From sea water to hydrogen — no desalination required

Researchers from RMIT University claim to have developed a cheaper and more energy-efficient way to make hydrogen directly from sea water, skipping the need for desalination and its associated cost, energy consumption and carbon emissions. Their method has been detailed in a lab-scale study published in the journal Small.

Hydrogen has long been touted as a clean future fuel and a potential solution to critical energy challenges, especially for industries that are harder to decarbonise like manufacturing, aviation and shipping. But almost all the world’s hydrogen currently comes from fossil fuels and its production is responsible for around 830 million tonnes of carbon dioxide a year — equivalent to the annual emissions of the United Kingdom and Indonesia combined.

Furthermore, emissions-free ‘green’ hydrogen, made by splitting water, is so expensive that it is largely commercially unviable and accounts for just 1% of total hydrogen production globally. As explained by Dr Nasir Mahmood, a Vice-Chancellor’s Senior Research Fellow at RMIT, green hydrogen production processes are both costly and rely on fresh or desalinated water.

“To be truly sustainable, the hydrogen we use must be 100% carbon-free across the entire production life cycle and must not cut into the world’s precious freshwater reserves,” said Mahmood, who serves as lead researcher on the new study.

“Our method to produce hydrogen straight from sea water is simple, scalable and far more cost-effective than any green hydrogen approach currently in the market.”

To make green hydrogen, an electrolyser is used to send an electric current through water to split it into its component elements of hydrogen and oxygen. These electrolysers currently use expensive catalysts and consume a lot of energy and water — it can take about nine litres to make one kilogram of hydrogen. They also have a toxic output in the form of chlorine.

“The biggest hurdle with using sea water is the chlorine, which can be produced as a by-product,” Mahmood said. “If we were to meet the world’s hydrogen needs without solving this issue first, we’d produce 240 million tons per year of chlorine each year — which is three to four times what the world needs in chlorine. There’s no point replacing hydrogen made by fossil fuels with hydrogen production that could be damaging our environment in a different way,” Mahmood said.

“Our process not only omits carbon dioxide, but also has no chlorine production.”

The new approach, devised by a team in RMIT’s Materials for Clean Energy and Environment (MC2E) research group, uses a special type of catalyst developed to work specifically with sea water. Their study focused on producing highly efficient, stable catalysts that can be manufactured cost-effectively.

“These new catalysts take very little energy to run and could be used at room temperature,” Mahmood said.

PhD candidate Suraj Loomba added, “While other experimental catalysts have been developed for seawater splitting, they are complex and hard to scale.

“Our approach focused on changing the internal chemistry of the catalysts through a simple method, which makes them relatively easy to produce at large scale so they can be readily synthesised at industrial scales.”

Mahmood said the technology has promise to significantly bring down the cost of electrolysers — enough to meet the Australian Government’s goal for green hydrogen production of $2/kg, to make it competitive with fossil fuel-sourced hydrogen.

With a provisional patent application having been filed for the new method, the RMIT researchers are working with industry partners to develop aspects of their technology. The next stage in the research is the development of a prototype electrolyser that combines a series of catalysts to produce large quantities of hydrogen.

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