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Enhancement of thermoelectric performance and mechanical reliability in electrodeposited chitosan nanofiber-bismuth telluride nanocomposite
(2026-07-01)
Tian, Jianghan
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Gobpant, Jakrit
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Van Toan, Nguyen
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Theekhasuk, Nattharika
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Pham, Cong Kha
Thermoelectric generators (TEGs) offer a promising route for converting waste heat into electrical energy; however, the practical implementation of high-performance micro-TEGs (μTEGs) is limited by the material performance and mechanical fragility of thick bismuth telluride (Bi<inf>2</inf>Te<inf>3</inf>) films. Although thick thermoelectric layers are required to sustain sufficient temperature gradients, conventional fabrication often induces residual stress, leading to cracking and structural failure. In this work, we introduce a sustainable synthesis strategy by incorporating bio-derived chitosan nanofibers (ChNFs) into the electrodeposition process. The amino and hydroxyl functional groups of ChNFs promote interfacial bonding and nucleation, enabling the rapid growth of dense, crack-free composite films with thicknesses up to 1000 μm. The introduction of ChNFs also creates abundant phonon-scattering interfaces, significantly reducing lattice thermal conductivity from 1.48 to 0.29 W m−1 K−1 and resulting in a 303% increase in the room-temperature figure of merit (ZT), from 0.12 to 0.50. At an optimal loading of 0.0123 wt%, the composite films exhibit a 15% increase in hardness while maintaining structural integrity. These results demonstrate a multifunctional materials design strategy that simultaneously enhances thermoelectric performance, mechanical robustness, and fabrication scalability. The ChNF–Bi<inf>2</inf>Te<inf>3</inf> nanocomposites provide a viable green pathway for developing reliable thick films for next-generation self-powered electronics and compact waste-heat harvesting systems.
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Dual optimization of ZT and output power in bulk Bi2Te3 through metal-assisted chemical etching
(2026-03-01)
Theekhasuk, Nattharika
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Sakulkalavek, Aparporn
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Ono, Takahito
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Sakdanuphab, Rachsak
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Nguyen, Duc Nam
Thermoelectric materials offer a promising route for sustainable energy harvesting by directly converting waste heat into electricity, enabling compact, solid-state, and environmentally friendly energy solutions. Among them, bismuth telluride (Bi₂Te₃) stands out as the benchmark material for near-room-temperature applications due to its excellent electronic transport properties and commercial maturity. However, achieving high-performance in bulk or thick-film Bi₂Te₃ remains a formidable challenge. Conventional strategies such as doping, alloying, and nanoinclusion, while successful in thin films, often fail to translate effectively to bulk systems due to issues like pore collapse, poor uniformity, and degraded electrical connectivity. These limitations hinder the formation of efficient phonon-scattering architectures without compromising charge transport, resulting in limited improvement in the thermoelectric figure of merit (ZT). In this study, we present a novel and scalable nanoengineering strategy that applies metal-assisted chemical etching (MACE) to fabricate nanoporous surface layers on bulk Bi₂Te₃ for the first time. Unlike conventional nanostructuring techniques, MACE enables the formation of oriented nanostructures via a simple wet-chemical process, offering high tunability, low cost, and compatibility with large-area substrates. To reduce interfacial resistance, nickel was subsequently electrodeposited onto the nanostructured surface, forming a conformal contact layer that improves charge extraction and output performance. By systematically tuning the MACE duration, the optimized nanostructured Bi₂Te₃ sample exhibited a 2.3-fold improvement compared to the pristine bulk sample. Furthermore, due to the increased surface area from the nanoporous architecture, the internal resistance and output power of the nanostructured Bi₂Te₃ devices demonstrated 25-fold and 5.8-fold improvments, respectively, relative to the untreated sample. These remarkable improvements are attributed to the synergistic effect of enhanced phonon scattering within the nanoporous layer and improved charge transport enabled by the conformal nickel coating. This work not only introduces a powerful nanostructuring route for Bi₂Te₃ but also establishes a practical platform for high-performance, thick-film thermoelectric devices. The findings offer deep insight into the structure, property, and performance relationships governing thermoelectric efficiency and pave the way toward the scalable fabrication of next-generation thermoelectric modules for real-world applications such as industrial waste heat recovery and self-powered electronics.
