One potential clean source of energy is hydrogen made by electrolyzers that split water into hydrogen and oxygen. To make the gas sustainably, solar or wind power can generate the electricity to drive the electrochemical reaction. However, places with high solar and wind potential are often short on water. Now Kevin Li and a team from the University of Melbourne, have built a device that can suck water out of desert-dry air to make H2 (Nat. Commun. 2022, DOI:10.1038/s41467-022-32652-y).
Their system sops up moisture with a sponge-like material that doubles as the electrolyte in electrolyzers powered by solar panels and wind turbines. The device rips H and O from water, and sequesters the reduced H2 gas in a storage tank for later use.
“There’s a huge amount of water in the air,” Li says. “It’s almost undepletable,” he says. Desert air is around 20% relative humidity, but the team’s system works in air with as little as 4% humidity. The device also uses a high current density to run the electrochemical reaction, meaning that they can use a small electrolyzer to pump out H2.
The prototype system churned out high-purity H2 gas for 12 days outside the group’s lab building in Melbourne, and the group has another device that’s been running for 8 months with no problems. The trick to pulling in enough water to drive this output was finding an efficient spongy material made from either a combination of melamine and potassium hydroxide, or glass foam and sulfuric acid.
The material allows the device to absorb water and channel it directly to the electrolyzer’s cathode to make H2 gas. In previous water-harvesting devices, chemists have used solid materials that have to go through extra steps to condense the water before it can be reduced to H2, Li says. “Here, when the water is absorbed, it’s liquid,” he says.
Li envisions the system as an add-on to existing solar panels. During the day, solar panels tend to create too much energy for the electrical grid to handle and the excess gets dumped. Putting this new system underneath panels could instead convert the leftover energy to H2 gas, Li says. Then at night, the H2 could be burned to make electricity.
A big limitation with using water electrolysis to make H2 is that scientists need clean, fresh water, says Athanasios Chatzitakis, an electrochemical researcher at the University of Oslo. Technology, such as this new device that pulls water from the air, essentially gets around that problem. It’s a promising way to make clean fuels like green H2.
This story was updated on Sept. 15, 2022, to correct the description of desert air. It is around 20% relative humidity, not 20% water.