Potassium-ion batteries are a promising alternative to lithium-ion batteries. However, it is challenging to achieve fast charging/discharging and long cycle life with the current electrode materials because of the sluggish potassiation kinetics. Here we report a soft carbon anode, namely highly nitrogen-doped carbon nanofibers, with superior rate capability and cyclability. The anode delivers reversible capacities of 248 mAh g–1 at 25 mA g–1 and 101 mAh g–1 at 20 A g–1, and retains 146 mAh g–1 at 2 A g–1 after 4000 cycles. Surface-dominated K-storage is verified by quantitative kinetics analysis and theoretical investigation. A full cell coupling the anode and Prussian blue cathode delivers a reversible capacity of 195 mAh g–1 at 0.2 A g–1. Considering the cost-effectiveness and material sustainability, our work may shed some light on searching for K-storage materials with high performance.
Sodium ion batteries (SIBs) represent an effective energy storage technology with potentially lower material costs than lithium ion batteries. Here we show that the electrochemical performance of SIBs, especially rate capability, is intimately connected to the electrode design at the nanoscale by taking anatase TiO2 as an example. Highly ordered three-dimensional (3D) Ni-TiO2 core-shell nanoarrays were fabricated using nanoimprited AAO templating technique and directly used as anode. The nanoarrays delivered a reversible capacity of ~200 mA h g-1 after 100 cycles at the current density of 50 mA h g-1 and were able to retain a capacity of ~95 mA h g-1 at the current density as high as 5 A g-1 and fully recover low rate capacity. High ion accessibility, fast electron transport, and excellent electrode integrity were shown as great merits to obtain the presented electrochemical performance. Our work demonstrates the possibility of highly ordered 3D heterostructured nanoarrays as a promising electrode design for Na energy storage to alleviate the reliance on the materials' intrinsic nature, and provides a versatile and cost-effective technique for the fabrication of such perfectly ordered nanostructures.
Self-supported metallic nanopore arrays with highly oriented nanoporous structures are fabricated and applied as ideally nanostructured electrodes for supercapacitor applications. Their large specific surface area can ensure a high capacitance, and their highly oriented and stable nanoporous structure can facilitate ion transport.
Coherent jamming is one of the important trends in modern radar electronic warfare. High-speed sampling of wideband radio frequency (RF) signals and high isolation of two receive-transmit antennas are key technologies for the realization of coherent jamming. However, these technologies present significant challenges to engineering application. In this paper, a novel repeater jamming based on interrupted sampling technique is presented. For a jammer with a receive-transmit time-sharing antenna, a radar signal is sampled with a low rate by the jammer. Then, a train of false targets will be achieved after the jamming signal feed the matched filter of a pulse compression radar. For the case of the linear frequency modulated (LFM) pulse compression radars, mathematic principles of the interrupted-sampling repeater jamming is developed, and then the efficiency of the jamming is described and stated as expressions of key parameters which are also beneficial to the jamming design for other coherent radars.interrupted-sampling, repeater jamming, ambiguity function, pulse compression, linear frequency modulated signal
Applicable surface enhanced Raman scattering (SERS) active substrates require high enhancement factor (EF), excellent spatial reproducibility, and low-cost fabrication method on a large area. Although several SERS substrates with high EF and relative standard deviation (RSD) of signal less than 5% were reported, reliable fabrication for large area SERS substrates with both high sensitivity and high reproducibility via low-cost routes remains a challenge. Here, we report a facile and cost-effective fabrication process for large-scale SERS substrate with Ag inter-nanoparticle (NP) gaps of 5 nm based on ultrathin alumina mask (UTAM) surface pattern technique. Such closely packed Ag NP arrays with high density of electromagnetic field enhancement ("hot spots") on large area exhibit high SERS activity and excellent reproducibility, simultaneously. Rhodamine 6G molecules with concentration of 1 × 10(-7) M are used to determine the SERS performance, and an EF of ∼10(9) is obtained. It should be noted that we obtain RSDs about 2% from 10 random spots on an area of 1 cm(2), which implies the highly reproducible signals. Finite-difference time-domain simulations further suggest that the enhanced electric field originates from the narrow gap, which agrees well with the experimental results. The low value of RSD and the high EF of SERS signals indicate that the as-prepared substrate may be promising for highly sensitive and uniform SERS detection.
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