Nonergodicity in nanoscale electrodes

The response of nanoscale electrodes displays deviations from conventional voltammetry theory that include a reduction in the limiting current and enhanced current fluctuations. We study the power spectra of these fluctuations in well characterized conical electrodes with radii between 2 and 10 nm. The fluctuations are found to display non-trivial power laws. We propose a model based on reversible adsorption of the redox species onto the nanoelectrode. This model is consistent with the non-stationary character of both the limiting current and the adsorption of molecules onto metal electrodes. Our model predicts the electrochemical reaction is nonergodic and sets fundamental limits on the sensitivity of uncoated nanoelectrodes. Faradaid currents in nanoelectrodes reveal enhanced fluctuations and exhibit aging and nonergodicity. This behaviour is explained by ionic reversible adsorption.