https://umbc.webex.com/umbc/j.php?MTID=m23085fadb503677aab0a5c861b4bfe7c
Advisor: Deepa Madan
Title: High Performance Flexible and Scalable Thermoelectric Device and its Application as a Self-Sufficient Power Supply for Wearable Electronic Devices
Abstract: The rise of wearable electronics has emphasized the need for alternative power sources, as traditional batteries have limitations in terms of portability and cost. One promising solution is thermoelectric power generation, which can harvest waste heat or body heat to power these devices using thermoelectric(TE) materials. To address the global demand for low-cost, flexible thermoelectric generators (TEGs), this work describes a novel, energy-efficient TEG fabrication method of controlling the composite microstructure using 4synergetic factors.
The combination of (1) a small amount of chitosan binder (0.05 wt%), (2)heterogeneous (mixed nanoscale and microscale) TE particles, (3) applied mechanical pressure of 20 MPa combined with curing at a low temperature of120°C for 30 mins and (4) thickness variation (170, 240, 300 μm), results in an enhanced TE property of TEGs. The combination of these four factors controls the micro and nanostructure of the films to decouple their electrical and thermal conductivity effectively by achieving a improved electrical conductivity and a reduced thermal conductivity. This resulted in figures of merit (ZTs) of 0.89 and 0.5 for p-BST and n-BTS thinner (170 µm) films, respectively, comparable to other additive manufacturing methods despite eliminating the high-temperature, long-duration curing process. The process was also used to fabricate a 6-couple TEG device, which could generate 357.6 µW with a power density of 5.0 mW/cm2 at a dT of 40 K. The device demonstrated air stability and flexibility for 1000 cycles of bending. Finally, the device was integrated with a voltage step-up converter to power an LED and charge and discharge capacitor at a ?T of 17 K, demonstrating its applicability as a self-sufficient power source.
This work also further explored possibilities and approaches to integrate the TEGs to real world applications. Although the TE results are promising, there are still 2 factors to concern, (1) chalcogenides materials like p-BST and n-BTS are toxic and earth-rare, (2) The temperature difference will not be ideal as it in the research labs. Therefore, it is important to find new materials and methods to address these concerns. Tetrahedrites are promising thermoelectric materials in high-temperature applications because they are non-toxic and earth-abundant. MXene (Ti3C2) is a novel 2D material which has ultra-high electrical conductivity. Herein, this work demonstrates the fabrication of scalable and sustainable Cu12Sb4S13 (CAS) based composite films and flexible TEG devices(f-TEGs) with 2D MXene nanosheets using the previously developed energy efficient method for room temperature applications. 2D MXene nanosheets introduced energy-barrier scattering and nanoscale features to effectively increase the room-temperature ZT to 0.22, 10% higher than bulk CAS, by decoupling electrical conductivity, Seebeck coefficient, and thermal conductivity. CAS and 2D MXenes were found to be environmentally safe through a bacterial viability study. The process is used to create a 5-leg f-TEG device producing a power of 5.3 µW and a power density of 140 at a dT of 25 K. Therefore, this work demonstrates that combining scalable and sustainable materials and methods is an effective strategy for high-performance room-temperature f-TEGs that could potentially harvest the low waste heat energy of the human body
