Scientists in Tokyo have discovered the key catalyst needed to develop the 'perfect' photocatalyst, using ruthenium.

Using the correct combination of doped semiconductors, the team from the Tokyo University of Science created a solid solution of zinc sulfide, copper indium sulfide and silver indium sulfide.

Then the catalyst was loaded with ruthenium metal and a highly active photocatalyst was created, with a much broader wavelength absorption.

Scientists are constantly trying to imitate green plants and photosynthesis to make energy usable, to catalytically release hydrogen from water to make fuel cells produce electricity.

Now Akihiko Kudo, of Tokyo University of Science, says progress has been made: "Everything depends on the catalyst. To make the system commercially viable, the catalyst must use sunlight efficiently."

A common problem is that when photocatalysts split water upon irradiation with UV light they leave a large portion of light unused - this new creation, however, works when irradiated with visible light.

"If this works in practice, hydrogen could be obtained by using unwanted side-products from chemical factories and power plants: hydrogen sulfide and sulfur dioxide are sources of sulfides and sulfites," Mr Kudo added.