Abstract
Circadian humidity fluctuation is an important factor that affects human life all over the world. Here we show that spherical cap-shaped ionic liquid drops sitting on nanowire array are able to continuously output electricity when exposed to outdoor air, which we attribute to the daily humidity fluctuation induced directional capillary flow. Specifically, ionic liquid drops could absorb/desorb water around the liquid/vapor interface and swell/shrink depending on air humidity fluctuation. While pinning of the drop by nanowire array suppresses advancing/receding of triple-phase contact line. To maintain the surface tension-regulated spherical cap profile, inward/outward flow arises for removing excess fluid from the edge or filling the perimeter with fluid from center. This moisture absorption/desorption-caused capillary flow is confirmed by in-situ microscope imaging. We conduct further research to reveal how environmental humidity affects flow rate and power generation performance. To further illustrate feasibility of our strategy, we combine the generators to light up a red diode and LCD screen. All these results present the great potential of tiny humidity fluctuation as an easily accessible anytime-and-anywhere small-scale green energy resource.
Highlights
Circadian humidity fluctuation is an important factor that affects human life all over the world
When a fluid is placed on solid surfaces, the fluid wets the solid with an equilibrium contact angle (CA) θC, defined by the Young’s equation[10–14]. Our design is such that a wellshaped fluid drop containing IL (1-Octyl-3-methylimidazolium chloride), selected due to negligible evaporation losses alongside their large moisture absorption/desorption capability when exposed to air[15], is pinned on poly(dimethylsiloxane) (PDMS) nanowire array with certain CA
This sustainable power supply is attributed to continuous WCS variation created by the fluctuating RH that ensures the bulk IL is either unsaturated or oversaturated
Summary
Circadian humidity fluctuation is an important factor that affects human life all over the world. We show that spherical cap-shaped ionic liquid drops sitting on nanowire array are able to continuously output electricity when exposed to outdoor air, which we attribute to the daily humidity fluctuation induced directional capillary flow. To maintain the surface tension-regulated spherical cap profile, inward/outward flow arises for removing excess fluid from the edge or filling the perimeter with fluid from center This moisture absorption/desorption-caused capillary flow is confirmed by in-situ microscope imaging. When a fluid is placed on solid surfaces, the fluid wets the solid with an equilibrium contact angle (CA) θC, defined by the Young’s equation[10–14] Our design is such that a wellshaped fluid drop containing IL (1-Octyl-3-methylimidazolium chloride), selected due to negligible evaporation losses alongside their large moisture absorption/desorption capability when exposed to air[15], is pinned on poly(dimethylsiloxane) (PDMS) nanowire array with certain CA Our concept for integrating IL drop with humidity fluctuation to generate electricity is based on the following hypothesis: (1) moisture absorption/desorption within IL drop would cause directional flow along solid/liquid interfaces, (2) such flow would induce a potential difference due to ion re-distribution
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