Scientists create green hydrogen fuel from air

September 10, 2022

Hydrogen can now be made using only electricity and the moisture in the air, scientists have found. According to a paper published on September 6 in the journal Nature Communications, this "green hydrogen" is produced by electrolyzing the humidity in the air, rather than the traditional liquid water, which may allow the provision of hydrogen fuel to dry and remote regions, with minimal environmental impact, especially if using renewable energy. The paper's authors have been able to electrolyze the air's water in humidity as low as 4 percent.

"We have developed a so-called "direct air electrolyzer" in short, DAE," Gang Kevin Li, a senior lecturer in the Department of Chemical Engineering at The University of Melbourne, and co-author of the paper, told Newsweek.

"This module uses a hygroscopic electrolyte exposed to the atmosphere constantly. Such electrolyte has a high potential to extract moisture from air spontaneously (without external energy input), making it readily available for electrolysis and hydrogen production once coupled with a (renewable) power supply," he said.

Electrolysis has traditionally been used only to gather hydrogen and oxygen from liquid water, placing two electrodes into water and running an electrical current through it. At the anode, the positively charged electrode, electrons are ripped away from H2O, forming positive hydrogen ions and O2 molecules. At the negative cathode, electrons are given to the hydrogen ions, forming H2 gas: hydrogen.

However, this approach has traditionally required access to pure liquid water. This limits the use of liquid water electrolysis to areas where water is plentiful, else it may lead to competition with limited supplies of drinking water. By harvesting the water already in the air, the DAE eliminates this risk, and the cost associated with it, and enables the production of hydrogen anywhere.

"The ability to use moisture from air makes this DAE module applicable in remote, arid and semi-arid environments where the accessibility to fresh water is a big problem," said Li. "Most areas on earth with high solar and wind potentials lack fresh water. For example, a desert is deemed a good place for solar power but no fresh water."

"It works for almost all air environments on earth. Our DAE module was tested at 4 [percent] relative humidity which is drier than any desert."

Average daytime relative humidity in the Mojave Desert ranges from 10 percent to 30 percent during the day and can approach 50 percent during the night, meaning that the DAE would still work even in arid locales.

According to the paper, the authors' prototype of this device was tested using input energy from the sun and found to have a stable Faradaic efficiency—the efficiency with which charge is transferred—of around 95 percent over the course of 12 consecutive days.

The benefit of this new technique is that it can both run and produce renewable energy: the electricity used in the electrolysis may be used from renewable sources like wind or solar, and the hydrogen produced may be used as hydrogen fuel, or even to power hydrogen nuclear fusion reactions.

According to the authors, these findings may enable future solar-to-fuel conversion devices to operate anywhere on Earth, overcoming the water shortage problem in the case of widespread deployment of hydrogen production.

"This device could be] placed in areas with abundant solar or wind power but facing water scarcity. It will also be applicable for remote and scattered hydrogen production," Li said.