Molecular assemblies created to convert water to hydrogen gas

Wonder where the fuel will come from for tomorrow's hydrogen-powered vehicles? Virginia Tech researchers are developing catalysts that will convert water to hydrogen gas.

Supramolecular complexes created by chemistry Professor Karen Brewer's group convert light energy (solar energy) into a fuel that can be transported, stored, and dispensed, such as hydrogen gas.

The process has been called artificial photosynthesis, says Brewer. "Light energy is converted to chemical energy. Solar light is of sufficient energy to split water (H2O) into hydrogen (H2) and oxygen (O2) gas, but this does not happen on its own; we need a catalyst to make this reaction occur."

One major challenge is to use light to bring together the multiple electrons needed for fuel production reactions. Electrons are the negatively charged particles that surround an atom's nucleus, allowing atoms to react and form bonds.

Previous research has focused on collecting electrons using light energy. The Brewer group has gone the next step. In 2004, they announced the creation of molecular machines that use light to bring electrons together (photoinitiated electron collection), then deliver the electrons to the fuel precursor, in this case, water, to produce hydrogen. And in summer 2005, they announced additional molecular assemblies that absorb light more efficiently and activate conversion more efficiently. "We have come up with other systems to convert light energy to hydrogen. So we have a better understanding of what parts and properties are key to having a molecular system work," Brewer says.

The researchers are working with the Air Force Research Laboratory, which is modeling what happens in the molecular systems after light is absorbed. "The AFRL researchers are interested in how light causes charge separation in large molecular systems. We have been working together to understand the initial stages of the light activation process in our molecular assemblies," Brewer says.

"Previously we concentrated on collecting light and delivering it to the catalyst site. Now we are concentrating on using this activated catalyst to convert water to hydrogen," Brewer says. "Once we know more about how this process happens, using our supramolecular design process, we can plug in different pieces to make it function better."

The National Science Foundation and the ACS Petroleum Research Fund supported the basic research. The group has now received one of eight solar to hydrogen grants awarded nationwide by the Department of Energy under the hydrogen initiative.