Fabrication and Characterization of Nanoporous Gold Electrodes for Sensor Applications

Nanoporous gold electrodes are fabricated by etching white gold leaf in nitric acid. Samples of various thickness and alloy composition are used and etch time is varied. Electrode pore structure is characterized by scanning electron microscopy. Significant coarsening of ligament and pore structure is observed as etching time is varied from 5 to 90min. Nanoporous gold electrode impedance is determined via electrochemical impedance spectroscopy. Test cells are constructed for this purpose consisting of two electrodes and an electrolyte. Both water and dichloroethane are examined as electrolyte solvents. A constant phase element with exponent greater than 0.9 is shown to provide an excellent description of interface impedance behavior for these test cells. Optimization is used to determine pseudo-capacitance and exponent in each case. A comparison of nanoporous gold electrode impedance to planar gold electrode impedance is made to derive the effective area of the nanoporous gold electrode. It is found in all cases that interfacial impedances are much lower (>40x) than those of conventional electrodes. Test results show that significant variations in effective area can occur depending on the electrolyte employed.