Passive Moisture‐Driven Cooling via Low‐Cost and Shape‐Stabilized Hygroscopic Composite Foam for High‐Power Electronics

ABSTRACT Efficient thermal management is essential for modern high‐power electronics such as photovoltaic panels, lithium‐ion batteries, and integrated circuits, where excessive heat severely compromises device performance, reliability, and lifespan. Hererin, we propose a low‐cost and energy‐free cooling strategy through a porous hygroscopic melamine foam (MF) composite modified with boron nitride (BN) and lithium bromide (LiBr)‐containing poly(vinyl alcohol) (PVA) gel. Sonication‐assisted hydrolysis produces hydroxylated BN nanosheets that form hydrogen bonds with PVA, enhancing the thermal conductivity and structural stability. LiBr provides strong hygroscopicity, enabling the composite to dynamically absorb moisture during low‐power or standby operation and release it through evaporation under high‐power working conditions, leveraging the high latent heat of water vaporization for passive cooling. The shape‐stabilized composite film with conformal device attachment effectively reduces the simulated chip surface temperature by 37°C during cyclic operation and suppresses the battery peak temperature by up to 26°C at a ultrahigh discharge rate of 8 C. Moreover, it lowers the photovoltaic panel temperature by 15°C under 1000 W m −2 illumination, improving the power output with enhancement of photoelectric conversion efficiency from 13% to 13.5%. This lightweight, scalable, and durable advanced composite material offers a sustainable and maintenance‐free approach for next‐generation electronic, battery, and energy‐harvesting systems.