Dukhyun Choi

Highly integrated electronic devices require materials that can mitigate electromagnetic interference (EMI) while simultaneously monitoring localized overheating within a limited package space. In this study, we report a three-dimensional (3D)-printed thermoplastic polyurethane/carbon nanotube (TPU/CNT) multifunctional composite module fabricated via fused deposition modeling (FDM). This module integrates EMI shielding and temperature-gradient-based sensing into a single structure. To this end, TPU/CNT filaments containing 0–20 wt% CNT were prepared via melt compounding and filament extrusion, and their printability was evaluated through melt flow index measurements and printing tests. Although the 20 wt% CNT composite exhibited high electrical conductivity (~600 S/m), its low melt flowability caused severe under-extrusion. Consequently, a TPU/CNT composite containing 10 wt% CNT was selected as the optimal printable composition to achieve sufficient electrical and thermoelectric sensing performance. Infill density was used as a structural design parameter to tune conductive-path connectivity and electromagnetic attenuation. The optimized 10 wt% TPU/CNT module with a 75% infill achieved a maximum total shielding effectiveness of 30.25 dB in the Ku band (12.4–18 GHz), exhibiting absorption-dominant shielding behavior. In addition, this module yielded a Seebeck coefficient of 39.96 μV/K, producing an output voltage of ~0.40 mV at a temperature gradient of 10 K. These findings demonstrate a viable composition–structure design pathway for FDM-printable multifunctional composites that combine EMI shielding and thermal sensing. The integrated suppression of electromagnetic transmission and self-generated thermal-event signals highlights the potential relevance of this pathway for developing anti-tamper (AT)-aware smart packaging.

Hydrogels have emerged as promising materials for flexible and self‐powered electronic devices due to their high ionic conductivity and mechanical adaptability. We developed a polyacrylamide–polyethylenimine (PAAm–PEI) organohydrogel using a glycerol–water binary solvent system and systematically investigated the effects of various alkali and alkaline earth metal salts on triboelectric performance. Among them, LiCl‐incorporated organohydrogels demonstrated superior overall characteristics, achieving ∼400 V, and an exceptional strain of up to 3000%, high transparency (∼87%), and excellent antifreeze and anti‐evaporation properties. The LiCl ions formed robust hydrogen bonding and ionic interactions with water, effectively suppressing ice crystallization and minimizing water loss. The resulting organohydrogel‐based triboelectric nanogenerator (H‐TENG) maintained 91.4% and 80% of its initial output after exposure to 60°C and −20°C, respectively, and recovered 85% of voltage after self‐healing within 10 s. Moreover, by integrating a hybrid CNN–LSTM deep learning model, the TENG achieved a high classification accuracy of 95.64% in Morse code recognition, demonstrating reliable intelligent sensing capability. This work not only provides an effective strategy to balance ionic conductivity, mechanical flexibility, and optical transparency in organohydrogels, but also highlights the potential of deep learning‐assisted TENG systems for advanced human–machine interfaces and next‐generation wearable electronics.

Rapid breakthroughs in IoT and AI have raised demand for portable, self‐powered, flexible sensor devices. Hydrogels with high conductivity, mechanical tunability, environmental adaptability, and biocompatibility are a clever way to develop flexible sensors for triboelectric nanogenerators. TENG application is limited by the paucity of suitable biomaterials and the need for highly conductive fillers such 2D materials, which trade off transparency, output, and sensing. A unique, very transparent, highly stretchable, high‐output performance biomimetic stevia/PVA hydrogel‐based triboelectric nanogenerator (S‐TENG) is investigated to overcome this issue. Due to its abundant dynamic hydrogen bonding, cost‐effective biomimetic stevia is added to polyvinyl alcohol (PVA) to increase hydrogel cross‐linking and crystalline domains. These structural advancements give the S‐hydrogel 2–5 times the mechanical strength and 3–8 times the electrical output of 2D‐, bio‐, and transparent‐material‐based TENGs, while maintaining transparency. The S‐hydrogel may be recycled and recovered by water‐assisted dissolution and re‐gelation, keeping its voltage output. The improved S‐TENG is a self‐powered sensor for various human motions with great sensitivity and a 13‐ms reaction time. The XGBoost method had the greatest classification accuracy of 95.29% among eleven machine learning models, showing the promise of self‐powered sensors for many applications.

