Sustainable and flexible hydrovoltaic power generator for wearable sensing electronics
Graphical abstract
A sustainable flexible hydrovoltaic power generator (HPG) driven by water evaporation with high performance in portability, flexibility, and long-term, stable electricity generation was developed. Based on the sustainable and flexible HPG, we constructed a wearable self-powered flexile sensing system, and demonstrated its real-time motion monitoring ability, which provides a novel way to further utilize environmental energy for flexible and wearable devices.
Introduction
With the current boom in wearable electronics, a variety of flexible devices show promise for future lifestyles [[1], [2], [3], [4]]. Conventional batteries have difficulties meeting the requirements of flexible electronics due to their rigid format [5,6]. Harvesting energy directly from the ambient environment is a promising way to construct self-powered flexible smart systems. In recent years, various types of environmental energy harvesting technologies, such as photovoltaic [7,8], thermoelectric [[9], [10], [11]], triboelectric [[12], [13], [14]] and piezoelectric [15,16] induced power generation, have been successfully demonstrated. However, these environmental energy harvesting technologies usually have high environmental requirements [17], which limit their applications in wearable electronics. A promising flexible and renewable power source based on ambient environmental energy harvesting technology for wearable electronics with abundant reserves and little dependence on environmental conditions is still in urgent demand.
Natural water is the most abundant resource covering over 70% of Earth's surface [18], and it can flow and evaporate spontaneously by absorbing thermal energy, regardless of geographic location or environmental conditions [[19], [20], [21], [22]]. Recently, it has been reported a new energy conversion effect in the materials called hydrovoltaic effect, which is generating electricity from the direct interaction of nanostructures with flowing, waving, dropping and evaporating water [[23], [24], [25]]. Wanlin Guo and his coworkers reported that moving a droplet of ionic liquid along graphene can generate a pulse voltage of ~30 mV [26]. Jun Zhou and his colleagues found when deionized (DI) water covers the bottom end of a centimeter-sized carbon black sheet on a quartz substrate, sustained electricity with a short circuit current of 150 nA can be generated at ambient conditions [27]. In addition, the evaporation-driven water flow within an all-printed porous carbon film can reliably generate a maximum output power of up to 172 nW at ambient conditions [28]. However, how to realize stable electricity generation with higher output under deformation condition, and get rid of the fixed bulky water tank are the challenges for HPGs to serve as a portable power supply for flexible and wearable electronics.
Herein, we developed a sustainable flexible hydrovoltaic power generator by bonding functionalized conductive carbon black (FCB) onto a three-dimensional sponge (3DS) with polyvinyl alcohol (PVA) and further assembled the PVA@FCB@3DS with superabsorbent hydrogel. Driven by capillarity and water evaporation on the surface of the PVA@FCB@3DS film, sustainable electricity is generated when water in the superabsorbent hydrogel oozes and flows spontaneously through the nanochannels between the functionalized PVA@FCB nanoparticles. The flexible HPG can reliably generate an open circuit voltage (Voc) of up to 0.658 V and a short circuit current (Isc) of up to 63 μA with an optimized output power of 8.1 μW and a lifetime over 150 h at ambient conditions (20.4 °C, 55% RH). Attributed to the bonding effect of PVA, FCB nanoparticles are firmly attached to the 3DS skeleton, allowing it to go through dozens of kneading and bending cycles without any materials becoming dislodged. Moreover, a voltage of 3.67 V and a current of 358 μA are achieved by the simple connection of 6 units of HPGs in series and parallel, which can easily power a commercial calculator. Furthermore, we constructed a wearable self-powered flexile sensing system based on the sustainable and flexible HPG, and demonstrated its real-time motion monitoring ability, which provides a novel way to further utilize environmental energy for flexible and wearable devices.
