Researchers at the Swiss Federal Institute of Technology in Lausanne, led by Michael Gratzel, have developed methods for generating fuels such as hydrogen through solar water splitting. To do this, they either use photoelectrochemical cells that directly split water into hydrogen and oxygen when exposed to sunlight, or they combine electricity-generating cells  with an electrolyzer that separates the water molecules.

By using the latter technique, Gratzel's post-doctoral student Jingshan Luo and his colleagues were able to obtain a spectacular performance. Their device converts into hydrogen 12.3 per cent of the energy diffused by the Sun on perovskite absorbers – a compound that can be obtained in the laboratory from common materials, such as those used in conventional car batteries, eliminating the need for rare-earth metals in the production of usable hydrogen fuel.

This high efficiency provides stiff competition for other techniques used to convert solar energy, researchers said. "Both the perovskite used in the cells and the nickel and iron catalysts making up the electrodes require resources that are abundant on Earth and that are also cheap," said Luo.

"However, our electrodes work just as well as the expensive platinum-based models customarily used," Luo added. On the other hand, the conversion of solar energy into hydrogen makes its storage possible, which addresses one of the biggest disadvantages  faced by renewable electricity – the requirement to use it at the time it is produced.

"Once you have hydrogen, you store it in a bottle and you can do with it whatever you want to, whenever you want it," said Gratzel. Such a gas can be burned - in a boiler or engine - releasing only water vapour. It can also pass into a fuel cell to generate electricity on demand, researchers said. They hope the 12.3 per cent conversion efficiency they achieved will soon get even higher.

The study is published in the journal Science.


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