Enormous free-energy dissipation takes place when fresh river water mixes with salty sea water. This so-called osmotic energy, which normally goes to waste, can be harvested with nanostructured membranes that are put between the two types of water. Porous materials with intrinsic nano or sub-nanochannels, such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) are considered good candidates for nanofluidic osmotic energy harvesting. Here, researchers demonstrate an ...