Photosynthesis in a beaker?
17 Sep 2001
In a step toward creating energy from sunlight as plants do, MIT researchers Professor Daniel G. Nocera and former graduate student Alan F. Heyduk have a invented a compound that produces hydrogen gas with the help of a catalyst and a zap of light.
Creating a molecule to replace a leaf - essentially, photosynthesis in a beaker - could provide a cheap, clean future energy source, Professor Nocera said.
'We have been seeking a future alternative fuel source by studying the principles that govern the conversion of photon energy into chemical potential,' he said. 'Our strategy is to use the energy of sunlight to drive reactants uphill to energy-rich products, thus harnessing the sun's energy to create a renewable energy source in the future.'
Nocera and Heyduk created a compound based on the metal rhodium. When the rhodium photocatalyst is dissolved in solution, the researchers add to it a hydrogen-containing acid (also called a hydrohalic acid - one example is hydrochloric acid), and shine light on it.
'In the leaf, sugar and oxygen are energy-rich products. In our beaker, the sought-after fuels are hydrogen and a halogen, produced catalytically from the photochemical splitting of hydrohalic acid,' Nocera said.
The structure of the rhodium compound allows it to break the hydrohalic acid's chemical bonds. Hydrogen gas, with a byproduct of bromides and chlorides, is produced. The by-products are chemically trapped and recycled into the reaction.
While not as complete and efficient as photosynthesis, this system comes close to the ideal use of a molecular catalyst as part of a homogeneous reaction for which scientists have been searching for more than three decades.
Nocera says that their new process is not perfect, but it is a beginning that may re-ignite solar energy research that has been largely dormant since the 1970s.
'As it stands, we have performed half of the photosynthetic reaction by generating hydrogen. If we can now get the other half of the process to work (getting the halogen), we would have a framework for future energy production,' Nocera said.
