Powder-to-Hydrogel System with Fast Water Absorption for Evaporative Cooling

Water-based evaporative cooling plays an important role in industrial thermal management. Porous hydrogels, which retain water within interconnected channels to serve as reservoirs for continuous evaporation, are promising materials for water-efficient cooling. However, compatibility between in situ formation and fast water absorption of the material as a coating remains a challenge. Here, we report a powder-to-hydrogel system enabling in situ formation of superhydrophilic porous hydrogel coating in a facile manner. An ionic polymer providing phenylboronic acid was introduced into a poly-(vinyl alcohol) (PVA) and tannic acid (TA) powder system. Upon hydration, the powders rapidly converted into a hydrogel coating, where the ionic polymer was chemically anchored to the PVA-TA network via the formation of boronate ester bonds. This structural integration can drastically double the water uptake speeds and the overall water absorption capacity compared to pristine PVA-TA. Consequently, in a simulated solar panel cooling experiment with intermittent spraying, this coating successfully suppressed the temperature rise by over 48% compared to that of conventional strategies. Featuring large water capacity and rapid replenishment, this powder-based coating offers significant advantages for superior, long-lasting industrial cooling.