Dresden 2020 – wissenschaftliches Programm
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O 17.8: Vortrag
Montag, 16. März 2020, 17:15–17:30, TRE Phy
Microcalorimetric investigation of silver deposition from silver cyanide complexes — •Franziska Karcher, Marco Schönig, and Rolf Schuster — Institute of Physical Chemistry, Karlsruher Institute of Technology, 76131 Karlsruhe, Germany
Electrochemical silver deposition from cyanide containing solutions is of great technical importance. However, the detailed mechanism of this reaction is still controversially discussed in the literature. Here we study the deposition and dissolution process of silver in 0.01 M KAg(CN)2 electrolyte with different concentrations of KCN by electrochemical microcalorimetry. Measuring the reversibly exchanged heat during an electrochemical reaction enables the determination of the reaction entropy, which, in turn, allows conclusions on the reaction mechanism.
The results show that in solutions with additional KCN the silver deposition takes place by direct reduction of the [Ag(CN)2]−-complex after the dissociation of the predominant [Ag(CN)3]2−-complex. Based on the microcalorimetric measurements the reduction of an adsorbed species seems unlikely. In solutions with low or no additional KCN the formation of a passivating surface layer on the Ag-electrode is detectable. From determination of its formation entropy we conclude that this surface layer consists of solid AgCN.