Analysis of irreversible oxidation wave of adsorbed CO at Pt(1 1 1), Pt(1 0 0) and Pt(1 1 0) electrodes

The oxidation wave of CO preadsorbed at 50 mV on Pt(1 1 1), (1 0 0) and (1 1 0) electrodes in phosphate buffer solution of pH 3 was observed as a function of the sweep rate. The sweep rate dependence of the peak current and peak potential, as well as the form of the wave, were examined on the basis of the Gilman mechanism that the electron transfer from a complex consisting of CO and oxygen containing species is the rate-determining step. An electron transfer step from CO itself was excluded. The peak current and peak potential analyses and the wave simulation gave the same value for f, the change in the interaction energy during the formation of the activated complex from the reactants. f was sweep-rate and surface-structure dependent. The nature of f was discussed.Nomenclature symmetry factor - reversible work required to bring an adsorbed species from its standard state - µ electrochemical potential - electrode potential referred to the reversible hydrogen electrode - _p peak potential - _1/2 width at half height of the oxidation wave - (a) adsorbed state - f() mutual interaction energy of the activated complex inRT units - f(R) mutual interaction energy of the reactants in RT units - f f() –f(R) - i oxidation current density, mA cm^–2 - i _p peak current, mA CM^–2 - k rate constant - Q ₀ electric charge, mCcm^–2 - v sweep rate, m Vs^–1 This paper is dedicated to Professor Brian E. Conway on the occasion of his 65th birthday, and in recognition of his outstanding contribuion to electrochemistry.     

B3LYP study of water adsorption on cluster models of Pt(1 1 1), Pt(1 0 0) and Pt(1 1 0): Effect of applied electric field

A density functional theory (DFT) study of the adsorption of a water molecule on Pt(1 1 1), Pt(1 0 0) and Pt(1 1 0) surfaces has been carried out using cluster models, at the B3LYP/LANL2DZ,6-311++G(d,p) level. The water molecule binds preferentially at the top site on Pt(1 1 1) and Pt(1 0 0) with adsorption energy around −27 kJ mol⁻¹, and is oriented with the molecular plane nearly parallel to the metal surface and the H atoms pointing away from it. On Pt(1 1 0) a hollow site is preferred, with adsorption energy of −32 kJ mol⁻¹. Potential energy barriers for the rotation around an axis normal to the surface have been estimated to be below 1 kJ mol⁻¹ for Pt(1 1 1) and Pt(1 0 0) when water is adsorbed on top. Upon application of an external electric field (inducing positive charge density on the metal) adsorbed water is additionally stabilized on the three surfaces, especially at the top adsorption site, and adsorption on Pt(1 1 1) and Pt(1 0 0) becomes more favoured than on Pt(1 1 0). Good agreement has been found between harmonic vibrational frequencies calculated at the B3LYP/LANL2DZ,6-311++G(d,p) level and experimental frequencies for adsorbed water monomers on Pt(h k l) surfaces.     

Unconventional 0-, 1-, and 2-dimensional single-crystalline copper sulfide nanostructures

We report the synthesis of several unconventional 0-, 1- and 2-dimensional copper sulfide nanostrucutures by the chemical vapor deposition method. The key factor for morphology and structure control of a variety of copper sulfide products is the tuning of deposition and growth temperature to fit for the surface energy barriers and promote different growth directions. At a high growth temperature (480 °C) that provides enough thermal energy, a 0-D octahedral copper sulfide single crystal structure was synthesized. At a slightly lower growth temperature (460 °C), a new 1-D copper sulfide nanorod structure with a nanocrystal head was discovered for the first time. At a much lower growth temperature (150 °C), 2-D copper sulfide nanoflakes with a single crystal hexagonal structure were obtained. These novel structural varieties of copper sulfide can lead to discovering more unconventional material structures and growth mechanisms of other transitional metal chalcogenides, and may allow for new copper sulfide based devices and applications.     

Electrosorbed carbon monoxide monolayers on Pt(1 1 1)

We review structures of high-density CO monolayers on Pt(1 1 1) surfaces in CO-saturated electrolytes or in gaseous CO at near atmospheric pressure, using surface X-ray scattering (SXS) and scanning tunneling microscopy (STM). In electrolytes, we confirmed the well-known (2 × 2)-3CO and (√19 × √19)-13CO structures and were able to study the transition between them. For gas-phase studies, we were able to stabilize extremely well-ordered CO monolayers by emersion transfer from an electrochemical cell. We found that the hexagonal close-packed (2 × 2)-3CO structure is the equilibrium phase at room temperature in ∼1 atm CO gas pressure. This commensurate (C) phase transforms continuously to an incommensurate (IC) phase at elevated temperature (a second-order phase transition). We also confirm that the (√19 × √19)-13CO structure is stable at lower CO partial pressure. This C phase transforms discontinuously to an IC phase (a first-order phase transition). A tentative phase diagram and a brief review of structure details of the (2 × 2)-3CO and (√19 × √19)-13CO phases will be presented.