Nanogenerators: Principles, Materials, and Applications in Energy Harvesting

Nanogenerators harness energy from ambient mechanical, thermal, or frictional energy for portable and self‐powered devices. Piezoelectric nanogenerators (PENGs) utilize zinc oxide (ZnO) nanowires and lead zirconate titanate (PZT) to convert vibrations, demonstrating voltages of up to 66 V and power densities of up to 170 µW/cm 2 , particularly with magnesium‐doped gallium nitride (GaN:Mg) and zinc oxide coaxial structures or configurations. Li‐doping allowed 5 times the current output. Triboelectric nanogenerators (TENGs) utilize contact electrification, achieving maximum power densities of 5.55 W/m 2 in MXene‐based systems or 34.26 W/m 3 from oscillating ocean waves. Pyroelectric nanogenerators (PyNGs) utilize temperature fluctuations to generate approximately 1.8 V from low‐frequency acoustic waves in polyvinylidene fluoride (PVDF). Thermoelectric generators (TEGs) using a Bismuth telluride/Antimony telluride (Bi 2 Te 3 /Sb 2 Te 3 ) film will generate 193 µW at a 50 K Δ T , or 71.8 µW/cm 2 in the airflow, powering a battery‐free Electrocardiogram (ECG) monitor. The materials of importance are Bi 2 Te 3 (ZT = 1), ZnO, MXenes, and lead telluride (PbTe). Nanogenerators will have applications ranging from wearables (generating 120 mV from body heat) to biomedical implants, smart tires (for a total of approximately 1.79 mW), and ocean buoys. Major challenges with nanogenerators are low output, durability, and scalability when developing into commercial products. Hybridization and nanostructuring methodologies will enhance commercialization for nanogenerators.