Piezoelectric Active Humidity Sensors Based on Lead-Free NaNbO3 Piezoelectric Nanofibers

Abstract

The development of micro-/nano-scaled energy harvesters and the self-powered sensor system has attracted great attention due to the miniaturization and integration of the micro-device. In this work, lead-free NaNbO3 piezoelectric nanofibers with a monoclinic perovskite structure were synthesized by the far-field electrospinning method. The flexible active humidity sensors were fabricated by transferring the nanofibers from silicon to a soft polymer substrate. The sensors exhibited outstanding piezoelectric energy-harvesting performance with output voltage up to 2 V during the vibration process. The output voltage generated by the NaNbO3 sensors exhibited a negative correlation with the environmental humidity varying from 5% to 80%, where the peak-to-peak value of the output voltage generated by the sensors decreased from 0.40 to 0.07 V. The sensor also exhibited a short response time, good selectively against ethanol steam, and great temperature stability. The piezoelectric active humidity sensing property could be attributed to the increased leakage current in the NaNbO3 nanofibers, which was generated due to proton hopping among the H3O+ groups in the absorbed H2O layers under the driving force of the piezoelectric potential.

Fabrication and Materials Integration of Flexible Humidity Sensors for Emerging Applications

“…In the work published by Gu et al , 17 NaNbO 3 nanofibers were proposed as enablers for flexible humidity sensors, along with a provision of piezoelectric energy harvesting, which is facilitated by flow of electrons to an external circuit and generation of a piezoelectric potential under bending stress.…”

“…(c) Synthesis of NaNbO 3 nanofibers by far-field electrospinning, spin-coating of PDMS onto nanofibers, lift-off to transfer nanofibers onto PDMS, and electrode deposition by sputtering through a shadow mask. Adapted with a CC BY license from ref ( 17 ). Copyright 2016 MDPI.…”

“… 29 Similarly, piezoelectric sodium niobate (NaNbO 3 ) nanofiber-based humidity sensors were reported where nanofibers were prepared by far-field electrospinning on silicon substrates and then transferred to PDMS elastomers. 17 The transfer procedure involved a three-step approach including spin-coating PDMS, curing, and lifting off the PDMS from the substrate. Upon transferring of nanofibers, interdigitated electrodes were formed by sputtering on a shadow mask to complete the device fabrication ( Figure 5 c).…”

Emerging applications driving innovations in gas sensing

“…In 2016, workers from the Chinese Academy of Science reported a self-powered humidity sensor based on piezoelectric NaNbO 3 (sodium niobate) nanofibres (NFs) (Gu et al, 2016). The fabrication process is illustrated in Figure 7 which yielded a flexible sensor with dimensions of approximately 2 ϫ 1 ϫ 0.2 cm 3 .…”

High Ionic Conductivity in Oxygen-Deficient Ti-Substituted Sodium Niobates and the Key Role of Structural Features

“…29 Downsizing NaNbO 3 affects the relative proportion of polymorphs. 31,32 It recently attracted interest for size-induced fer-roelectric 33-36 and photocatalytic [37][38][39][40] properties, but also for piezoelectric 41 devices. Substituting potassium for sodium leads to K x Na 1-x NbO 3 , which belongs to the most promising piezoelectrics for the replacement of the current industrial technologies based on hazardous lead titanates and zirconates.…”