Researchers from MIT developed a carbon-based sponge that can be used to make a steam-based energy generation device. They say that such a device can reach an energy efficiency of 85%, better than current solar-powered commercial devices.
The newly developed sponge is made from a combination of graphite flakes and carbon foam. It floats on water, and when sunlight hits it, it creates a hotspot which draws up water through the pores in the material, which evaporates as steam. The process generates very little heat and can produce steam at low solar intensity (the lowest optical concentration reported thus far).