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This paper describes the electrochemical behavior of shape controlled, deliberately large Au nanoparticles that have been synthesized using a seed-mediated growth method in the presence of cetyl trimethyl ammonium bromide. Transmission electron microscopy micrographs and selected area electron diffraction patterns revealed 40 nm Au nanoparticles with a preferentially cubic shape suggesting a high amount of (100) surface sites. In situ electrochemical structure-sensitive reactions such as lead underpotential deposition confirm that the surface of the nanoparticles contains a large quantity of wide (100) domains. As a consequence, the nanoparticles showed a very high catalytic activity for the four electron oxygen reduction paths in alkaline media. Thus, water was obtained as the final product of the reaction in the whole potential range, while hydrogen peroxide was obtained only in the lower potential region, in a similar way as reported for Au (100) electrodes.

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The surface structure of gold nanorods has been determined by studying the behavior of electrochemical reactions sensitive to the structure and compared to that obtained by other structure characterization techniques. Lead underpotential deposition (UPD) reveals that the surface of the nanorods is composed by (111) and (110) domains, while (100) domains are practically absent from the surface. In the case of the oxygen reduction reaction, the formation of hydrogen peroxide as a final product of the reaction in the whole potential range also indicates that (100) domains are absent on the surface of the nanoparticles, corroborating the previous result. These results are compared with other surface structure information provided by other techniques.

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