No abstract

In order to examine the relationship between the oxygen reduction reaction (ORR) activity of a fuel cell catalyst and its structure and/or electronic state, carbon-supported Pt and Pt alloys having various structures, compositions, and morphologies were studied. Regardless of the atomic ordering or morphology (core−shell or random alloy) of the catalyst, the ORR activity was primarily dependent on the Pt−Pt bond distance. Among these materials, Pt 2 Co, having the shortest Pt−Pt distance, exhibited the highest ORR activity. The activities of this catalyst per unit surface area and per unit mass were approximately 10 times and 6 times higher than those of a commercially available carbon supported Pt electrocatalyst (Pt/C). This work also found a monotonic increase in catalytic activity with decreasing Pt−Pt distance.

A carbon-supported Pt-shell Au-core electrocatalyst (Pt/Au/C) was prepared by sequential deposition of Pt ions on the surface of Au nanoparticles supported on carbon. The area-specific activity of the oxygen reduction reaction (ORR) for the prepared Pt/Au/C in 0.1 M HClO4 aqueous solution was approximately 2 times higher than that for a commercial carbon-supported Pt electrocatalyst (Pt/C). The core–shell structure was confirmed using electrochemical methods and Pt and Au K-edge X-ray absorption fine structure (XAFS) analysis. XAFS analyses indicated that the Pt–Pt bond distance for the Pt/Au/C catalyst was shorter than that for Pt foil and the Pt/C catalyst. In addition, the Au–Au distance was much shorter than that for Au foil. The reason for the high ORR activity of Pt/Au/C is considered to be shorter Pt–Pt bond distance as compared to that of Pt/C.

Time dependent density functional theory study of the near-edge x-ray absorption fine structure of benzene in gas phase and on metal surfaces J. Chem. Phys. 129, 064705 (2008) A new spectroelectrochemical cell for in situ measurement of Pt and Au K-edge X-ray absorption fine structure A new spectroelectrochemical cell to investigate the structure of Pt/Au nanoclusters using Pt and Au K-edge X-ray absorption fine structure (XAFS) measurements under the electrochemical conditions is developed. K-edge XAFS measurements for Pt and Au require a sample as thick as 1-2 cm, which prevents homogeneous potential distribution. We can measure in situ Pt and Au K-edge XAFS spectra and determine reasonable electrochemical surface areas using our developed spectroelectrochemical cell. This work provides a new approach to analyze Pt/Au core-shell nanoclusters. The new cell is designed to be applied to both spectra with high absorption-edge energies such as the K-edge of Pt and Au and those with low absorption-edge energy such as Pt L-edge. © 2014 AIP Publishing LLC.