Piezoelectric energy conversion by lead-free perovskite BaTiO₃ nanotube arrays fabricated using electrochemical anodization

Synthesis approaches for diverse morphologies of 1D piezoelectric ceramic nanomaterials are still challenging to investigate nanoscale properties and applications. In this work, we demonstrated a vertically grown barium titanate (BaTiO₃; BT) nanotube (BT NT) arrays fabricated using optimized electrochemical anodization and hydrothermal reaction. The centimeter-scale synthesized BT NT arrays with a high aspect ratio of up to 300 showed the complete perovskite crystal structure and the notable piezoelectric coefficient of ~180 pm·V⁻¹. A single BT NT-based piezoelectric device was fabricated on a flexible plastic substrate using a highly controlled focused ion beam-assisted method. The single BT NT device produced a piezoelectric voltage of ~150 mV and a current of ~3 nA when the NT was mechanically stimulated by bending and releasing, which are higher than previously reported values for 1D piezoelectric nanoscale materials. Finally, a flexible piezoelectric energy harvester (f-PEH) was achieved using vertically grown BT NT arrays with an elastomer as a vertically aligned nanocomposite; its generated maximum open-circuit voltage and short-circuit current were ~1.0 V and ~20 nA, respectively. The approach in this study can propose the vision for more advanced 1D piezoceramic nanomaterials and future piezoelectric nanodevices.