The electrochemical oxidation behaviors of the surfaces of platinum nanoparticles, one of the key phenomena in fuel cell developments, were investigated in situ and in real time, via time-resolved hard X-ray diffraction and energy dispersive X-ray absorption spectroscopy. Combining two complementary structural analyses, dynamical and inhomogenous structural changes occurring at the surfaces of nanoparticles were monitored on an atomic level with a time resolution of less than 1 s. After oxidation at 1.4 V vs RHE (reversible hydrogen electrode) in a 0.5 M H(2)SO(4) solution, longer Pt-O bonds (2.2-2.3 A that can be assigned to OHH and/or OH species) were first formed on the surface through the partial oxidation of water molecules. Next, these species turned to shorter Pt-O bonds (2.0 A, adsorbed atomic oxygen), and atomic oxygen was incorporated into the inner part of the nanoparticles, forming an initial monolayer oxide that had alpha-PtO(2)-like local structures with expanded Pt-Pt bonds (3.1 A). Finally, quasi-three-dimensional oxides with longer Pt-(O)-Pt bonds (3.5 A, precursor for beta-PtO(2)) grew on the surface, at almost 100 s after oxidation. Despite the very complex oxidation mechanism on the atomic level, XANES analysis indicated that the charge transfer from platinum to the adsorbed oxygen species was almost constant and rather small, that is, about 0.5 electrons per oxygen, up to two monolayers of oxygen. This means that ionic polarization hardly develops at this stage of the surface platinum's "oxide" growth.

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Tantalum-oxide-based oxygen-reduction-reaction (ORR) catalysts have the ORR activity only when they are synthesized from tantalum carbonitrides. Namely pure Ta 2 O 5 does not show ORR activity, and carbon or nitrogen in precursors is inevitable to form ORR active sites and to promote ORR. To clarify this reason, we investigated structural and surface electronic properties of tantalum-oxide-based catalysts, which were synthesized by gradually oxidizing tantalum carbonitride under low partial pressure of oxygen at 1000 °C, by using X-ray absorption spectroscopy, transmission electron microscopy, and Raman spectroscopy. The results indicate that oxidized tantalum carbonitrides with high ORR activity had oxygen vacancies near the surface, indicating that the vacancies could work as an active site for ORR. We also found that carbon was deposited on the oxide's surface during oxidation of tantalum carbonitrides. The deposited carbon seems to play two important roles in formation of oxygen vacancies (ORR active sites) providing reductive atmosphere, and in producing electron conduction paths on rather insulating oxides' surface.

In situ scanning tunneling microscopy (STM) revealed that highly ordered adlayers of fullerene monomer (C60) and [2 + 2]-type dimer (C120) were formed on Au(111) by immersing the surface in benzene solution containing C60 or C120 molecules. High-resolution STM images allowed us to determine packing arrangements of C60 and C120 on a Au(111) surface in an aqueous HClO4 solution. The (2 3 × 2 3)R30°and the so-called in-phase structures of the C60 adlayer were found on the Au(111) surface, whereas the (2 3 × 4 3)R30°a nd (2 3 × 5 3)R30°structures were observed for the C120 dimer. Each C120 dimer was imaged in a dumbbell shape by in situ STM.

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We analyzed the local structure of the surface Ta-oxide phase of TaCN/Ta2O5 core-shell particles that have a high oxygen reduction activity by using surface-sensitive conversion-electron-yield x-ray absorption spectroscopy, suppressing the contribution from the TaCN cores. The radial structure analysis revealed that the catalytically-active Ta2O5 phase in the TaCN/Ta2O5 particle surface contains oxygen-vacancy defects with shorter Ta–O bonds leading to the slight expansion of the first Ta–O shell. Such oxygen defects are likely responsible for the oxygen reduction capability by creating electronically favorable oxygen adsorption sites and electron conduction pathways.

Partially oxidized zirconium carbonitrides (Zr-CNO) were evaluated as a non-precious-metal cathode used for polymer electrolyte fuel cells. The zirconium-oxide-based catalysts were prepared from zirconium carbonitrides under controlled oxygen partial pressures from 10 −2 to 10 −18 atm at 1000 • C. The ORR activity of Zr-CNO showed a volcano-like tendency against the degree of oxidation (DOO). We found a significant lattice-parameter decrease for highly active Zr-CNOs, and this could be ascribed for the formation of oxygen-and zirconium-vacancies in monoclinic ZrO 2 . On the other hand, carbon originated from starting materials was deposited on the surface of Zr-CNOs during the partial oxidation process. We also found that the oxygen content on the surface of highly active Zr-CNOs was drastically decreased when the amount of carbon significantly decreased during partial oxidation processes. This result indicates that the deposited carbon acted as a strong reduction agency. From XPS and XRD analyzes, there is a linear relationship between the ORR current and amount of oxygen vacancy formed in monoclinic phase. Therefore, we believe that oxygen vacancy formed in monoclinic phase could act as active sites for the ORR.Polymer electrolyte fuel cells (PEFCs) are efficient and clean electrochemical power generation devices that produce electricity from H 2 and O 2 gases. Platinum-based oxygen reduction reaction (ORR) catalysts are used as the best catalyst for cathodes of PEFCs at present. Its high cost and poor availability, however, makes the development of non-noble metal catalysts highly desirable. While many studies have been done to develop non-platinum cathode catalysts for PEFCs, such as cobalt-or iron-based macrocyclic complexes (N 4 -chelate type such as phtalocyanines, porphyrins, and tetraazaanulens), 1-3 metal chalcogenides (Mo x Ru y Se z, Ru x X y (where X = S, Se, and Te)), 4-8 and carbon-based catalysts, 9-11 these compounds are, actually, unstable in acidic and oxidizing atmosphere, and less-stable than that of platinum based cathode catalysts. [11][12][13][14][15][16][17] In contrast, we have been focusing on the materials' stability to sever cathode conditions, viz., strong acidic and corrosive environments, and have developed the group 4 and 5 metal-oxidebased catalysts that have high ORR activities that are comparable to that of platinum, simultaneously exhibiting highly tolerant behaviors for the PEFC cathode condition. [18][19][20][21][22][23][24] The results of our studies on transition-metal-oxide-based ORR catalysts have suggested that the best ORR activity is obtained when transition-metal carbonitrides, such as ZrC x N y , TaC x N y , NbC x N y , are partially oxidized. Since the transition metal oxides themselves show no remarkable ORR activity, carbon and/or nitrogen that are included in the starting materials should play a role in emergence and enhancement of ORR activity of oxide-based ORR catalysts.

[70]Fullerene (C70) was directly incorporated into the cell membrane using an exchange reaction from a C70-gamma-cyclodextrin (gamma-CDx) complex within 10 min and the incorporated C70 acted as a photodynamic sensitiser for a cancer cell.