A new equation has been deduced from which a direct determination of the standard rate constant from linear sweep voltammograms can be made.Some questions related with the detection limit of irreversibility by means of the linear voltammetric method are also discussed.

A direct scanning tunneling microscopy ex-situ determination on the nanometer scale of the topography of electrochemically highly activated platinum electrodes is presented. A correlation between catalytic activity and surface microtopography becomes evident. This result gives support to a structural model for the activated electrode surface. In the model, a volume with a pebble-like structure allows electrocatalytic processes to occur practically free of diffusion relaxation contributions under usual voltammetric conditions. Catalytic activity and surface roughness are of the outmost importance in heterogeneous catalysis, including electrocatalysis. The term roughness usually implies the existence of both macropores (macroroughness), which to a great extent are responsible for additional diffusional relaxation,' and micropores (microroughness), which concern the effective catalytic area.2 Despite the close relationship between microroughness and catalytic activity, many real systems involve complex macro-and micropore structures which make the direct determination of microroughness a difficult task. A new approach to overcome this drawback is forseen by using metal surfaces which offer large catalytic activity, negligible micropore diffusional relaxation, and distribution of active sites very close to that of the starting materiaL3 This is the case, among others, with platinum electrodes in acid solutions, which have been subjected to a relatively fast square potential cycling, over a potential range such that a hydrous metal oxide multilayer is formed and immediately afterwards is electroreduced to yield a substantially increased active area. The new surface

A definition of electrogenerated luminescence (ECL) is given. Chemiluminescent reactions of different kinds are cited, as well as various types of pathway to the formation of the emitting excited state. After a consideration of the energetic and kinetic requirements for ECL-producing reactions, the experimental conditions are examined. The important concept of ECL efficiency is introduced, as well as the feasibility of elucidating the mechanisms of ECL reactions. Some interesting new ECL systems are mentioned, together with examples of analytical applications of such schemes.

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A systematic study of the electrooxidation mechanism of hydrazine on Pt electrodes in 0.5 M H2S04 solutions has been made. The experimental rate equation found is This can be theoretically explained by a five step mechanism. The log I vs. log Chyd linear plot that results in the determination of the reaction order respect to hydrazine concentration can be used as a working curve for quantitative analytical determination of hydrazine concentrations. A mechanistic explanation has been found for the unusual dependence of the Tafel slope with the pH value.