Bromide adsorption

Ocko B M, Wang X J and Wandlowski Th 1997 Bromide adsorption on Ag(OOI) A potential induced two-dimensional Ising order-disorder transition Phys. Rev. Lett. 79 1511-14... 

Shi Z, Lipkowski J, Mirwald S and Pettinger B 1996 Electrochemical and second harmonic generation study of bromide adsorption at the Au(111) surface J. Chem. See. Faraday Trans. 92 3737-46... 

Lutzenkirchen-Flecht D and Strehblow FI-FI 1998 Bromide adsorption on silver in alkaline solution A surface analytical study Ber. Bunsenges. Phys. Chem. 102 826-32... 

Bromide adsorption on Au(lll) has also been studied, applying in situ surface X-ray scattering (SXS) and STM [56]. The potential-dependent adlayer density agreed well with the earlier pubKshed bromide surface excess densities, obtained in electrochemical measurements. At very positive potentials, a bromide-induced step-flow etching of Au occurred. 

These studies led to the detailed assignment of voltammetric features of bromide adsorption to the respective structural properties, stability, and transition kinetics. 

Cuesta and Kolb [52] have studied bromide adsorption on Au(lOO) electrodes using in situ STM. Two quasi-hexagonal structures were found, which was in agreement with the previously published SXS data. 

Fig. 10. Voltammetry of bromide adsorption on Cu(l 10). The voltammogram is featureless in the absence of halide.

Table 1.7. Specific surface areas of phyllosilicates determined by nitrogen, water vapor, or iV-cetyl pyridinium bromide adsorption...

This behavior is consistent with a cumulative disorder in the c 2 x p)R45° phase [259]. The results for bromide adsorption on Au(lOO) under electrochemical control indicate that continuous C —> UIC transitions are not restricted to the vacuum environment. 

Images may be analyzed by approximating the adlattice structure as a high-order commensurate overlayer and comparing the result with the simulated Moire patterns. Reasonable agreement with the X-ray data for electrocompression has been found for the case of bromide adsorption on Au(lll) [83]. Similar effects have been extensively investigated for other noble metal-anion systems, for example, Au-I, [6, 7]. 

Pt(lll) disk potential is swept across the first voltammetric peak, the associated adsorption of bromide is demonstrated by the concomitant decrease of the ring current below its unshielded value. The same observation is made for the subsequent, more positive peak, which clearly relates this process to further bromide adsorption on the Pt(lll) disk. Following these two characteristic voltammetric peaks, the Pt(lll) disk current diminishes to a double-layerlike structure above 0.2 V. At the same time, the ring current remains below until the positive potential Kmit is reached. 

In a preliminary report of the results for bromide adsorption onto Pt(lll), it was shown that an incommensurate (3 X 3) hexagonal bromide adlayer is present on the Pt(lll) surface in the potential range 0.05-0.7 V [60]. From fits to the scattering profile at the lowest-order diffraction peak, the peak position... 

The isotherm for bromide adsorption (Fig. 14c) shows that increasing the potential in the double-layer region causes a continuous increase in the bromide coverage. The data shown in Fig. 15 and in other experiments, however, are not consistent with the notion that the additionally adsorbed bromide leads to a continuous compression of the incommensurate bromide adlayer, as this would cause the sharp peak at/ = 0.67 to shift gradually to higher wave vector. An alternative explanation of our results is that bromide forms a series of high-order commensurate (HOC) structures on the Pt(lll) surface, that is, at all potentials the structure corresponds to a close-packed monolayer but that the periodicity depends critically on the ratio of the bromide and Pt lattice parameters. At 0.2 V, the unit cell corresponds to a (3 x 3) structure with a basis of four Br atoms. At 0.6 V, the unit cell is a (7 x 7) structure containing 25 Br atoms, that is, with a 7 5 ratio of the Br and Pt lattice parameters. 

Fig. 16 RRDE results for a Pt(OOl) electrode in 0.1 M HCIO4 + 10 M Br (a) Disk current (b) corresponding ring current and (c) the potential-dependent charge due to bromide adsorption obtained from (a) and (b).

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