A research team from the University of Cambridge has created an innovative floating device that uses solar energy to convert contaminated water or seawater into clean hydrogen fuel and purified water. This device is particularly useful in areas with limited resources or no grid, as it can operate on any open water source and does not rely on external power.
It is inspired by photosynthesis, the process by which plants convert sunlight into food. However, unlike earlier "artificial leaves" that could use clean water sources to produce green hydrogen fuel, this new device can use polluted water sources or seawater while producing clean drinking water.
Tests of the device have shown it is capable of producing clean water from highly polluted water sources, seawater and even the River Camb in Cambridge city centre. The relevant results were published in the journal Nature Water.
Technical challenges and breakthroughs
Dr Chanon Pornrungroj, co-first author of the paper from the University of Cambridge's Department of Chemistry, said: "Combining solar fuel production and water purification in one device is very tricky. Solar-driven water splitting (where water molecules are split into hydrogen and oxygen) needs to start with completely pure water, as any contaminants can poison the catalyst or cause unnecessary chemical side reactions."
Co-first author Ariffin Mohamad Annuar said: "In remote or developing areas, clean water is relatively scarce and the infrastructure required to purify water is not easy to obtain, so water splitting is extremely difficult. A device that can use contaminated water can solve two problems at the same time: it can split the water to make clean fuel, and it can also make clean drinking water."
Pornrungroj and Mohamad Annuar are both members of Professor Erwin Reisner's research group. They deposited the photocatalyst on a nanostructured carbon mesh that absorbs both light and heat very well. The photocatalyst uses the water vapor it generates to generate hydrogen. The water-repellent treated porous carbon mesh both helps the photocatalyst float and keeps it away from the water below, preventing contaminants from interfering with its function.
In addition, the new installation can harness more of the sun's energy. "The light-driven process of making solar fuel uses only a small part of the solar spectrum, leaving a large amount of the spectrum that is not being utilized," Mohamed-Anouar said.
The research team used a white UV-absorbing layer on top of the floating device to produce hydrogen by dividing water. The remaining light in the solar spectrum is transmitted to the base of the device, vaporizing the water.
"We're able to make better use of the light - we get water vapor for hydrogen production, and the rest is water vapor," Pornrungroj said. "In this way, we're really mimicking a real leaf because we can now incorporate the process of transpiration into it."
potential global impact
Devices that can simultaneously create clean fuel and clean water using only solar energy could help solve the energy and water crises facing many parts of the world. For example, indoor air pollution from cooking with "dirty" fuels such as kerosene kills more than 3 million people every year, according to the World Health Organization. This number could be significantly reduced if green hydrogen was used for cooking. 1.8 billion people worldwide still lack safe household drinking water.
"It's also very simple in design: in just a few steps we can create a device that works well with a variety of water sources. It's very tolerant of contaminants, and the floating design allows the substrate to work in very turbid or muddy water. It's a very versatile system," Mohamed-Anouar said.
Leissner, who led the research, said: "Our device is still just a proof-of-principle, but we need these solutions if we are to develop a truly circular economy and a sustainable future. The climate crisis is closely linked to pollution and health issues, and developing a method that helps solve both problems simultaneously will change the lives of many people."
Compiled from: ScitechDaily