Power density

About: Power density is a research topic. Over the lifetime, 9534 publications have been published within this topic receiving 197264 citations. The topic is also known as: volumic power & volume power density.

Accelerated OH– Transport in Activated Carbon Air Cathode by Modification of Quaternary Ammonium for Microbial Fuel Cells

Abstract: Activated carbon (AC) is a promising catalyst for the air cathode of microbial fuel cells (MFCs) because of its high performance and low cost. To increase the performance of AC air cathodes, the acceleration of OH– transport is one of the most important methods, but it has not been widely investigated. Here we added quaternary ammonium to ACs by in situ anchoring of a quaternary ammonium/epoxide-reacting compound (QAE) or ex situ mixing with anion exchange resins in order to modify ACs from not only the external surface but also inside the pores. In 50 mM phosphate buffer solution (PBS), the in situ anchoring of QAE was a more effective way to increase the power. The highest power density of 2781 ± 36 mW/m2, which is 10% higher than that of the control, was obtained using QAE-anchored AC cathodes. When the medium was switched to an unbuffered NaCl solution, the increase in maximum power density (885 ± 25 mW/m2) was in accordance with the anion exchange capacity (0.219 mmol/g). The highest power density of...

Composition and Structure Optimized BiFeO3 -SrTiO3 Lead-Free Ceramics with Ultrahigh Energy Storage Performance.

Abstract: Dielectric ceramic capacitors have attracted increasing attention as advanced pulsed power devices and modern electronic systems owing to their fast charge/discharge speed and high power density. However, it is challenging to meet the urgent needs of lead-free ceramics with superior energy storage performance in practical applications. Herein, a strategy for the composition and structural modification is proposed to overcome the current challenge. The lead-free ceramics composed of BiFeO3 -SrTiO3 are fabricated. A low hysteresis and high polarization can be achieved via composition optimization. The experimental results and finite element simulations indicate that the two-step sintering method significantly influences the decrease in the grain size and improvement in the breakdown strength (EBDS ). A high EBDS of ≈750 kV cm-1 accompanied by a large maximum polarization (≈40 µC cm-2 ) and negligible remanent polarization (<2 µC cm-2 ) contribute to the ultrahigh energy density and efficiency values of the order of 8.4 J cm-3 and ≈90%, respectively. Both energy density and efficiency exhibit excellent stability over the frequency range of 1-100 Hz and temperatures up to 120 °C, along with the superior power density of 280 MW cm-3 , making the studied BiFeO3 -SrTiO3 ceramics potentially useful for high-power energy storage applications.

Maximum power generation in a piezoelectric pulse generator

Abstract: This investigation presents and discusses maximization techniques for a high-power piezoelectric pulse generator. Maximizing the piezoelectric generator's output power is done by maximizing the product of generated voltage and output current. The maximization methods are derived from the mechanical and electrical models of the generator and provide design guidelines as to the geometric dimensions of the piezoelectric material and circuital conditions that will produce maximum power in the device. The theoretical results show the peak stack voltage to increase with an increasing thickness to area ratio of the piezoelectric material and with increasing applied force. However, in contrast to the peak output voltage, the peak output current increases with the decreasing of thickness to area ratio of the material. In addition to the physical dimension, the peak stack current increases as the value of the antenna inductor decreases. The output power of the piezoelectric generator, which is the product of output voltage and current, linearly increases with the thickness to area ratio. This result is due to the fact that the output voltage is larger comparing to the output current. Experimental results are also given to verify the theoretical results and represent the performance of several types of piezoelectric materials with different thickness to area ratios. The experimental results show good agreement with theoretical predictions. The results also show the peak power output of the experimental generator ranging from 7 to 28 kW with a corresponding power density from 9 to 173 kW/cm/sup 3/.

Highly efficient and broadband Si homojunction structured near-infrared light emitting diodes based on the phonon-assisted optical near-field process

Abstract: We fabricated a highly efficient, broadband light emitting diode driven by an optical near field generated at the inhomogeneous domain boundary of a dopant in a homojunction bulk Si crystal and evaluated its performance. To fabricate this device, a forward current was made to flow through a Si p–n junction to anneal it. During this process, the device was irradiated with near-infrared light, producing stimulated-emission light using a two-step phonon-assisted process triggered by the optical near field, and the annealing rate was controlled in a self-organized manner. The device emitted light in a wide photon energy region of 0.73–1.24 eV (wavelength 1.00–1.70 μm). The total power of the emitted light with 11 W of electrical input power was as high as 1.1 W. The external power conversion efficiency of the emitted light was 1.3%, the differential external power conversion efficiency was 5.0%, the external quantum efficiency was 15%, and the differential external quantum efficiency was 40%. The dependency of the emitted light power density on the injected current density clearly showed a characteristic reflecting the two-step phonon-assisted transition process.

Electrical properties and their thermal stability for silicon nitride films prepared by plasma‐enhanced deposition

Abstract: The structural and electrical properties for plasma chemical vapor deposition amorphous silicon nitride films prepared from SiH4‐N2‐Ar mixtures have been investigated. Substrate temperature varied between 250 and 350 °C, and rf power density was set up in a range between 0.51 and 1.19 W/cm2 (13.56 MHz). Film composition changes toward a Si rich state with increasing substrate temperature or decreasing rf power density. Film density increases with increasing substrate temperature and rf power density. Film with a high degree of perfection (N/Si ratio=1.33 and density=3.2 g/cm3), is obtained at 350 °C and 1.19 W/cm2. Average electronic polarizability, dielectric strength, and Poole‐Frenkel barrier height become smaller, stronger, and larger, respectively, when film structure approaches perfection. The electrical properties are degraded largely by annealing (700 °C, in a N2 gas), when as‐grown films structure is far from perfection. This instability of electrical properties is attributed to the increase of trap density due to dehydrogenation and densification.