Metal-free flexible triboelectric nanogenerator based on bifunctional carbon fiber for mechanical energy harvesting and human activity monitoring

Conductive electrodes in triboelectric nanogenerators (TENGs) typically use metal-based materials. However, such devices have limited flexibility and challenges in humid environments. To overcome this issue, we present a metal-free flexible TENG made from bifunctional carbon fiber paper that serves as both a conductive electrode and an efficient tribo-positive friction layer. The electrical performance of carbon fiber paper-based TENG (CFP-TENG) at 3 Hz demonstrated a peak-to-peak voltage of 109.1 V, a current of 10.8 μA, and a power density of ∼ 0.093 W/m² at 7 MΩ external resistance. A 20 µF capacitor is also charged, and 38 light-emitting diodes (LEDs) arranged in the letter 'DGU' can be lighted. The CFP-TENG device's high flexibility allows it to sustain 12,000 repeated mechanical contact-separation cycles and fold, twist, and roll the device without degrading performance. In addition, the hydrophobic characteristic of carbon fiber ensures the improved moisture resistance of the CFP-TENG device compared to conventional copper electrodes. Furthermore, the CFP-TENG is successfully integrated into various human joints as a self-powered motion sensor for tracking real-time human activity monitoring, including finger motion detection, arm motion, walking, and running activities. A metal-free TENG based on bifunctional carbon fibers paves the way for energy- harvesting solutions and self-powered biomedical sensors.