Extracting hydrogen and critical metals from nuisance seaweed

Every summer since 2011, the brown seaweed Sargassum has blanketed beaches along the Atlantic and Caribbean coasts, hurting local ecosystems and economies. Warmer temperatures have led to explosive growth of this marine algae and sparked efforts to convert the problem biomass to valuable products.

At the American Chemical Society's Spring 2025 meeting, researchers from the University of California, Los Angeles, reported methods to make hydrogen fuel and extract rare earth elements (REEs), which are critical for batteries and electronics, from Sargassum. Seaweed is known to absorb metal ions from seawater, with some species accumulating up to 40% of their dry weight as minerals.

The research is part of a project funded by Schmidt Sciences, a nonprofit founded by the couple Eric Schmidt, a former CEO of Google, and Wendy Schmidt, a businessperson and philanthropist. The goal is to make commercial products from the millions of metric tons of Sargassum economically, said UCLA material scientist and engineer Aaron Moment. “The project aims to find every possible avenue towards using the atoms and elements that are in seaweed.”

Moment, Ah-Hyung Alissa Park, and colleagues have developed an alkaline thermal treatment to break down the polysaccharides in seaweed to produce hydrogen. Because the seaweed absorbs carbon dioxide to grow, the hydrogen is considered carbon-neutral.

The team cooks wet, salty seaweed at 500° C in the presence of sodium hydroxide, a nickel catalyst, and nitrogen gas. Sodium hydroxide reacts with the biomass to give 90% pure hydrogen gas, as well as sodium carbonate. The nickel catalyst pushes any carbon monoxide formed during the reaction to react with water and produce CO₂ and hydrogen via the water-gas shift reaction. The process gives over 60 mmol of hydrogen per gram of dry sargassum. Postdoctoral researcher Wonhyeong Lee presented the results at a symposium organized by the Division of Cellulose and Renewable Materials (CELL) on Monday.

That’s not where the seaweed story ends. The researchers plan to recover REEs from the biomass residue left behind after producing hydrogen. On Sunday, at another CELL session of the ACS Spring meeting, postdoctoral researcher Dasol Choi discussed Sargassum’s ability to absorb REEs. Choi is growing Sargassum in the lab in water with various REE concentrations to measure metal uptake. She found that seaweed absorbs more of the heavier elements than lighter ones.

There is almost no data on the content of REEs in Sargassum, says the University of York’s Thierry Tonon, who was not involved in the work. “More information on the REE content of such biomass will be useful to assess their potential for the recovery of these elements.”

The UCLA team is now developing a way to extract REEs from the biomass using molten salt electrolysis, a process used today to produce aluminum metal by reducing aluminum oxide in a molten salt electrolyte.

Moment said the team is also developing acid washing techniques to make the metal recovery process selective and cost-effective. And they are evaluating the use of molten salt electrolysis to convert sodium carbonate to carbon nanotubes to get further value from the waste.

A lot of work has been done to make valuable products from land plants and other brown algae, but there needs to be more exploration of how Sargassum might be valorized, Tonon says, so these research projects are important. Going from lab scale to industrial scale is always a challenge, he adds, and the researchers should make sure that the methods they develop are sustainable.

The UCLA team is collaborating with Carbonwave, a company that already harvests metric tons of seaweed to make fertilizer and vegan leather. The researchers plan to conduct a thorough assessment of the process to evaluate its environmental sustainability and economic viability. Moment said that their process could have an advantage here. “It costs a lot of energy to remove water from seaweed, but it doesn’t have to be dried [for our] hydrogen-generation process.”