Scientists from the Central University of Gujarat and Woxsen University in India have created a new composite material for triboelectric nanogenerators, devices that can generate electricity from mechanical movements such as pressure, vibration or human motion. The nanocomposite is based on graphite nitride, titanium dioxide and conductive polymer polyaniline, which are embedded in a polymer matrix of polyvinylidene fluoride (PVDF), a flexible polymer with good dielectric and piezoelectric properties. This combination makes it possible to significantly improve energy conversion efficiency by controlling electrical charges at the molecular level.
Conventional triboelectric generators function by bringing two materials with different electron-attracting properties into contact. During friction, one material becomes positively charged and the other negatively charged, and a current is generated when they are separated. However, the efficiency of these devices is often limited: some part of the charge gets lost, and the materials do not always transfer the stored energy to an external circuit efficiently. The Indian scientists have proposed a solution to this problem by adding special fillers to the polymer film so as to perform three functions at the same time: trapping the charge, preventing it from dissipating and ensuring its rapid transfer to the electrode.
In order to obtain this material, the researchers first synthesized its individual components. They produced graphite nitride (g-C₃N₄) in the form of thin nanosheets via thermal treatment of thiourea. Then, they used chemical polymerization to stitch aniline molecules to these sheets while adding titanium dioxide (TiO₂) nanoparticles. This resulted in a structure resembling a sheet coated with nanoparticles and interwoven with conductive polymer chains. The composite was then mixed with a solution of PVDF in dimethylformamide and deposited on a glass substrate coated with a transparent conductive layer of indium tin oxide via spin coating, a method that produces a uniform thin film just a few micrometers thick. The opposite layer was made of Teflon, a material with a high tendency to accumulate negative charges.
The new device operates in a vertical contact-separation mode. When the upper Teflon layer is pressed against the lower PVDF-based composite layer, triboelectric charges are generated at the interface. When the spring is released, the layers separate, which creates a potential difference, and electrons flow through the external circuit, generating a current. Seeking the optimal balance of properties, the scientists developed four versions of the generator, varying the Teflon concentration from 30% to 60% by weight. They conducted all measurements manually at room temperature, simulating real-world operating conditions, and processed the signals using a special script that automatically extracted each keystroke cycle, removed noise and calculated the key parameters.
The results showed a clear tradeoff between voltage and current. The device with 60% Teflon reached a maximum open-circuit voltage of 4.56 volts, since this material creates a very high surface charge density. However, the short-circuit current was comparatively low at 0.9–1.2 μA. Meanwhile, the generator with 30% Teflon produced a voltage of 3.2–3.4 volts, while the current reached 2.86 μA and the charge transferred per cycle stood at approximately 200 nanocoulombs, almost an order of magnitude greater than that of the 60% Teflon sample. The researchers explain that lowering the Teflon content improves mechanical contact and the effective permittivity of the layers, which accelerates charge transfer while reducing the accumulated potential.
The analysis of operational stability was particularly revealing. Cycle by cycle, the scientists assessed the parameter spread and found that the 30% sample demonstrated more uniform current pulses and a smaller interquartile range, indicating more stable operation. The crest factor (the ratio of peak current to root mean square) for this sample was 3.2 versus 4.3 for the 60% sample, which confirms that the former operates in a more predictable and stable manner. Therefore, it is possible to adjust the composition to choose high voltage for sensors or high current with a large charge transfer for powering devices.
It should be noted that the prototype has not reached record-high voltage, as some devices can deliver hundreds of volts. However, the Indian scientists did not intend to hit new records, but rather systematically studied the operation of their triple system. Their chief conclusion is that a well-chosen composite makes it possible to control the tradeoff between voltage and current, while variation in Teflon concentration can customize the device for any application, from sensors and wearable electronics to autonomous power sources for low-power devices.
