Abstract
Thermopower waves are a recently developed energy conversion concept utilizing dynamic temperature and chemical potential gradients to harvest electrical energy while the combustion wave propagates along the hybrid layers of nanomaterials and chemical fuels. The intrinsic properties of the core nanomaterials and chemical fuels in the hybrid composites can broadly affect the energy generation, as well as the combustion process, of thermopower waves. So far, most research has focused on the application of new core nanomaterials to enhance energy generation. In this study, we demonstrate that the alignment of core nanomaterials can significantly influence a number of aspects of the thermopower waves, while the nanomaterials involved are identical carbon nanotubes (CNTs). Diversely structured, large-area CNT/fuel composites of one-dimensional aligned CNT arrays (1D CNT arrays), randomly oriented CNT films (2D CNT films), and randomly aggregated bulk CNT clusters (3D CNT clusters) were fabricated to evaluate the energy generation, as well as the propagation of the thermal wave, from thermopower waves. The more the core nanostructures were aligned, the less inversion of temperature gradients and the less cross-propagation of multiple thermopower waves occurred. These characteristics of the aligned structures prevented the cancellation of charge carrier movements among the core nanomaterials and produced the relative enhancement of the energy generation and the specific power with a single-polarity voltage signal. Understanding this effect of structure on energy generation from thermopower waves can help in the design of optimized hybrid composites of nanomaterials and fuels, especially designs based on the internal alignment of the materials. More generally, we believe that this work provides clues to the process of chemical to thermal to electrical energy conversion inside/outside hybrid nanostructured materials.
Highlights
Chemical combustion technologies deliver a high energy density, and the output can be directly converted into a number of types of mechanical and thermal energy
In summary, we explored the effect of the structure of large-area carbon nanotubes (CNTs)/fuel composites on the energy generation from thermopower waves
The thermopower waves in the three different nanostructured composites were characterized by the propagation of the combustion front, the real-time voltage signal, the total energy generation, and the specific power
Summary
Chemical combustion technologies deliver a high energy density, and the output can be directly converted into a number of types of mechanical and thermal energy. Most research at the micro/nanoscale has focused on the conversion of chemical energy into mechanical or thermal energy by combustion because the mechanical apparatus required for the chemical-to-electrical energy conversion are difficult wave propagation [10] accelerates charge carriers through the nanostructured materials, which results in electrical energy generation. Research on thermopower waves has focused on the enhanced energy generation obtainable by applying highSeebeck-coefficient materials in the room-temperature to high-temperature regime. For high-Seebeck-coefficient materials in the lowtemperature regime, Bi2Te3 films and Bi2Te3-Sb2Te3 have been used as the core thermoelectric materials for generating thermopower waves, and the maximum output voltages reached 150 and 200 mV, respectively [11]. As for the high-Seebeck-coefficient materials in the high-temperature regime, metal oxides such as ZnO [13,14] and MnO2 [15] have been employed to enhance the output voltage. The core thermoelectric materials play an important role in the generation of thermopower waves, other factors which implement the thermopower waves, such as the core material alignment and the chemical fuel composition, can affect the fundamental phenomena and response
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