US Navy announces plans to make jet fuel out of seawater

Researchers at the Naval Research Laboratory (NRL) in Washington, DC, have demonstrated that it is possible to obtain CO₂ and hydrogen from seawater, then convert these to hydrocarbons suitable for fuelling aircraft.

Keeping ships and aircraft fuelled is a major operation for any navy. The US Navy has 15 refuelling ships — known as oilers — and last year these delivered 600 million gallons of fuel to ships under way. Generating their own fuel would free up the ships from these logistics and make the navy less dependent on imported oil, said Nancy Willauer, a research chemist who worked on the project.

The technology uses electrochemistry to recover CO₂ from seawater, where it is present at a concentration 140 times greater than in air, mostly as bicarbonate with traces of carbonate and dissolved CO₂ gas (carbonic acid). The navy team developed a device called an electrochemical acidification cell, which uses ion-permeable polymer membranes and an electric current to lower the pH of the seawater. The three forms of carbon in the water exist in a state of equilibrium, and making the water more acidic alters the balance between them, making gaseous CO₂ the most stable form. The cell produces hydrogen gas at its cathode as a by-product.