Imaging the electrocatalytic activity of single nanoparticles

An IBEC researcher has collaborated on a paper published in Nature Nanotechnology that outlines an effective new way to characterize and improve nanoparticle catalysts, which play essential roles in biomedicine, industry and everyday life by affecting the rate at which chemical reactions take place.

Nanoparticle catalysts are used in making polymers and biofuels, synthesising new drugs, pollution control devices and fuel cell technology, and both characterising them and finding more effective ones is vital.

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Image: P-ECi current density image of a single platinum nanoparticle at −0.5 potential. Scale bar 3 µm.

In the paper published in August, IBEC’s senior researcher in the Nanoprobes and Nanoswitches group, Ismael Díez-Pérez – in collaboration with researchers at Arizona State University’s Biodesign Institute – reveals an innovative way to measure the catalytical reactions of single nanoparticles, as well as multiple particles printed in arrays.

“Most catalytic materials made in labs contain varying nanoparticles with different electrocatalytical activities, but until now it has only been possible to measure the average properties across all of them, and not the properties of individual particles,” Ismael explains. “If we can measure single nanoparticle catalytical reactions, we can figure out how the size, crystal orientation, and composition of the nanoparticle relates to the efficiency of a catalytical reaction, as well as imaging whole arrays of such reactions, which may be used for fast screening.”

In the study, nanoparticles are investigated using a new technique previously developed by the same group, plasmonic electrochemical imaging. This works by optically imaging electrochemical reactions based on surface plasmon resonance, a detection process that occurs when a polarized light hits a prism covered by a thin metal layer. “Basically, we measure electrochemical reactions not by looking at the electrodes, but by concentrating on the reactions near them,” says Ismael. “These cause changes in light reflectivity, which the new technique converts to an optical image.”

Using the technique, the researchers were able to investigate individual nanoparticles, which appear as spots on an array that emerge over time as the potential changes. Results showed that electrocatalytic current increases proportionally with nanoparticle density. The scientists were also able to study the electrocatalytic activity of platinum nanoparticles printed in a microarray, showing for the first time the feasibility of high-throughput screening of catalytic nanoparticle activity.

The fast, non-invasive new technique also shows promise for the search for new catalysts, and may be applied in other areas where conventional electrochemical detection methods are currently used.

Díez Pérez, I., Wang, L., Wiktor, P., Gu, Y., L., Z., W., W., Lu, J., Wang, S., Gong, Q. & Tao, N. (2012). Imaging the electrocatalytic activity of single nanoparticles. Nature Nanotechnology, 7, 668–672