Using hydrogen to power vehicles could be the future releasing us from reliance on fossil fuels, and water is it obvious source, but how to get one from the other? Now a semiconductor has been found that uses energy from sunlight to do this efficiently. 

The usual way to yield hydrogen from water is by splitting the water molecules with an electric current, but this is inefficient and costly. For years researchers have hoped to harness sunlight to do the job, using a process analogous to photosynthesis. 

Some light-sensitive semiconductors can do this, but are inefficient. Now Martin Dembuth and colleagues at the Max Planck institute for Bioinorganic Chemistry in Mulheim, Germany, found a solar-powered water splitter that does this more efficiently. It only uses 4-per-cent of the visible light that hits it, but that is double previous attempts, says Demuth. It also absorbs the hydrogen it makes, solving the puzzle of how to store the gas once it is produced. 

When Demuth’s team suspended the semiconductor titanium disilicide TiSi2 in water and exposed it to lights that stimulate sunlight, they produced hydrogen and oxygen (Angewandte Chemie, D0I: 10.1002/anie.200701626). Both gases were initially absorbed by the TiSi2, but could be released by heating. Because the hydrogen is released at a lower temperature than the oxygen, it can be extracted in pure form using gentle heat. 

“This may prove to be a significant advance”, said photochemist James Durrant of Imperial College London.