Ultrasmall y-Fe203 nanodots （- 3.4 nm） were homogeneously encapsulated in interlinked porous N-doped carbon nanofibers （labeled as Fe2O3@C） at a considerable loading （-51 wt.%） via an electrospinning technique. ...Ultrasmall y-Fe203 nanodots （- 3.4 nm） were homogeneously encapsulated in interlinked porous N-doped carbon nanofibers （labeled as Fe2O3@C） at a considerable loading （-51 wt.%） via an electrospinning technique. Moreover, the size and content of Fe2O3 could be controlled by adjusting the synthesis conditions. The obtained Fe203@C that functioned as a self-standing membrane was used directly as a binder- and current collector-free anode for sodium-ion batteries, displaying fascinating electrochemical performance in terms of the exceptional rate capability （529 mA.h.gq at 100 mA-g-1 compared with 215 mA-h-g-1 at 10,000 mA.g-1） and unprecedented cyclic stability （98.3% capacity retention over 1,000 cycles）. Furthermore, the Na-ion full cell constructed with the Fe2O3C anode and a P2-Na2/3Ni1/3Mn2/302 cathode also exhibited notable durability with 97.2% capacity retention after 300 cycles. This outstanding performance is attributed to the distinctive three-dimensional network structure of the very-fine Fe203 nanoparticles uniformly embedded in the interconnected porous N-doped carbon nanofibers that effectively facilitated electronic/ionic transport and prevented active materials pulverization/aggregation caused by volume change upon prolonged cycling. The simple and scalable preparation route, as well as the excellent electrochemical performance, endows the Fe2O3@C nanofibers with great prospects as high-rate and long-life Na-storage anode materials.展开更多
Impedance matching is important for achieving high-efficiency microwave absorbers. The high conductivity of dielectric loss materials such as pure metals and carbon nanomaterials generally results in poor absorption o...Impedance matching is important for achieving high-efficiency microwave absorbers. The high conductivity of dielectric loss materials such as pure metals and carbon nanomaterials generally results in poor absorption owing to the low impedance matching between the absorbers and air. Carbon nanostructures are very promising candidates for high-efficiency absorption because of their attractive features including low density, high surface area, and good stability. Herein, a new strategy is proposed to improve the impedance matching of dielectric loss materials using electrospun carbon nanofibers as an example. The carbon nanofibers are coated with specifically designed gradient multilayer nanofilms with gradually increasing electroconductibility synthesized by doping ZnO with different A1203 content （AZO） by atomic layer deposition. The gradient nanofilms are composed of five layers of dielectric films, namely, pure A1203, AZO （5：1, the pulse cycle ratio of ZnO to A1203）, pure ZnO, AZO （10：1）, and AZO （20：1）. The versatile gradient films serve as intermediate layers to tune the impedance matching between air and the carbon nanofiber surfaces. Therefore, the carbon nanofibers coated with gradient films of rationally selected thicknesses exhibit remarkably enhanced microwave absorption performance, and the optimal reflection loss reaches -58.5 dB at 16.2 GHz with a thickness of only 1.8 mm. This work can help further understand the contribution of impedance matching to microwave absorption. Our strategy is general and can be applied to improve the absorption properties of other dielectric loss materials and even for applications in other fields.展开更多
文摘Ultrasmall y-Fe203 nanodots （- 3.4 nm） were homogeneously encapsulated in interlinked porous N-doped carbon nanofibers （labeled as Fe2O3@C） at a considerable loading （-51 wt.%） via an electrospinning technique. Moreover, the size and content of Fe2O3 could be controlled by adjusting the synthesis conditions. The obtained Fe203@C that functioned as a self-standing membrane was used directly as a binder- and current collector-free anode for sodium-ion batteries, displaying fascinating electrochemical performance in terms of the exceptional rate capability （529 mA.h.gq at 100 mA-g-1 compared with 215 mA-h-g-1 at 10,000 mA.g-1） and unprecedented cyclic stability （98.3% capacity retention over 1,000 cycles）. Furthermore, the Na-ion full cell constructed with the Fe2O3C anode and a P2-Na2/3Ni1/3Mn2/302 cathode also exhibited notable durability with 97.2% capacity retention after 300 cycles. This outstanding performance is attributed to the distinctive three-dimensional network structure of the very-fine Fe203 nanoparticles uniformly embedded in the interconnected porous N-doped carbon nanofibers that effectively facilitated electronic/ionic transport and prevented active materials pulverization/aggregation caused by volume change upon prolonged cycling. The simple and scalable preparation route, as well as the excellent electrochemical performance, endows the Fe2O3@C nanofibers with great prospects as high-rate and long-life Na-storage anode materials.
文摘Impedance matching is important for achieving high-efficiency microwave absorbers. The high conductivity of dielectric loss materials such as pure metals and carbon nanomaterials generally results in poor absorption owing to the low impedance matching between the absorbers and air. Carbon nanostructures are very promising candidates for high-efficiency absorption because of their attractive features including low density, high surface area, and good stability. Herein, a new strategy is proposed to improve the impedance matching of dielectric loss materials using electrospun carbon nanofibers as an example. The carbon nanofibers are coated with specifically designed gradient multilayer nanofilms with gradually increasing electroconductibility synthesized by doping ZnO with different A1203 content （AZO） by atomic layer deposition. The gradient nanofilms are composed of five layers of dielectric films, namely, pure A1203, AZO （5：1, the pulse cycle ratio of ZnO to A1203）, pure ZnO, AZO （10：1）, and AZO （20：1）. The versatile gradient films serve as intermediate layers to tune the impedance matching between air and the carbon nanofiber surfaces. Therefore, the carbon nanofibers coated with gradient films of rationally selected thicknesses exhibit remarkably enhanced microwave absorption performance, and the optimal reflection loss reaches -58.5 dB at 16.2 GHz with a thickness of only 1.8 mm. This work can help further understand the contribution of impedance matching to microwave absorption. Our strategy is general and can be applied to improve the absorption properties of other dielectric loss materials and even for applications in other fields.
