Gold is known as a shiny, yellow noble metal that does not tarnish, has a face centred cubic structure, is non-magnetic and melts at 1336 K. However, a small sample of the same gold is quite different, providing it is tiny enough: 10 nm particles absorb green light and thus appear red. The meltingtemperature decreases dramatically as the size goes down. Moreover, gold ceases to be noble, and 2–3 nm nanoparticles are excellent catalysts which also exhibit considerable magnetism. At this size they are still metallic, but smaller ones turn into insulators. Their equilibrium structure changes to icosahedral symmetry, or they are even hollow or planar, depending on size. The present tutorial review intends to explain the origin of this special behaviour of nanomaterials.

The large majority of chemical compounds underwent at least one catalytic step during synthesis. While it is common knowledge that catalysts enhance reaction rates by lowering the activation energy it is often obscure how catalysts achieve this. This tutorial review explains some fundamental principles of catalysis and how the mechanisms are studied. The dissociation of formic acid into H₂ and CO₂ serves to demonstrate how a water molecule can open a new reaction path at lower energy, how immersion in liquid water can influence the charge distribution and energetics, and how catalysis at metal surfaces differs from that in the gas phase. The reversibility of catalytic reactions, the influence of an adsorption pre-equilibrium and the compensating effects of adsorption entropy and enthalpy on the Arrhenius parameters are discussed. It is shown that flexibility around the catalytic centre and residual substrate dynamics on the surface affect these parameters. Sabatier's principle of optimum substrate adsorption, shape selectivity in the pores of molecular sieves and the polarisation effect at the metal–support interface are explained. Finally, it is shown that the application of a bias voltage in electrochemistry offers an additional parameter to promote or inhibit a reaction.

Properties of the oxygen molecule, atomic oxygen, and intermediate products of its reduction, OH, OOH, <mml:math display="inline"><mml:msub><mml:mo>H</mml:mo><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mo>O</mml:mo><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math>H2O2 on (111), (100), and (110) Pt surfaces have been investigated using periodic density functional theory. The Pt surfaces are modeled as four-layer slabs. Adsorption energies and geometries, as well as the charge-transfer properties are calculated. Computed characteristics of the adsorbed oxygen reduction intermediates supply known tendencies of the low index Pt surface activities under different experimental conditions. Electric field dependencies of the properties of all species adsorbed on a <mml:math display="inline"><mml:msub><mml:mi mathvariant="normal">Pt</mml:mi><mml:mrow><mml:mn>9</mml:mn></mml:mrow></mml:msub><mml:mo stretchy="false">(</mml:mo><mml:mn>111</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:math>Pt9(111) cluster have been also studied. Lowering the field causes an increase of the O-O bond length of <mml:math display="inline"><mml:msub><mml:mo>O</mml:mo><mml:mrow><mml:mn>2</mml:mn><mml:mi mathvariant="normal">ads</mml:mi></mml:mrow></mml:msub><mml:mo>,</mml:mo></mml:math>O2ads, attracting the molecule to the Pt surface and increasing the charge transfer from Pt to 2π^* orbitals of the oxygen molecule. The weakening of the O-O bond is evidenced by a decrease of the O-O stretching frequency. The charge-transfer from the <mml:math display="inline"><mml:msub><mml:mi mathvariant="normal">Pt</mml:mi><mml:mrow><mml:mn>9</mml:mn></mml:mrow></mml:msub></mml:math>Pt9 cluster to the adsorbates is observed for all species. In our calculations hydrogen peroxide was unstable on all three low-index Pt surfaces and dissociated into two hydroxyls or a water molecule and atomic oxygen. The results of the calculations are discussed in the context of the mechanism of oxygen reduction. © 2004 The Electrochemical Society. All rights reserved.

A novel method allows the monitoring of radical formation and membrane degradation in-situ in a working fuel cell which is placed in the microwave resonator of an electron paramagnetic resonance (EPR) spectrometer. By introduction of a spin trap molecule at the cathode the formation of immobilized organic radicals on the membrane surface is observed for F-free membranes, revealing the onset of oxidative degradation. For Nafion® there is much less evidence of degradation, and the hydroxyl radical is detected instead. At the anode, free radical intermediates of the fuel oxidation process are observed. No traces of membrane degradation are detected on this side of the fuel cell.

Magnetization measurements of well-characterized monodisperse Pt clusters consisting of $13\pm 2$ atoms in a zeolite confirm the predicted extraordinary magnetic polarization with up to 8 unpaired electrons on a cluster, corresponding to a magnetic moment of $0.65(5){\mu }_B$ per atom. The effect is partly quenched by hydrogen chemisorption. The study provides insight into the electronic structure of the cluster and is fundamental for an understanding of how magnetism develops in small clusters.

High membrane conductivity is one of the key parameters in polymer electrolyte fuel cell applications. We introduce an electrochemical atomic force microscopy method that provides simultaneously the surface topography of a Nafion 112 membrane and the conductivity of ion channels with an unprecedented resolution of ca. 10 nm. For given conditions, a large fraction of the channel ports is found to conduct exactly the same number of protons per unit time. This is taken as evidence for an optimum pore size and structure for proton conduction, or alternatively, for an efficient connectivity of the ion channel network, so that the same conductivity is measured at all exit pores. The time response following a potential step and the influence of the relative humidity on the transport properties is investigated. The method will be of relevance for tailoring the production technology to yield an optimised micromorphology, and it permits detailed tests of membrane models and provides data for theoretical modelling of proton conductivity.