The cocktail of elements in seawater, including hydrogen, oxygen, sodium and others, is essential for life on Earth. However, this complex chemistry poses a problem when trying to separate hydrogen gas for sustainable energy use.

Recently, a team of scientists from the Department of Energy’s SLAC National Accelerator Laboratory, Stanford University, the University of Oregon and Manchester Metropolitan University discovered a method for extracting hydrogen from the ocean. They achieve this by channeling seawater through a double membrane system and electricity.

Their innovative designs have succeeded in producing hydrogen gas without producing large amounts of harmful byproducts. The results of their research, recently published in the journal joules can contribute to efforts to produce low-carbon fuels.

“Many water-to-hydrogen systems today attempt to use a single-layer or single-layer membrane. “Our work brought the two levels together,” said Adam Nylander, a research fellow at the SUNCAT Center for Interface Science and Catalysis, a SLAC-Stanford joint institute. Their architecture allowed us to control the movement of ions in seawater in our experiment.”

Hydrogen is a low-carbon fuel that is currently used in many ways, such as a long-term energy storage option (suitable for weeks, months, or longer energy storage) for fuel cell electric vehicles and electric vehicles. nets

Many attempts to obtain hydrogen start with fresh or desalinated water, but these methods can be expensive and energy intensive. Purified water is easier to work with because it contains less floating matter – chemical elements or molecules. But the researchers say water purification is expensive, requires energy, and complicates the devices. The other option, natural freshwater, is a more limited resource on the planet and contains a number of impurities that are problematic for today’s technology.

The team implemented a bipolar or bilayer membrane system to work with seawater and tested it using electrolysis, a method that uses electricity to drive ions or charged elements to trigger the desired reaction. Joseph Perryman, a SLAC researcher and postdoctoral fellow at Stanford University, said they began developing it by controlling chloride, the most harmful element to the seawater system.

“There are many reactive substances in seawater that can interfere with the hydrogen reaction, and sodium chloride is one of the main culprits, which makes seawater salty,” Perryman said. “Chlorine, in particular, that reaches the anode and is oxidized shortens the life of the electrolysis system and can become really dangerous due to the toxic nature of oxidation products, including molecular chlorine and bleach.”

The bipolar membrane in the experiment provides access to the conditions necessary for the formation of hydrogen gas and prevents chloride from entering the reaction center.

“We’re actually doubling down on ways to stop this chloride reaction,” Perryman said.

house for hydrogen

An ideal membrane system performs three main functions: separating hydrogen and oxygen from seawater; helps to transport only useful hydrogen and hydroxide ions by limiting other seawater ions; and will help prevent undesirable reactions. Combining all three is difficult, and the team’s research aims to discover systems that can effectively combine all three of these needs.

Specifically, in their experiments, protons with positive hydrogen ions pass through one of the membrane layers where they can be collected and are converted to hydrogen gas by interacting with a negatively charged electrode. The second membrane in the system only allows negative ions such as chloride to pass through.

Daniela Marin, a graduate student, said that as an added protection, one layer of the membrane contains negatively charged groups attached to the membrane, making it difficult for other negatively charged ions, such as chloride, to move into places they shouldn’t. at Stanford University. Chemical Engineering Faculty student and co-author. The negatively charged membrane proved highly effective at blocking nearly all chloride ions in the team’s experiments, and their system worked without producing toxic byproducts such as bleach and chlorine.

In addition to improving the seawater-hydrogen membrane system, the researchers provide a better general understanding of how seawater ions move across membranes. This knowledge could help scientists develop stronger membranes for other applications, such as oxygen production.

“There is also interest in using electrolysis to generate oxygen,” said Marin. “Understanding ion flux and conversion in our bipolar membrane system is also critical to this effort. In our experiment we showed how to use a bipolar membrane to produce oxygen gas as well as hydrogen production.”

Next, the team plans to improve their electrodes and membranes by building them from materials that are more common and easier to mine. The team said this design improvement could make it easier to scale the electrolysis system to the size needed to produce hydrogen for energy-intensive activities such as the transportation sector.

The researchers also hope to transport the electrolysis cells to SLAC’s Stanford Synchrotron Radiation Facility (SSRL), where they can study the atomic structure of catalysts and membranes using intense X-rays.