Scientists have unveiled a self-powered ionic nanogenerator sensor. It offers flexible, high-sensitivity, real-time temperature monitoring up to 70 °C, ideal for wearable electronics and thermal management.
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As wearable technology becomes increasingly smaller and more powerful, managing heat is becoming increasingly important. Excess heat reduces efficiency and risks damaging sensitive components, making reliable, real-time temperature monitoring essential for device reliability.
Conventional sensors often rely on external power and lack the flexibility needed for seamless integration into compact systems. Researchers have turned to triboelectric nanogenerators (TENGs), devices that convert mechanical energy into electricity, as a potential alternative. Lightweight and cost-effective, TENGs have shown promise. But, their performance typically drops at higher temperatures, as thermionic emission occurs.
A Flexible, Self-Powered Solution
In a recent paper in Advanced Functional Materials, researchers have developed a new ionic temperature-sensing TENG, or iTS-TENG, that overcomes these weaknesses.
Researchers produced iTS-TENG using a composite ionic elastomer made from thermoplastic polyurethane (TPU) and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM]+[TFSI]-) at different wt. % (0-30 %).
The researchers fabricated transparent, stretchable films and paired them with a fluoropolymer to create the device’s positive and negative layers. When pressure is applied, the iTS-TENG generates an electrical signal that varies with temperature without an external power source.
Results and Discussion
The sensor takes advantage of the changes to TPU as it approaches its glass transition temperature, Tg. As it approaches Tg, the material begins to deform, weakening π-π stacking, Coulombic forces, and hydrogen bonding. This leads to the release of free ions and the formation of electrical double layers (EDLs), substantially boosting capacitance and output.
Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), and atomic force microscopy (AFM) confirmed temperature-induced microphase separation in the films. This resulted in increased amorphous content and a Tg of 58.05 °C, improving ion mobility and EDL formation. Electrochemical impedance spectroscopy (EIS) further supported these findings, showing reduced impedance and higher capacitance at elevated temperatures.
The study illustrated the ionic elastomer's superior thermal response and durability over repeated cycles between 30 °C and 70 °C. Interestingly, the iTS-TENG with 10 wt.% ionic liquid (IL) performed best, delivering an output voltage of 740 V and a current of 17.24 µA at 70 °C, approximately 1.4 times higher than devices using TPU alone.
The sensor also showed linear temperature sensitivity of 3.865 V °C-1 during heating and -3.645 V °C-1 during cooling, with excellent reproducibility over 20 thermal cycles. Finite element modeling (FEM) revealed that a more organized internal structure and mobile free ions allowed faster heat transfer, while mechanical pressure further improved output by promoting ion release.
In a practical demonstration, the iTS-TENG successfully charged a 220 µF capacitor to 2 V within 400 seconds at 70 °C. However, devices with higher IL content showed decreased performance due to charge leakage, confirming that 10 wt.% IL is the optimal formulation.
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Applications In Wearable Electronics
The transparency, flexibility, and stretchability of the iTS-TENG make it ideal for integration into wearable technology, such as smart textiles and skin-mounted health monitors.
Researchers demonstrated a real-time temperature monitoring system by connecting the iTS-TENG to an oscilloscope and a MATLAB-enabled laptop, which converted the triboelectric signals into temperature readings. The results closely matched those from commercial sensors across the 30–45 °C range. Being self-powered eliminates the need for external energy sources, reducing system complexity and enhancing usability.
Looking Ahead
The sensor’s fast response and linear behavior make it well-suited for dynamic environments. One remaining challenge is the inconsistency of mechanical input energy, which can affect output stability. Future designs may incorporate improved mechanical structures or artificial intelligence-based signal processing to stabilize performance further.
This research highlights how material innovation can overcome long-standing limitations of TENGs at elevated temperatures, offering a scalable, self-sufficient platform for energy harvesting and temperature sensing in next-generation electronics.
Journal Reference
Hwang, H, J., et al. (2025). Self-Powered Real-Time Temperature Sensing Based on Flexible Ionic Elastomer on Triboelectric Nanogenerators. Advanced Functional Materials, e04081. DOI: 10.1002/adfm.202504081, https://advanced.onlinelibrary.wiley.com/doi/10.1002/adfm.202504081
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