June 2005

From The Lab: Nanotechnology

Continued from page 1

By Monya Baker (edit)

Sheer Energy
Thinner, cheaper fuel cell catalysts

Context: Fuel cells are much ballyhooed as the future of energy production. In a fuel cell, hydrogen and oxygen combine to produce electricity and water, but getting them to react in a controllable way requires an expensive platinum catalyst. To make current fuel cell designs economically viable, the amount of platinum used must be reduced by nine-tenths. Now, researchers from Brookhaven National Laboratory and the University of Wisconsin-Madison have shown that using less platinum can lead to a more efficient catalyst. The discovery opens a new route to cheaper, more efficient fuel cells.

Methods and Results: Junliang Zhang and colleagues coated five different metals with a layer of platinum one atom thick and tested them in a model system meant to mimic a fuel cell. In such a system, hydrogen and oxygen gases collect on the metal surface, where they react to form water and release electric current. For most of the platinum "monolayers," the reaction occurred more slowly than it does on the thicker platinum layer currently used in fuel cells, but adding a monolayer of platinum to palladium sped up the reaction. To explain their experimental results, the authors simulated the system using a technique called density-functional theory. Their computations predicted how the performance of the platinum monolayer would be affected by atoms from the underlying layer of metal. The theory aligned well with their experiments and showed that adding a platinum monolayer to palladium balances two competing needs: it is reactive enough to break the bonds between oxygen atoms yet does not cling to the oxygen atoms so tightly that it prevents them from reacting with hydrogen.

Why it Matters: Because fuel cells are efficient and do not directly generate harmful emissions, many expect them to become a source of power for cars, homes, and even portable electronics like cell phones. If the amount of platinum they require can be reduced to a monolayer, commercial fuel cells could enjoy a quick and broad entry into the market. Tailoring the surfaces of metals to boost their catalytic capacities should also have applications in chemical manufacturing and pollution control. If such applications can be found through theoretical analysis, then cleaner, faster, and more efficient production techniques won't take such a toll on research and development budgets.

Source: Zhang, J., et al. 2005. Controlling the catalytic activity of platinum monolayer electrocatalysts for oxygen reduction with different substrates. Angewandte Chemie International Edition 44:2132-2135.