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 (E F) 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 E F. This is consistent with the d-band model claiming that the closer the d-band center is to E F the larger the oxygen adsorption energy is.

Site-dependent redox potentials of the Pt dissolution reaction, Pt → Pt2+(aq) + 2e−, from Pt particles with and without carbon supports were calculated by a first principles method. The calculation result showed a clear site-dependence in which the redox potentials for the Pt atoms at edges are lower than those for Pt atoms at flat surfaces. This site-dependence is roughly correlated with the d-band center of the dissolving Pt atom, and Pt atoms with higher d-band centers dissolve more easily to the solution. The effects of perfect and defected graphenes on the redox potential are less than 0.1 V. For the platinum atom attaching to the carbons, a slightly negative effect (lowering the redox potential) is obtained, because the bond strength between Pt particles and carbons is enhanced by the defect creation after the dissolution reaction.

A first principles-based mean field model was developed for the oxygen reduction reaction (ORR) taking account of the coverage- and material-dependent reversible potentials of the elementary steps. This model was applied to the simulation of single crystal surfaces of Pt, Pt alloy and Pt core-shell catalysts under Ar and O(2) atmospheres. The results are consistent with those shown by past experimental and theoretical studies on surface coverages under Ar atmosphere, the shape of the current-voltage curve for the ORR on Pt(111) and the material-dependence of the ORR activity. This model suggests that the oxygen associative pathway including HO(2)(ads) formation is the main pathway on Pt(111), and that the rate determining step (RDS) is the removal step of O(ads) on Pt(111). This RDS is accelerated on several highly active Pt alloys and core-shell surfaces, and this acceleration decreases the reaction intermediate O(ads). The increase in the partial pressure of O(2)(g) increases the surface coverage with O(ads) and OH(ads), and this coverage increase reduces the apparent reaction order with respect to the partial pressure to less than unity. This model shows details on how the reaction pathway, RDS, surface coverages, Tafel slope, reaction order and material-dependent activity are interrelated.

The catalyst poisoning property of a novel ionomer, NBC4, which has two sulfonimide acid groups in its side chain ended with a perfluorobutane, instead of sulfonic acid groups as Nafion does, was theoretically and experimentally compared with that of Nafion. A density functional theory combined with a continuum electrolyte theory showed that the adsorption is weaker for sulfonimide anion than for sulfonate anion on Pt (111) surface. Electrochemical measurements using Pt (111) surfaced single crystal electrodes covered with the ionomer films showed the weaker anion adsorption and higher ORR activity by ca. 50% at 0.82 V vs the reversible hydrogen electrode for NBC4 than for Nafion.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 131.215.225.9 Downloaded on 2015-06-21 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 131.215.225.9 Downloaded on 2015-06-21 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 131.215.225.9 Downloaded on 2015-06-21 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 131.215.225.9 Downloaded on 2015-06-21 to IP

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A first principles theory combined with a continuum electrolyte theory is applied to adsorption of sulfuric acid anions on Pt (111) than the lower one.