THE INNER LIFE OF RUST: ElectronTransfer at the Water-Metal Interface

Electrochemistry, Batteries and Rust

When Gregory Voth and his colleagues say "ET," chances are they're not talking about the cute alien in the Spielberg movie. To Voth, a theoretical chemist at the University of Pennsylvania, ET means electron transfer, one of the most fundamental processes in chemistry.

"There's this whole field of electrochemistry," he says, "that goes back to Faraday." Michael Faraday's 19th century experiments passing electricity through water and other compounds laid the groundwork for modern understanding that matter has discrete particles of electricity -- electrons -- that transfer their allegiance during chemical reactions.

In daily life, ET affects us in many ways. The batteries in our cars and portable stereos depend on it. Perhaps its most familiar and unwelcome guise is reddish-brown oxidized metal, AKA rust. In the United States alone, more than $10 billion a year goes to replace corroded equipment and to protect existing structures. "Imagine how much money we could save," says Voth, "in infrastructure and repair, and in our own personal lives, if we could find better ways to prevent corrosion."

Voth's research is aimed in that direction. He and his colleagues have mounted the first major foray of computer simulation into this important field. Using the CRAY C90 at the Pittsburgh Supercomputing Center, they recently completed a massive computation that, for the first time, simulates a typical electrochemical reaction -- an electron transferring from a platinum electrode to an iron ion immersed in water. His surprising, interesting results lead to the conclusion that quantum methods are required to accurately simulate ET processes in water.

Voth and his colleagues are beginning to simulate more complex electrochemical systems such as multiple ions of different species and a first-principles treatment of the electrode surface. This visualization shows a snapshot from a simulation that includes a chlorine counterion (Cl-) and an iron ion in water with a platinum electrode. Inclusion of the counterion, more realistically represents the chemical environment of an ET reaction in electrolytic solution. Ultimately, Voth and his colleagues want to include many ions and counterions in a single simulation.

Researcher: Gregory Voth, University of Pennsylvania
Hardware: CRAY C-90
Software: User-developed code
Keywords: Electron transfer (ET), process, chemistry, electrochemistry, rust, corrosion, batteries, simulation, quantum methods, metal, water, solvent, electrode, electrolytic solution, ions, electrolyte, equilibrium, instantaneous fluctuation, quantum chemistry, free energy, energy cost, transition states, "umbrella sampling", iron, platinum, energy barrier, Feynman path integral technique.

Related Material on the Web:
Information on the Voth research group
Projects in Scientific Computing, PSC's annual research report.

References, Acknowledgements & Credits