Isolated diatomic Zn-Co metal–nitrogen/oxygen sites with synergistic effect on fast catalytic kinetics of sulfur species in Li-S battery

Lithium-sulfur batteries are severely restricted by low electronic conductivity of sulfur and Li_(2)S,shuttle effect,and slow conversion reaction of lithium polysulfides(LiPSs).Herein,we report a facile and highyield strategy for synthesizing dual-core single-atom catalyst(ZnCoN_(4)O_(2)/CN)with atomically dispersed nitrogen/oxygen-coordinated Zn-Co sites on carbon nanosheets.Based on density functional theory(DFT)calculations and LiPSs conversion catalytic ability,ZnCoN_(4)O_(2)/CN provides dual-atom sites of Zn and Co,which could facilitate Li^(+)transport and Li_(2)S diffusion,and catalyze LiPSs conversion more effectively than homonuclear bimetallic single-atom catalysts or their simple mixture and previously reported singleatom catalysts.Li-S cell with ZnCoN_(4)O_(2)/CN modified separator showed excellent rate performance(789.4 mA h g^(-1)at 5 C)and stable long cycle performance(0.05%capacity decay rate at 6C with 1000cycles,outperforming currently reported single atomic catalysts for LiPSs conversion.This work highlights the important role of metal active centers and provides a strategy for producing multifunctional dual-core single atom catalysts for high-performance Li-S cells.

A flexible and superhydrophobic upconversionluminescence membrane as an ultrasensitive fluorescence sensor for single droplet detection

A Ln^(3+)-doped(Yb^(3+),Tm^(3+)or Yb^(3+),Er^(3+)co-doped)NaYF4 nanoparticle/polystyrene hybrid fibrous membrane(HFM)was fabricated using an electrospinning technique.The HFM shows upconversion luminescence(UCL),flexibility,superhydrophobicity and processability.The UCL membrane can be used as a fluorescence sensor to detect bioinformation from a single water droplet(~10μl).Based on the fluorescence resonance energy transfer,the detection limits of this sensor can reach 1 and 10 ppb for the biomolecule,avidin,and the dye molecule,Rhodamine B,respectively,which are superior to most of the fluorescence sensors reported in previous works.After the fluorescence detection,the target droplet was easily removed without residues on the UCL membrane surface due to its superhydrophobic property,which exhibits an excellent recyclability that cannot be achieved by traditional liquid-based detection systems.