Same Metal Substrate

The Sauerbrey equation for electrochemical deposition can be rewritten as follows  

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The metal was uniformly deposited on the surface of the EQCM, namely that the current distribution was ideally uniform (see Appendix). 

In calculating the slopes of these lines, it was further assumed that electroplating occurred at a Faradaic efficiency of 100% for all three metals. 

In order to minimize changes of the properties of the EQCM and the morphology of the surface, low current densities were applied and thin deposits were formed. In all cases presented below, the deposit thickness was less than 50 nm, and the current density did not exceed 0.1 mA/cm.  

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We first discuss the structure sensitivity on the same metal substrates. The fact that the kinetics of the ORR on Pt(hkf) (Figs. 28 and 29), Cu(hkl) (Fig. 31), and Au hkl) (Fig. 32) are orders of magnitude lower in acid solutions containing strongly adsorbing anions indicates that the structure sensitivity is due primarily to the structure-sensitive adsorption of spectator species, for example, by the (1 — aa) term. The (1 — aa) term is determined by both the pzc of the substrate as well as the match... 

A vitreous enamel coating is, as the name implies, a coating of a glassy substance which has been fused onto the basis metal to give a tightly adherent hard finish resistant to many abrasive and corrosive materials. The purpose of modern vitreous enamels is twofold, i.e. to confer corrosion protection to the metal substrate and at the same time to provide permanent colour, gloss and other aesthetic values. 

Once a passive film is formed on a metal surface, as long as the electrode potential remains in the passive potential region, the surface is stable, i.e., scarcely dissolved. However, if there are film-destructive anions like chloride ions in solution, the passive film is locally broken, so that local dissolution of the metal substrate proceeds at the same place. 

Similar to the case of CO, the dissociation propensity of NO depends largely on the substrate, following the same general trends. Alkali introduction on metal substrates promotes the dissociative adsorption of NO, both by weakening the N-O intramolecular bond and by stabilizing the molecular state which acts as a precursor for dissociation. 

Two types of metal deposition are distinguished that on the same metal and that on a substrate (matrix) consisting of another metal. In the latter case a number of special features can arise. 

Most often, these disperse metal catalysts are supported by an electronically conducting substrate or carrier that should provide for uniform supply or withdrawal of electrons (current) to or from all catalyst crystallites. The substrate should also serve to stabilize the disperse state of the catalyst and retard any spontaneous coarsening of the catalyst crystallites. Two situations are to be distinguished (1) the disperse metal catalyst is applied to a substrate consisting of the same metal, and (2) it is applied to a chemically different substrate (a foreign substrate). Platinized platinum is a typical example of the former situation. 

For technical purposes (as well as in the laboratory) RuOz and Ru based thin film electrodes are prepared by thermal decomposition techniques. Chlorides or other salts of the respective metals are dissolved in an aqueous or alcoholic solution, painted onto a valve metal substrate, dried and fired in the presence of air or oxygen. In order to achieve reasonable thicknesses the procedure has to be applied repetitively with a final firing for usually 1 hour at temperatures of around 450°C. A survey of the various processes can be found in Trasatti s book [44], For such thermal decomposition processes it is dangerous to assume that the bulk composition of the final sample is the same as the composition of the starting products. This is especially true for the surface composition. The knowledge of these parameters, however, is of vital importance for a better understanding of the electrochemical performance including stability of the electrode material. 

Schneir et. al. have avoided the nucleation problem by using the same metal (Au) for both deposition and substrate (Schneir, J. Hansma, P.K., Elings, V. Gurley, J. Wickramasinghe, K. ... 

Beside O P D it is well known that metal deposition can also take place at potentials positive of 0. For this reason called underpotential deposition (UPD) it is characterized by formation of just one or two layer(s) of metal. This happens when the free enthalpy of adsorption of a metal on a foreign substrate is larger than on a surface of the same metal [ 186]. This effect has been observed for a number of metals including Cu and Ag deposited on gold ]187]. Maintaining the formalism of the Nernst equation, deposition in the UPD range means an activity of the deposited metal monolayer smaller than one ]183]. 

Additional interactions and rearrangements in the transition state with other rescuing bases may take place because it is known from crystal structures that substrate atoms are not in line for nucleophilic attack in the hammerhead ribozyme (at least not in the published crystal structures). Also, a metal ion located -20 A away from the catalytic site was shown to be crucial for catalysis. This same metal ion appeared likely to take on an additional ligand in the transition state, suggesting that conformational changes had to take place before catalysis. ... 

The action of one-electron redox systems is readily understandable in the context of inner- and outer-sphere mechanisms, whereas two-electron redox systems require additional considerations. First, if a double one-electron transfer is possible from an organic substrate to the same metal ion, does it mean that the same molecule of an organic donor provides these two electrons, or do two molecules of the substrate act as one-electron donors ... 

In electroless deposition the two electrochemical reactions, reduction of oxidation of Redsoiution occur at the same electrode, at the same electrode-electrolyte interface [Eq. (8.2) and Fig. 8.1]. Thus, in electroless deposition there is a statistical division of the catalytic sites on the substrate into anodic and cathodic sites. Since these catalytic sites are part of the same piece of metal (substrate), there is a flow of electrons between these sites. 

Cation radicals of several metallated TPP and OEP complexes were reported to have unique IR active ring modes (21. These absorptions were observed in the region 1250-1290 cm for TPP complexes and 1520-1570 cm for OEP complexes. IR and raman active modes have also been observed for several different reduced oxygen species adsorbed on various metal substrates. Observations of the adsorption of oxygen on silver by surface enhanced raman spectroscopy (SERS) 22), show superoxide molecules (O2) have a frequency of 1053 cm, and peroxide (0 ) of 697 cm. This same study reported additional peaks were observed at 815 cm and 1286... 

Antimony sulphide deposition onto metallic substrates, together with PbS and Cu-S, was first reported in the original paper of Puscher [1] using thiosulphate and antimony tartrate. No characterization of this film was carried out nor properties given. The same method was also described recently, in 1931, using a number of different metals as substrates [2], It was noted that SbCls, when mixed with thiosulphate, reacted too rapidly, hence the use of the tartrate (tartaric acid is a complexant). Again, no characterization of the films was made. 

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