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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.

Summary Currently, the thermal management of electronics has been drawing growing attention. The use of latent heat emerges as an attractive means for intermittent heat dissipation. However, traditional phase change materials (PCMs) are limited by their relatively low enthalpies. In this paper, we demonstrate a passive thermal management strategy through the desorption process of water inside sorbents. The spontaneous adsorption enables self-recovery of working capacity at rest mode. The basic guideline for selecting proper sorbents is outlined. In the proof-of-concept test, we coated MIL-101(Cr) powders onto metallic substrates. The coating of 0.288 g achieved a temperature drop (maximum 8.6°C) for 25 min at a heating power of 1.5 W. The equivalent enthalpy of the coating can be up to 1,950 J/gcoating, indicating a significant improvement compared to that of traditional PCMs. Our results suggest that this strategy could find promising applications in a variety of practical scenes.

Summary Humidity management is essential and widely needed in various fields. Traditional moisture removal technologies are mostly based on cooling condensation or desiccant dehumidification. These methods come with inherent defects of energy efficiency and are bulky and complex for small-space humidity-control applications. Here, we demonstrate a full-solid-state humidity pump using the advantages of commercial thermoelectric coolers and silica gel materials. Silica gel is coated on the surface of heat sinks to minimize contact thermal resistance between the material and heat source while maintaining enough heat and mass transfer area between the desiccant and the air. The humidity pump device exhibits 0.61 g W−1 h−1 humidity transfer efficiency, corresponding to a humidity transfer rate of 28.38 g h−1. The proposed device neither uses refrigerant nor introduces liquid water. It opens up the possibility of use in localized humidity control applications with higher efficiency and a wider ambient temperature range than traditional technologies.

Summary Even if people live in an arid desert, they know that plenty of water exists in the air they breathe. However, the reality tells us the atmospheric water cannot help to slake the world's thirst. Thus an important question occurs: what are the fundamental limits of atmospheric water harvesting that can be achieved in typical arid and semi-arid areas? Here, through a thorough review on the present advances of atmospheric water-harvesting technologies, we identify the achievements that have been acquired and evaluate the challenges and barriers that retard their applications. Lastly, we clarify our perspectives on how to search for a simple, scalable, yet cost-effective way to produce atmospheric water for the community and forecast the application of atmospheric water harvesting in evaporative cooling, such as electronic cooling, power plant cooling, and passive building cooling.

To achieve higher energy efficiency and higher moisture removal capacity, a novel unitary solid desiccant air conditioner was proposed for hot and humid climate based on a novel concept of water-sorbing heat exchanger. The so-called water-sorbing heat exchanger is made by coating desiccants onto the coils used in traditional unitary air conditioners. As such, sensible load will be handled by convective heat transfer without overcooling and latent load will be treated by desiccants regenerated by heat of condensation. The air leaving the evaporator rightly satisfies the required supply-air. Evaporation temperature will increase and reheating is no longer needed. Condensation temperature will effectively decrease due to the enhancement of airside heat dissipation, which results from adsorbed water evaporating. One simple thermodynamic model was developed with some essential assumptions and the feasibility was theoretically analyzed. Parametric studies were conducted and power saving potentials of unitary so...

Summary 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 g⋅m−2⋅h−1. By applying such humidity pump, the indoor latent heat load can be handled independently, without any auxiliary unit, thus consuming no electricity., Graphical Abstract, Highlights • We propose a concept of moisture-permeable panel that enables moisture penetration • A humidity pump prototype using the moisture-permeable panel is designed • The humidity pump can reduce the indoor relative humidity to a medium level, Engineering; Energy Systems; Materials Science; Energy Materials

The humidity control has a broad and substantial demand all over the industrial, commercial and residential situations. The current humidity pumping technologies require high-intensive maintenance due to the complexity of the mechanical structures. Furthermore, the indirect utilization of solar energy increasing both cost and energy loss. Here, we demonstrate a new humidity pumping concept based on multi-layer 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 energy source. A proof-of-concept prototype is designed and established, and successfully dehumidifies the indoor air with a best dehumidification rate of 33.8 g·m-2·h-1. By applying such humidity pump, the indoor latent heat load can be handled independently and consumes no electricity. To our scope, this is the first design to realize humidity pumping under one sun illumination without any auxiliary unit.