Multifunctional Film Assembled from N‑Doped Carbon Nanofiber with Co–N_(4)–O Single Atoms for Highly Efficient Electromagnetic Energy Attenuation

Single-atom materials have demonstrated attractive physicochemical characteristics.However,understanding the relationships between the coordination environment of single atoms and their properties at the atomic level remains a considerable challenge.Herein,a facile waterassisted carbonization approach is developed to fabricate well-defined asymmetrically coordinated Co–N_(4)–O sites on biomass-derived carbon nanofiber(Co–N_(4)–O/NCF)for electromagnetic wave(EMW)absorption.In such nanofiber,one atomically dispersed Co site is coordinated with four N atoms in the graphene basal plane and one oxygen atom in the axial direction.In-depth experimental and theoretical studies reveal that the axial Co–O coordination breaks the charge distribution symmetry in the planar porphyrin-like Co–N_(4) structure,leading to significantly enhanced dielectric polarization loss relevant to the planar Co–N_(4) sites.Importantly,the film based on Co–N_(4)–O/NCF exhibits light weight,flexibility,excellent mechanical properties,great thermal insulating feature,and excellent EMW absorption with a reflection loss of−45.82 dB along with an effective absorption bandwidth of 4.8 GHz.The findings of this work offer insight into the relationships between the single-atom coordination environment and the dielectric performance,and the proposed strategy can be extended toward the engineering of asymmetrically coordinated single atoms for various applications.

PVDF/6H-SiC composite fiber films with enhanced piezoelectric performance by interfacial engineering for diversified applications

Piezoelectric silicon carbide(SiC)has been quite attractive due to its superior chemical and physical properties as well as wide potential applications.However,the inherent brittleness and unsatisfactory piezoelectric response of piezoelectric semiconductors remain the major obstacles to their diversified applications.Here,flexible multifunctional PVDF/6H-SiC composite fiber films are fabricated and utilized to assemble both piezoelectric nanogenerators(PENGs)and stress/temperature/light sensors.The open cir-cuit voltage(V_(oc))and the density of short circuit current(I_(sc))of the PENG based on the PVDF/5 wt%6H-SiC composite fiber films reach 28.94 V and 0.24μA cm^(-2),showing a significant improvement of 240%and 300%compared with that based on the pure PVDF films.The effect of 6H-SiC nanoparticles(NPs)on inducing interfacial polarization and stress concentration in composite fiber films is proved by first-principles calculation and finite element analysis.The stress/temperature/light sensors based on the composite fiber film also show high sensitivity to the corresponding stimuli.This study shows that the PVDF/6H-SiC composite fiber film is a promising candidate for assembling high-performance energy harvesters and diverse sensors.

Revealing the interface-rectifying functions of a Li-cyanonaphthalene prelithiation system for SiO electrode

Chemical prelithiation is regarded as a crucial method for improving the initial Coulombic efficiency(ICE)of Li-storage anodes.Herein,a substituent-engineered Li-cyanonaphthalene chemical prelithiation system is designed to simultaneously enhance the ICE and construct a multifunctional interfacial film for SiO electrodes.X-ray photoelectron spectroscopy(XPS),electron energy-loss spectroscopy(EELS),nuclear magnetic resonance(NMR)spectroscopy and atomic force microscopy(AFM)prove that the Licyanonaphthalene prelithiation reagent facilitates the formation of a rectified solid electrolyte interface(SEI)film in two ways:(1)generation of a gradient SEI film with an organic outer layer(dense Ncontaining organics,ROCO_(2)Li)and an inorganic LiF-enriched inner layer;(2)homogenization of the horizontal distribution of the composition,mechanical properties and surface potential.As a result,the prelithiated SiO electrode exhibits an ICE above 100%,enhanced CEs during cycling,better cycle stability and inhibition of lithium dendrite formation in the overcharged state.Notably,the prelithiated hard carbon/SiO(9:1)‖LHCoO_(2) cell displays an enhancement in the energy density of 62.3%.