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Chemical etching of glass substrates
(2026-01-01)
Van Toan, Nguyen
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Toda, Masaya
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Xue, Gaopeng
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Gobpant, Jakrit
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Sakulkalavek, Aparporn
MEMS and microfluidics represent the forefront of technological innovation, spearheading a transformative era in precision control over fluids and mechanical components at scales that were once unimaginable. These groundbreaking technologies have transcended conventional boundaries and are now at the heart of numerous applications [1-3], spanning a wide spectrum of industries. From pioneering advancements in advanced medical diagnostics, where the manipulation of minute biological samples is essential, to the intricate networks that facilitate seamless telecommunications [4, 5], MEMS and microfluidics have become indispensable tools, exemplifying unparalleled efficiency, versatility, and cost-effectiveness. The ability to navigate and manipulate the microscopic and nanoscopic realms with precision opens new frontiers, promising advancements that not only redefine our technological landscape but also significantly impact the way we approach challenges across diverse sectors.
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Flexible thermoelectric cooler with optimized fill factor and radiative cooling integration for energy-efficient wearable thermal management
(2025-12-01)
Gobpant, Jakrit
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Sakulkalavek, Aparporn
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Sriniratkul, Pannarai
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Sa-I, Saowanee
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Rudradawong, Chalermpol
The growing demand for skin-interfaced electronics in health monitoring, sports, and personal comfort highlights the need for compact, energy-efficient, and conformable cooling systems. However, existing thermoelectric coolers (TECs) are rigid, bulky, and power-intensive, making them unsuitable for wearable applications. To address this limitation, we present a flexible thermoelectric cooler (FTEC) with a compact footprint of 40 × 40 × 2.26 mm3, featuring discrete p- and n-types thermoelectric leg arrays with systematically varied fill factors (FF = 9 %, 16 %, 25 %, and 36 %). Optimization revealed that the 16 % FF configuration provides the most energy-efficient architecture, achieving a cold-side temperature of −5.9 °C and a coefficient of performance (COP) of 3.25 at 6 W input, while balancing cooling capacity and electrical loss. To improve heat dissipation without increasing bulk, ultrathin graphite and radiative cooling (RC) layers were integrated. Three configurations, including baseline (no thermal layer), graphite-enhanced, and RC-enhanced FTECs, were systematically evaluated. Under ambient conditions (33 °C), the RC- enhanced FTEC maintained a cold-side temperature of approximately 23 °C for 6 h during low-current operation of 0.3 A. Beyond intrinsic performance, the optimized FTEC was benchmarked against both commercial rigid TEC modules and state-of-the-art flexible TECs. Compared to widely used Peltier devices (TEC1–12705 and TEC1–12710), our FTEC achieved comparable ΔT with nearly 65 % lower power consumption, owing to fill factor optimization and RC-enhanced heat rejection. Mechanical flexibility was validated through bending tests, confirming both thermal and electrical stability. Finally, integration with an ESP32-based proportional–integral–derivative (PID) control system enabled real-time wearable cooling, successfully reducing skin temperature from 33 °C to 31 °C in on-body trials. This work demonstrates.
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Flexible thermoelectric generator with radiative cooling for body-heat-driven self-powered Bluetooth low energy sensing system
(2025-10-01)
Gobpant, Jakrit
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Van Toan, Nguyen
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Ono, Takahito
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Tuoi, Truong Thi Kim
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Tran, Ngoc Dang Khoa
Wearable electronics and wireless IoT sensors are increasingly expected to operate in a self-powered manner. However, their practical deployment remains limited due to the lack of compact, flexible, and sustainable energy sources. Thermoelectric generators (TEGs), which convert body heat into electricity, present a promising solution but are typically hindered by small temperature gradients and the requirement of bulky heat sinks that compromise flexibility. To address these challenges, we developed an ultra-thin flexible thermoelectric generator (FTEG) integrated with a radiative cooling (RC) layer that passively enhances heat dissipation under natural convection. The device, fabricated using high-performance thermoelectric materials on a soft silicone substrate, maintained a total thickness of just 2.26 mm. Finite element modeling and experimental validation confirmed that the RC layer effectively increased the temperature gradient across thermoelectric legs, significantly improving the output power compared to conventional graphite-based or no-cooling designs. The FTEG achieved a maximum normalized power density of 3.51 μW/cm2 under temperature conditions representative of wearable use (T<inf>skin</inf> of 32 °C and T<inf>ambient</inf> of 26 °C). The harvested energy was then stored using a power management circuit and capacitor. This stored energy was successfully used to power a Bluetooth Low Energy (BLE) sensing module, enabling stable wireless transmission driven entirely by body heat. These results highlight the practical potential of integrating passive radiative cooling into flexible thermoelectric systems, paving the way for high-performance, battery-free wearable electronics and autonomous IoT applications.

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