Hierarchically Porous Fiber‐Based Nanofluidic Diode as an Efficient Multimode Hygroelectric Generator

Abstract

Harvesting electrical energy from different forms of water by using the hydrovoltaic effect is a promising approach to green energy acquisition. However, at present, different devices are required to obtain electrical energy from different water forms, and the output performance of the devices is not high, which greatly reduces the convenience and effectiveness of harvesting electrical energy from different water forms. Here, a carbon nanofiber electrode with a hierarchical porous structure capable of promoting water molecule adsorption, rapid penetration, and diffusion is reported. Besides, the electrode acts as a nanofluidic diode with anodic aluminum oxide in which the built‐in electric field drives selective separation and directional transport of ions and efficient ion/electron current conversion at the electrodes. Unlike typical hygroelectric devices, the device can work with moisture (93% relative humidity, 25 °C, open‐circuit voltage (VOC) ≈ 1.1 V, short‐circuit current density (JSC) ≈ 27 µA cm−2), water droplets (2 µL, VOC ≈ 1.03 V, JSC ≈ 640 µA cm−2), and bulk water (VOC ≈ 1.15 V, JSC ≈ 256 µA cm−2). It provides an efficient way to generate electricity in multiform water environment, greatly broadening the working scene and improving the adaptability of the device in complex weather environments.

Ion‐Diode‐Like Heterojunction for Improving Electricity Generation from Water Droplets by Capillary Infiltration

“…The built‐in electric field formed by the ion diode and adsorption EDLs inhibited the downward diffusion of H + (equivalent to ion rectification) and minimized the influence of the reverse diffusion current on the infiltration‐induced current (Figure 3d(iii)). [ 18,28 ]…”

“…The built-in electric field formed by the ion diode and adsorption EDLs inhibited the downward diffusion of H + (equivalent to ion rectification) and minimized the influence of the reverse diffusion current on the infiltration-induced current (Figure 3d(iii)). [18,28] To further illustrate the relationship between ion rectification and performance improvement, we tested the electrical characteristics of the ion-diode heterojunction. Figure 3c shows that the J-V curves are consistent with the nonlinear response of an ion diode.…”

“…Moreover, the measured J-V curves also exhibit rectification behavior, which weakens with ion migration and water evaporation. [28][29][30] As the current response slowly decreases after reaching its peak due to water evaporation and saturation of ionic gradients, the rectification also weakens; therefore, we recorded the J-V and current-time curves of the WDHEG under a squarewave bias voltage (from +2 to −2 V) after operating for different times (Figure 3e,f). As shown in Figure 3e, ion rectification can be observed in the formed diode-like heterojunction, where the current at a positive voltage (+2 V) is considerably larger than that at a negative voltage (−2 V).…”

“…In theory, iondiode-based asymmetric structures are capable of improving the current and can potentially be applied to enhance the performance and explain the mechanism. [28] Recently, an anion-cation heterostructured hydrogel with a current rectification ratio reaching 4.5 has been designed for moisture electricity generation; the hydrogel can adjust the ion gradients through ion rectification to achieve a long-term, uninterrupted output, with a voltage of 0.1 V and current of 0.4 μA. [29,30] Several HEGs based on the streaming potential and simultaneous use of asymmetric structures (e.g., heterojunctions) have been reported; however, their mechanism remains unclear.…”

All‐Printed Flexible Hygro‐Thermoelectric Paper Generator

“…In contrast to the renewable energies such as solar, wind, and hydrogen, which are currently constrained by either geographical or climatic requirements, the alternative promises hygroelectricity (HE) [1][2][3][4][5][6] or thermoelectricity (TE), [7][8][9][10][11][12] which rely on the lowgrade humidity or heat resources in ambient air environments, DOI: 10.1002/advs.202206483 that is highly desirable due to its affordability, ubiquity, and easy accessibility without geographic or climatic limitations, thereby enabling the useful generation of renewable energy to support wireless, self-powered systems. [13,14] However, in recent years the most important research has generally focused on two distinctly different energy harvesting strategies of HE and TE; HE is typically produced by the moist-diffusion effect, [15,16] while TE is generally induced by the Seebeck effect, the Soret effect, or the thermogalvanic effect, [17,18] and more importantly, each of them operates completely the different settings.…”