Section snippets
Fabrication of PVA@FCB@3DS film
A PU three-dimensional sponge (3DS) (Qingdao Jili New Sponge Co., Ltd, China) was cut to desired sizes, followed by sonication cleaning in ethanol for 20 min. Then, the sponge was oven dried at 80 °C to produce a clean piece of 3DS. Next, 100 mg of conductive carbon black particles (CBs) with an average diameter of 30–45 nm and specific surface area of 100–110 m2 g−1, purchased from Nanjing XFNANO Materials Tech Co., LTD., China, were dispersed in 200 mL of ethanol by strong sonication (300 W)
Results and discussion
Fig. 1a shows a schematic diagram of the HPG, which is mainly composed of superabsorbent hydrogel, a PVA@FCB@3DS film, and a PET/PDMS enclosure. Commercial superabsorbent hydrogel is encapsulated in a PET/PDMS enclosure as the water source. Its main component is formed with polyacrylic acid branches [29], which can absorb an amount of water more than 150 times its mass and release water slowly at ambient conditions (shown in Fig. 1b and Figs. S1a–b). The PVA@FCB@3DS film is prepared by simple
Conclusion
In summary, a sustainable flexible HPG driven by water evaporation with high performance in portability, flexibility, and long-term, stable electricity generation was developed. The HPG can be easily fabricated by bonding FCB onto a 3DS with PVA and further assembling the PVA @FCB@3DS with solid superabsorbent hydrogel. Based on the constructed EDL nanochannels, the HPG can take advantage of the spontaneous evaporation of water to continuously convert ambient heat into electricity without any
Author declaration
We wish to draw the attention of the Editor to the following facts which may be considered as potential conflicts of interest and to significant financial contributions to this work.We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome.
We confirm that the manuscript has been read and approved by all named authors and that there are no other persons
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors acknowledge the funding support from the National Key R&D Program of China (2018YFB1304700, 2017YFA0701101), the National Natural Science Foundation of China (61574163, 61801473), the Science Foundation for Distinguished Young Scholars of Jiangsu Province, China (BK20170008). And the NANO-X Workstation scientifically supported this research.
Lianhui Li received his M.S. degree in 2017 from Shanghai University, China. Currently he is a Ph.D. candidate majoring in Physical Chemistry from School of Nano Technology and Nano Bionics at University of Science and Technology of China (USTC) since 2017. His research interests include flexible wearable sensors, flexible power generation.
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Lianhui Li received his M.S. degree in 2017 from Shanghai University, China. Currently he is a Ph.D. candidate majoring in Physical Chemistry from School of Nano Technology and Nano Bionics at University of Science and Technology of China (USTC) since 2017. His research interests include flexible wearable sensors, flexible power generation.
Mingming Hao is a Ph.D candidate majoring in Physical Chemistry from School of Nano Technology and Nano Bionics at University of Science and Technology of China (USTC) since 2019. His researches mainly include hydrogel materials and flexible sensors.
Xianqing Yang received her B. S. degree in applied chemistry from Nanjing Xiaozhuang University, China in 2017. Now she is a master candidate majoring in chemical engineering from School of Nano Technology and Nano Bionics at University of Science and Technology of China (USTC) since 2017. Her research interests mainly focus on the epidermal electronics, self-powered devices, and electronic skin.
Fuqin Sun received the B.S. degree in Electronic Information Engineering from QufuNormal University, China, in 2016. He is pursuing his Ph.D. degree in Electronic Science and Technology from the University of Science and Technology of China, Hefei, Anhui, China. His current research interests are in the area of flexible sensors and flexible neuromorphic devices.
Yuanyuan Bai is currently a postdoctoral researcher in Suzhou Institute of Nano-Tech and Nano-Bionics at Chinese Academy of Sciences. People's Republic of China. She received the B.Sc. and Ph.D in electronic science and technology from Xi'an Jiaotong University, China, in 2010 and 2016 respectively. Her research interests focus on multifunctional smart sensing materials and devices, and their applications in wearable electronics.
Haiyan Ding is an assistant researcher at Suzhou Institute of Nanotech and Nanobionics, Chinese Academy of Sciences. She received her B.S. (2007) and M.S. (2010) degree from Soochow University. Her research mainly focuses on flexible wearable sensors.
Shuqi Wang is currently a postdoctoral researcher in Suzhou Institute of Nano-Tech and Nano-Bionics at Chinese Academy of Sciences. People's Republic of China. He received the B.Sc. in biotechnology (2010) and Ph.D in chemistry (2016) from University of Science and Technology Beijing, China. His research interests focus on the synthesis of nanomaterials for electrochemical biosensors, and their application in wearable health monitoring.
Ting Zhang is a Professor at Suzhou Institute of Nanotech and Nanobionics, Chinese Academy of Sciences. He received his B.S. (1999) and M.S. (2002) degree from Nankai University, and Ph.D. degree in chemical engineering at University of California, Riverside in 2007. His research mainly focuses on the development of smart materials, micro/nanosensing devices and smart microsystems for medical diagnostics, robotics, and environmental monitoring applications. He has published more than 70 peer-review papers in journals like Advanced Materials, Science Advances, Nano Letters, Nano Energy, etc., and applied more than 50 patents (several patents have been licensed and successfully applied in Industry).