Green hydrogen produced with near 100% efficiency using seawater


It’s not quite splitting the Red Sea, but new research into splitting seawater to produce hydrogen may be a scientific miracle that puts us on a path to replacing fossil fuels with the environmentally-friendly alternative.

“We have split natural seawater into oxygen and hydrogen with nearly 100 percent efficiency, to produce green hydrogen by electrolysis, using a non-precious and cheap catalyst in a commercial electrolyser,” says project leader Professor Shi-Zhang Qiao from the University of Adelaide’s School of Chemical Engineering.

Electrolysis is the process of splitting water (H2O) into hydrogen and oxygen using electricity. So, the process itself requires energy.

The process also requires catalysts. But not all catalysts are created equal. Catalysts used in electrolysis tend to be rare precious metals like iridium, ruthenium and platinum.

Typical non-precious catalysts are transition metal oxide catalysts, for example cobalt oxide coated with chromium oxide.

The new breakthrough in splitting seawater to produce green energy was achieved by adding a layer of Lewis acid (a specific type of acid, for example chromium(III) oxide, Cr2O3) on top of the transition metal oxide catalyst.

While using cheaper materials, the process is shown to be very effective.

“The performance of a commercial electrolyser with our catalysts running in seawater is close to the performance of platinum/iridium catalysts running in a feedstock of highly purified deionised water,” explains the University of Adelaide’s Associate Professor Yao Zheng.

Another typical part of the electrolysis process is some form of treatment of the water. For that reason, freshwater is the main source of green hydrogen. But freshwater is increasingly scarce.

So, scientists are looking to seawater, particularly in regions with long coastlines and abundant sunlight.

“We used seawater as a feedstock without the need for any pre-treatment processes like reverse osmosis desolation, purification, or alkalisation,” Zheng adds. “Current electrolysers are operated with highly purified water electrolyte. Increased demand for hydrogen to partially or totally replace energy generated by fossil fuels will significantly increase scarcity of increasingly limited freshwater resources.”

Seawater electrolysis is relatively new compared to pure water electrolysis. Complications include side reactions on the electrodes, as well as corrosion.

“It is always necessary to treat impure water to a level of water purity for conventional electrolysers including desalination and deionisation, which increases the operation and maintenance cost of the processes,” Zheng says. “Our work provides a solution to directly utilise seawater without pre-treatment systems and alkali addition, which shows similar performance as that of existing metal-based mature pure water electrolyser.”

The team hopes to scale their experiment up for commercial production in generating hydrogen fuel cells and ammonia synthesis.

Their research is published in Nature Energy.

Cosmos, 31 January 2023