Moisture thermal battery with autonomous water harvesting for passive electronics cooling

Passive cooling ofhigh-powerelectronicswithminimumenergyand water input is critical for the global water-energy nexus but has been challenging because of the large fluctuation in power and heat loads between the on/off-peak hours. Here we develop a moisture thermal battery (MTB) by coating superabsorbent hydrogel onto a pin fin heat sink with a large surface. The MTB leverages large latent heat and high thermal conductance of water evaporation for electronics cooling during on-peak hours and, importantly, autonomously harvests atmospheric moisture and stores the water during off hours. The MTB provides a thermal capacity of up to 200 kWhm^-2forevaporative cooling with a record-high effective heat transfer coefficient of up to 1,000 W m^-2 K^-1 for a passive device (no external power). The MTB suppresses the temperature f luctuation of a high-power field effect transistor and a computer CPU between the on- and off-peak hours by 15 K.