https://www.umass.edu/news/article/engineers-umass-amherst-harvest-abundant-clean-energy-thin-air-247
No energy density is given. So it might just be an interesting curiosity. This whole concept is of particular interest to me because of the nanoporous metals I was making several years ago. The nanoporous aluminum I made was a gradient of solid aluminum at one surface and highly nanoporous on the opposite surface. The nanoporous surface was about the blackest material I have ever seen. Carbon black looks rather light brown next to it. The nanoporous aluminum has a number of strange properties. A tiny drop of water on its surface disappears and the spot become hot. If you press a finger on it, it will remove the top layer of skin, leaving a fingerprint made of the skin itself. Interesting, but possibly of no practical use.
