Nanostructured Oxides Thermoelectric Materials And Energy Harvesting Devices For Civil Infrastructure Applications
Thermoelectric generators (TEG) are solid-state devices that can convert thermal energy directly into electricity through the Seebeck phenomenon. Over 2.5 quadrillion BTU/year of energy generated in the US is wasted as a form of heat, which can be reclaimed as electricity using conformal TEG (cTEG) to power electronic devices, such as IoT sensors and other microelectronics. However, the potential impact of TE technology for power generation is hindered by the challenges at both materials and device levels, including toxic materials and manufacturing process. This research aims to explore the possibility of using non-toxic and earth-abundant oxide-based TEG as energy sources for powering IoT sensors and their related applications in civil infrastructure.
The use of nanostructured oxides in TE applications has attracted much interest due to their high performance and long-term stability at elevated temperatures. In particular, CuAlO2 and PdBi2O4 show great potential for high performance p-type TE materials due to their high thermal stability, simple stoichiometry, and non-toxicity. In this study, the impact of small nanostructure and dopants on the TE properties of these oxides are systematically investigated. Advanced characterization techniques are used to examine the structure-process-property relationship of as-synthesized materials and their related TE performance. CuAlO2 and PdBi2O4 show high Seebeck coefficient and low thermal conductivity, which are desirable as TE materials. The flat band structure for these materials leads to high Seebeck coefficient due to large density of state effective mass. Phonon scattering contributes to low thermal conductivity for these materials. However, it is necessary to increase their electrical conductivity to achieve high TE efficiency. To better analyze the electrical and thermal properties, a generalized TE quality factor (b-factor) was used to compute the optimized carrier concentration and fermi level for CuAlO2 and PdBi2O4 to achieve optimum power factor. Fe has been used in this study as an effective dopant to increase electrical property while reduce thermal conductivity of CuAlO2 based on previous literatures. The highest zT value 1.2×10-2 was achieved for CuAl0.8Fe0.2O2 at 750K.
In addition, a scalable fabrication process for cTEG device was also developed in this research. To overcome current expensive and discrete device fabrication process, a novel roll-to-roll manufacturing method for cTEG was discussed in detail. The study has further explored the potential application of using cTEG to power IoT sensors in underground pipeline monitoring system. A simulation work has carried out in this study to guide the experimental design and fabrication of cTEG with a goal of achieving electrical and thermal properties co-optimization. This research has also resulted in a prototype of cTEG using the proposed scalable manufacturing method for energy harvesting for civil infrastructure applications. The produced cTEG prototype with 4 pairs thermocouples in a size of 40×40 mm2 reaches a power output of 2.02 µW at ΔT =50˚C with a load voltage is 32 mV. It can connect with a DC-DC booster to meet the voltage requirement for powering IoT sensors for underground pipeline monitoring system.
The knowledge gained from this research will advance the understanding of the relationship between structural, electrical, and thermal properties of oxides materials. Also, it explores a scalable cTEG fabrication method, which enables many exciting opportunities of using TE technology for powering IoT sensors in civil infrastructure system.