Triboelectric nanogenerator based on changing the nanomorphology of polyoxometalates for gait monitoring of teenagers

Timely monitoring abnormal gaits of teenagers is crucial for their physical health and development. Triboelectric nanogenerators (TENGs) are widely used in the wearable field. Choosing high-performance and safe triboelectric materials to monitor abnormal gaits remains challenging. Polyoxometalates (POMs) nanomaterials can effectively serve as triboelectric materials due to rich surface morphology and large specific surface area. Herein, six different sized POMs nanorods (Ag₄SiW₁₂O₄₀·nH₂O) synthesized through self-assembly of POMs (H₄SiW₁₂O₄₀·nH₂O) were used as triboelectric materials. The TENG composed of nanorod with a diameter of 100 nm and a length of 400–1000 nm has optimal performance with the voltage, current density and charge are 104.3 V, 1127.1 μA·m⁻², and 15.38 nC, respectively, which are more than two times of the TENG composed of POMs (H₄SiW₁₂O₄₀·nH₂O). The optimized TENG maintained a voltage of around 100 V throughout the 1000 s stability test. The maximum power amounts to 25.2 μW at 500 MΩ external resistance. The reasons for the improved performance of nanorods TENG compared to POMs TENG are the increase in roughness and surface potential, which was confirmed through atomic force microscopy (AFM) and kelvin probe force microscopy (KPFM) testing. Furthermore, optimized TENG was applied to the feet of different teenagers and the left and right feet of the same person to monitor abnormal gait. The changes in voltage can sensitively display the inconsistency and abnormal situations of gaits. This study confirms the potential and unique advantages of POMs nanomaterials as triboelectric materials and provides a design scheme for gait monitoring.