Wetenschap - 12 december 2012

Light in the darkness

Albert Sikkema

The sun is the ultimate source of energy on the earth. We are already using its light to generate electricity, but with artificial photosynthesis we could make fuel out of it too. The building blocks for artificial leaves already exist; it only remains for nanoplumbers
to create a factory.

Thin foil on the roofs of cars, greenhouses and factories, which directly converts sunlight into fuel or chemical compounds: that is what the artificial leaves could look like which would supply us with energy after the oil runs out. It still sounds like science fiction, but may not be so for long if researchers on the BioSolar Cells programme have anything to do with it. They aim to have a prototype of this kind of solar cell ready in two and a half years’ time. ‘And we are going to make it,’ says René Klein Lankhorst, director of BioSolar Cells and on the staff at Plant Research International. More than 200 staff of nine universities and dozens of small businesses are working on developing biological solar cells under the auspices of BioSolar Cells. Expectations are running high: two years ago the Dutch government and a handful of companies and research institutes invested 43 million euros in the project.

The aim of the project is to develop a new form of solar energy. Solar energy as we know it is generated by solar cells which convert light into electricity. That is useful, but electricity does have its disadvantages as well. It is difficult to store and to transport, and it cannot be used outside the network, in cars for example. So it would be a valuable development to be able to convert solar energy into chemical substances that could be used for fuel. The good news is: what the researchers want to do is already happening. On a large scale, even. In fact, all life on earth is directly or indirectly dependent on the capacity of plants and other organisms to convert sunlight into chemicals through photosynthesis. But how exactly do they do this, and could we imitate it on a large scale? That is the question the BioSolar Cells researchers hope to be able to answer soon.

More efficient than plants
Much is already known about the process. Plants capture sunlight in three stages, explains Klein Lankhorst. ‘Stage one is when chloroplasts full of chlorophyll absorb and capture the sunlight. They form a kind of antenna with a battery. In stage two, that battery delivers energy for dividing water into oxygen, protons and electrons. This is done with the help of certain enzymes. And in stage three, the protons and electrons are linked with CO2. Then you get sugars which the plant uses to manufacture biomass.’

The researchers want to do more than copy this trick; they want to improve on it. ‘Plants are not at all efficient in capturing sunlight,’ says Klein Lankhorst. ‘They capture 0.5 percent of it at most. That is enough for the plant, but not for us. In theory an artificial leaf that only makes simple compounds can capture 48 percent of the sunlight. We have already achieved 5 percent, capturing the sunlight in the form of hydrogen. The programme has already developed three concepts for producing oxygen and hydrogen from sunlight. Wageningen researchers recently came up with an important component for artificial leaves. They developed a new way of converting hydrogen and CO2 into methanol, so that the solar cell can also make hydrocarbons. This opens up the prospect of an application for directly producing fuels from sunlight.

In two and a half years’ time, the first phase of the programme will be over and the budget will be used up. Before then Klein Lankhorst wants to submit a follow-up proposal to the Energy and Chemistry top sector. He hopes that the prototype of the artificial leaf will convince companies capable of marketing this kind of organic solar cell. ‘Because we don’t have them on board yet. There are companies in our consortium collaborating on the development of artificial leaves, but they are mainly innovative high-tech companies. We are now looking for companies in the chemistry and energy sectors with deep pockets.

Photo: Gerard-Jan Vlekke