2D MoO₃/PVDF–HFP Nanocomposites for Flexible Piezoelectric Nanogenerator and Wireless Mechanosensor Applications

Abstract

Recent advancements in wireless, flexible, and selfpowered sensors have opened avenues for real-time monitoring of mechanical pressure stimuli at remote locations with utmost resolution and precision. This work reports on the development of a 2-D MoO 3 /PVDF−HFP composite-based flexible and highly efficient piezoelectric nanogenerator (PNG). The influence of 2-D α-phase MoO 3 (α-MoO 3 ) nanoflakes on the polymorphism of poly(vinylidene fluoride-co-hexa-fluoropropylene) (PVDF−HFP) was systematically investigated with the aim of maximizing the electroactive β phase. A series of α-MoO 3 nanoflakes-incorporated flexible, transparent, and self-standing PVDF−HFP composite films with varying loading weight percentages of 1, 1.5, and 2% (PMO1, PMO1.5, and PMO2, respectively) were prepared by the solution casting technique. PMO2 exhibited a high β-phase fraction of 76% and was used to fabricate a facile and flexible PNG device. Gentle finger tapping onto the PNG showed an excellent open-circuit output voltage (50 V across 30 MΩ resistance) with a maximum power density of 1512 W m −3 and a conversion efficiency of 30.4%. The PNG demonstrated a promising performance for qualitatively detecting dynamic pressure stimuli. It was able to precisely monitor and discriminate the bending motion of different fingers and fine motions of proximal interphalangeal and metacarpophalangeal joints of the index finger. A (4 × 4) sensing matrix comprising the PNG was successfully employed to detect the spatial distribution of static pressure stimuli (with a sensitivity of ∼15.5 MPa −1 ), and the developed matrix was able to precisely record the shape and size of the objects placed onto it. The PNG-based sensor was also integrated with an android mobile interface through wireless technology for remote sensing applications. Hence, the fabricated PNG can be a promising device for wireless monitoring of mechanical pressure stimuli in different cutting-edge technologies such as healthcare monitoring, robotics, and wearable electronics.