Automatic monitoring refractive index variations of transient solution during electrochemical reactions

We propose and experimentally demonstrate the automatic measurement of 2D refractive index (RI) changes in aqueous solution at electrode/electrolyte interface based on a Mach-Zehnder interferometer. During the electrochemical reactions, local variations of the electrolyte's RI, which correlate with the concentration of dissolved species, change the phase of the object beam when the beam pass through the electrolyte. With the application of an adaptive band-pass filter, the RI changes can be obtained automatically from interferograms, which enable direct visualization of the concentration change of the soluble species. As a proof of principle demonstration, the system is employed to detect the soluble species during the potentiodynamic sweep of the copper electrode in 0.5 mol dm−3 NaBr solution at 10 mV s−1. The RI changes at the Cu/NaBr solution interface provide direct evidence of the reaction mechanisms of copper corrosion in NaBr solution.