Hydrogen has long been touted as a potentially revolutionary green source of energy. Burning the gas produces nothing more polluting than water vapour, and making it is trivially easy. Just hook up some electrodes to an electric current, then dunk them in water. Try it with a nine-volt battery and a couple of wires and you’ll soon see bubbles of hydrogen forming on one wire and oxygen on the other. Given that the chemistry is so simple, and we have access to literally oceans of raw materials, why haven’t we already transitioned to a hydrogen economy?
Unfortunately, unless your water is incredibly pure, you will initiate a load of other wholly undesirable chemical reactions. This means direct electrolysis of sea water is unfeasible. You could desalinate the water first, but this requires more energy than would be obtained from burning the hydrogen.
Thankfully, a team from Nanjing Tech University, China have recently solved this problem by combining the evaporation and electrolysis steps inside a single reactor. The reactor consists of two chambers – one with sea water, the other with salt-free water and the electrodes. Separating the chambers are a pair of waterproof breathable membranes (much like those in your waterproof jacket) with gas trapped between them.
Potassium hydroxide is added to the water in the inner chamber until it is at a higher concentration than the salt in the sea water. This means the water will diffuse from the sea water chamber to the higher concentration chamber within. But the only way it can move from one chamber to the other is via the gas-filled gap between the membranes. Liquid water can’t make it through, but water vapour can – leaving the salt behind. The clean water can then be safely split into hydrogen and oxygen.
The team have already extensively tested the system, producing over a million litres of hydrogen gas in just a few months. With cheap hydrogen production now within our sights, we can think about how to use it for transport, heavy industries and to heat our homes. We are one step closer to a source of green energy that is also easy and practical.
This piece is a preview from our New Humanist spring 2023 edition. Subscribe here.
