Sustainable Energy

Ultrathin Layers of Platinum Could Help Make Hydrogen Cars Affordable

A fast and easy way to deposit platinum could reduce the amount of the precious metal needed for fuel cells.

Fuel cells could replace conventional vehicles and reduce emissions by consuming natural gas—if they can be produced cheaply enough.

One potential use for the abundance of natural gas discovered in shale deposits across the United States—and potentially in other countries around the world—could be producing hydrogen for fuel-cell vehicles.

Going platinum: An electron microscope image shows platinum accumulated on a layer of gold.

But such fuel cells remain expensive, in part because they use the precious metal platinum to facilitate the chemical reactions that produce electricity within the cell. A new method for quickly and cheaply depositing ultrathin layers of platinum, described today in the journal Science, might make it practical to reduce the amount of platinum used in fuel cells, thereby lowering the cost of fuel cells significantly.

Current methods for applying atom-thick layers of platinum are slow and complicated. The new approach is “incredibly cheap and easy to implement,” says Thomas Moffat, a metallurgy researcher at the National Institute of Standards and Technology, who led the work.

The approach might make it possible to manufacture fuel cells that have significantly thinner layers of platinum than what’s typically used now. GM, which is developing fuel cell vehicles, wouldn’t comment on how much platinum in used in its current fuel cell prototypes, but Charles Freese, general director of GM Fuel Cells, says: “This is an interesting approach that could eventually contribute to making fuel cells commercially viable.”

Moffat and colleagues at the National Institute of Science and Technology showed that platinum dissolved in a solution can be deposited on a gold surface in one-atom thick layers by alternately applying a positive and negative voltage.

The negative voltage causes two things: first, an atom-thick layer of platinum forms; and second, once those atoms are in place, a layer of hydrogen forms, thus preventing any more platinum from accumulating. Switching to a positive voltage then burns off the hydrogen, preparing the surface to receive another atom-thick layer of platinum when the negative voltage is applied again. In this way, the researchers can quickly and easily build layers of any desired atomic thickness.

The technique is orders of magnitude faster than one common method: depositing ultrathin layers of materials by first vaporizing the material that will be deposited, says Jay Switzer, professor of chemistry at Missouri University of Science and Technology, who was not involved with the project. It’s also simpler than another technique, which involves first depositing copper, and then using chemical reactions to replace that copper with platinum, he says.

The researchers have shown that the process works for depositing platinum, and say it might also work for materials such as nickel. The atomic control that the process affords could lead to new multi-metal catalysts. It could also give insights into how changing the thickness of a material, one atom at a time, changed its properties, Switzer says.

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