摘要：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.

摘要：Electrocatalysis is a promising approach to clean energy conversion due to its high efficiency and low environmental pollution. Noble metal materials have been studied to show high activity toward electrocatalyltic reactions, although such applications remain restricted by the high cost and poor durability of the noble metals. By precisely adjusting the catalyst composition, size, and structure, electrocatalysts with excellent performance can be obtained. atomic layer deposition(ALD) is a technique used to produce ultrathin films and ultrafine nanoparticles at the atomic level. It possesses unique advantages for the controllable design and synthesis of electrocatalysts. Furthermore, the homogenous composition and structure of the electrocatalysts prepared by ALD favor the exploration of structure-reactivity relationships and catalytic mechanisms. In this review, the mechanism, characteristics, and advantages of ALD in fabricating nanostructures are introduced first. Subsequently, the problems associated with existing electrocatalysts and a series of recently developed ALD strategies to enhance the activity and durability of electrocatalysts are presented. For example, the deposition of ultrafine Pt nanoparticles to increase the utilization and activity of Pt, fabrication of core–shell, overcoat, nanotrap, and other novel structures to protect the noble-metal nanoparticles and enhance the catalyst stability. In addition, ALD developments in synthesizing non-noble metallic electrocatalysts are summarized and discussed. Finally, based on the current studies, an outlook for the ALD application in the design and synthesis of electrocatalysts is presented.

摘要：The oxygen reduction reaction （ORR） is essential in research pertaining to life science and energy. In applications, platinum-based catalysts give ideal reactivity, but, in practice, are often subject to high costs and poor stability. Some costefficient transition metal oxides have exhibited excellent ORR reactivity, but the stability and durability of such alternative catalyst materials pose serious challenges. Here, we present a facile method to fabricate uniform CoxOy nanoparticles and embed them into N-doped carbon, which results in a composite of extraordinary stability and durability, while maintaining its high reactivity. The half-wave potential shows a negative shift of only 21 mV after 10,000 cycles, only one third of that observed for Pt/C （63 mV）. Furthermore, after 100,000 s testing at a constant potential, the current decreases by only 17%, significantly less than for Pt/C （35%）. The exceptional stability and durability results from the system architecture, which comprises a thin carbon shell that prevents agglomeration of the CoxOy nanoparticles and their detaching from the substrate.

摘要：Designing photoelectrodes with particular nanostructure and composition has been regarded as a promising approach to improve the photoelectrochemical(PEC) water splitting efficiency. We report the design and synthesis of a three-dimensional(3D) nanostructure with CuO nanocones as backbones and ZnO nanorods as branches,using a facile water bath reaction process together with the atomic layer deposition(ALD) technology. As utilized in photocathodes, the optimized CuO/ZnO nanostructure, 37 cycles of ALD ZnO seedlayer and 55 min of water bath reaction of ZnO nanorods, demonstrate highly improved PEC performance. The ratio of photo to dark current density for the 3D CuO/ZnO is 6.4, much higher than the value of 2.7for the CuO electrode. The enhanced activity is attributed to the synergistic effects of effective carrier separation and collection, reduced charge recombination, and increased carrier lifetime in the CuO/ZnO heterojunction. This work demonstrates the feasibility of designing novel 3D nanostructures by ALD technology as efficient photoelectrodes.