SPECTROELECTROCHEMISTRY OF COLLOIDAL SILVER

The spectroelectrochemical response of small silver particles was stud ied in aqueous solution using an optically transparent, thin layer ele ctrode. The position of the surface plasmon band of the colloidal silv er was found to depend on the applied electrode potential. It varied f rom 400 nm in air, corresponding to a redox potential of +0.15 V vs Ag /AgCl, to about 392 nm at -0.6 V vs Ag/AgCl. A value of 80 +/- 10 mu F cm(-2) for the double-layer capacitance of the silver-water interface was obtained on the basis of the spectroelectrochemical shift. The eq uilibration kinetics of the particles with the electrode obeyed the Co ttrell equation. However, the number of electrons transferred at each particle-electrode encounter was found to be potential dependent and r eached 1600 +/- 300 at potentials more negative than -0.4 V vs Ag/AgCl . The evidence suggests that this particle charging current occurs via electron tunneling across the particle and electrode double layers an d not by contact electrification. Changes in the redox potential of th e particles due to added chemical reductants could also be directly mo nitored by laser doppler electrophoresis.