DETROIT – Hydrogen could be an important part of our future energy supply: It can be stored, transported and burned as needed. However, most of the hydrogen available today is a by-product of natural gas production, and this has to change for climate protection reasons. The best strategy so far to produce environmentally friendly “green hydrogen” is to split water into hydrogen and oxygen using electricity that comes from renewable energy sources, for example photovoltaic cells.
However, it would be much easier if sunlight could be used directly to split water. This is exactly what new catalysts are now making possible, in a process called “photocatalytic water splitting.” The concept is not yet used industrially. At TU Wien, important steps have now been taken in this direction: on an atomic scale, scientists have realized a new combination of molecular and solid-state catalysts that can do the job while using relatively inexpensive materials.
Solutions have now been found for both tasks. Tiny inorganic clusters consisting of only a small number of atoms are anchored on a surface of light-absorbing support structures such as titanium oxide. The combination of clusters and carefully chosen semiconductor supports lead to the desired behavior.
The clusters responsible for oxidizing oxygen are made up of cobalt, tungsten and oxygen, while clusters of sulfur and molybdenum are especially suitable for creating hydrogen molecules. The researchers at TU Wien were the first to deposit these clusters on a surface made of titanium oxide, where they can act as catalysts for water splitting.
“Titanium oxide is sensitive to light, that was already well known,” says Alexey Cherevan. “The energy of the absorbed light leads to the creation of free-moving electrons and free-moving positive charges in the titanium oxide. These charges then allow the clusters of atoms sitting on this surface to facilitate the splitting of water into oxygen and hydrogen.”
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