Abstract
The study of the adsorption behaviour of SCN- and S2O32- at a silver substrate contributes substantially to an improved insight into the electrochemical formation of a silver image in photographic development processes. (Surface-enhanced) Raman (SER) spectroscopy and quantum chemical calculations reveal the existence of an S coordination for both species with Ag, forming 1,1-AgSCN and 1,1-AgS2O3- surface complexes, respectively, at the Ag electrode surface. At an electrode potential of -0.1 V vs. SCE, the SER peaks of adsorbed SCN- intensify when the bulk concentration is increased from 1×10-4 to 6×10-3M, whereas those of adsorbed S2O32- are already measurable at a bulk concentration of 1×10-5M and saturate at 3×10-4M. In both cases, the AgS bond weakens when the potential is lowered from -0.1 to -0.5 V vs. SCE. The correspondence between SER and capacity measurements reveals that a decrease in potential also causes a decrease in the AgSCN surface concentration. The 1,1-AgS2O3- complex even disappears at potentials below -0.2 V vs. SCE. The formation of a physical adsorption state at lower potentials is suggested. © 1998 John Wiley & Sons, Ltd.
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