Supersonically Sprayed Cobalt Titanate and PVDF for Flexible Piezoelectric Nanogenerators

Abstract

Piezoelectric nanogenerators (PENGs) are the core components of self-powered devices used in sensors, ecofriendly wearable gadgets, and biomedical implants. This study introduces and demonstrates a flexible PENG with supersonically cold-sprayed films of cobalt titanate (CTO) and polyvinylidene fluoride (PVDF). An electrically poled PENG produces a maximum output voltage of 34.8 V under a tapping force of 20 N, whereas a CTO/PVDF-based PENG exhibits 25.4 V across a loading resistance ( $R_{\text{L}}$ ) of 50 MΩ and generates a short-circuit current of 30 μA at 0.1 MΩ. Furthermore, the maximum power density is 25 μW·cm-2 at $R_{\text{L}}=0.6$  MΩ. Cyclic tapping and bending test results show that open-circuit voltages (Voc) of 25.4 and 5.8 V are produced under the tapping cycle of $N_{\text{tap}}=4200$ and bending cycle of $N_{\text{bend}}=750$ , respectively, confirming the mechanical durability of the PENG. Thus, the potential of CTO/PVDF films for use in PENGs with various functionalities can be confirmed based on the $V_{\text{oc}}$ values generated from bending, mobile tapping, walking, and lifting movements.