Extraction of Evaporation-Driven Electrokinetic Streaming Potential from V₂O₅ Nanochannels through Secondary Sources

Abstract

The electrokinetic streaming potential derived from the natural evaporation process through nanoscale capillary channels is gaining increasing attention for its potential to be a self-sufficient and maintenance-free energy resource. An evaporation-induced energy-harvesting device displaying energy density up to 40 mWm–2 was fabricated by exploiting atomically thin two-dimensional (2D) nanofluidic channels of a reconstructed V2O5 membrane. Systematic studies were also performed to uncover the effects of internal device parameters, like channel dimensions, membrane thickness, and electrode separation, and external environmental conditions such as relative humidity and atmospheric temperature on energy efficiency. Most importantly, physical damages to the V2O5 device can be healed just by adding a drop of water. The evaporation-induced nanogenerators can be connected to add up the voltage and current values generated by individual devices. Besides, two methods are proposed here to overcome practical hurdles associated with these kinds of devices. In the first method, secondary materials (like cloth and paper) are employed to draw water molecules from the reservoir and transfer it to surface-active nanofluidic channels. In the second method, a hydrophilic gel membrane of agar, LiCl, and glycerol is used to mimic the natural hydrological cycle for continuous power output even in low humid conditions.

Evaporation-driven electrokinetic energy conversion: Critical review, parametric analysis and perspectives

“…Taking the same numbers as in the above estimates of the fully-wet length (and postulating 0.08 efficiency of EK conversion), we obtain the power density of about 10 mW/m 2 . This is in line with the largest experimental values reported up to date (see, for example, [24]) although in most cases the power densities were essentially lower. Thus for instance, they were around 150 µW/m 2 [50], 100 µW/m 2 [51], 130 µW/m 2 [13], 800 µW/m 2 [28], or 80 µW/m 2 [29].…”

“…Thus for instance, the OCV considerably increased in the temperature range from 22˚C to 82˚C, which can be of interest in the context of waste heat harvesting [50]. Moreover, the SCC increased about 5 times when temperature increased from 24˚C to 55˚C in quantitative agreement with the increase in saturated-vapor pressure [24]. Further positive correlations with temperature [19,29,47] and airflow rate [12,13,28,29,47] have been observed.…”

“…The simple model below assumes that the porous medium is isotropic and its specific properties (porosity, pore size, electrokinetic-charge density, electric conductivity) are the same across the film thickness. This is important to note in view of some experimental studies using clearly anisotropic materials (see, for example, [24]). In experiments, the film thicknesses have been much smaller than the other dimensions.…”

“…This occurs when the exchange-current densities are sufficiently large compared to the measured current densities. Moreover, an overwhelming majority of published studies on the EK energy harvesting from evaporation (the only exceptions being [19] where Ag/AgCl were employed and possibly [24], which used a silver paste) used nonreversible electrodes. A considerable part of studies employed carbon-based electrodes (for example, a CNT ink [25]).…”

“…The model postulates effective zeta-potential as one of the principal properties controlling the performance. Numerous studies have reported on determination of zeta-potential though often without providing any details on the method and conditions of the measurements (in particular, ionic composition and pH of solution) [12,24,28,29,34,47,49]. From the context, one can conclude that zeta-potentials were determined (probably using commercial instruments) from electrophoretic mobility (often in distilled water) of nanoparticles used to prepare the nanoporous films.…”