Nano Lett. http://dx.doi.org/10.1021/nl203975u (2011)

Electron microscopy is routinely used to characterize the structure of metal nanoparticles, and with the help of electron energy-loss spectroscopy, chemical maps with atomic resolution can also be obtained. A chemical map of a single particle can, however, take hours to record. Therefore, acquiring a statistically significant sample of a system that contains nanoparticles with a variety of different compositions, such as a heterogeneous catalyst, is impractical. David Muller, Zhongyi Liu and colleagues at Cornell University, General Motors and Florida International University have now shown that the improved electron optics of an aberration-corrected electron microscope can allow hundreds of platinum–cobalt nanoparticles to be chemically mapped.

The US team used a scanning transmission electron microscope that can correct up to the fifth-order of aberrations and allows data to be collected around a thousand times faster than on a conventional microscope. With the instrument, the platinum–cobalt nanoparticles — which are promising as a fuel-cell catalyst but are known to degrade over time — were mapped at various stages of ageing in a proton-exchange-membrane fuel cell. By mapping ensembles of nanoparticles, the precise structure and composition of the catalyst could be linked to its bulk electrochemical performance with statistical confidence.