A new sandwich-style triboelectric nanogenerator improves smart flooring by harvesting motion-based energy, even in wet conditions, using Ecoflex composites.
(Nanowerk Spotlight) In modern building design, the floor remains an underutilized surface. While walls, ceilings, and appliances have grown smarter and more connected, flooring has largely retained a passive role—despite being the most consistent interface between humans and their built environment. Each step, press, or shift in weight represents mechanical energy that is typically wasted. Yet the floor is also a strategic location for sensing, automation, and passive energy harvesting.
Making use of this surface could transform how we monitor security, assist with elder care, manage lighting, or track physical activity in a home or public space. Until now, most attempts to embed sensors or energy harvesters into flooring have been held back by durability issues, environmental vulnerability, and inconsistent performance under everyday conditions like humidity and wear.
Triboelectric nanogenerators (TENGs), which convert mechanical motion into electricity using frictional contact between materials, offer a possible solution. Unlike batteries or traditional sensors, TENGs can operate without an external power supply and can be made from flexible, inexpensive materials. This makes them appealing for applications in wearable technology, soft robotics, and smart infrastructure.
However, when applied to floors, conventional TENGs have struggled with practical limitations. Their electrodes are often exposed, making them susceptible to oxidation or degradation, especially in wet or humid environments. Performance also tends to decline under repeated use, and many systems remain too fragile or complex to integrate into washable, flexible flooring.
a) A schematic depicting the casting process of the EC-BT-FG composite film, showcasing the intricate layers and materials involved. b) A detailed illustration of the SWSE-TENG fabrication, highlighting the innovative steps in its construction. (Image: Reprintede with permission from Wiley-VCH Verlag)
The system centers on Ecoflex, a soft silicone elastomer known for its flexibility and high electron affinity, making it suitable as a tribonegative surface—one that tends to attract and retain electrons during frictional contact. However, Ecoflex on its own has drawbacks. Its insulating properties can lead to inefficient charge transfer during the separation phase of contact, which reduces output. To overcome this, the researchers embedded two functional fillers: barium titanate (BT), a ceramic material with piezoelectric properties, and a graphite-fluorinated polymer (FG), which boosts surface charge density and helps trap electrons through its fluorine and graphite content.
Several combinations of these fillers were tested, each at different weight ratios within the Ecoflex matrix. Among these, the EC-5-5 composite—containing 5% BT and 5% FG by weight—emerged as the most effective. This formulation achieved the highest balance of dielectric constant, piezoelectric responsiveness, and static charge retention. Compared to pure Ecoflex, EC-5-5 exhibited a significant increase in both its ability to store electrical charge and its responsiveness to mechanical pressure. X-ray diffraction confirmed that all three materials retained their crystalline structure and remained physically blended, rather than chemically reacting, which helped preserve their individual functionalities.
The researchers fabricated a triboelectric nanogenerator using the EC-5-5 composite in a sandwich-style configuration. In this design, an aluminum electrode is embedded between two layers of the EC-5-5 film, which increases contact area and shields the electrode from exposure. When tapped by a hand wearing a nitrile glove—chosen for its positive triboelectric properties—the device generated an open-circuit voltage of 1000 volts and a short-circuit current of 25 microamperes. These output levels represent substantial improvements over earlier single-layer designs and are sufficient for powering low-energy electronics or triggering wireless signals.
This design also addresses a core limitation of past TENG-based flooring: resistance to environmental stress. The sandwich structure allows the electrode to be completely enclosed, protecting it from moisture and physical damage. Performance remained stable after the device was immersed in water for over 24 hours. Even at 100% relative humidity, it continued to operate with output only gradually reduced. This water resistance is partly due to the hydrophobic nature of the Ecoflex composite, confirmed by contact angle measurements, which showed a water contact angle of 97°, indicating the surface repels water rather than absorbing it.
The device was also tested under a range of real-world conditions. Its output remained reliable between −5 and 70°C. Tapping speed and applied force were also varied. Higher forces and faster tapping produced greater voltage, as expected, due to improved surface contact and faster charge separation. When connected to capacitors, the device successfully stored energy and powered a stopwatch for short intervals. It also demonstrated durability during extended testing, maintaining consistent performance after 30 days of environmental exposure.
To assess its practicality for smart home applications, the system was installed in flooring panels and tested under human activity. During walking and running, it consistently produced detectable voltage signals. Even light bending of the panel generated electrical output. The researchers further demonstrated its use as a safety feature by integrating it with LEDs positioned near exit paths and doorways. In a security scenario, the device was embedded in a floor mat connected to an audible alarm, triggering a sound when someone stepped on it—offering a non-camera-based method for intrusion detection. The device also showed potential for use in sports settings, detecting boundary line contact in kabaddi, a team sport that relies heavily on foot placement.
One key strength of the system lies in its balanced material composition. Barium titanate enhances charge retention and piezoelectric output, but at higher concentrations, it tends to agglomerate, which can reduce electrical performance. Similarly, while FG increases surface charge density, too much of it can create conductive pathways that lead to charge leakage. The EC-5-5 ratio avoids these pitfalls by balancing the two effects—enhancing output without sacrificing stability.
While the system performed well in wet environments, it did not function while fully submerged. In underwater conditions, conductive pathways in the surrounding water allowed generated charges to dissipate, preventing voltage build-up. Although this limits its use for submerged energy harvesting, it creates an opportunity to use the device as a water exposure sensor—detecting water intrusion in basements, under appliances, or in flood-prone areas.
The sandwich-style design introduces some trade-offs. As the film thickness increases, output decreases due to higher internal resistance and reduced proximity between the electrode and the surface. Thicker films also reduce flexibility, making them less suitable for integration into curved surfaces or under thin carpet layers. Therefore, future improvements may involve optimizing thickness or developing multi-zone films with variable stiffness and responsiveness.
Compared to previously reported TENG-based smart floors, the device described here offers significantly higher output. Earlier systems often produced less than 200 volts and rarely exceeded 1 mW/m². The EC-5-5-based sandwich TENG achieved a peak power density of 1.55 W/m², more than an order of magnitude improvement. This level of performance makes it a viable candidate for self-powered sensing in environments where wiring is impractical or aesthetic discretion is desired.
Overall, the work demonstrates a durable, flexible, and wash-resistant triboelectric nanogenerator that integrates effectively into floor surfaces. By combining a mechanically robust material with a protected electrode configuration and a finely tuned composite formulation, the researchers have developed a system with meaningful potential for applications in smart infrastructure. Whether used to guide emergency lighting, monitor human presence, or detect boundary crossings in sports, this approach advances the technical feasibility of flooring that does more than just support weight—it supports function.
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