The use of hydrogen as an energy carrier is considered crucial for moving away from fossil fuels. Hydrogen can be used to store climate-friendly energy that is generated, for example, in solar parks. For this purpose, electrolysis is operated, which splits water into oxygen and hydrogen.

In many regions, however, this will be difficult because there is a lot of sunshine but little water: from North Africa to the Arabian Peninsula to India and Australia.

An international research team has presented a process that does not require a water connection for electrolysis, but simply uses humidity. Even extremely dry air with a relative humidity of only four percent still contains enough water for the process, reports the team led by Gang Kevin Li from the University of Melbourne.

Their prototype produced high-purity hydrogen for twelve consecutive days without a hitch, they write in the journal Nature Communications. It contains a spongy structure with a hygroscopic, i.e. water-attracting, material – similar to silica gel. There is one electrode each on the top and bottom. The resulting oxygen is released into the air, the hydrogen is collected and the quantity and purity are analyzed.

In the practical test, their device delivered up to 93 liters of hydrogen per square meter and hour, the researchers report. In fact, the prototype is even smaller. Larger modules with one and ten square meters are to be built next year.

They would be useful for solar and wind parks, but also for small, decentralized systems, such as for remote settlements. However, the researchers leave open the costs at which hydrogen can be produced.

Clumsy and expensive, but creative

“The concept of using the humidity in the air with a hygroscopic material and thus also generating hydrogen in dry areas is elegant,” says Roel van de Krol, an expert on solar fuels at the Helmholtz Center Berlin for Materials and Energy, who is involved in the study was not involved. He and other colleagues took a closer look at the process. Together they come to the conclusion that this will hardly ever be implemented.

“The device has a complicated structure and it needs a thick layer of material to get water out of the air,” he explains. But that is at the expense of electrolysis. The choice of material also seems unfavorable to him. For example, Li and colleagues used platinum for the electrodes. “That would be avoided for cost reasons.”

“I like creative ideas like this,” says van de Krol, “because they encourage new approaches.” In this specific case, however, he believes it is better to separate the individual process steps: build a separate system to extract water from the air win, and then lead this into a stand-alone electrolyser. “That could work.”

The potential of hydrogen production in dry areas should not be underestimated. Around one fifth of humanity live in dry areas where water stress quickly occurs or where it is already shaping society. If “green hydrogen” could do without the precious resource from the underground – and at an acceptable cost – that would be an important step.