There is a lot of water in the world, but only 2.5% of it is fresh. People are fascinated by the idea of making hydrogen by passing an electric current through water to split it into its components — hydrogen and oxygen. When they think of all the water in the oceans of the world, they see a virtually unlimited supply of hydrogen just waiting to be unlocked from its watery bonds.
Unfortunately, before seawater is suitable for use in an electrolyzer — which will split they water molecules into hydrogen and oxygen — the seawater first needs to be desalinated, a process that uses reverse osmosis technology. After that, before it goes into the electrolyzer, it must be purified and ionized using costly precious metals catalysts like platinum and iridium.
Hydrogen Directly From Seawater
Researchers at the University of Adelaide say they have a solution. According to a report published January 30 in the journal Nature Energy, the team has succeeded in making hydrogen directly from seawater in a process that uses cheap, plentiful catalysts like cobalt oxide with chromium oxide on its surface as the catalyst.
“We have split natural seawater into oxygen and hydrogen with nearly 100 per cent efficiency, to produce green hydrogen by electrolysis, using a non-precious and cheap catalyst in a commercial electrolyser,” said Professor Shizhang Qiao, the team’s co-lead, according to Engadget. Fellow co-leader Yao Zheng added, “Our work provides a solution to directly utilize seawater without pre-treatment systems and alkali addition, which shows similar performance as that of existing metal-based mature pure water electrolyzer.”
CleanTechnica readers like to read the details of research like this rather than flowery press releases, so here is the abstract of the study. The rest is behind a paywall.
The use of vast amounts of high-purity water for hydrogen production may aggravate the shortage of freshwater resources. Seawater is abundant but must be desalinated before use in typical proton exchange membrane (PEM) electrolysers. Here we report direct electrolysis of real seawater that has not been alkalised nor acidified, achieving long-term stability exceeding 100 h at 500 mA cm−2 and similar performance to a typical PEM electrolyser operating in high-purity water.
This is achieved by introducing a Lewis acid layer (for example, Cr2O3) on transition metal oxide catalysts to dynamically split water molecules and capture hydroxyl anions. Such in situ generated local alkalinity facilitates the kinetics of both electrode reactions and avoids chloride attack and precipitate formation on the electrodes. A flow-type natural seawater electrolyser with Lewis acid-modified electrodes (Cr2O3–CoOx) exhibits the industrially required current density of 1.0 A cm−2 at 1.87 V and 60 °C.
In a press release, the University of Adelaide says seawater is an almost infinite resource and is considered a natural feed stock electrolyte. This is more practical for regions with long coastlines and abundant sunlight. However, it isn’t practical for regions where seawater is scarce.
Seawater electrolysis is still in early development compared with pure water electrolysis because of electrode side reactions, and corrosion arising from the complexities of using seawater.
“It is always necessary to treat impure water to a level of water purity for conventional electrolyzers including desalination and deionisation, which increases the operation and maintenance cost of the processes. Our work provides a solution to directly utilize seawater without pre-treatment systems and alkali addition, which shows similar performance as that of existing metal-based mature pure water electrolyser,” said Zheng.
The research team will now turn its attention to scaling up the system by using a larger electrolyzer so it can be used in commercial processes such as hydrogen generation for fuel cells and ammonia synthesis.
The Clean Hydrogen Dynamic
Not to put too fine a point on it, Australia has all the natural resources needed to become the Saudi Arabia of clean energy. It has enough open land bathed in sunlight to power the entire planet, assuming it could be harvested and distributed efficiently. There is no problem with NIMBYism in the center of Australia, where open land is available for hundreds of miles in any direction. It is also an island — a rather large one but an island nonetheless — surrounded by the sea on all sides. Combine abundant renewable energy with unlimited seawater and presto! The world becomes a market for hydrogen produced Down Under.
Hydrogen is tricky stuff, however. The most reactive of all the elements, it is difficult to contain and transport. That’s where ammonia — a molecule made up of hydrogen and nitrogen atoms — comes into play. Ammonia can be transported quite conveniently and inexpensively via existing pipelines and cargo ships. In fact, it can be used as a “green” fuel for those very same vessels and help lower carbon emissions from shipping while transporting green ammonia to foreign markets. Our Australian correspondent, David Waterworth, wrote in 2021 that BP is investing in a green ammonia hub in Western Australia near Perth.
My colleague Tina Casey wrote last year, “The dream of a global economy powered by renewable hydrogen is coming into sharper focus, except for one key sticking point. Getting hydrogen from one place to another adds costs. Energy loss is also an issue. An inexpensive, efficient, and sustainable transportation medium would fill the gap, and apparently green ammonia is first in line.”
She also reported this finding from the US Department of Energy, “Ammonia is one of the only materials that can be produced cheaply, transported efficiently and transformed directly to yield hydrogen and a non-polluting byproduct.”
Not only is ammonia suitable as a hydrogen carrier, it is also used extensively as a fertilizer in agriculture. The problem is, about 95% of fertilizer is made from ammonia produced from fossil fuels — mostly methane. Bringing “green” fertilizers to market would significantly lower global carbon emissions — although the issue of excess nitrogen flowing into nearby rivers and streams still remains a matter of considerable concern.
The Takeaway
Hydrogen from seawater is a dream, one that could play an important role in reducing the amount of carbon dioxide that gets pumped into the atmosphere every second of every day. The researchers at the University of Adelaide offer the promise of affordable green hydrogen from sunlight and seawater. That hydrogen could lower the carbon intensity of steel making and cement manufacturing, as well as agriculture and shipping.
We are in a climate emergency and need all the help we can get to turn down the temperature of the Earth. This research could be an important step forward in that quest.
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- Source: https://cleantechnica.com/2023/02/04/researchers-create-hydrogen-from-seawater-without-pre-treatment/