Highly sensitive and dynamically stable strain sensors based on porous-designed Fe nanowires/multi-walled carbon nanotubes with stable bi-conducting networks

Flexible sensors for high strain sensitivity and dynamic stability are important for the development of human-interactive and health-monitoring devices. However, establishing a stable conductive network with low-conductivity material filling that can resist tensile strain failure and achieve high device performance still faces significant challenges. Herein, a highly stretchable and sensitive strain sensor with strong dynamic stability and low conductive materials filling was fabricated based on highly conductive multi-walled carbon nanotubes (MWCNTs) and Fe nanowires (NWs) to construct a porous-designed bi-conducting network using a salt sacrificial template approach. The porous-designed Fe NW/MWCNT strain sensor (PFMS) with low material filling (3.6 wt.% Fe NWs and 10.6 wt.% MWCNTs) showed high sensitivity with a gauge factor (GF) of 134.98 (strain range 0–22%) and 569.37 (strain range 22%–60%), which is much higher compared with the pure MWCNT strain sensor with a GF of 7.46. This is attributed to the significant change in the contact area and contact resistance of the Fe NW/MWCNT bi-conducting network during tensile strain. In addition, the PFMS exhibited high repetitive stability over 2000 stretching-releasing cycles. When attached to the human body, the PFMS functions as a health-monitoring device, that can accurately distinguish human motions such as the bending of fingers, knees, and elbows. Finally, the proposed strategy pens a novel avenue for constructing porous conductive networks using polymer composites and is highly competitive for developing high-performance strain sensors.