2 July 2009
Artificial leaf can boost solar energy
By using an artificial leaf, it may soon be possible to convert sunlight into energy.
That can happen by modifying chlorophyll from an alga so it resembles the extremely efficient light antennae of bacteria. After determining the structure of these light antennae, it should be possible to convert sunlight to energy.
In order to generate fuel from sunlight you need two things: an antenna that harvests light and a light-driven catalyst.
The antenna: The fastest light harvesters come from nature, in green leaves, algae, and bacteria. The light antennae of bacteria—chlorosomes—are the fastest of all. They have to be capable of harvesting minimal quantities of light particles in highly unfavorable light conditions, such as deep in the sea. These chlorosomes consist of chlorophyll molecules. The art is to imitate these systems very precisely.
German colleagues from the University of Würzburg in Professor Huub de Groot’s team modified chlorophylls from the alga Spirulina, so they resembled the pigments of bacteria. De Groot’s Leiden University group then studied the structure of these semi-synthetic light antennae.
“Nanotechnology and supramolecular systems are becoming increasingly important, but it is very difficult to determine their structure,” de Groot said. “So-called cartoons are frequently made that give a schematic indication of what their structure could be.”
De Groot and his colleagues successfully determined the detailed molecular and supramolecular structure of their artificial self-assembled light antennae. They did this using a combination of solid state NMR and X-ray diffraction. X-ray diffraction enabled them to determine the overall structure, and NMR allowed them to penetrate deeply into the molecules.
“We already knew that the light antennae in bacteria form a structure rather like the annual rings of a tree trunk,” de Groot said. “The molecules in these semi-synthetic antennae seem to stack in a different way; they are flat. But this, too, is one of four ways we had thought in advance were possible.”
The researchers still have to determine how the light antennae of modified Spirulina chlorophylls work in practice.
Last month, de Groot reported with a combination of NMR and another technique with an electron microscopy, he resolved the structure of the light antennae of the bacteria themselves. This allowed the researchers to explain how the antennae were able to function so quickly and so efficiently.
For related information, go to www.isa.org/manufacturing_automation.