“Osmosis power plants” could use the potential difference between salt water and fresh water, e.g. in the estuaries of large rivers, to generate electrical energy by reverse electrodialysis. Liping WEN and colleagues from the Institute for Physics and Chemistry at CAS in Beijing investigated suitable composite membranes for this purpose. They produced a nanoporous composite membrane from silk nanofibrils and aluminium oxide as carrier substrate. The negatively charged surface of the fibroin ensures ion transport, while the amphoteric aluminum oxide allows for current flow over a wide pH range. Depending on the salt concentration, energy densities of up to 2.86 W.m2 were achieved.