All-fiber pyro- And piezo-electric nanogenerator for IoT based self-powered health-care monitoring

In this work, an all-fiber pyro- and piezo-electric nanogenerator (PPNG) is designed using multiwall carbon nanotube (MWCNT) doped poly(vinylidene fluoride) (PVDF) electrospun nanofibers as the active layer and an interlocked conducting micro-fiber based electrode for converting both thermal and mechanical energies into useful electrical power. The PPNG generates high electrical throughput (output voltage ∼35 V, maximum power density ∼34 μW cm-2 and power conversion efficiency (ηpiezo) ∼ 19.3%) with an ultra-fast response time of ∼10 ms. Owing to the higher piezoelectric charge co-efficient (|d33| ∼ 51.3 pC N-1) and figure of merit (FoM ≈ 5.95 × 10-11 Pa-1) of PVDF-MWCNT nanofibers in comparison to the neat PVDF nanofibers (|d33| ∼ 22 pC N-1 and FoM ≈ 9.7 × 10-12 Pa-1) the PPNG operates a range of consumer electronic components such as capacitors and light emitting diodes. Furthermore, the electroactive phase content (∼87%) is improved in the active layer due to the interfacial interaction between the surface charges at from the π-electron cloud of the MWCNT and -CH2- dipoles of the PVDF chain. Additionally, the PVDF-MWCNT nanofibers possess fifteen times higher pyroelectric coefficient (∼60 nC m-2 K-1) compared to that of neat PVDF nanofibers (4 nC m-2 K-1). As a result, the PPNG is capable of converting very large temperature fluctuations (ΔT ∼ 14.30 K) to electrical energy (such as the open-circuit voltage of 250 mV and a short-circuit current of 83 pA). Besides this, it is capable of detecting very low-level thermal fluctuations (as low as ΔT ∼ 5.4 K) with responsivity of ∼1.48 s and possesses very high mechano-sensitivity (∼7.5 V kPa-1) which makes it feasible for use as a biomedical sensor since the body temperature and bio-mechanical signals (such as breathing temperature, pulse rate, vocal cord vibrations, coughing sound, and so on) have an immense signature of health conditions. As a proof-of-concept, the all-fiber PPNG is employed as a biomedical sensor by integrating with the Internet of Things (IoT) based human health care monitoring system as well as for remote care of infectious diseases (e.g., applicable for pneumonia, COVID-19) by transferring the pulse response, body temperature, coughing and laughing response wirelessly to a smartphone.