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Researchers have developed a way to generate hydrogen from air, decoupling production from freshwater resources and providing a new direction for a carbon-free future.
Hydrogen – green hydrogen in particular – is generally agreed to be the ultimate clean energy.
Unlike fossil fuels, which we know contribute to the large-scale CO2 emissions causing global warming, burning hydrogen doesn’t release carbon dioxide or any other greenhouse gases.
Green hydrogen goes a step further by using renewable energies in production.
Like conventional hydrogen production, it is collected through a process called electrolysis, in which water is split into hydrogen and oxygen using a power source. But here, that power is from renewable sources – whether solar, wind, geothermal or tidal.
Since hydrogen can ‘store’ power produced by renewable sources, it complements renewables by offering a continuous supply of power.
So promising is green hydrogen for a low-carbon economy, many see it as Australia’s next great export, due to its ample source of solar and wind.
Fresh water or hydrogen?
But producing hydrogen through water electrolysis relies on a very clean water supply, which is a scarce commodity. According to UN-Water, 2.3 billion people live in water-stressed countries, of which 733 million live in high and critically water-stressed countries (UN-Water, 2021).
Already, industrial power plants, agriculture and other industries use a substantial amount of water, which is competing with supply for the human population. Purification processes are possible, but they add complexity and cost to hydrogen production that challenges feasibility.
Then there is the geographic mismatch between renewable electricity and freshwater availability. Areas rich in solar and wind and therefore ideal for green hydrogen production, often suffer water shortage, making competition for fresh drinking water even higher stakes. Places like this include much of middle Asia, West Asia, and India, North Africa, West of North America, and a large part of Australia.
Bringing water in as an alternative not only poses logistical challenges, but may not be possible as shortage increases. An entire hydrogen-based economy would certainly increase the global risk of freshwater shortage.
Turning air into hydrogen
Researchers at the University of Melbourne are close to providing a way to overcome these issues, with a working prototype of a device that produces hydrogen without consuming freshwater resources.
The technology, which was recently published in Nature Communications, is called Direct Air Electrolyser (DAE) and works by draining water directly from the air before then going through the standard electrolysis process.
Lead researcher Dr Kevin Gang Li, a senior lecturer in Chemical Engineering, says the idea came to him while considering hydrogen production where water supply presents a challenge.
“We see an area that has no groundwater and think it’s unsuitable for hydrogen production. But there is always abundant fresh water in air.”
“Even Alice Springs, which is in part of desert, has around 20 per cent relative humidity. This is more than enough for us to produce hydrogen onsite using renewable energy.”
The DAE, which Dr Li has been working on with PhD student, Jining Guo, is like other electrolysers in that it is made of a panel of metal plates – the electrodes – which supply a current (taken from renewables) for the water splitting process.
But the secret is the porous medium between the plates which is soaked with hygroscopic ionic solution – a chemical that can absorb moisture from air spontaneously.
“It's simple, but this material likes to take water molecules from the air. When they’ve been taken from air, they become liquid and ready for electrolysis. That's the core of this invention.”
“If you expose the device to air, it will produce hydrogen. That's why we call it Direct Air Electrolyser. You use air as the feed to the device, not liquid water like electrolysers currently do.”
It appears to be the first report of pure hydrogen production directly from the air.
Fig.1 The module for direct hydrogen production from the air. Source: Nature Communications.
Removing barriers to green hydrogen production
By harvesting hydrogen from air, the device decouples hydrogen production from geographic limitations of the world’s freshwater resources. This opens up access to places that will need it in the future and provides a range of economic and environmental benefits.
For high carbon industries, such as mining, the DAE could allow complete decarbonisation by combining the technology with solar and other renewables, which are currently used in an effort to lower emissions, as well as in remote places without power supply.
“Renewables could still be used during the day, but the DAE could convert part of the solar to hydrogen, which can be stored, to allow for a continuous supply of power that would remove any reliance on fossil fuels,” Dr Li says.
Fuel for mining trucks, which will also be needed in the future, could be hydrogen too.
Another potential large-scale opportunity is integrating the technology with existing systems to lower emissions – such as if it was paired with gas grids – or to boost green hydrogen production. Energy companies could embed it within their existing solar farms to produce sustainable hydrogen for global export.
If we move into a hydrogen-based economy, having a way for remote communities, or those in arid or semi-arid landscapes, to produce hydrogen on site will be significant as well, Dr Li says.
“I think our technology will be quite promising to these areas. And it’s not small. There's a huge part of this planet that actually doesn't have enough fresh water supply. Getting hydrogen there is going to be really important for the future.”
A new direction for hydrogen production driven by sustainable energy
The technology won’t entirely replace conventional hydrogen production – which would still be used when fresh water is available and cheap; rather, the DAE will be a perfect complementary. But after two and a half years in the lab, they know the device can be easily upscaled and coupled with renewables, can generate high-purity hydrogen continuously at relative humidities as low as 4 per cent, and that it's technically and structurally viable, and low maintenance.
Potential applications are vast, and pure hydrogen could be generated anywhere on earth.
With a working prototype and patent, next steps are to do large-scale tests to find out how it performs in harsh conditions, including icing temperatures, rain and extremely dry climates, and at a much larger size.
“We are in the process to scale up the DAE – from a five-layer stack to one meter square, then 10 meters and so on. And we can simulate a dry climate in lab, but that's not a real desert. So, we want to take it to Alice Springs and spend a couple of weeks, see how it goes.”
From there, the focus will be energy integration, as well as storage and supply to bring it to the final stages before it becomes a commercial product. The upscale of the DAE technology has attracted investment from top global venture capitals.
How close this is, is yet to be seen. But we are much closer to having an affordable, easy way to produce very green hydrogen, which could be economically prolific, and doesn’t drain our limited freshwater resources.
UN-Water, 2021: Summary Progress Update 2021 – SDG 6 – water and sanitation for all. Version: July 2021. Geneva, Switzerland.
First published on 7 September 2022.
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