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In a step forward for renewable energy storage, researchers in Harvard’s Department of Chemistry and Chemical Biology have accomplished the continuous splitting of impure water into pure hydrogen and oxygen gas by leveraging a process called forward osmosis, according to an article published earlier this month.
The article, titled “Continuous electrochemical water splitting from natural water sources via forward osmosis,” was published in the journal Proceedings of the National Academy of Sciences on March 2. In the paper, Samuel S. Veroneau, first author and a Chemistry Ph.D. candidate, and Daniel G. Nocera, a professor in the department widely known for his work on renewable energy, outline their use of forward osmosis and electrochemical water splitting to generate hydrogen gas, which is effective in storing renewable energy.
Veroneau said he and Nocera built upon the natural process of osmosis in order to split impure water from natural sources like the ocean.
“If you put a grape in the ocean, it’ll start to shrivel up as osmosis begins to take place,” Veroneau explained.
Currently, hydrogen generation from water requires the use of purified water, which necessitates “huge multibillion dollar reverse osmosis desalination facilities,” Veroneau said. He and Nocera’s method allows for the use of impure water, so there is no need for a separate water purification system.
As a result, a key benefit of this method is driving down the cost of building hydrogen generation plants, an important factor for developing nations, Nocera said.
“You can use any water source, and you can do it in a very distributed way,” Nocera said. “That’s the type of energy you need to get to the poor: renewable energy that can be done in a distributed way.”
The argument in favor of fossil fuels largely involves their relatively low cost and their efficiency in storing energy, and a major challenge has been “trying to recapitulate that benefit in renewable energies,” Veroneau said. The forward osmosis method, however, matches the benefits of fossil fuels with its low costs and efficiency.
A common misconception, Nocera said, is that this process will use up all of the planet’s water sources in order to store energy.
“When you split [water], you’re using sunlight, you’ve stored the energy in the rearranged bonds of water to make hydrogen and oxygen, so when you recombine them, you get that energy back and water back,” Nocera said.
Nocera added that the researchers are working with the U.S. Navy to use oxygen gas — the other product of water splitting — to “get more breathable oxygen” out of seawater.
Looking forward, Veroneau said he hopes to improve the practicality of their research.
“We made this with 15 milliliters of water, and if you want to do this on the scale of the globe you need millions of Olympic swimming pools worth of water, so our part in this is making it as good as we can with our little test tubes in the lab,” he said.
Nocera is also widely known for inventing the bionic leaf, which artificially simulates photosynthesis in order to create renewable fuel.
“In the bionic leaf there’s an organism. It eats hydrogen from water splitting, and then it breathes carbon dioxide in from the air, and it combines hydrogen and carbon dioxide and it makes a fuel,” Nocera said.
The forward osmosis method “dovetails” with the bionic leaf by supplying the organism with hydrogen gas from impure water sources, he added.
The scientists said they hope their research will ultimately help developing nations establish sources of renewable energy.
“You can’t have a sustainable planet if you’re ignoring the poor,” Nocera said. “I usually say their voice is a whisper, but it’s going to be a cacophony because of numbers in the next 30 to 40 years, and nobody’s listening.”
“So in our research, we try to listen to that whisper of a voice that we know is going to be a megaphone in 30 years,” he said. “The goal of our research is to try to answer that — not just answer renewable energy, it’s renewable energy for the poor and the poor parts of the world.”
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