Weak adsorption of anions on gold: measurement of partial charge transfer using Fast Fourier Transform electrochemical impedance spectroscopy

Using electrochemical impedance spectroscopy (EIS) based on the Fast Fourier Transform (FFT) method, we have investigated the adsorption properties of F−, NO3− and CH3COO− on Au in aqueous electrolytes. The results show that these anions adsorb on Au in considerably small amounts. The adsorption reactions are associated with partial charge transfer across the interface. We present a theoretical framework to analyze these data. Certain previously reported impedance features of simple adsorption reactions are found as special cases of the present analysis. By combining theory and experiment, we determine the double layer capacitance, adsorption capacitance, and the amount of partial charge transfer as functions of the applied voltage. The theoretical framework of the present work can be applied to both cases of weak and strong adsorption, and can be extended to describe coadsorption of different anions.