The low coverage reversible potential for underpotential deposition of hydrogen on platinum in acid electrolyte is calculated quantum mechanically with two approaches, (i) one using the calculated reaction energy for the overall reaction and an added constant and (ii) the other based on a model of the electrochemical interface. The former yields 0.40 V and the latter 0.48 V, both close to the observed value of ∼0.40 V. Electrode-potential-dependent activation energies are calculated using the interface model for the reduction of the hydronium ion to form the Pt−H bond and for the reverse oxidation reaction over the −0.3 to 3.0 V range. To make this possible, the model explicitly excludes the hydrogen evolution reaction at the cathodic end and water oxidation at the anodic end of the potential range. Cathodic and anodic symmetry factors are determined from the slopes of the activation energy curves, which are used as models for the corresponding activation free energy curves. They are extended into the Marcus-inverted regions for oxidation and reduction. The symmetry factors add to 1.0 in the normal region and in the inverted regions and are not linear functions of the electrode potential.

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An atom superposition and electron delocalization molecular orbital (ASED-MO) study shows that tin atoms alloyed substitutionally into platinum electrode surfaces are inactive in generating OH(ads) for the electro-oxidation of the CO(ads) poison generated during the operation of methanol fuel ceils. Such tin atoms, though they donate to Pt, are not good acceptors for HH20 lone-pair donation bond formation because of the way in which their 5p orbitals mix with the Pt valence band. Thus substitutional Sn atoms in the Pt surface do not attract or activate H20. OH is also found to adsorb weakly to substitutional Sn atoms compared to surface Pt atoms, the opposite of the diatomic SnO and Pro bond strengths. This is because the OH is essentially reduced by neighboring Pt atoms and not the Sn atom to which it is bound. When bound to substitutional Sn atoms, OH is calculated to be relatively active in oxidizing CO(ads) on adjacent Pt atoms, but the inability of the surface to generate such OH implies a different mechanism must be responsible for the electrocatalysis, perhaps involving adsorbed Sn atoms or Sn complexes.

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Controlled placement of microparticles is of prime importance in production of microscale superstructures. In this work, we demonstrate the remote control of microparticle placement using a photoactivated surface profile of a liquid crystal elastomer (LCE) coating. We employ light-responsive LCEs with preimposed patterns of molecular orientation (director) in the plane of coating. Upon UV illumination, these in-plane director distortions translate into deterministic topographic change of the LCE coating. Microparticles placed at the interface between the LCE coating and water, guided by gravity, gather at the bottom of photoinduced troughs. The effect is reversible: when the substrates are irradiated with visible light, the coatings become flat and the microparticle arrays disorganize again. The proposed noncontact manipulation of particles by photoactivated LCEs may be useful in development of drug delivery or tissue engineering applications.