Nanoscale Electrodes by Conducting

Electrochemical characterization was carried out using an externally connected potentiostat equipped with a femtoammeter and a frequency response analyzer (Modulab, Solartron Analytical), which were calibrated using high impedance circuits comprising 0.01100 G resistors and 110 pF capacitors. Electrochemical characterization was carried out in potentiostatic mode; voltages are applied across the entire cell (probe
CsHSO4
composite electrode), with the probe as the working electrode and the large composite electrode serving as the counter and reference electrode. All voltages reported in this work are, therefore, with respect to the large composite counter electrode, that is, an air electrode reference which is 1.13 V relative to 2H  2e º H2 at 150 °C. To reduce contributions of external noise, the microscope was placed in a copper mesh Faraday cage which, like the shielding for the electrical leads, was grounded though the potentiostat ground. The microscope body, which was separately grounded, was electrically isolated from the cage. Stray capacitance and other spurious contributions were found to depend on the current range of the potentiostat, and therefore, open circuit corrections were obtained by withdrawing the probe from the sample and taking impedance measurements at each current range. Point-wise open circuit corrections were applied to all impedance spectra presented; a representative open circuit correction is shown in Figure 10. Short circuit measurements, obtained by contacting the conductive probe to a piece of gold foil, displayed the behavior of a pure resistor with a resistance on the order of 5 k, negligible relative to the high impedances of the nanoprobe setup employed in this work.