Back in 2014, we heard how MIT scientists had developed a graphite/carbon "sponge" which used sunlight to convert water into steam very efficiently. They've now improved on the design, creating a device that produces super-heated steam. It could be used in remote regions to sterilize medical equipment, among other applications.

The idea behind the original device was that it would float on the surface of a container of water, absorbing heat from incoming sunlight and using it to convert that water into steam. One potential problem, however, lay in the fact that it might absorb contaminants from the water, causing the material to degrade.

To get around this, the new device is suspended above the surface of the water, not actually contacting it. About the size and thickness of an e-reader, it's composed of three sandwiched layers – there's a metal ceramic composite on top, a porous carbon foam in the middle, and a material that efficiently emits infrared heat on the bottom.

The top layer absorbs short-wavelength solar energy from sunlight, causing the whole device to heat up. That heat is emitted out of the bottom layer in the form of longer-wavelength infrared radiation, which the water absorbs more readily than sunlight.

As a result, the water heats up to 100 ºC (212 ºF), producing steam. That steam rises back up into the device, where the middle layer of sun-heated carbon foam heats the steam further. That super-heated steam is channeled out through a tube in the device, for subsequent use in tasks such as sterilization, cooking or cleaning. It could also simply be condensed into distilled or desalinated drinking water, if the water from which the steam was made was polluted or salty.

The system has been tested on a rooftop at MIT, where it produced 146 ºC (295 ºF) steam from a basin of water within 3.5 hours under clear, bright skies. It was placed in a polymer enclosure that helped keep heat from escaping, plus it was aided by a curved mirror that concentrated sunlight onto its surface.

"It's a completely passive system — you just leave it outside to absorb sunlight," says York University's Asst. Prof. Thomas Cooper, who led the project while a postdoc at MIT. "You could scale this up to something that could be used in remote climates to generate enough drinking water for a family, or sterilize equipment for one operating room."

A paper on the research was recently published in the journal Nature Communications.

Source: MIT