Artificial leaf

Artificial leaf devices can produce clean hydrogen from water

Image credit: Virgil Andrei

Devices made of readily available oxide and carbon-based materials can produce clean hydrogen from water over weeks, research has shown.

A team of researchers from the University of Cambridge and Imperial College London has created devices that can mimic the natural photosynthesis process but produce fuels like hydrogen instead of sugars.

These artificial leaf devices were made from bismuth oxyiodide (BiOI) and other sustainable materials, harvesting sunlight to produce O2, H2 and CO. The discovery could help overcome some of the key challenges in solar fuel production.

Currently, most Earth-abundant light-absorbing materials have limited performance or stability. Initially, BiOI was also rejected as a solution for solar fuel applications due to its poor stability in water. However, the study published in Nature Materials states that this non-toxic semiconductor alternative could be key to the production of green hydrogen.

“A few years ago, we demonstrated that BiOI solar cells are more stable than those using state-of-the-art perovskite light absorbers,” said Dr Robert Hoye, a lecturer at Imperial College London. “We wanted to see if we can translate that stability to green hydrogen production.”

The researchers were able to increase the stability of these artificial leaf devices by inserting BiOI between two oxide layers. The robust oxide-based device structure was coated with a water-repellent graphite paste, which prevented moisture infiltration, prolonging the stability of the bismuth oxyiodide light-absorbing pixels from minutes to a couple of months.

Through the use of these leaf devices, BiOI can become a viable light harvester for stable green hydrogen production.

"We have been working on this material for some time, due to its wide-ranging potential applications, as well as its simplicity of fabrication, low toxicity and good stability,” said Judith Driscoll, a professor at the University of Cambridge.

The team also found that, when the devices comprised multiple light-harvesting areas (called ‘pixels’), they demonstrated a higher performance than conventional devices with a single larger pixel of the same total size. This finding could make the scale-up of novel light harvesters much easier and faster for sustainable fuel production.

Hydrogen production has been deemed a fundamental field of research in the UK’s journey towards net-zero. Although most hydrogen is currently supplied from fossil fuels, researchers are now working to find ways to generate hydrogen more sustainably, such as by harvesting sunlight and splitting water to produce green hydrogen.

The new ways of making BiOI artificial leaf devices more stable can now be translated to other novel systems, helping to bring them towards commercialisation.

“This is an exciting development! At the moment, few solar fuel systems show stabilities which are compatible to real-world applications. With this work, we make a step forward towards establishing a circular fuel economy”, said Professor Erwin Reisner, one of the corresponding authors.

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