RESUMEN
Although water is almost transparent to visible light, we demonstrate that the air-water interface interacts strongly with visible light via what we hypothesize as the photomolecular effect. In this effect, transverse-magnetic polarized photons cleave off water clusters from the air-water interface. We use 14 different experiments to demonstrate the existence of this effect and its dependence on the wavelength, incident angle, and polarization of visible light. We further demonstrate that visible light heats up thin fogs, suggesting that this process can impact weather, climate, and the earth's water cycle and that it provides a mechanism to resolve the long-standing puzzle of larger measured clouds absorption to solar radiation than theory could predict based on bulk water optical constants. Our study suggests that the photomolecular effect should happen widely in nature, from clouds to fogs, ocean to soil surfaces, and plant transpiration and can also lead to applications in energy and clean water.
RESUMEN
We report in this work several unexpected experimental observations on evaporation from hydrogels under visible light illumination. 1) Partially wetted hydrogels become absorbing in the visible spectral range, where the absorption by both the water and the hydrogel materials is negligible. 2) Illumination of hydrogel under solar or visible-spectrum light-emitting diode leads to evaporation rates exceeding the thermal evaporation limit, even in hydrogels without additional absorbers. 3) The evaporation rates are wavelength dependent, peaking at 520 nm. 4) Temperature of the vapor phase becomes cooler under light illumination and shows a flat region due to breaking-up of the clusters that saturates air. And 5) vapor phase transmission spectra under light show new features and peak shifts. We interpret these observations by introducing the hypothesis that photons in the visible spectrum can cleave water clusters off surfaces due to large electrical field gradients and quadrupole force on molecular clusters. We call the light-induced evaporation process the photomolecular effect. The photomolecular evaporation might be happening widely in nature, potentially impacting climate and plants' growth, and can be exploited for clean water and energy technologies.
RESUMEN
Harvesting waste heat with temperatures lower than 100 °C can improve the system efficiency and reduce greenhouse gas emissions, yet it has been a longstanding and challenging task. Electrochemical methods for harvesting low-grade heat have aroused research interest in recent years due to the relatively high effective temperature coefficient of the electrolytes (>1 mV K-1) compared with the thermopower of traditional thermoelectric devices. Compared with other electrochemical devices such as the temperature-variation based thermally regenerative electrochemical cycle and temperature-difference based thermogalvanic cells, the thermally regenerative electrochemically cycled flow battery (TREC-FB) has the advantages of providing a continuous power output, decoupling the heat source and heat sink, and recuperating heat, and compatible with stacking for scaling up. However, the TREC-FB suffers from the issue of stable operation due to the challenge of pH matching between catholyte and anolyte solutions with desirable temperature coefficients. In this work, we demonstrate a pH-neutral TREC-FB based on KI/KI3 and K3Fe(CN)6/K4Fe(CN)6 as the catholyte and anolyte, respectively, with a cell temperature coefficient of 1.9 mV K-1 and a power density of 9 µW cm-2. This work also presents a comprehensive model with a coupled analysis of mass transfer and reaction kinetics in a porous electrode that can accurately capture the flow rate dependence of the power density and energy conversion efficiency. We estimate that the efficiency of the pH-neutral TREC-FB can reach nearly 9% of the Carnot efficiency at the maximum power output with a temperature difference of 37 K. Via analysis, we identify that the mass transfer overpotential inside the porous electrode and the resistance of the ion exchange membrane are the two major factors limiting the efficiency and power density, pointing to directions for future improvements.
RESUMEN
There is broad demand for humidity control for industrial, commercial, and residential applications. Current humidity pumping technologies require intensive maintenance because of the complexity of their mechanical structures. Furthermore, indirect utilization of solar energy increases both cost and energy loss. Here, we demonstrate a new humidity pumping concept based on multilayer moisture permeable panels. Such panels, with a simple structure, may allow the penetration of moisture from indoor (adsorption) to outdoor (desorption) with little heat loss. One-sun illumination is introduced as the direct energy source. A proof-of-concept prototype is designed and established, successfully dehumidifying indoor air with the best dehumidification rate of 33.8 gâ m-2â h-1. By applying such humidity pump, the indoor latent heat load can be handled independently, without any auxiliary unit, thus consuming no electricity.