Chirality lies at the heart of chemistry, governing the structure-function relationships of biomolecules, pharmaceuticals, and catalysts. However, rapid and label-free enantioselective analysis remains an enduring challenge due to the intrinsic similarity of enantiomers' physicochemical properties. Here, we report a contact electrification-based triboelectric sensing platform for the enantioselective recognition of chiral amino acids, achieved by coating CuO nanowires. The approach exploits chirality-dependent interfacial electron transfer, whereby differences in molecular orbital alignment and work function between enantiomers generate distinct electronic signatures during controlled contact-separation with acetone. Kelvin probe force microscopy, ultraviolet photoelectron spectroscopy, and density functional theory calculations reveal that subtle differences in side-chain geometry modulate nanoscale surface potentials and electron cloud overlap, leading to quantifiable shifts in charge transfer efficiency. The method achieves millisecond-scale discrimination across charged, polar uncharged, and sulfur-containing amino acids, with orthogonal evidence from molecule specific enantioselective contact-electrocatalytic degradation of methyl orange. By transducing stereochemical information directly into measurable electrical outputs, this work demonstrates a mechanistically grounded chemical sensing paradigm, offering a versatile platform for pharmaceutical quality control and biomolecular diagnostics.

Liquid–solid triboelectric nanogenerators (L‑S TENGs) have emerged as promising self‑powered sensing platforms; however, their practical deployment is still limited by poor environmental stability and a lack of quantitative understanding of interfacial charge dynamics. Unlike previous reviews that mainly summarized structural configurations and energy‑harvesting applications, this work focuses on sensing mechanisms, interfacial physics, and design strategies that govern L‑S TENG performance. Critical insights are further provided into unsolved challenges—including salinity effects, stability of active interfaces, and integration in wearable and microfluidic systems—and outline future research directions toward reliable, multifunctional L‑S TENG sensors. This perspective‑driven review aims to bridge the gap between conceptual mechanism understanding and practical sensing applications.

Triboelectric nanogenerators (TENGs) have attracted a lot of attention recently because they can power wearable electronics and small energy‐harvesting devices. However, the use of rigid materials has limited applicability in TENGs, particularly in flexible electronic devices. Hence, to address this challenge, flexible materials are gaining interest as an alternative to conventional rigid materials. This work introduces a hydrogel‐based TENG that is easy to fabricate, offers high production efficiency, superior mechanical flexibility, and self‐healing capabilities. The incorporation of Fe ³⁺ ions into a crosslinked network of chitosan (CHI) and polyacrylic acid (PAA) macromolecular chains significantly enhances the hydrogel's conductivity and the TENG's output performance. Under a 2 N load, a single‐electrode mode of hydrogel‐TENG (H‐TENG) produced output voltage and current of 150 V and 6 µA, respectively. Moreover, the hydrogel retains its good mechanical stretchability (250%), good electrical conductivity, strong adhesion, and robust self‐healing ability. After just 5 min of self‐healing, this H‐TENG device also exhibited effective and sustained self‐healing performance of the electrical output signal. Due to its high output voltage, stretchability, self‐healing property, and sensitivity to mechanical stimuli, this H‐TENG holds great promise as a wearable energy harvesting device and a highly accurate self‐powered body motion sensor.

Triboelectric nanogenerators (TENGs) can convert mechanical energy into electricity. They are good candidates for sustainable energy for growing power demands of the Internet of Things and artificial intelligence. However, durability and stability of TENGs may decrease with repeated use. In this study, we proposed CNT sponges (CS) for producing TENGs with high durability and stability. First, a CS was fabricated by coating a polyurethane sponge with an ink made of multi-walled carbon nanotubes (CNTs) and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). The microstructure of the CS surface and the pore structure under compression were then analyzed to understand the working principle of CS-TENG. Finally, the output performance of the CS-TENG was verified as a function of external force and the durability of the CS-TENG was demonstrated through compression and cycle tests. Results indicate that CNT-based nanocomposites can be utilized to fabricate highly durable and stable TENGs.

