Spatially-resolved interfacial electrochemistry: Ohmic microscopy

A method is herein described that allows spatially resolved capacitive currents at electrodelelectrolyte interfaces to be recorded in situ by monitoring the ohmic drop in the electrolyte, Δφ_sol, using two microreference electrodes. Measurements were performed in 0.1 M H ₂SO₄ aqueous solutions using Au and Pt either as single or dual working electrodes, that is, connected to one another, in an otherwise conventional three-electrode electrochemical cell. Plots of Δφ _sol versus E, the potential of the dual AuIPt electrode with respect to the main reference electrode, recorded during voltammetric cycles, yielded curves bearing features characteristic of the Au|0.1 M H₂SO ₄ or Pt|0.1 M H₂SO₄ interface depending on whether the microreference electrodes were placed close to the Au or Pt electrode surface, respectively. Extensions of this methodology to measurements in the micrometer domain are discussed briefly.