Potassium-ion batteries(PIBs)are considered promising alternatives to lithium-ion batteries owing to cost-effective potassium resources and a suitable redox potential of-2.93 V(vs.-3.04 V for Li+/Li).However,the explo...Potassium-ion batteries(PIBs)are considered promising alternatives to lithium-ion batteries owing to cost-effective potassium resources and a suitable redox potential of-2.93 V(vs.-3.04 V for Li+/Li).However,the exploration of appro-priate electrode materials with the correct size for reversibly accommodating large K+ions presents a significant challenge.In addition,the reaction mecha-nisms and origins of enhanced performance remain elusive.Here,tetragonal FeSe nanoflakes of different sizes are designed to serve as an anode for PIBs,and their live and atomic-scale potassiation/depotassiation mechanisms are revealed for the first time through in situ high-resolution transmission electron micros-copy.We found that FeSe undergoes two distinct structural evolutions,sequen-tially characterized by intercalation and conversion reactions,and the initial intercalation behavior is size-dependent.Apparent expansion induced by the intercalation of K+ions is observed in small-sized FeSe nanoflakes,whereas unexpected cracks are formed along the direction of ionic diffusion in large-sized nanoflakes.The significant stress generation and crack extension originating from the combined effect of mechanical and electrochemical interactions are elucidated by geometric phase analysis and finite-element analysis.Despite the different intercalation behaviors,the formed products of Fe and K_(2)Se after full potassiation can be converted back into the original FeSe phase upon depotassiation.In particular,small-sized nanoflakes exhibit better cycling perfor-mance with well-maintained structural integrity.This article presents the first successful demonstration of atomic-scale visualization that can reveal size-dependent potassiation dynamics.Moreover,it provides valuable guidelines for optimizing the dimensions of electrode materials for advanced PIBs.展开更多
Nanoparticles of tin-doped ferrites SnxFe3-xO4 (x=0, 0.1, 0.2, 0.3, 0.4, 1.0) were prepared by the precipitation exchange method. The particles of all specimens are crystalline with mean diameter in the range of 4-8 n...Nanoparticles of tin-doped ferrites SnxFe3-xO4 (x=0, 0.1, 0.2, 0.3, 0.4, 1.0) were prepared by the precipitation exchange method. The particles of all specimens are crystalline with mean diameter in the range of 4-8 nm, and the lattice parameters enlarge with increasing tin content. Magnetization and Mssbauer data indicate that the specimens are paramagnetic. The saturation magnetization decreases, as well as the magnetization and the coercive field increase, with increasing tin-content, the possible causes of which were discussed.展开更多
CdS nanoclusters were synthesized by using n-octylthiol as a ligand and n-hexadecyltrimethyl-ammonium bromide (or n-tetrabutylammonium bromide) as an organic cation. Sizeselective precipitation techniques have enabled...CdS nanoclusters were synthesized by using n-octylthiol as a ligand and n-hexadecyltrimethyl-ammonium bromide (or n-tetrabutylammonium bromide) as an organic cation. Sizeselective precipitation techniques have enabled the preparation of different CdS Q-nanoparticles with narrow size distribution and mean diameters ranging from 2 to 5 nm. UV-Vis spectroscopy, transmission electron microscopy and small-angle X-ray scattering were used to determine the mean cluster size. Their size quantization effect has been observed in UV-Vis spectra, fluorescence spectra and small-angle X-ray diffraction, but it became too weak to be observed for large particles (2r > 10 nm). Moreover, their photo-catalysis has been studied by ESR technique and the results revealed that the photo-catalytic reaction occurred in the solution system and some free radicals such as CH2-OH in methanol, or CH3-CH-OH in ethanol were generated if some CdS Q-particles were added to methanol (or ethanol) and initiated by UV light at the same time, which may be very crucial in organic synthesis.展开更多
基金This work was supported by the National Key R&D Program of China(Grant No.2018YFB1304902)the National Natural Science Foundation of China(Grant Nos.12004034,U1813211,22005247,11904372,51502007,52072323,52122211,12174019,and 51972058)+1 种基金the Gen-eral Research Fund of Hong Kong(Project No.11217221)China Postdoctoral Science Foundation Funded Project(Grant No.2021M690386).
文摘Potassium-ion batteries(PIBs)are considered promising alternatives to lithium-ion batteries owing to cost-effective potassium resources and a suitable redox potential of-2.93 V(vs.-3.04 V for Li+/Li).However,the exploration of appro-priate electrode materials with the correct size for reversibly accommodating large K+ions presents a significant challenge.In addition,the reaction mecha-nisms and origins of enhanced performance remain elusive.Here,tetragonal FeSe nanoflakes of different sizes are designed to serve as an anode for PIBs,and their live and atomic-scale potassiation/depotassiation mechanisms are revealed for the first time through in situ high-resolution transmission electron micros-copy.We found that FeSe undergoes two distinct structural evolutions,sequen-tially characterized by intercalation and conversion reactions,and the initial intercalation behavior is size-dependent.Apparent expansion induced by the intercalation of K+ions is observed in small-sized FeSe nanoflakes,whereas unexpected cracks are formed along the direction of ionic diffusion in large-sized nanoflakes.The significant stress generation and crack extension originating from the combined effect of mechanical and electrochemical interactions are elucidated by geometric phase analysis and finite-element analysis.Despite the different intercalation behaviors,the formed products of Fe and K_(2)Se after full potassiation can be converted back into the original FeSe phase upon depotassiation.In particular,small-sized nanoflakes exhibit better cycling perfor-mance with well-maintained structural integrity.This article presents the first successful demonstration of atomic-scale visualization that can reveal size-dependent potassiation dynamics.Moreover,it provides valuable guidelines for optimizing the dimensions of electrode materials for advanced PIBs.
基金This work was financially supported by National Natural Science Foundation of China (No. 60376014).
文摘Nanoparticles of tin-doped ferrites SnxFe3-xO4 (x=0, 0.1, 0.2, 0.3, 0.4, 1.0) were prepared by the precipitation exchange method. The particles of all specimens are crystalline with mean diameter in the range of 4-8 nm, and the lattice parameters enlarge with increasing tin content. Magnetization and Mssbauer data indicate that the specimens are paramagnetic. The saturation magnetization decreases, as well as the magnetization and the coercive field increase, with increasing tin-content, the possible causes of which were discussed.
文摘CdS nanoclusters were synthesized by using n-octylthiol as a ligand and n-hexadecyltrimethyl-ammonium bromide (or n-tetrabutylammonium bromide) as an organic cation. Sizeselective precipitation techniques have enabled the preparation of different CdS Q-nanoparticles with narrow size distribution and mean diameters ranging from 2 to 5 nm. UV-Vis spectroscopy, transmission electron microscopy and small-angle X-ray scattering were used to determine the mean cluster size. Their size quantization effect has been observed in UV-Vis spectra, fluorescence spectra and small-angle X-ray diffraction, but it became too weak to be observed for large particles (2r > 10 nm). Moreover, their photo-catalysis has been studied by ESR technique and the results revealed that the photo-catalytic reaction occurred in the solution system and some free radicals such as CH2-OH in methanol, or CH3-CH-OH in ethanol were generated if some CdS Q-particles were added to methanol (or ethanol) and initiated by UV light at the same time, which may be very crucial in organic synthesis.
