This paper presents the correlation between the d-band center of Pt nanoclusters and the catalytic activity for an oxygen reduction reaction (ORR). The size-dependent d-band center was determined for Pt nanoclusters deposited on glassy carbon substrates by photoelectron spectroscopy using synchrotron radiation light. It is found that the d-band center moves toward the Fermi level (EF) with decreasing cluster size, as predicted by the first-principles calculations using linear combinations of pseudoatomic orbitals and norm-conserved pseudopotentials. The ORR activity of Pt nanoclusters measured by linear sweep voltammetry with the rotating disk electrode method reveals that the activity is diminished with decreasing cluster size and with moving the d-band center toward the EF. This is consistent with the d-band model claiming that the closer the d-band center is to EF the larger the oxygen adsorption energy is.
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