Fuel from sunlight

Solar energy is renewable and environmentally-friendly – in many ways a perfect solution to global warming and the looming energy crisis. But what happens when the sun isn’t shining? And what happens when the solar panels are placed a long way from where the energy is being consumed?

The answer is to convert solar energy into types of fuel that can be transported to where they’re needed, and stored for a rainy day. One such fuel is hydrogen.

In the same way that plants convert sunlight, water and carbon dioxide into food and oxygen, a system called photocatalytic water splitting converts sunlight and water into hydrogen. The system is often referred to as artificial photosynthesis.

Photocatalytic water splitting relies on a photocatalyst to facilitate the reaction. Photocatalysts are made from metal oxides, and they need to perform the water splitting reaction many times over without degrading.

Professor Kazunari Domen and his team from the University of Tokyo are researching how to make better, longer-lasting photocatalysts. They have developed an aluminium-doped SrTiO₃ catalyst, which retains 80% of its initial activity after 55 days of continuous use.

This catalyst has been used before, but was known to decompose quite quickly with use. During photocatalytic water splitting, the UV light generates negatively-charged electrons, and corresponding positively-charged 'holes' in the catalyst. 'Holes' have strong oxidising properties, and it is thought that if there are too many of them they can damage the photocatalyst.

To solve this problem, the researchers have added a cocatalyst called cobalt oxyhydroxide, which prevents holes from accumulating. This makes the catalyst much more durable and long-lasting.

Professor Domen hopes his work could help to solve the energy crisis. "Renewable hydrogen could become available abundantly and inexpensively through successful implementation of large-scale photocatalytic water splitting systems," he says. "This will reduce environmental load and improve the sustainability of our lives."

This article is free to read in our open access, flagship journal Chemical Science: Kazunari Domen et al., Chem. Sci., 2019, Advance Article. DOI: 10.1039/C8SC05757E. You can access our 2019 ChemSci Picks in this article collection.