Aug 21 2007
In an effort to develop alternative energy sources such as fuel cells and solar fuel from "artificial" photosynthesis, scientists at the U.S. Department of Energy's Brookhaven National Laboratory are taking a detailed look at electrons - the particles that set almost all chemical processes in motion.
Electron transfer plays a vital role in numerous biological processes, including nerve cell communication and converting energy from food into useful forms. It's the initial step in photosynthesis as well, where charges are first separated and the energy is stored for later use - one of the concepts behind energy production using solar cells. Understanding and controlling the movement of electrons through individual molecules also could allow for the development of new technologies such as extremely small circuits, or help scientists find catalysts that give fuel cells a much-needed boost in efficiency and affordability. Three Brookhaven chemists will discuss how these applications are related to their most recent findings at the 234th National Meeting of the American Chemical Society.
Brookhaven chemist James Muckerman works with a team of researchers to design catalysts inspired by photosynthesis, the natural process by which green plants convert sunlight, water, and carbon dioxide into oxygen and carbohydrates. The goal is to design a bio-inspired system that can produce fuels like methanol or hydrogen directly from carbon dioxide or water, respectively, using renewable solar energy. To replicate one of the important steps in natural photosynthesis, Muckerman uses molecular complexes containing the metal ruthenium as catalysts to drive the conversion of water into oxygen, protons, and electrons. Specifically, Muckerman's group has set out to determine the electronic activity of a catalyst recently developed in Japan. Unlike previous ruthenium catalysts, which have a very short life, this catalyst has quinone ligands attached to each of its ruthenium centers. These electron-accepting molecules appear to make the catalyst very active and stable. The challenge is to determine exactly how the catalyst works.
"It was a controversial result," said Muckerman, who compares the lab results to calculations based on theory. "I believe that the reaction occurs by ruthenium-mediated electron transfer from water molecules bound to the metal centers to the quinone ligands. These electron transfers are initiated by proton transfers from the bound water moieties to the aqueous solution. The ruthenium atoms maintain the same charge state during the entire catalytic cycle, indicating that this catalyst works in a totally different way than the other catalysts."