Browsing by Author "Ovalle-Robles, Raquel"
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Item A New Catalyst-Embedded Hierarchical Air Electrode For High-Performance Li-O₂ Batteries(2013-06-05) Lim, H. -D; Song, H.; Gwon, H.; Park, K. -Y; Kim, J.; Bae, Y.; Kim, H.; Jung, S. -K; Kim, T.; Kim, Y. H.; Lepr©, Xavier; Ovalle-Robles, Raquel; Baughman, Ray H.; Kang, K.; 0000 0003 5232 4253 (Baughman, RH); Lepr©, Xavier; Ovalle-Robles, Raquel; Baughman, Ray H.The Li-O₂ battery holds great promise as an ultra-high-energy- density device. However, its limited rechargeability and low energy efficiency remain key barriers to its practical application. Herein, we demonstrate that the ideal electrode morphology design combined with effective catalyst decoration can enhance the rechargeability of the Li-O₂ battery over 100 cycles with full discharge and charge. An aligned carbon structure with a hierarchical micro-nano-mesh ensures facile accessibility of reaction products and provides the optimal catalytic conditions for the Pt catalyst. The new electrode is highly reversible even at the extremely high current rate of 2 A g⁻¹. Moreover, we observed clearly distinct morphologies of discharge products when the catalyst is used. The effect of catalysts on the cycle stability is discussed.Item Thermoacoustic Sound Projector: Exceeding the Fundamental Efficiency of Carbon NanotubesAliev, Ali E.; Codoluto, Daniel; Baughman, Ray H.; Ovalle-Robles, Raquel; Inoue, Kanzan; Romanov, Stepan A.; Nasibulin, Albert; Kumar, Prashant; Priya, Shashank; Mayo, Nathanael K.; Blottman, John; 0000 0003 5232 4253 (Baughman, RH); Aliev, Ali E.; Codoluto, Daniel; Baughman, Ray H.The combination of smooth, continuous sound spectra produced by a sound source having no vibrating parts, a nanoscale thickness of a flexible active layer and the feasibility of creating large, conformal projectors provoke interest in thermoacoustic phenomena. However, at low frequencies, the sound pressure level (SPL) and the sound generation efficiency of an open carbon nanotube sheet (CNTS) is low. In addition, the nanoscale thickness of fragile heating elements, their high sensitivity to the environment and the high surface temperatures practical for thermoacoustic sound generation necessitate protective encapsulation of a freestanding CNTS in inert gases. Encapsulation provides the desired increase of sound pressure towards low frequencies. However, the protective enclosure restricts heat dissipation from the resistively heated CNTS and the interior of the encapsulated device. Here, the heat dissipation issue is addressed by short pulse excitations of the CNTS. An overall increase of energy conversion efficiency by more than four orders (from 10⁻⁵ to 0.1) and the SPL of 120 dB re 20 μPa @ 1 m in air and 170 dB re 1 μPa @ 1 m in water were demonstrated. The short pulse excitation provides a stable linear increase of output sound pressure with substantially increased input power density ( > 2.5 W cm⁻²). We provide an extensive experimental study of pulse excitations in different thermodynamic regimes for freestanding CNTSs with varying thermal inertias (single-walled and multiwalled with varying diameters and numbers of superimposed sheet layers) in vacuum and in air. The acoustical and geometrical parameters providing further enhancement of energy conversion efficiency are discussed.Item Thermoacoustic Sound Projector: Exceeding the Fundamental Efficiency of Carbon Nanotubes(IOP Publishing Ltd) Aliev, Ali E.; Codoluto, Daniel; Baughman, Ray H.; Ovalle-Robles, Raquel; Inoue, Kanzan; Romanov, Stepan A.; Nasibulin, Albert G.; Kumar, Prashant; Priya, Shashank; Mayo, Nathanael K.; Blottman, John B.; 0000 0003 5232 4253 (Baughman, RH); 0000-0001-5845-5137 (Baughman, RH); Aliev, Ali E.; Codoluto, Daniel; Baughman, Ray H.The combination of smooth, continuous sound spectra produced by a sound source having no vibrating parts, a nanoscale thickness of a flexible active layer and the feasibility of creating large, conformal projectors provoke interest in thermoacoustic phenomena. However, at low frequencies, the sound pressure level (SPL) and the sound generation efficiency of an open carbon nanotube sheet (CNTS) is low. In addition, the nanoscale thickness of fragile heating elements, their high sensitivity to the environment and the high surface temperatures practical for thermoacoustic sound generation necessitate protective encapsulation of a freestanding CNTS in inert gases. Encapsulation provides the desired increase of sound pressure towards low frequencies. However, the protective enclosure restricts heat dissipation from the resistively heated CNTS and the interior of the encapsulated device. Here, the heat dissipation issue is addressed by short pulse excitations of the CNTS. An overall increase of energy conversion efficiency by more than four orders (from 10⁻⁵ to 0.1) and the SPL of 120 dB re 20 μPa @ 1 m in air and 170 dB re 1 μPa @ 1 m in water were demonstrated. The short pulse excitation provides a stable linear increase of output sound pressure with substantially increased input power density (> 2.5 W cm⁻². We provide an extensive experimental study of pulse excitations in different thermodynamic regimes for freestanding CNTSs with varying thermal inertias (single-walled and multiwalled with varying diameters and numbers of superimposed sheet layers) in vacuum and in air. The acoustical and geometrical parameters providing further enhancement of energy conversion efficiency are discussed.