A new approach to producing usable energy from solar power not only makes hydrogen gas from water but also separates it. Peter Ritterskamp and colleagues at the Max Planck Institutes for Bioinorganic Chemistry and for Coal Research have shown that titanium disilicide, an inexpensive semiconductor that had not been identified as useful for splitting water, will do the job.

The titanium disilicide has a wide variation in band-gap (unusual for semiconductors), allowing it to absorb light efficiently across a broad spectrum. When a powder of the material is added to water, the light energy will split the water into hydrogen and oxygen. The hydrogen is freely released, but the oxygen remains bound to the surfaces of the powder. Heating to more than 100 °C in the dark releases the oxygen and reactivates the powder. More important is that this powder is not degraded as a catalyst, unlike some other semiconductors.