Piezoelectric power generation of vertically aligned lead-free (K,Na)NbO₃ nanorod arrays

We report piezoelectric power generation at room temperature, as well as at elevated temperature, using vertically aligned lead-free (K,Na)NbO₃ nanorod arrays on a conducting substrate. Ferroelectric (K_0.6Na _0.4)NbO₃ nanorod arrays having a high piezoelectric coefficient of ca. 180 pm V^-1 were epitaxially grown on a conducting SrRuO₃/SrTiO₃ substrate via the facile hydrothermal method at low temperature (ca. 190 °C). After electric poling, the (K,Na)NbO ₃ nanorod array-based nanogenerator generated a stable high power density of ∼101 μW cm^-3 at 20 °C, almost 16 times greater than a BaTiO₃ nanowire-based vibrational energy harvester (ca. 6.27 μW cm^-3). The (K,Na)NbO₃ nanorod array-based nanogenerator exhibited little frequency dependence on external force over a relatively low-frequency range (≤10 Hz) and showed long-term durability even at 100 °C, with a power density of 29 μW cm^-3. This work demonstrates the potential of eco-friendly nanogenerators based on (K,Na)NbO₃ nanorod arrays for high-output power generation under various environmental conditions.