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April 20th 2019

Clean, renewable fuels such as hydrogen gas can be produced by catalytically splitting water into oxygen, positively charged hydrogen and electrons. This process also takes place in nature in the form of photosynthesis in plant leaves. Researchers from this programme have copied nature by making an artificial leaf. However the next step of splitting the water is still a considerable challenge for this artificial leaf.

An efficient process requires  good and stable catalysts, which can also be attached to electrode surfaces. Recently the researchers electrochemically tested such a robust catalyst, which can be simply anchored to the surface. The catalyst tested, which was made from iridium, worked for more than 12 hours without any decrease in activity. 

Just like a plant leaf
Recently another iridium catalyst has been developed that can split water. The team from professor Joost Reek and professor Fred Brouwer (University of Amsterdam) have combined this catalyst with a chromophore (a molecule that is responsible for light absorption), sodium persulphate and light.

In this system, the chromophore (a platinum porphyrin) is excited by light and consequently loses an electron. The sodium persulphate, which was specifically added to the system for this purpose, captures this released electron. The chromophore now has sufficient oxidation energy to oxidise the iridium catalyst and split the water. Just like in a plant leaf, oxygen, electrons and positive hydrogen ions (H+) are produced in this reaction.

The researchers are now trying to attach the independent components of this system to the electrode surfaces in such a way that the leaf can function optimally. In the leaf, electrons (that are now absorbed by sodium persulphate) will react with positive hydrogen ions to make hydrogen. In the final system, sunlight will therefore catalytically drive the production of this sustainable hydrogen fuel.