novel strategy for CO_(2) utilization.

Preparation and photochromic properties of pyrazolones/polyvinyl alcohol composite films

Novel photochromic composite films have been successfully fabricated by dispersing pyrazolone derivative：1,3-Diphenyl-4-（3-chlorobenzal）-5-hydroxypyrazole 4-phenylsemicarbazone（la） into hydrosol of polyvinyl alcohol（PVA）.The microstructure,photochromic behaviors and thermal bleaching properties were investigated by Raman spectroscopy,X-ray powder diffraction（XRD）,field emission scanning electron microscopy（FE-SEM） and ultraviolet-visible absorption spectroscopy（UV-vis）.The results showed that la was not only blended but also well dispersed in the PVA polymer films with a suitable content of chromophore.Upon UV light irradiation,the composite films gradually changed from colorless to yellow and recovered fully to the initial state upon thermal bleaching.The time constants of photochromic reactions were almost the same as those of la observed in their crystalline state,indicating that the photochromic phenomenon is barely disturbed by the polymer matrix.