With renewable energy becoming cheaper, there’s a growing impetus to find ways of economically storing it. Batteries can handle short-term fluxes in production but may not be able to handle longer-term shortfalls or seasonal changes in power output. Hydrogen is one of several options being considered that has the potential to serve as a longer-term bridge between periods of high renewable productivity.

But hydrogen comes with its own issues. Obtaining it by splitting water is pretty inefficient, energy-wise, and storing it for long periods can be challenging. Most hydrogen-producing catalysts also work best with pure water—not necessarily an item that’s easy to obtain as climate change is boosting the intensity of droughts.

A group of researchers based in China has now developed a device that can output hydrogen when starting with seawater—in fact, the device needs to be sitting in seawater to work. The key concept for getting it to work will be familiar to anyone who understands how most waterproof clothing works.