Simultaneous Normalized Optical Reflectivity and Microgravimetric Measurements at Electrode/Electrolyte Interfaces: The Adsorption of Bromide on Gold in Aqueous Media

A system is herein described for the simultaneous acquisition of in situ microgravimetric (QCM) and UV-visible reflectance data (ΔR/R) of metal film electrodes sputtered on the surface of optically polished quartz crystals. This dual-technique approach makes it possible to establish correlations between the changes in weight and relative reflectivities associated with the adsorption of ions (and other species) on the electrode surface as a function of the applied potential without uncertainties derived from electrode surface preparation. Simultaneous in situ QCM-ΔR/R measurements for the adsorption of bromide on gold from aqueous electrolytes yielded results in excellent agreement with those reported by other authors for each independent technique. In particular, plots of the change in the resonant frequency of the QCM vs ΔR/R were found to be linear in the potential region in which bromide adsorption is expected to occur for concentrations of bromide spanning more than 2 orders of magnitude.