New Spanish nanomaterial cools surfaces by up to 12.9C without electricity

A team of researchers at the Institute of Micro and Nanotechnology (IMN-CNM, CSIC) has developed a nanomaterial capable of cooling sun-exposed surfaces without using electricity, an alternative that could ease the growing energy bill for cooling, which already accounts for nearly 20% of global electricity consumption.

The research, led by the Functional Nanoscale Devices for Energy (FINDER) group and published in the journal Nanophotonics, is based on daytime passive radiative cooling, a technique that exploits a peculiarity of the Earth's atmosphere: there is a band in the infrared spectrum, between 8 and 13 micrometres, through which heat escapes directly into space without being trapped.

A material that emits well in that window and also reflects solar radiation can end up colder than the surrounding air, with no plug or compressor involved.

A polymer with just the right properties

The scientists opted for polyvinylidene fluoride (PVDF), a polymer already known for its ability to emit heat in the infrared.

Cristina Vicente, a researcher at IMN-CNM and leader of the COOLed project, explains that this material "brings together a combination of properties" that make it ideal: as well as emitting heat efficiently, it withstands ultraviolet radiation and repels water, which gives it a self-cleaning effect, and stands up well to the elements.

The key to the breakthrough lies less in the material itself than in how it was shaped. The team infiltrated the polymer into nanoporous templates of anodised aluminium oxide, creating three-dimensional structures whose internal geometry they can control with great precision, something that is crucial because the optical performance of these coolers depends on their design at the nanometre scale.

The numbers back up the promise: the optimised version of the material, treated with ultrafast cooling after the polymer infiltration, reflects on average 82.4% of solar radiation and emits 96.7% of heat in the infrared window from 8 to 13 micrometres, the band through which that heat escapes into space.

On paper, this combination translates into a cooling capacity of 182.3 watts per square metre under solar irradiance of 1,000 W/m². The rooftop test in Tres Cantos, with a peak solar irradiance of 962 W/m², confirmed that figure in the field.

Almost 13 degrees cooler on the rooftop

The theory was put to the test last summer, with outdoor trials on the centre's rooftop in Tres Cantos, Madrid.

After the material was subjected to ultraviolet light treatment that whitens it and improves its solar reflectance, the results came in: on the hottest, driest and sunniest days, the treated surface stayed up to 12.9°C cooler than a sample without coating.

The researchers themselves stress that the technology is still under development, but emphasise that the manufacturing process is relatively cheap and compatible with existing industrial processes.

That opens the door to applications ranging from façades and roofs of buildings to electronic devices, vehicles and even personal cooling systems, all with the same goal: reducing dependence on air conditioning and the emissions that come with it.

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