Continuous Energy Harvesting from Ubiquitous Humidity Gradients using Liquid‐Infused Nanofluidics

Abstract

Humidity‐based power generation that converts internal energy of water molecules into electricity is an emerging approach for harvesting clean energy from nature. Here it is proposed that intrinsic gradient within a humidity field near sweating surfaces, such as rivers, soil, or animal skin, is a promising power resource when integrated with liquid‐infused nanofluidics. Specifically, capillary‐stabilized ionic liquid (IL, Omim+Cl‐) film is exposed to the above humidity field to create a sustained transmembrane water‐content difference, which enables asymmetric ion‐diffusion across the nanoconfined fluidics, facilitating long‐term electricity generation with the power density of ≈12.11 µW cm‐2. This high record is attributed to the nanoconfined IL that integrates van der Waals and electrostatic interactions to block movement of Omim+ clusters while allowing for directional diffusion of moisture‐liberated Cl+. This humidity gradient triggers large ion‐diffusion flux for power generation indicates great potential of sweating surfaces considering that most of the earth is covered by water or soil.

Ionic Hydrogel for Efficient and Scalable Moisture‐Electric Generation

“…[1,12,13] Many methods have been attempted to improve their output performance, including asymmetrical structure, [14,15] chemical modification, [16,17] interface mediation, [18] heterogeneous system, [9] sunlight-coordinated moisture-electricity, [19] and new materials. [20,21] Since 2015, Qu et al has pioneered the work from graphene-based MEGs [22,23] with instantaneous output signal, followed by polymer-based MEGs with continuous power generation. [13,[24][25][26] Up to now, most of MEGs still suffer from an intermittent mode output signals or an inferior current density in the range of nano-amperes in a continuous mode or micro-amperes in an intermittent mode.…”

“…[ 1,12,13 ] Many methods have been attempted to improve their output performance, including asymmetrical structure, [ 14,15 ] chemical modification, [ 16,17 ] interface mediation, [ 18 ] heterogeneous system, [ 9 ] sunlight‐coordinated moisture‐electricity, [ 19 ] and new materials. [ 20,21 ] Since 2015, Qu et al. has pioneered the work from graphene‐based MEGs [ 22,23 ] with instantaneous output signal, followed by polymer‐based MEGs with continuous power generation.…”

Insights into Ionic Liquids: From Z-Bonds to Quasi-Liquids

“…The long-tail chains in the cations mainly interact with each other via hydrophobic interactions, whereas the anion is bound to the cluster via the Z-bond ( Figure 6 a). 51 The local rearrangement and charge separation substantially affect the properties of ILs, such as viscosity and dissolution. In industrial applications, the viscosity of ILs is usually high and imparts constraints on the mass transport and reaction processes, where researchers prepare and use water–IL mixtures rather than pure ILs to decrease the viscosity.…”

An Asymmetric Hygroscopic Structure for Moisture‐Driven Hygro‐Ionic Electricity Generation and Storage

“…This is mostly achieved by creating a built-in water gradient, which can be accomplished either by asymmetric moisturisation of the active materials in a sealing device, [18] or by relying on the environmental humidity gradient. [21] Maintaining this water gradient, and hence the electric field across the active materials, is challenging, as the The interactions between moisture and materials give rise to the possibility of moisture-driven energy generation (MEG). Current MEG materials and devices only establish this interaction during water sorption in specific configurations, and conversion is eventually ceased by saturated water uptake.…”

“…This is mostly achieved by creating a built‐in water gradient, which can be accomplished either by asymmetric moisturisation of the active materials in a sealing device, [ 18 ] or by relying on the environmental humidity gradient. [ 21 ] Maintaining this water gradient, and hence the electric field across the active materials, is challenging, as the saturated water uptake eventually leads to an even water distribution. Recently, significant progress was made by demonstrating the formation of a durable built‐in water gradient for long‐lasting MEG output.…”