The device takes its inspiration from photosynthesis, the process by which plants convert sunlight into food. However, unlike earlier versions of the ‘artificial leaf’, which could produce green hydrogen fuel from clean water sources, this new device operates from polluted or seawater sources and can produce clean drinking water at the same time, explain the researchers. It could be useful in resource-limited or off-grid environments, since it works with any open water source and does not require outside power, they add.

The results of tests on the new technology are reported in the journal Nature Water.

‘Bringing together solar fuels production and water purification in a single device is tricky,’ explains Dr Chanon Pornrungroj from Cambridge’s Yusuf Hamied Department of Chemistry, the paper’s co-lead author. ‘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.’

Co-lead author Ariffin Mohamad Annuar continues: ‘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. 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.’

The new device features a photocatalyst deposited on a nanostructured carbon mesh that is a good absorber of both light and heat, which generates the water vapour used by the photocatalyst to create hydrogen. The porous carbon mesh helps 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 is reported to use more of the Sun’s energy. The research 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 vapourises 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,’ explains Pornrungroj. ‘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 make clean fuel and clean water at once using solar power alone could help address the energy and the water crises facing so many parts of the world. For example, the indoor air pollution caused by cooking with ‘dirty’ fuels, such as kerosene, is responsible for more than three million deaths annually, according to the World Health Organization. Cooking with green hydrogen instead could help reduce that number significantly. And 1.8 billion people worldwide still lack safe drinking water at home, note the researchers.

‘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,’ says Professor Erwin Reisner, who led the research.