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Scaling up the production capacity of spark discharge generated nanoparticles is crucial for their industrial application. Among various options, high-frequency spark discharge generation is a promising route as the mass production rate of nanoparticles should simply scale linearly with the spark frequency. However, reports of spark discharge generators operating above 1 kHz are scarce in the literature, as spark discharges at higher frequencies have been observed to be irregular, leading to premature spark discharges that result in a significantly lower mass production rate. In this study, we present a wire-to-plate electrode configuration that suppresses premature spark discharges during high-frequency operations above 1 kHz, and investigate the factors that contribute to the occurrence of premature spark discharges by comparing the performance of the wire-to-plate electrode configuration to those of rod-to-rod and wire-to-rod configurations. We identified that spark duration should be minimized to achieve stable spark discharge events as it correlates to the time required for the spark plasma to be completely removed from the spark zone, and found that increasing local electric field intensity and carrier gas velocity are both beneficial to achieving stable high frequency spark discharges. Lastly, using the wire-to-plate electrodes, we show that stable operation without premature spark discharges can be achieved up to 17.9 kHz and the copper nanoparticle production rate scales as expected (up to 7.6 mg/h) when premature spark discharges are eliminated during high frequency operations. Copyright © 2017 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]

The electrode configuration in a spark discharge generator plays a critical role in the characteristics of the process. For instance, the rod-to-rod configuration is unable to prevent nanoparticles from agglomerating due to slow local carrier gas velocity. On the other hand, the recently developed pin-to-plate configuration is able to produce unagglomerated nanoparticles; however, the geometric mean diameter and the number concentration of produced nanoparticles change over time as the pin gets eroded. In this work, we present a novel wire-in-hole-type spark discharge generator (WH-SDG) which is able to generate unagglomerated nanoparticles with a constant size distribution over a long time. The WH-SDG, which consists of a metal wire and a grounded plate with a hole in which the metal wire is located in the center, effectively suppressed changes in the electrode morphology and the gap distance, which cause the minimal variation of the spark discharge voltage and frequency in time. Therefore, the WH-SDG was able to maintain a constant size distribution of the generated nanoparticles for 12 h. In addition, it was found that the WH-SDG could control the diameter of nanoparticles by regulating the gas flow rate into generator, and could produce nanoparticles from various metals such as copper and palladium. Copyright 2015 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]

Li–O 2 batteries have attracted great attention because of their high theoretical energy density, which exceeds the highest possible value of currently used Li-ion batteries. The operation of Li–O 2 batteries include the formation and decomposition of Li 2 O 2 at the cathode, and cell degradation occurs because such discharge products accumulate on the pores and cause pore clogging. For reversible charge–discharge process, in this study, a biaxially multilayered high crystalline carbon nanotube (CNT) web was designed and fabricated by a modified direct spinning method, which was the first demonstration that realize the biaxially multilayered structure in one-step process. The high crystallinity of the CNT surface reduced its decomposition and the biaxial alignment of CNT enabled the web to be opened for O 2 gas and electrolytes without pore clogging. The pore size distribution verified that effective pores were better developed in the biaxially multilayered CNT web, which facilitated the flow of O 2 gas and electrolytes. The use of this specially designed CNT as a cathode improved the cyclability by 75% and dramatically reduced the overpotential. For the practical use of Li–O 2 batteries, a 3D folded cell with biaxially multilayered CNT web electrode is fabricated and demonstrated 30 cycles at 100 W h/kg cell cutoff. [Display omitted] [ABSTRACT FROM AUTHOR]