For billions of years, nature has been harnessing the energy from the sun through photosynthesis. This way, plants, algae and cyanobacteria use sunlight to split water and produce energy-rich chemical compounds from carbon dioxide (CO₂). This energy is then transferred to animal that eat these plants, and animals that eat plant-eating animals, including us humans. It’s clear that without photosynthesis, there would be no life as we know it. 

A photosynthesis dream

Society today is highly dependent on energy, so why not profit from a process that’s been evolutionary refined for billions of years? Synthetic photosynthesis is a hot trend in biotech right now, but while scientists have known the basic reactions involved in photosynthesis for a very long time, developing a complex artificial photosynthesis system that mimics all the transmuting steps has proved to be no easy task. Researchers at the Max Planck Institute for Chemical Energy Conversion in Mülheim an der Ruhr and the Commissariat à l’Énergie Atomique (CEA) in Saclay, France have provided new insight in how photosynthesis happens and along with it, brought us one step closer to a new energy dream.

Namely, the researchers investigated an important cofactor involved involved in photosynthesis, a manganese-calcium complex. The cofactor uses solar energy to split water into O2, and it was only now that the scientists determined the exact structure of this complex right before this crucial stage in the chemical reaction takes place. This way, the researchers have provided a basic blueprint for a synthetic system that might one day store sunlight energy in chemical energy carriers.

The job wasn’t easy; the team had to painstakingly go through an extraction and purification process of photosystem II – the large protein membrane where light-induced catalytic water splitting takes place. Then came the actual characterization work for the manganese-calcium complex, which they performed using electron paramagnetic resonance (EPR), a technique which makes it possible to visualize the distribution of the electrons in a molecule or metal complex and thus provides deep insight into the individual stages of water-splitting.

“These measurements generated new information and enabled the solvation of problems concerning the detailed analysis of molecular structures in the reaction cycle that are not accessible using other methods,” says Dr Alain Boussac from the CEA Saclay.

One might argue that we already harness the sun. Indeed, solar cells are great but the electricity they provide is unreliable and be served as baseload. This means that if we can’t develop efficient energy storage systems, solar or wind energy will always be in second place, behind fossil and nuclear. In contrast, a viable artificial photosynthesis system can store energy from the sun directly into chemical energy, ready for use at any time and any place.

“Synthetic solar fuels open up wide-ranging possibilities for renewable energy technologies, in particular for the transport and infrastructure sectors, which are still reliant on fossil fuels,” says Professor Wolfgang Lubitz, Director at the Max Planck Institute for Chemical Energy Conversion. “An efficient light-driven, water splitting catalyst based on common metals such as manganese would represent huge progress here. The insight gained into nature’s water splitting enzyme through this research has laid the foundations for such developments.”

The findings were reported in the journal Science.