Hydrogen has the potential to be one of the best alternatives to fossil fuels with net zero emissions. However, using freshwater to produce hydrogen on a large scale ultimately threatens the survival of life because it strains limited freshwater reserves.
Seawater, an unlimited resource, could be an alternative, but its salty nature causes corrosion and causes several competing reactions, hindering its use. The required desalination of seawater prior to use in an electrolyser is not only energy intensive and costly, but also leaves an environmental footprint.
To overcome this, researchers at RMIT University have developed a cheaper and more energy-efficient way to make green hydrogen directly from seawater. The new method splits the seawater directly into hydrogen and oxygen, bypassing the need for desalination and its associated costs, energy consumption and carbon emissions.
“We know that hydrogen has enormous potential as a clean energy source, especially for the many industries that cannot easily switch to renewable energy,” said lead researcher Dr. Nasir Mahmood, Senior Research Fellow of the Vice Chancellor at RMIT. “But to be truly sustainable, the hydrogen we use must be 100% carbon-free throughout the product lifecycle and must not deplete the world’s precious freshwater reserves.”
“Our method of producing hydrogen directly from seawater is simple, scalable and much more cost-effective than any green hydrogen approach currently on the market. With further development, we hope this can promote the establishment of a thriving green hydrogen industry in Australia.”
To make green hydrogen, an electrolyser is used to send an electrical current through water to split it into its constituent elements hydrogen and oxygen. These electrolyzers currently use expensive catalysts and consume a lot of energy and water. It can take about nine liters to make one kilogram of hydrogen. In addition, they have a large production of toxic chlorine, according to RMIT researchers.
“The biggest hurdle in using seawater is the chlorine, which can be produced as a by-product,” said Mahmud. “If we were to meet the world’s hydrogen needs without solving this problem first, we would be producing 240 million tons of chlorine every year – three to four times the world’s chlorine needs. It makes no sense to replace hydrogen made by fossil fuels with hydrogen production that could otherwise harm our environment. Our process not only omits carbon dioxide, but also produces no chlorine.”
The new approach devised by the RMIT team uses a special type of catalyst developed to work specifically with seawater. The new, highly efficient, stable catalysts require very little energy to operate and can be used at room temperature.
Unlike most other experimental catalysts, which are complex and difficult to scale, the new approach focused on changing the internal chemistry of the catalysts through a simple method. This makes them relatively easy to produce on a large scale, so they can be easily synthesized on an industrial scale.
The researchers say their technology promises to significantly reduce the cost of electrolyzers to make it competitive with hydrogen from fossil fuels. The next step in the research is the development of a prototype electrolyser that combines a series of catalysts to produce large amounts of hydrogen. They are also working with industry partners to develop aspects of this technology.
- Suraj Loomba, Muhammad Waqas Khan, Muhammad Haris, Seyed Mahdi Mousavi, Ali Zavabeti, Kai Xu, Anton Tadich, Lars Thomsen, Christopher F. McConville, Yongxiang Li, Sumeet Walia, Nasir Mahmood. Nitrogen doped porous nickel molybdenum phosphide plates for efficient sea water splitting. Klein, 2023; DOI: 10.1002/smll.202207310