RESUMO
We investigate hydrogen evolution on plain and nanostructured electrodes with a theory developed by us. On electrodes involving transition metals the most strongly adsorbed hydrogen is often only a spectator, while the reaction proceeds via a weakly adsorbed species. For Pt(111) the isotherms for both species are calculated. We explain why a nanostructure consisting of a monolayer of Pd on Au(111) is a good catalysts, and predict that Rh/Au(111) should be even better. Our calculations for a fair number of metals are in good agreement with experiment.
Assuntos
Eletroquímica/métodos , Ouro/química , Hidrogênio/química , Nanoestruturas/química , Nanotecnologia/métodos , Platina/química , Adsorção , Catálise , Eletrodos , Modelos Químicos , Propriedades de Superfície , TermodinâmicaRESUMO
The dependence of the aggregation number (N(agg)) on composition and concentration of sodium oleate-cetyltrimethylammonium bromide mixed micelles as revealed by cyclic voltammetry experiments shows a complex relationship with the total concentration and the composition of surfactant mixtures. This behavior is related to the evolution with composition of the HLB values and with the composition and the excess free energy of mixed micellization, and is explained by the inclusion of the double bonds of oleate chains in the micellar Stern layers. The increase in size probably leads to a reduction of the micelle surface available for the polar headgroups, causing a reduction in the proportion of double bonds in the hydrocarbon-water interface and a change in the mixed micelle composition. Therefore, the generally held supposition that the composition of mixed micelles does not change with concentration seems rather unrealistic.