Self‐powered flexible thermal‐management systems have garnered interests in wearable electronic devices and AI semiconductors. However, their efficiency and reliability remain limited in practical applications. In this study, an ionic temperature‐sensing triboelectric nanogenerator (iTS‐TENG) is proposed with an ionic elastomer containing thermoplastic polyurethane (TPU) and ionic liquids (ILs). The TPU matrix undergoes deformation of microphase separation by thermal stimulation near the glass transition temperature. Furthermore, ILs facilitate the formation of electrical double layers as charge carriers and enhance the thermal sensitivity as heat carriers under mechanical and thermal stimuli. Thus, iTS‐TENG demonstrates enhanced outputs (734 V) and high thermal sensitivity (3.87 V/°C) from room temperature to 70 °C, with fast response time and reproducibility (more than 20 cycles). Finally, real‐time and self‐powered iTS‐TENG is demonstrated, showing that the sensed temperature is comparable to a commercial temperature sensor. These results indicate that iTS‐TENG is suitable for thermal‐management applications in self‐powered wearable electronic systems.

Sodium‐ion batteries (SIBs) have the potential to be a cost‐effective and sustainable solution for large‐scale energy storage systems (ESSs) due to the abundance of sodium reserves. Na ₂ Ti ₆ O ₁₃ has been considered as a suitable candidate for use as an anode material in SIBs owing to its environmental friendliness, low cost, and excellent cycling stability. Despite its advantages, Na ₂ Ti ₆ O ₁₃ has intrinsic limitations such as electrical conductivity. To overcome these obstacles, a sandwich‐structured Na ₂ Ti ₆ O ₁₃ /reduced graphene oxide (rGO) composite is synthesized through a liquid‐phase exfoliation and restacking method using electrostatic interactions. The Na ₂ Ti ₆ O ₁₃ /rGO composite showed remarkable improvement in both reversible discharge capacity and cycle stability. In comparison to bare Na ₂ Ti ₆ O ₁₃ with a discharge capacity of 20.1 mAh g ⁻¹ after 500 cycles, the Na ₂ Ti ₆ O ₁₃ /rGO1 composite displayed a discharge capacity of 196.5 mAh g ⁻¹ at a current density of 0.1 A g ⁻¹ and a voltage range of 0.01–2.5 V. Furthermore, the Na ₂ Ti ₆ O ₁₃ /rGO1||Na ₃ V ₂ (PO ₄ ) ₃ full cell are assembled, discharging an energy density of 251.3 Wh kg ⁻¹ _anode with a power density of 228.1 W kg ⁻¹ _anode after 100 cycles in a voltage range of 1.0–4.0 V.

At present, the output power density of nanogenerators (NGs) is insufficient to meet the substantial energy demands of many electronic devices, which significantly limits their further development in energy-harvesting applications. Therefore, optimizing the output performance of NGs is crucial for their advancement. This article focuses on the underlying principles and representative examples of nanogenerators, particularly those developed from nano- or microscale functional materials and utilized as nano- or micro-power sources. We introduce the fabrication and assembly of nanowire-based NGs, with an emphasis on materials such as zinc oxide (ZnO), gallium nitride (GaN), aluminum nitride (AlN), and Nylon-11 in terms of piezoelectric nanogenerators (PENGs) and triboelectric nanogenerators (TENGs). Additionally, we show fiber-based NGs incorporating materials such as poly(vinylidene fluoride) (PVDF), its copolymer poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), and poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP) in applications, such as yarns and textiles. Methods for surface modification and dielectric property control are discussed as strategies for optimizing the electrical energy output at the nano- or microscale. Furthermore, ZnO-based PENGs and cellulose-based TENGs are introduced as potential nano- or micro-power sources. Innovative applications such as flame-retardant textile TENGs, pyroelectric NGs, and implantable TENGs (iTENGs) for pacemakers are also discussed. Graphical abstract Nano- or microscale functional materials and optimized surface modification/control are the key to achieving nanogenerators as nano- or micro-power sources for next-generation Internet of Things (IoT)/wearable electronics.