Hierarchical Engineering of Sorption-Based Atmospheric Water Harvesters.

Harvesting water from air in sorption-based devices is a promising solution to decentralized water production, aiming for providing potable water anywhere, anytime. This technology involves a series of coupled processes occurring at distinct length scales, ranging from nanometer to meter and even larger, including water sorption/desorption at the nanoscale, condensation at the mesoscale, device development at the macroscale and water scarcity assessment at the global scale. Comprehensive understanding and bespoke designs at every scale are thus needed to improve the water-harvesting performance. For this purpose, a brief introduction of the global water crisis and its key characteristics is provided to clarify the impact potential and design criteria of water harvesters. Next the latest molecular-level optimizations of sorbents for efficient moisture capture and release are discussed. Then, novel microstructuring of surfaces to enhance dropwise condensation, which is favorable for atmospheric water generation, is shown. After that, system-level optimizations of sorbent-assisted water harvesters to achieve high-yield, energy-efficient, and low-cost water harvesting are highlighted. Finally, future directions toward practical sorption-based atmospheric water harvesting are outlined.

Quasi-waffle solar distiller for durable desalination of seawater.

Water purification via interfacial solar steam generation exhibits promising potential. However, salt crystallization on evaporators reduces solar absorption and obstructs water supply. To address it, a waffle-shaped solar evaporator (WSE) has been designed. WSE is fabricated via a zinc-assisted pyrolysis route, combining low-cost biomass carbon sources, recyclable zinc, and die-stamping process. This route enables cost-effective production without the need of sophisticated processing. As compared to conventional plane-shaped evaporators, WSE is featured by extra sidewalls for triggering the convection with the synergistic solute and thermal Marangoni effects. Consequently, WSE achieves spontaneous salt rejection and durable evaporation stability. It has demonstrated continuous operation for more than 60 days in brine without fouling.

A smart thermal-gated bilayer membrane for temperature-adaptive radiative cooling and solar heating.

Due to the huge energy consumption of traditional cooling- and heating-based electricity, passive radiative cooling and solar heating with a minimum carbon footprint using the outer space and Sun as natural thermodynamic resources have attracted much attention. However, most passive devices are static and monofunctional, and cannot meet the practical requirements of dynamic cooling and heating under various conditions. Here, we demonstrate a smart thermal-gated (STG) bilayer membrane that enables fully automatic and temperature-adaptive radiative cooling and solar heating. Specifically, this device can switch from reflective to absorptive (white to black) in the solar wavelength with the reduction in optical scattering upon ambient temperature, corresponding to a sunlight reflectivity change from 0.962 to 0.059 when the temperature drops below ∼30 °C, whereas its mid-infrared emissivity remains at ∼0.95. Consequently, this STG membrane achieves a temperature of ∼5 °C below ambient (a key signature of radiative cooling) under direct sunlight (peak solar irradiance >900 W m-2) in summer and a solar heating power of ∼550 W m-2 in winter. Theoretical analysis reveals the substantial advantage of this switchable cooling/heating device in potential energy saving compared with cooling-only and heating-only strategies when widely used in different climates. It is expected that this work will pave a new pathway for designing temperature-adaptive devices with zero energy consumption and provide an innovative way to achieve sustainable energy.