Researchers have developed a floating, solar-powered device that can convert contaminated water or seawater into clean hydrogen fuel and purified water anywhere on the planet. Because it works with any open water source and does not require any outside power, the device developed by researchers at the University of Cambridge could be useful in resource-limited or off-grid environments.
It is based on photosynthesis, which is the process by which plants convert sunlight into food. However, unlike previous versions of the ‘artificial leaf,’ which could generate green hydrogen fuel from clean water sources, this new device can generate clean drinking water from polluted or seawater sources.
The device was demonstrated to be capable of producing clean water from highly polluted water, seawater, and even the River Cam in central Cambridge. The findings were published in the journal Nature Water.
Our device is still a proof of principle, but these are the sorts of solutions we will need if we’re going to develop a truly circular economy and sustainable future. The climate crisis and issues around pollution and health are closely related, and developing an approach that could help address both would be a game-changer for so many people.
Professor Erwin Reisner
“It’s difficult to combine solar fuel production and water purification in a single device,” said co-lead author Dr Chanon Pornrungroj of Cambridge’s Yusuf Hamied Department of Chemistry. “Solar-driven water splitting, where water molecules are broken down into hydrogen and oxygen, need to start with totally pure water because any contaminants can poison the catalyst or cause unwanted chemical side-reactions.”
“In remote or developing regions, where clean water is relatively scarce and the infrastructure necessary for water purification is not readily available, water splitting is extremely difficult,” said Ariffin Mohamad Annuar, co-author of “A device that could work using contaminated water could solve two problems at once: it could split water to make clean fuel, and it could make clean drinking water.”
Pornrungroj and Mohamad Annuar, both members of Professor Erwin Reisner’s research group, devised a design that accomplished just that. They deposited a photocatalyst on a nanostructured carbon mesh, which is a good absorber of both light and heat and thus generates the water vapour required by the photocatalyst to produce hydrogen. The porous carbon mesh, treated to repel water, served both to help the photocatalyst float and to keep it away from the water below so that contaminants do not interfere with its functionality.
In addition, the new device uses more of the Sun’s energy. “The light-driven process for making solar fuels only uses a small portion of the solar spectrum – there’s a whole lot of the spectrum that goes unused,” said Mohamad Annuar.
The team used a white, UV-absorbing layer on top of the floating device for hydrogen production via water splitting. The rest of the light in the solar spectrum is transmitted to the bottom of the device, which vaporises the water.
“This way, we’re making better use of the light – we get the vapour for hydrogen production, and the rest is water vapour,” Pornrungroj told reporters. “This way, we’re truly mimicking a real leaf, since we’ve now been able to incorporate the process of transpiration.”
A device that can produce both clean fuel and clean water using only solar power could aid in addressing the global energy and water crises. According to the World Health Organization, indoor air pollution caused by cooking with ‘dirty’ fuels such as kerosene is responsible for more than three million deaths per year. Cooking with green hydrogen instead could significantly reduce that figure. And 1.8 billion people worldwide still lack safe drinking water at home.
“It’s such a simple design as well: in just a few steps, we can build a device that works well on water from a wide variety of sources,” Mohamad Annuar, the project’s founder, said “It’s so tolerant of pollutants, and the floating design allows the substrate to work in very cloudy or muddy water,” said Pornrungroj, a researcher. “It’s a highly versatile system.”
“Our device is still a proof of principle, but these are the sorts of solutions we will need if we’re going to develop a truly circular economy and sustainable future,” Reisner, the researcher in charge of the study, said. “The climate crisis and issues around pollution and health are closely related, and developing an approach that could help address both would be a game-changer for so many people.”
