Researchers Successfully Split Seawater to Produce Green Hydrogen Without Pre-Treatment

Researchers have produced green hydrogen by splitting seawater, without the use of pre-treatments like reverse osmosis desolation, purification or alkalisation, in a new study. The team used an inexpensive catalyst to split seawater into oxygen and hydrogen, with nearly 100% efficiency.

Researchers from the University of Adelaide, Tianjin University, Nankai University and Kent State University used seawater with a catalyst and and electrolyser. The results are published in the journal Nature.

“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,” Shizhang Qiao, professor at the University of Adelaide, said in a statement.

The team used a non-precious catalyst, such as cobalt oxide (CoO_x) with chromium oxide (Cr₂O₃), to split the seawater, eliminating the need for pre-treatments. Pre-treatments are typically necessary to desalinate the seawater before it can be used in electrolysers, since seawater may lead to 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,” said Yao Zheng, associate professor at the University of Adelaide’s School of Chemical Engineering. “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.”

Electrode side reactions, high costs and corrosion have kept seawater electrolysis in early development, but freshwater supply shortages have led researchers to improve upon seawater electrolysis as an alternative. Seawater is considered an abundant resource for coastal regions, and a natural feedstock electrolyte. 

“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,” Zheng said.

The researchers plan to use a larger electrolyser to scale up the process, ultimately generating green hydrogen for fuel cells and ammonia synthesis.

Scientists outside of this study are also working toward improving electrolysers to split seawater without an additional desalination pre-treatment. In January 2023, researchers from Shenzhen University and Nanjing Tech University published a study after developing a membrane-based electrolyser to split seawater without corrosion, side reactions, or pre-treatments.

“This strategy realizes efficient, size-flexible and scalable direct seawater electrolysis in a way similar to freshwater splitting without a notable increase in operation cost, and has high potential for practical application,” the researchers of the electrolyser study said. “Importantly, this configuration and mechanism promises further applications in simultaneous water-based effluent treatment and resource recovery and hydrogen generation in one step.”

Scaling up the development of seawater electrolysers and the use of non-precious catalysts rather than pre-treatments may make hydrogen production more sustainable and cost-effective over time.