Electrochemical Characterization of the Surface Area of Nanoporous Gold Films

The surface area of nanoporous gold films of thickness up to 930 nm and with a pore size of approximately 30 nm was characterized by various electrochemical methods, including Cu underpotential deposition (UPD), surface Au oxidation/reduction reaction, and electrochemical impedance spectroscopy (EIS). The different approaches provide surface area values that are comparable and, in all cases, linearly increasing with thickness. However, whereas Cu UPD and Au oxidation/reduction methods yielded surface area values in good quantitative agreement, estimates based on EIS measurements were found to be 1.5-1.75 times larger. This discrepancy is tentatively attributed to the high curvature of the nanoporous samples that may cause differences in the density of adsorption sites and/or specific capacitance with respect to planar surfaces.