Could cars one day run on thin air?

By Rob Waugh

It sounds like science-fiction, but in the future, cars could run on air itself – specifically, on the water carried within humid air.

Researchers at the University of Melbourne have created a prototype dry-air electrolyser that harvests hydrogen from air instead of liquid water.

In the near future, hydrogen is expected to be commonly used as a ‘clean’ fuel which creates no carbon dioxide during combustion.

The device absorbs moisture, then turns it into hydrogen and oxygen – the hydrogen can then be used as fuel.

The prototype device created by the Melbourne team was able to work for 12 consecutive days, even in a dry environment of around 4% humidity.

The researchers write: “This so-called direct air electrolysis (DAE) module can work under a bone-dry environment with a relative humidity of 4%, overcoming water supply issues and producing green hydrogen sustainably with minimal impact to the environment. “

The scientists said that the technology could help to overcome one of the key challenges of using hydrogen as a fuel – the availability of freshwater.

They write: “Green hydrogen produced by water splitting using renewable energy is the most promising energy carrier of the low-carbon economy. However, the geographic mismatch between renewables distribution and freshwater availability poses a significant challenge to its production.

–Such direct air electrolysis devices hold the potential for generating abundant hydrogen in arid and semi-arid areas with negligible disruption to the regional air humidity and minimal impact to the environment.

–Further improvement of the surface-to-volume ratio by engineering channels or increasing the aspect ratios of the sponge material will guarantee the rate of water uptake which is essential to the upscaling of the direct air electrolysis units.”

Earlier this year, Stanford scientists worked out a way to turn carbon dioxide captured from the air or from power plants into fuel that is “basically” petrol.

The new Stanford process can turn captured carbon into propane, butane or other hydrocarbon fuels.

The scientists hope that in the long run, the process can create a fuel that can be used, captured, then used again – and may unlock innovative processes that would allow captured CO2 to be turned into a solid and buried underground.

Matteo Cargnello, a chemical engineer at Stanford University, said: “We can create gasoline [petrol], basically. To capture as much carbon as possible, you want the longest chain hydrocarbons. Chains with eight to 12 carbon atoms would be the ideal.”

A new catalyst, invented by Cargnello and colleagues, moves toward this goal by increasing the production of long-chain hydrocarbons in chemical reactions.

It produced 1,000 times more butane – the longest hydrocarbon it could produce under its maximum pressure – than the standard catalyst given the same amounts of carbon dioxide, hydrogen, catalyst, pressure, heat and time.