Moisture-Driven Power Generation for Multifunctional Flexible Sensing Systems

Abstract

Flexible self-powered multifunctional sensing systems provide a promising direction for the development of wearable electronics. Although increased efforts have been devoted to developing self-powered integrated devices, the development of flexible and adaptable sensing systems with miniaturized stable power supplies is highly desirable yet greatly challenging. Herein, an ambient moisture-induced self-powered wearable sensing system was fabricated by integrating a porous polydopamine layer with a hydroxy group gradient (called g-PDA) based moisture-enabled power generator and a flexible pressure sensor. Due to the large amount of gradient-distributed free cations (H+) and locally confined anions produced in wide electrode spaces during hydration of the thin porous g-PDA film, the moisture-induced potential and effective output power density of the g-PDA-based power generator rapidly reaches up to 0.52 V and 0.246 mW cm–2, respectively. Importantly, the voltage output within 120 s only has 6% change, and a continuously open-circuit voltage can be maintained after 1900 s of attenuation, which is a breakthrough for the duration of humidity generation. Finally, a self-powered wearable multifunctional sensing system has been demonstrated to be able to provide real-time monitoring of human physiological signals, without an external power supply, which opens new opportunities for future self-powered multifunctional sensing systems.

Moisture‐Enabled Electricity Generation: From Physics and Materials to Self‐Powered Applications

“…Reproduced with permission. [ 183 ] Copyright 2019, American Chemical Society. e) A flexible, transparent generator with PSS–PVA as an active layer showing excellent self‐healing capability.…”

“…Many proton conductive polymers like polydopamine (PDA), [ 183 ] polypyrrole (PPy), [ 184 ] PSSA, Nafion, poly(vinyl alcohol) (PVA), poly(acrylic acid), hydroxyethyl cellulose, and natural polysaccharides including guar gum and alginate sodium have demonstrated capability to generate electricity under exposure to moisture (Figure 13c,d). [ 82 ] These polymers contain a variety of sulfonated or oxygenated functional groups (e.g., hydroxyl, carboxylic groups, and sulfonic acid group), which release free protons when in contact with water molecules.…”

“…Based on the role played by electricity in an electronic loop, we can separate the functionality of MEGs in self‐powered systems into two categories: 1) the MEG acts as a sensor, implying that the generator itself works as a sensing unit; 2) the MEG acts as a power source, where the generator provides the power to drive other electronics. Some practical applications at present include proximity sensing, [ 42 ] humidity sensing, [ 209 ] tactile sensing, [ 40 ] electronic skin, [ 210 ] breathing monitoring, [ 183,211 ] environmental monitoring, [ 209 ] sweat monitoring, [ 90 ] information storage, [ 134 ] and electronic displays. [ 42 ] Most of these studies are still in the evaluation stage, but suggest that many promising applications may be enabled by the availability of moisture‐enabled electricity generation.…”

Self-powered wearable electronics

“…When the biosensor attached to a finger and the gel electrode connected to a person's chest, OECTs can acquire clear and stable heart rate signals, with a power-conversion efficiency (PCE; 10.49%) superior to that of other flexible OPVs, resulting in a high power-per-weight (11.46 W/g). In 2019, Li et al designed a novel moisture-driven flexible multifunctional sensing system and his system was prepared by connecting a flexible piezoresistive sensor in series with a moisture-enabled power generator based on a porous polydopamine layer with a hydroxy group gradient (Li et al, 2019) (Figure 7d). The environmentalmoisture-induced self-powered sensing system is under a high sensitivity to both humidity and pressure, which can provide real-time monitoring of human physiological signals such as breathing and pulse by collecting ambient moisture and converting into electricity.…”

Deep learning-enabled triboelectric smart socks for IoT-based gait analysis and VR applications

“…To further improve the quality of life, the invention of various wearable sensors based on electrocardiograph 4 , electromyogram 5 , body temperature 6 , heart rate 7 , strain sensors 8 , etc., offers opportunities in both fitness service and medical diagnostics by the long-term monitoring of physiological signals. In particular, the detection of the human motions is significantly valuable in creating insights into the user's health status, activity quantifying, and the establishment of an effective channel between humans and machines 9,10 . When it comes to the continuous and convenient monitoring of diversified human motion states, cameras and inertial measurement unit (IMU) sensors are the widely adopted devices for smart home applications 11,12 .…”