The good info is apparently in table S2 of "supporting materials", where they compare energy harvesting devices. That's not part of what you can read for free.

Some kind of energy harvesting device that could generate a few milliwatts in ambient indoor conditions would be very useful. We have lots of things with AA batteries in them that use very little power but need a new battery every year or so. That's the potential here. This isn't going to replace oil.