Australian and international researchers have developed an electrolyser. It collects water vapour and converts it into green hydrogen that could be used for anything, including fueling your car.
The breakthrough, led by a team at the University of Melbourne, paves the way to produce renewable hydrogen. It has the immediate benefit of not needing to consume precious drinking water.
In a study published in Nature Communications, the prototype device, which absorbs moisture from the air and splits it into hydrogen and oxygen, is powered by solar and wind.
The researchers test their prototype electrolyser under a range of relative humidity levels. They went as low as 4 per cent and found that it steadily produces high purity hydrogen. In one case, it created hydrogen for more than 12 consecutive days without any input of liquid water.
This is important because current hydrogen electrolyser technology usually requires access to increasingly limited resources of pure water. This unique device could be scaled to provide fuel in remote, arid and semi-arid regions.
The team noted that even the Sahel region in western and central northern Africa has an average relative humidity of about 20%. In comparison, the average daytime relative humidity at Uluru in the central desert of Australia is 21%.
How does the collection of green hydrogen work?
The team’s Direct Air Electrolysis (DAE) module comprises a water harvesting unit in the middle and electrodes on both sides. It is paired with gas collectors and integrated with a renewable power supply. The researchers opted to conduct a lot of the testing using solar.
A porous medium such as a melamine sponge is soaked with a hygroscopic (or water-attracting) substance to absorb moisture from the air via the exposed surfaces.
The team tested a range of hygroscopic materials, including potassium acetate, potassium hydroxide, and sulfuric acid. They found that all three materials spontaneously absorbed moisture from the air and formed ionic electrolytes.
It found that the direct air electrolysis modules successfully produced hydrogen gases at a very low relative humidity level or higher humidity for more than 12 days, with a continual supply of air and power.
A solar-driven prototype with five parallel electrolysers has been devised to work in the open air. It achieved an average hydrogen generation rate of 745 L per day−1m−2 cathode. The team also demonstrated a wind-driven prototype.
What the researchers say
“Few studies have been trying to mitigate the water shortage for electrolysis,” said the report’s authors, led by Jining Guo, Yuecheng Zhang, Ali Zavabeti, and Kaifei Chen.
“Direct saline splitting can produce hydrogen. However, it faces a serious challenge of handling chlorine byproduct,” they add, noting that other methods trialled have resulted in low purity hydrogen.
In their research, the team showed that moisture in the air could directly be used for hydrogen production via electrolysis, owing to its universal availability and natural inexhaustibility. There are 12.9 trillion tons of water in the air at any moment. Some materials, such as potassium hydroxide, sulfuric acid, and propylene glycol, can absorb water vapour from bone-dry air. The team demonstrated a method to produce high-purity hydrogen by electrolysing in-situ hygroscopic electrolytes exposed to air.
This work opens a sustainable pathway to producing green hydrogen without consuming liquid water.
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