Electrochemical characterization of the surface area of nanoporous gold films

The surface area of nanoporous gold films of thickness up to 930 nm and pores tens of nanometers in size 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 a higher specific capacitance of nanoporous gold, possibly due both to the presence of residual surface Ag and to the high curvature of the nanoporous structures, that may have different interfacial properties as compared to planar surfaces.