Topographic Changes during Silver Electrodissolution in Aqueous 1 M HCIO4

Topographic changes occur at the terrace domain of a silver single crystal immersed in aqueous 1 M perchloric acid at 298 K, and held at constant electrodissolution current density (j) and temperature. These changes can be followed by in-situ STM sequential imaging [25],

At low values of j (j < 15 |aA cm"2) silver electrodissolution proceeds at step edges (Fig. 4) without roughening (Fig. 5). In this case, the dynamic scaling analysis of STM profiles results in /? = 0, a figure which is consistent with a layer-by-layer dissolution mechanism as established by the FM model [3].

Fig. 4. 85 x 85 nm2 in-situ STM images obtained during the electrodissolution of silver in 1 M HC104 at constant current density 4 pA cm"2 at 298 K.

Conversely, for j > 15 pA cm"2, the silver topography becomes rougher (Fig. 6) to attain the steady roughness regime after a critical time (Fig. 5). In this case, according to the dynamic scaling analysis of STM images, the dissolving metal surface can bedescribed as a self-affine fractal surface with a = 0.90±0.06, and p= 0.36±0.08. The value of a, which is in accordance with those expected from growth models including surface diffusion [8], confirms previous conclusions about the electrodissolution mechanism of silver in acid aqueous solutions derived from electrochemical kinetic data, in which a relevant role was played by the surface diffusion of silver atoms at low overpotential.

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